NC0004961_RBSS_SARP_Rev0_Appx E_20161219

Amec Foster Wheeler Environment & Infrastructure, Inc. December 2016
Duke Energy Coal Combustion Residuals Management Program
Riverbend Steam Station Site Analysis and Removal Plan
Revision 0
APPENDIX E: ENGINEERING EVALUATIONS AND
ANALYSES OF RIVERBEND CLOSURE DESIGN
GRADING PLANS
Riverbend Ash Basin Closure Plan
Amec Foster Wheeler Project No. 6226-14-0007
CALC-1. 01-STORMWA TER, Rev. 0
December 2015
CALCULATION COVER SHEET
Project
Ash Basin Closure Design Grading Plans for Riverbend Steam Station
Calc/Analysis No.
CALC-1.01
STORMWATER-00
AMEC Project No.
6226-14-0007
Title
Stormwater Evaluation
Client Contract
NA
Sheet No. 1 of 15
Discipline
Civil
Computer Program
Microsoft Office Excel 2007, AutoCAD Civil 3D 2013, H droCAD 10.0
Version / Release No.
Purpose and Objective
These calculations establish the pre -development and post -development base
stormwater runoff flows for the Riverbend Steam Station site at each of the
watershed outfalls identified on the plans. This package also contains the
calculations used to evaluate the erosion & sediment control measures required
during the construction phase of the project. The objective is to evaluate stormwater
management system requirements and to demonstrate that stormwater management
may be achieved for the proposed closure design of the ash ponds and storage areas
at the Riverbend Steam Station.
Quality Assurance Conditions (e.g. safety
classification)
NA
Summary of Conclusion
Throughout the development process for closing the Riverbend Steam Station ash ponds and storage areas, Amec Foster Wheeler's design
principles entail an appropriately conservative approach to managing the stormwater runoff during the construction and post -construction phases
of the project. The approach focuses on conveying stormwater runoff from the upland areas to Mountain Island Lake in a stable manner while
providing multiple features with capacity to improve surface water quality. Based on the defined assumptions and requirements of the scope of
work, the proposed stonnwater management system has been shown to be feasible.
Revision Log
Rev. No.
Revision Description
00
Initial issue.
Sign Off
Rev. No.
CIO
Origi a or (Print)
2j l
7S�MA
Verification Method
D
Design Review
Verifier (Print)
Sign ,t
Technical Lead (Print)
Aign / Date
Chad N. Brown
Richard Hiner, PE
Brian Chrisman, PE
Additional Reviewer (Print)
Signature
Date

Riverbend Ash Basin Closure Plan CALC-1.01-STORMWATER, Rev. 0
Amec Foster Wheeler Project No. 6226-14-0007 December 2015
2

RECORD OF REVISION

Revision
No. Date Revisions Made
00 12/2015 Initial issue

Riverbend Ash Basin Closure Plan CALC-1.01-STORMWATER, Rev. 0
Amec Foster Wheeler Project No. 6226-14-0007 December 2015
3

TABLE OF CONTENTS
CALCULATION COVER SHEET .............................................................................................................. 1
RECORD OF REVISION ............................................................................................................................. 2
1.0 OBJECTIVE ........................................................................................................................................... 5
2.0 ASSUMPTIONS ..................................................................................................................................... 5
3.0 COMPUTER PROGRAM IDENTIFICATION ..................................................................................... 5
4.0 CALCULATION APPROACH AND INPUT........................................................................................ 6
4.1 PRE-CONSTRUCTION PHASE ................................................................................................................ 6
4.1.1 Watershed Delineation ............................................................................................................. 6
4.1.2 Land Use and Soils (CN Values) .............................................................................................. 6
4.1.3 Time of Concentration .............................................................................................................. 6
4.1.4 Summary of Results ................................................................................................................... 7
4.2 CONSTRUCTION PHASE ....................................................................................................................... 7
4.2.1 Watershed Delineation ............................................................................................................. 8
4.2.2 Land Use and Soils (CN Values) .............................................................................................. 8
4.2.3 Time of Concentration .............................................................................................................. 8
4.2.4 Erosion and Sediment Control Measures ................................................................................ 8
4.2.5 Summary of Results ................................................................................................................... 9
4.3 POST-CONSTRUCTION PHASE ............................................................................................................ 13
4.3.1 Watershed Delineation ........................................................................................................... 13
4.3.2 Land Use and Soils (CN Values) ............................................................................................ 13
4.3.3 Time of Concentration ............................................................................................................ 13
4.3.4 Summary of Results ................................................................................................................. 13
5.0 CONCLUSIONS AND DISCUSSIONS .............................................................................................. 14
6.0 WORK CITED ...................................................................................................................................... 15

Riverbend Ash Basin Closure Plan CALC-1.01-STORMWATER, Rev. 0
Amec Foster Wheeler Project No. 6226-14-0007 December 2015
4

LIST OF TABLES
Table 1: Pre-Construction Conditions .......................................................................................................... 7
Table 2: Pre-Construction Peak Flows ......................................................................................................... 7
Table 3: Construction Phase Conditions ...................................................................................................... 9
Table 4: Construction Phase Peak In-Flows ............................................................................................... 10
Table 5: Sediment Basin Summary Table ................................................................................................. 10
Table 6: Sediment Basin Peak Discharges ................................................................................................. 11
Table 7: Clean Water Diversion Ditch Summary Table (Stability Check) ................................................ 11
Table 8: Clean Water Diversion Ditch Summary Table (Capacity Check) ............................................... 12
Table 9: Rip Rap Outlet Protection Design Table (Sediment Basins) ....................................................... 12
Table 10: Rip Rap Outlet Protection Design Table (Clean Water Diversions) ......................................... 12
Table 11: Post-Construction Conditions .................................................................................................... 14
Table 12: Post-Construction Peak Flows ................................................................................................... 14

LIST OF FIGURES
F-01: Pre-Construction Drainage Map
F-02: During-Construction Phase 1 Drainage Map
F-03: During-Construction Phase 2 Drainage Map
F-04: Post-Construction Drainage Map

REFERENCES
Reference 1: Rainfall Data
Reference 2: Pre-Construction HydroCAD Output
Reference 3: During-Construction HydroCAD Output
Reference 4: Calculations for Erosion and Sediment Control Measures
(Sediment Basins, Clean Water Diversion Ditches, Rip Rap Aprons)
Reference 5: Post-Construction HydroCAD Output

Riverbend Ash Basin Closure Plan CALC-1.01-STORMWATER, Rev. 0
Amec Foster Wheeler Project No. 6226-14-0007 December 2015
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1.0 OBJECTIVE

The objective is to evaluate stormwater management system requirements and to demonstrate that
stormwater management may be achieved for the proposed closure design grading plans for the ash ponds
and storage areas at the Riverbend Steam Station. These calculations establish the pre-construction,
construction, and post-construction stormwater runoff base flows for the Riverbend Steam Station site at
each of the watershed outfalls identified in the plans. This package also provides the calculations used to
evaluate the erosion & sediment control (E&SC) measures that are required during the construction phase
of the project based on the assumptions below.

2.0 ASSUMPTIONS

For this design, a number of assumptions have been established and are listed below.

 Existing outfall locations will remain reasonably unchanged during and after construction.
 For Curve Number (CN) calculatons, coal ash is considered by the industry to behave as a non-
plastic silt and is assumed to have physical properties most comparable to Hydrologic Soil Group
(HSG) B soil. HSG B soils have a moderate infiltration rate when thoroughly wet and have
moderately fine to moderately coarse texture.
 The assumed excavation grades shown in the ash pond and ash stack footprints were developed
by interpolating boring log information and combining it with digitized topography from historic
Duke Energy construction documents. (V-0.5).
 Means and methods for dewatering the ash ponds have yet to be determined but should not directly
influence this work scope.
 The site will meet the permanent water quality and quantity requirements set forth by the North
Carolina Department of Environmental Quality (NCDEQ). Within the disturbed area of the site,
no impervious area will be added, therefore the post-construction runoff volume is expected to be
less than or equal to the pre-construction runoff volume. The entire disturbed area will be
stabilized and vegetated in the post-construction phase of the project. NCDEQ requirements will
be met as a result of the reduction of runoff quantity resulting from improvements to the land use
(ash pond to vegetated cover).
 This calculation utilizes industry standard methodology and the computational software products
Microsoft Excel, AutoCAD, FlowMaster, and HydroCAD.

3.0 COMPUTER PROGRAM IDENTIFICATION

The table below indicates the computer hardware, operating system, and software used by AMEC for the
data analysis and/or calculations presented herein.

User
(Computer Name)
Computer Hardware
(Service Tag No.)
Operating System Computer Software
Chad Brown

Dell Optiplex 390
(DG713039)
Microsoft Windows 7
Professional
Microsoft Office Excel
2007, Civil 3D AutoCAD
2013, HydroCAD 10.0
Bentley FlowMaster V8i

Riverbend Ash Basin Closure Plan CALC-1.01-STORMWATER, Rev. 0
Amec Foster Wheeler Project No. 6226-14-0007 December 2015
6

4.0 CALCULATION APPROACH AND INPUT

These stormwater calculations consider rainfall data and soil classifications for the Riverbend Steam Station
located at 175 Steam Plant Rd, Mount Holly, North Carolina (Coordinates: 35.3577, -80.9792). The rainfall
data was taken from the National Oceanic and Atmospheric Administration (NOAA) website Atlas 14
rainfall depths for the referenced latitude and longitude coordinates. The soil data was obtained from USDA
Soil maps. The rainfall data and soils data is provided in Reference 1 and Figure 2, respectively. The
Natural Resource Conservation Service (NRCS) method was used to calculate the peak stormwater runoff
flow rates at each outfall. The pre-construction condition utilizes the existing topography to calculate flows,
whereas the during-construction and post-construction flows are based on the excavation and final grading
plan.

4.1 Pre-Construction Phase

Peak flows for the 1-yr, 2-yr, and 10-yr storm events were determined using HydroCAD 10.0 for the pre-
construction condition. Three steps were taken to determine the base flows at each outfall of the site
identified within the plans: watershed delineation, land use and soil (CN) classification, and time of
concentration calculations.

4.1.1 Watershed Delineation

The three existing drainage basins were delineated using existing topography. The delineated watersheds
for the pre-construction condition are provided in F-01.

4.1.2 Land Use and Soils (CN Values)

Land uses for the project were determined by recent publically available aerial imagery, survey data, and
soil classifications. The hydrologic soil group (HSG) classifications for the site were obtained from USGS
Soils maps. Amec Foster Wheeler, in keeping with industry standard practices, has assumed coal ash to be
comparable to a non-plastic silt with physical properties similar to HSG B soils. HSG B soils have a
moderate infiltration rate when thoroughly wet and have moderately fine to moderately coarse texture.

4.1.3 Time of Concentration

The time of concentration for each delineated watershed was calculated using TR-55 methodology and
existing topography. The flow paths consist of sheet flow, shallow concentrated flow, and concentrated
flow segments.

Riverbend Ash Basin Closure Plan CALC-1.01-STORMWATER, Rev. 0
Amec Foster Wheeler Project No. 6226-14-0007 December 2015
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4.1.4 Summary of Results

The pre-construction results are displayed in the following tables. The HydroCAD output is provided in
Reference 2.

4.1.4.1 Pre-Construction Conditions

Table 1 displays the drainage area, weighted curve number, and time of concentrations for the pre-
construction delineated watersheds for the site.

Table 1: Pre-Construction Conditions
Watershed Drainage Area
(acres)
Weighted CN Time of
Concentration
(min)
Pre DA-01 95.0 87 29.4
Pre DA-02 32.6 68 34.0
Pre DA-03 27.9 68 31.6

4.1.4.2 Pre-Construction Peak Flows

Table 2 displays the pre-construction peak flows for each delineated watershed in cubic feet per
second (cfs).

Table 2: Pre-Construction Peak Flows
Watershed 1-yr (cfs) 2-yr (cfs) 10-yr (cfs)
Pre DA-01 126.7 168.3 282.0
Pre DA-02 9.7 17.5 43.6
Pre DA-03 8.8 15.8 39.3

4.2 Construction Phase

The construction phase of the project requires the use of erosion and sediment control measures to treat
sediment laden stormwater runoff before ultimately discharging the runoff from the site. Grades during
construction will be variable; therefore the drainage areas are determined using proposed excavation grades.
The proposed sediment basins (SB-03, SB-04, and SB-05) are the primary sediment control measures and
were designed to meet NCDEQ regulations. The sediment basins include a riser and outlet pipe along with
skimmers for dewatering. The existing ash pond and cinder pit dikes along Mountain Island Lake are
temporarily incorporated within the plan to prevent sediment-laden runoff from directly draining off-site.
Although the height of the dikes will be reduced during construction, leaving the vegetated dike in place
provides an effective means of separation from the construction site and Mountain Island Lake.

While coal combustion residual (CCR) is being excavated and removed from the site, SB-01 and SB-02
will act as pump-and-treat basins with no riser or discharge pipe. SB-01 has been designed to store the
runoff volume for the 25-yr storm with no pumping. SB-02 has been sized for the 10-yr storm with no
pumping and the existing dike along the cinder pit will help contain runoff volume and prevent runoff from
exiting the cinder pit area. After all of the CCR material is removed from the site, basin SB-03 can be can
be constructed by enlarging basin SB-02 and adding the riser and discharge pipe along with the skimmer.
Riverbend Ash Basin Closure Plan CALC-1.01-STORMWATER, Rev. 0
Amec Foster Wheeler Project No. 6226-14-0007 December 2015
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Once the rail spur is demolished and basin SB-03 is functioning as a traditional sediment basin, SB-01 can
be taken out of service and backfilled. Basin SB-03 will then serve the ash stack and cinder pit areas
through the remainder of construction until final stabilization is established.

4.2.1 Watershed Delineation

The construction phase drainage basins were delineated using existing topography and proposed excavation
grades. The delineated watersheds for the during-construction condition are provided in F-02 and F-03.

4.2.2 Land Use and Soils (CN Values)

Land uses for the project were determined by recent publically available aerial imagery, survey data, and
soil classifications. The hydrologic soil group (HSG) classifications for the site were obtained from USGS
Soils maps.

4.2.3 Time of Concentration

The time of concentration for each delineated watershed was calculated using TR-55 methodology and
existing topography, proposed excavation grades, and land uses. The flow paths include sheet flow, shallow
concentrated flow, and concentrated flow segments.

4.2.4 Erosion and Sediment Control Measures

The Sedimentation Control Commission (SCC) adopts rules, sets standards, and provides guidance for the
implementation of the N.C. Sedimentation Pollution Control Act of 1973 (SPCA). The law requires
installation and maintenance of sufficient erosion control practices to retain sediment within the
boundaries of the site. The following measures will be utilized for stormwater management and the
Erosion and Sediment Control Plan for the project. Sediment basins and channels were evaluated to
provide perspective on the size and geometry of required stormwater management features and to support
developing the proposed plans. Other E&SC practices (rip rap outlets, wattles, check dams, temporary
and permanent vegetation, etc.) are also used during the construction phases of this project as appropriate.

4.2.4.1 Sediment Basins

Temporary sediment basins will be used as the primary features for treatment of sediment laden
stormwater runoff of the site while construction is taking place. The basins are sized with a
minimum surface area (at riser crest elevation) equal to or greater than 435 square feet per cfs of
the construction phase Q10 peak inflow. A minimum sediment storage volume of 1,800 cubic
feet per acre of disturbed area is required for all temporary sediment basins. Sediment basins
utilize a riser/barrel configuration, baffles, and dewater through a skimmer. The minimum
dewatering time for each basin is 48 hours (NC Sedimentation Control Commission 2013). A
sediment basin summary table (Table 5) is provided in Section 4.2.5.3 of this calculation package.

Riverbend Ash Basin Closure Plan CALC-1.01-STORMWATER, Rev. 0
Amec Foster Wheeler Project No. 6226-14-0007 December 2015
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4.2.4.2 Diversion Ditches

Diversion ditches are runoff control measures used to subdivide the site into specific drainage areas.
The proposed clean water diversion ditches are designed to convey the Q25 flows and installed prior
to grading operations. Clean water diversion ditches keep water from flowing over unprotected
down slope areas as well as diverting clean water away from the sediment basins. Temporary
diversion ditches are installed during grading operation and keep sediment laden water on the
down-slope side of a disturbed area. Sediment laden runoff is guided to a sediment basin before
being released from the site (NC Sedimentation Control Commission 2013).

Clean Water Diversion Ditches 1 and 2 shown in F-02 and F-03 will convey non-sediment laden
runoff. Clean Water Diversion Ditch 1 will divert clean water away from disturbed areas directly
off-site and Clean Water Diversion Ditch 2 will divert clean water to SB-01 until all CCR material
is excavated and hauled off site. Once the excavation of CCR material is complete the existing
railroad tracks shall be removed, SB-03 constructed, and SB-01 taken out of service and backfilled.
Clean Water Diversion Ditch 2 at this point shall be extended as shown in F-03 and allowed to
discharge directly off-site. The industry design standard for land fill diversion ditches is based on
the 25-yr storm. As a conservative approach Clean Water Diversion Ditches 1 and 2 were designed
according to this standard instead of the NCDEQ required 10-yr storm.

4.2.5 Summary of Results

The during-construction results are displayed in the following tables. The HydroCAD output is provided
in Reference 3.

4.2.5.1 Construction Phase Conditions

Table 3 displays the drainage area, weighted curve number, and time of concentrations for the
during-construction delineated watersheds for the site. Undisturbed drainage areas are denoted in
Table 3 with “U”.

Table 3: Construction Phase Conditions
Watershed Drainage Area
(acres)
Weighted CN Time of
Concentration
(min)
DA-01 65.9 91 12.9
DA-02 20.9 91 6.9
DA-03A 22.4 86 5.6
DA-03B-U 20.4 69 24.7
DA-04 14.1 86 5.0

Riverbend Ash Basin Closure Plan CALC-1.01-STORMWATER, Rev. 0
Amec Foster Wheeler Project No. 6226-14-0007 December 2015
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4.2.5.2 Construction Phase Peak Flows

Table 4 displays the during-construction peak flows for each delineated basin. Undisturbed
drainage areas are denoted in Table 4 with “U”.

Table 4: Construction Phase Peak In-Flows

Basin 1-yr (cfs) 2-yr (cfs) 10-yr (cfs) 25-yr (cfs)
DA-01 164.4 209.6 330.0 401.5
DA-02 63.2 80.4 125.9 152.9
DA-03A 56.7 75.3 125.8 156.2
DA-03B-U 8.5 14.9 35.5 49.4
DA-04 36.7 48.6 81.2 100.8

4.2.5.3 Sediment Basin Summary

Table 5 displays the designed sediment basins. Undisturbed drainage areas are denoted in Table 5
with “U”. See Reference 4 for detailed Riser Sediment Basin Design Information Table.

Table 5: Sediment Basin Summary Table

Sed
Basin
Contributing
Drainage
Areas
Contributing
Disturbed
Area
(ac)
Min.
Volume
Req.
(ft3)
Q10
Inflow
(cfs)
Q25
Inflow
(cfs)
Min
Surface
Area
Req. (ft2)
SB-01* DA-03A
DA-03B-U
22.4 40,320 139.1 176.0 60,913
SB-02* DA-04 14.1 25,380 81.2 100.8 35,331
SB-03* DA-03A
DA-04
36.5 65,700 206.9 256.8 89,984
SB-04 DA-01
DA-02
86.8 156,240 433.7 527.8 188,646
SB-05 DA-01
DA-02
86.8 156,240 433.7 527.8 188,646

*Sediment Basin SB-01 acts as a reservoir for storing sediment laden runoff as well as diverted
clean water. The existing discharge pipe will be plugged and the storage volume within the basin
will be pumped and treated during the excavation of CCR. SB-01 is designed to store the entire
runoff volume from the 25yr-24hr storm. Sediment Basin SB-02 acts as a reservoir for storing
sediment laden runoff in the cinder pit area during the excavation of CCR material. Once all CCR
material is excavated and the existing rail road tracks are no longer in service, SB-03 shall be
constructed to service the sediment laden runoff from the Dry Stack and Cinder Pit area. Upon the
completed construction of SB-03 and the removal of the rail road tracks SB-01 can be backfilled
and taken out of service.

Riverbend Ash Basin Closure Plan CALC-1.01-STORMWATER, Rev. 0
Amec Foster Wheeler Project No. 6226-14-0007 December 2015
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Table 6 displays the peak discharges for each of the designed sediment basins.

Table 6: Sediment Basin Peak Discharges
Sediment Basin 1-yr (cfs) 2-yr (cfs) 10-yr (cfs)
SB-01
(Pumped and Treated)
NA NA NA
SB-02
(Pumped and Treated)
NA NA NA
SB-03 1.1 1.1 5.5
SB-04 2.3 2.3 19.0
SB-05 2.3 3.0 22.6

4.2.5.4 Clean Water Diversion Ditch Summary

Tables 7, and 8 display the designed clean water diversion ditches.

Table 7: Clean Water Diversion Ditch Summary Table (Stability Check)

Ditch No. Dimensions

Bottom
Width
(ft)
Side
Slopes
(H:V)
Avg
Gradient
(%)
Drainage
Area
(ac)
Peak
Flow
Q25*
(cfs)
Manning’s
“n”
(bare soil)
Calculated
Velocity**
(fps)
Calculated
Shear
Stress
(lb/ft2)
Erosion Control
Measure
1 2.5’ Deep
Trapezoidal
2 3:1 2.9 8.3 27.2 0.02 7.75 1.43 1.0’ Check Dam
and
Photodegradable
ERC Blanket
2
(Phase 1)
2.5’ Deep
Trapezoidal
2 3:1 3.2 6.0 13.6 0.02 6.43 1.14 1.0’ Check Dam
and
Photodegradable
ERC Blanket
2
(Phase 2)
3.0’ Deep
Trapezoidal
2 3:1 1.5 26.4 62.9 0.02 8.37 1.20 1.0’ Check Dam
and
Photodegradable
ERC Blanket
*Results from HydroCAD Software
**Reults from TENSAR North American Green Erosion Control Materials Design Software (ECMDS Version 5.0)

Riverbend Ash Basin Closure Plan CALC-1.01-STORMWATER, Rev. 0
Amec Foster Wheeler Project No. 6226-14-0007 December 2015
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Table 8: Clean Water Diversion Ditch Summary Table (Capacity Check)

Ditch No. Dimensions

Bottom Width
(ft)
Side Slopes
(H:V)
Min
Gradient
(%)
Drainage
Area
(ac)
Peak
Flow
Q25*
(cfs)
Manning’s
“n”
Depth
of
Flow**
(ft)
1 2.5’ Deep
Trapezoidal
2 3:1 0.5 8.3 27.2 0.066
(Vegetated)
2.00
2
(Phase 1)
2.5’ Deep
Trapezoidal
2 3:1 0.5 6.0 13.6 0.083
(Vegetated)
1.64

2
(Phase 2)
3.0’ Deep
Trapezoidal
2 3:1 0.5 26.4 62.9 0.052
(Vegetated)
2.59
*Results from HydroCAD Software
** Reults from TENSAR North American Green Erosion Control Materials Design Software (ECMDS Version 5.0)

4.2.5.5 Rip Rap Outlet Protection Design Table

Tables 9 and 10 display summary tables of the rip rap aprons designed for each of the sediment
basin discharge pipes and clean water diversion outfalls. See Reference 4 for detailed calculations
of the Rip Rap Outlets.

Table 9: Rip Rap Outlet Protection Design Table (Sediment Basins)
Description Pipe
Diameter
(in)
10-Yr
Velocity
(fps)*
Zone Apron
Length
(ft)**
Apron
Width
(ft)**
Stone
Class
**
Rip Rap
D50
(in)**
Apron
Thickness
(in)**
SB-03 Outlet 24 1.43 1 8 6 A 4 12
SB-04 Outlet 24 6.04 2 12 7 B 8 18
SB-05 Outlet 24 7.20 2 12 7 B 8 18
*Results from HydroCAD Software
**Aprons sized using the New York DOT Dissipater Method as outlined by NCDEQ (Erosion Control
Manual, Section 8.06)

Table 10: Rip Rap Outlet Protection Design Table (Clean Water Diversions)
Description Ditch
Bottom
Width
(in)
25-Yr
Velocity
(fps)***
Zone Apron
Length
(ft)**
Apron
Width
(ft)**
Stone
Class**

Rip Rap
D50
(in)**
Apron
Thickness
(in)**
Clean Water
Diversion Ditch 1
24 7.89 2 12 7 B 8 18
Clean Water
Diversion Ditch 2
(Phase 2)
24 10.26 2 12 7 B 8 18
** Aprons sized using the New York DOT Dissipater Method as outlined by NCDEQ (Erosion Control
Manual, Section 8.06)
***Results from FlowMaster Software

Riverbend Ash Basin Closure Plan CALC-1.01-STORMWATER, Rev. 0
Amec Foster Wheeler Project No. 6226-14-0007 December 2015
13

4.3 Post-Construction Phase

The site will meet the permanent water quality and quantity requirements set forth by the NCDEQ. No
impervious area will be added within the disturbed area of the site, therefore the post-construction runoff
volume will be less than or equal to the pre-construction runoff volume. The disturbed area will be stabilized
and vegetated in the post-construction phase of the project. The NCDEQ requirements will be met due to
the reduction of runoff quantity and improvements of land use (ash pond to vegetated cover) which may
ultimately improve stormwater quality.

Peak flows for the 1-yr, 2-yr, and 10-yr storm events were determined in the detailed design using
HydroCAD 10.0 for the post-construction condition. Three steps were taken to determine the base flows at
each outfall of the site: watershed delineation, land use and curve number (CN) classification, and time of
concentration calculations.

4.3.1 Watershed Delineation

The post-construction drainage basins were delineated using existing topography and proposed final grades.
The delineated watersheds for the post-construction condition are provided in F-04.

4.3.2 Land Use and Soils (CN Values)

Land uses for the project were determined by aerial imagery, survey data, proposed land uses, and soil
classifications. The hydrologic soil group (HSG) classifications for the site were obtained from USGS Soils
maps.

4.3.3 Time of Concentration

The time of concentration for each delineated watershed was calculated using TR-55 methodology, existing
topography, proposed contours, and land uses. Flow paths include sheet flow, shallow concentrated flow,
and concentrated flow segments.

4.3.4 Summary of Results

The post-development results are displayed in the following tables. The HydroCAD output is provided in
Reference 5.

4.3.4.1 Post-Construction Conditions

Table 11 displays the drainage area, weighted curve number, and time of concentrations for the
post-construction delineated watersheds for the site.

Riverbend Ash Basin Closure Plan CALC-1.01-STORMWATER, Rev. 0
Amec Foster Wheeler Project No. 6226-14-0007 December 2015
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Table 11: Post-Construction Conditions
Basin Drainage Area
(acres)
Weighted CN Time of
Concentration
(min)
Post DA-01 82.0 79 34.2
Post DA-02 23.0 78 30.8
Post DA-03 60.7 68 36.7

4.3.4.2 Post-Construction Peak Flows

Table 12 displays the post-construction peak flows for each delineated watershed in cubic feet per
second (cfs).

Table 12: Post-Construction Peak Flows
Watershed 1-yr (cfs) 2-yr (cfs) 10-yr (cfs)
Post DA-01 62.5 90.7 173.1
Post DA-02 17.6 25.9 50.3
Post DA-03 17.1 30.9 77.1

5.0 CONCLUSIONS AND DISCUSSIONS

The proposed stormwater management system for the Riverbend Steam Station has been evaluated for the
pre-construction, construction, and post-construction phases of the ash basin closure grading project. The
construction phase will use temporary sediment basins as the primary feature for erosion and sediment
control. These basins will be designed according to NCDEQ standards. The minimum surface area and
volume requirements of each sediment basin are included in this calculation package. The site will meet
the permanent water quality and quantity requirements set forth by the NCDEQ. No impervious area will
be added within the disturbed area of the site, therefore the post-construction runoff volume will be less
than or equal to the pre-construction runoff volume. The disturbed area will be stabilized and vegetated in
the post-construction phase of the project. The NCDEQ requirements will be met as a result of the
reduction of runoff quantity due to improvements in the land use (from ash pond to vegetated cover),
which may ultimately improve stormwater quality. The proposed stormwater management system
outlined in this calculation package has been shown to be feasible for the proposed ash basin closure
design of the Riverbend Steam Station.

Riverbend Ash Basin Closure Plan CALC-1.01-STORMWATER, Rev. 0
Amec Foster Wheeler Project No. 6226-14-0007 December 2015
15

6.0 WORK CITED

 NC Sedimentation Control Commission, NCDEQ, NC Arigultrural Extension Service. Erosion
and Sediment Control Planning and Design Manual. Raleigh, 2013.

 North Carolina Division of Water Quality. Stormwater Best Management Practices Manual.
Raleigh: NCDEQ, 2007.

Riverbend Ash Basin Closure Plan CALC-1.01-STORMWATER, Rev. 0
Amec Foster Wheeler Project No. 6226-14-0007 December, 2015
Figures

F-01: PRE-CONSTRUCTION DRAINAGE MAP

F-02: DURING-CONSTRUCTION DRAINAGE MAP (PHASE 1)

F-03: DURING-CONSTRUCTION DRAINAGE MAP (PHASE 2)

F-04: POST-CONSTRUCTION DRAINAGE MAP

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11
2015
ESC REVISIONS
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Amec Foster Wheeler Environment & Infrastructure, Inc.
2801YORKMONTROAD ,SUITE 100
CHARLOTTE, NO 28208
TEL [phone] FAX: [phone]
LIKENSUBE: NO ENS : F-1253 NC GEOLOGY: C-247
BC
DRAWING NO.
F - 04
AQ
31
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2014
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ISSUE'REVISION DESCRIPTION
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Riverbend Ash Basin Closure Plan CALC-1.01-STORMWATER, Rev. 0
Amec Foster Wheeler Project No. 6226-14-0007 December, 2015
Reference 1

RAINFALL DATA

NOAA Atlas 14, Volume 2, Version 3
Location name: Mount Holly, North Carolina, US*
Latitude: 35.3674°, Longitude: -80.9637°
Elevation: 719 ft*
* source: Google Maps
POINT PRECIPITATION FREQUENCY ESTIMATES
G.M. Bonnin, D. Martin, B. Lin, T. Parzybok, M.Yekta, and D. Riley
NOAA, National Weather Service, Silver Spring, Maryland
PF_tabular | PF_graphical | Maps_&_aerials
PF tabular
PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches)1
Duration Average recurrence interval (years)
1 2 5 10 25 50 100 200 500 1000
5-min 0.391
(0.361-0.424)
0.462
(0.427-0.503)
0.539
(0.497-0.586)
0.595
(0.547-0.645)
0.659
(0.602-0.713)
0.704
(0.640-0.762)
0.745
(0.673-0.806)
0.781
(0.701-0.847)
0.822
(0.730-0.894)
0.851
(0.748-0.929)
10-min 0.625
(0.577-0.677)
0.739
(0.683-0.804)
0.864
(0.796-0.938)
0.952
(0.874-1.03)
1.05
(0.960-1.14)
1.12
(1.02-1.21)
1.18
(1.07-1.28)
1.24
(1.11-1.34)
1.30
(1.15-1.42)
1.34
(1.18-1.46)
15-min 0.782
(0.721-0.846)
0.930
(0.858-1.01)
1.09
(1.01-1.19)
1.20
(1.11-1.30)
1.33
(1.22-1.44)
1.42
(1.29-1.54)
1.50
(1.35-1.62)
1.56
(1.40-1.69)
1.64
(1.45-1.78)
1.68
(1.48-1.84)
30-min 1.07
(0.989-1.16)
1.28
(1.19-1.40)
1.55
(1.43-1.69)
1.75
(1.60-1.89)
1.97
(1.80-2.13)
2.14
(1.94-2.31)
2.29
(2.07-2.48)
2.43
(2.18-2.64)
2.61
(2.31-2.83)
2.72
(2.40-2.97)
60-min 1.34
(1.23-1.45)
1.61
(1.49-1.75)
1.99
(1.83-2.16)
2.27
(2.09-2.46)
2.63
(2.40-2.84)
2.90
(2.63-3.13)
3.16
(2.85-3.41)
3.41
(3.06-3.70)
3.74
(3.32-4.07)
3.98
(3.50-4.34)
2-hr 1.55
(1.42-1.69)
1.87
(1.71-2.05)
2.33
(2.13-2.54)
2.67
(2.44-2.92)
3.12
(2.83-3.41)
3.47
(3.13-3.78)
3.81
(3.42-4.16)
4.15
(3.69-4.54)
4.60
(4.05-5.04)
4.94
(4.30-5.43)
3-hr 1.66
(1.52-1.82)
2.00
(1.83-2.19)
2.50
(2.28-2.74)
2.88
(2.63-3.16)
3.40
(3.09-3.72)
3.82
(3.44-4.18)
4.23
(3.79-4.63)
4.66
(4.14-5.11)
5.25
(4.58-5.76)
5.71
(4.92-6.28)
6-hr 2.02
(1.86-2.21)
2.43
(2.24-2.66)
3.04
(2.80-3.33)
3.52
(3.22-3.84)
4.17
(3.79-4.54)
4.69
(4.24-5.10)
5.21
(4.67-5.68)
5.75
(5.11-6.27)
6.50
(5.68-7.10)
7.09
(6.12-7.76)
12-hr 2.40
(2.21-2.61)
2.89
(2.67-3.16)
3.63
(3.34-3.96)
4.21
(3.86-4.58)
5.01
(4.56-5.44)
5.66
(5.11-6.14)
6.33
(5.66-6.85)
7.02
(6.21-7.60)
7.99
(6.95-8.64)
8.76
(7.52-9.49)
24-hr 2.75
(2.56-2.95)
3.32
(3.10-3.57)
4.17
(3.88-4.48)
4.84
(4.50-5.19)
5.75
(5.32-6.16)
6.47
(5.98-6.93)
7.21
(6.65-7.72)
7.96
(7.32-8.54)
8.99
(8.23-9.65)
9.79
(8.94-10.5)
2-day 3.23
(3.01-3.46)
3.88
(3.63-4.17)
4.84
(4.52-5.19)
5.59
(5.21-6.00)
6.61
(6.14-7.08)
7.42
(6.88-7.94)
8.24
(7.62-8.82)
9.08
(8.38-9.72)
10.2
(9.40-11.0)
11.1
(10.2-11.9)
3-day 3.43
(3.20-3.67)
4.12
(3.85-4.41)
5.11
(4.77-5.46)
5.88
(5.48-6.29)
6.94
(6.45-7.42)
7.78
(7.21-8.32)
8.64
(7.99-9.23)
9.51
(8.78-10.2)
10.7
(9.84-11.5)
11.6
(10.7-12.4)
4-day 3.63
(3.39-3.88)
4.35
(4.07-4.66)
5.37
(5.01-5.74)
6.17
(5.75-6.59)
7.27
(6.76-7.77)
8.15
(7.55-8.69)
9.03
(8.36-9.64)
9.94
(9.17-10.6)
11.2
(10.3-12.0)
12.1
(11.1-13.0)
7-day 4.18
(3.93-4.44)
4.98
(4.69-5.29)
6.06
(5.70-6.44)
6.92
(6.49-7.34)
8.10
(7.57-8.59)
9.03
(8.43-9.59)
9.98
(9.29-10.6)
11.0
(10.2-11.7)
12.3
(11.4-13.1)
13.3
(12.3-14.2)
10-day 4.78
(4.51-5.09)
5.69
(5.36-6.05)
6.84
(6.43-7.27)
7.73
(7.27-8.22)
8.94
(8.38-9.50)
9.88
(9.25-10.5)
10.8
(10.1-11.5)
11.8
(11.0-12.5)
13.1
(12.2-13.9)
14.1
(13.1-15.0)
20-day 6.42
(6.09-6.78)
7.58
(7.18-8.00)
8.94
(8.47-9.44)
10.0
(9.48-10.6)
11.5
(10.8-12.1)
12.6
(11.9-13.3)
13.7
(12.9-14.5)
14.9
(13.9-15.7)
16.4
(15.3-17.4)
17.6
(16.4-18.7)
30-day 7.92
(7.54-8.33)
9.32
(8.86-9.79)
10.8
(10.3-11.4)
12.0
(11.4-12.6)
13.5
(12.8-14.2)
14.7
(13.9-15.5)
15.9
(15.0-16.7)
17.0
(16.0-17.9)
18.6
(17.4-19.6)
19.7
(18.4-20.8)
45-day 9.95
(9.53-10.4)
11.6
(11.1-12.2)
13.3
(12.7-13.9)
14.6
(13.9-15.2)
16.2
(15.4-16.9)
17.4
(16.6-18.2)
18.6
(17.7-19.5)
19.8
(18.8-20.8)
21.3
(20.2-22.4)
22.4
(21.2-23.6)
60-day 11.8
(11.4-12.4)
13.8
(13.2-14.4)
15.6
(14.9-16.2)
17.0
(16.2-17.7)
18.7
(17.9-19.5)
20.1
(19.2-20.9)
21.3
(20.4-22.3)
22.6
(21.5-23.6)
24.2
(23.0-25.3)
25.4
(24.1-26.6)
1 Precipitation frequency (PF) estimates in this table are based on frequency analysis of partial duration series (PDS).
Numbers in parenthesis are PF estimates at lower and upper bounds of the 90% confidence interval. The probability that precipitation frequency estimates (for a
given duration and average recurrence interval) will be greater than the upper bound (or less than the lower bound) is 5%. Estimates at upper bounds are not
checked against probable maximum precipitation (PMP) estimates and may be higher than currently valid PMP values.
Please refer to NOAA Atlas 14 document for more information.
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PF graphical
Page 1 of 4Precipitation Frequency Data Server
7/8/2014http://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=35.3674&lon=-80.9637&data=...
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Maps & aerials
Small scale terrain
Map data ©2014 GoogleReport a map error50 km  
Page 2 of 4Precipitation Frequency Data Server
7/8/2014http://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=35.3674&lon=-80.9637&data=...
Large scale terrain
Large scale map
Large scale aerial
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US Department of Commerce
National Oceanic and Atmospheric Administration
National Weather Service
Office of Hydrologic Development
1325 East West Highway
Silver Spring, MD 20910
Map data © 2014 GoogleReport a map error2 km
Map data © 2014 GoogleReport a map error2 km
Imagery ©2014 TerraM etricsReport a map error2 km  
Page 3 of 4Precipitation Frequency Data Server
7/8/2014http://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=35.3674&lon=-80.9637&data=...
Riverbend Ash Basin Closure Plan CALC-1.01-STORMWATER, Rev. 0
Amec Foster Wheeler Project No. 6226-14-0007 December, 2015
Reference 2

PRE-CONSTRUCTION HYDROCAD OUTPUT

1S
PRE DA - 03
2S
PRE DA - 02
3S
PRE DA - 01
14L
Total Off-Site Runoff
Routing Diagram for Riverbend Ash Pond Closure
Prepared by AMEC, Printed 11/5/2015
HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Subcat Reach Pond Link
Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 2HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Area Listing (selected nodes)
Area
(acres)
CN Description
(subcatchment-numbers)
34.000 92 Ash, HSG B (3S)
0.926 85 Gravel roads, HSG B (1S, 2S)
1.610 89 Gravel roads, HSG C (3S)
29.634 69 Pasture/grassland/range, Fair, HSG B (1S, 2S)
28.770 79 Pasture/grassland/range, Fair, HSG C (3S)
1.240 98 Paved roads w/curbs & sewers, HSG B (2S)
3.730 88 Railbed - Gravel (1S, 2S)
20.900 98 Water Surface, HSG C (3S)
16.010 60 Woods, Fair, HSG B (1S, 2S)
8.770 73 Woods, Fair, HSG C (3S)
8.950 65 Woods/grass comb., Fair, HSG B (1S, 2S)
0.950 76 Woods/grass comb., Fair, HSG C (3S)
155.490 80 TOTAL AREA
Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 3HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Soil Listing (selected nodes)
Area
(acres)
Soil
Group
Subcatchment
Numbers
0.000 HSG A
90.760 HSG B 1S, 2S, 3S
61.000 HSG C 3S
0.000 HSG D
3.730 Other 1S, 2S
155.490 TOTAL AREA
Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 4HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Ground Covers (selected nodes)
HSG-A
(acres)
HSG-B
(acres)
HSG-C
(acres)
HSG-D
(acres)
Other
(acres)
Total
(acres)
Ground
Cover
Subcatchment
Numbers
0.000 34.000 0.000 0.000 0.000 34.000 Ash 3S
0.000 0.926 1.610 0.000 0.000 2.536 Gravel roads 1S,
2S,
3S
0.000 29.634 28.770 0.000 0.000 58.404 Pasture/grassland/range, Fair 1S,
2S,
3S
0.000 1.240 0.000 0.000 0.000 1.240 Paved roads w/curbs & sewers 2S
0.000 0.000 0.000 0.000 3.730 3.730 Railbed - Gravel 1S,
2S
0.000 0.000 20.900 0.000 0.000 20.900 Water Surface 3S
0.000 16.010 8.770 0.000 0.000 24.780 Woods, Fair 1S,
2S,
3S
0.000 8.950 0.950 0.000 0.000 9.900 Woods/grass comb., Fair 1S,
2S,
3S
0.000 90.760 61.000 0.000 3.730 155.490 TOTAL AREA
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 5HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 1S: PRE DA - 03
Runoff = 8.77 cfs @ 12.32 hrs, Volume= 1.169 af, Depth= 0.50"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"
Area (ac) CN Description
4.660 65 Woods/grass comb., Fair, HSG B
7.000 60 Woods, Fair, HSG B
* 2.190 88 Railbed - Gravel
0.830 85 Gravel roads, HSG B
13.240 69 Pasture/grassland/range, Fair, HSG B
27.920 68 Weighted Average
27.920 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
11.3 100 0.0100 0.15 Sheet Flow,
Range n= 0.130 P2= 3.32"
2.7 870 0.1100 5.34 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
0.3 135 0.0400 7.49 23.53 Pipe Channel, CMP_Round 24"
24.0" Round Area= 3.1 sf Perim= 6.3' r= 0.50'
n= 0.025 Corrugated metal
17.3 835 0.0260 0.81 Shallow Concentrated Flow,
Woodland Kv= 5.0 fps
31.6 1,940 Total
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 6HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Subcatchment 1S: PRE DA - 03
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
9
8
7
6
5
4
3
2
1
0
Type II 24-hr
1yr - 24 hrs Rainfall=2.75"
Runoff Area=27.920 ac
Runoff Volume=1.169 af
Runoff Depth=0.50"
Flow Length=1,940'
Tc=31.6 min
CN=68
8.77 cfs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 7HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 2S: PRE DA - 02
Runoff = 9.72 cfs @ 12.36 hrs, Volume= 1.363 af, Depth= 0.50"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"
Area (ac) CN Description
4.290 65 Woods/grass comb., Fair, HSG B
9.010 60 Woods, Fair, HSG B
* 1.540 88 Railbed - Gravel
0.096 85 Gravel roads, HSG B
1.240 98 Paved roads w/curbs & sewers, HSG B
16.394 69 Pasture/grassland/range, Fair, HSG B
32.570 68 Weighted Average
31.330 96.19% Pervious Area
1.240 3.81% Impervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
17.9 100 0.0300 0.09 Sheet Flow,
Woods: Light underbrush n= 0.400 P2= 3.32"
2.4 160 0.0500 1.12 Shallow Concentrated Flow, Woods
Woodland Kv= 5.0 fps
2.3 246 0.0120 1.76 Shallow Concentrated Flow, Grass
Unpaved Kv= 16.1 fps
2.2 555 0.0468 4.24 31.82 Channel Flow, Grass Swale
Area= 7.5 sf Perim= 30.1' r= 0.25' n= 0.030
2.2 692 0.0810 5.23 39.25 Channel Flow, Rip Rap Swale
Area= 7.5 sf Perim= 30.1' r= 0.25' n= 0.032
6.4 395 0.0150 1.03 15.48 Channel Flow,
Area= 15.0 sf Perim= 60.0' r= 0.25' n= 0.070
0.6 200 0.0200 5.30 16.64 Pipe Channel, CMP_Round 24"
24.0" Round Area= 3.1 sf Perim= 6.3' r= 0.50'
n= 0.025 Corrugated metal
34.0 2,348 Total
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 8HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Subcatchment 2S: PRE DA - 02
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
10
9
8
7
6
5
4
3
2
1
0
Type II 24-hr
1yr - 24 hrs Rainfall=2.75"
Runoff Area=32.570 ac
Runoff Volume=1.363 af
Runoff Depth=0.50"
Flow Length=2,348'
Tc=34.0 min
CN=68
9.72 cfs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 9HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 3S: PRE DA - 01
Runoff = 126.66 cfs @ 12.24 hrs, Volume= 12.056 af, Depth= 1.52"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"
Area (ac) CN Description
1.610 89 Gravel roads, HSG C
* 34.000 92 Ash, HSG B
20.900 98 Water Surface, HSG C
0.950 76 Woods/grass comb., Fair, HSG C
8.770 73 Woods, Fair, HSG C
28.770 79 Pasture/grassland/range, Fair, HSG C
95.000 87 Weighted Average
74.100 78.00% Pervious Area
20.900 22.00% Impervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
21.1 100 0.0200 0.08 Sheet Flow, Woods
Woods: Light underbrush n= 0.400 P2= 3.32"
2.3 225 0.1100 1.66 Shallow Concentrated Flow, Woods
Woodland Kv= 5.0 fps
0.8 290 0.1300 5.80 Shallow Concentrated Flow, Grass
Unpaved Kv= 16.1 fps
2.8 335 0.0150 1.97 Shallow Concentrated Flow, Ash
Unpaved Kv= 16.1 fps
2.4 3,675 25.38 Lake or Reservoir, Ash Ponds
Mean Depth= 20.00'
29.4 4,625 Total
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 10HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Subcatchment 3S: PRE DA - 01
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
140
120
100
80
60
40
20
0
Type II 24-hr
1yr - 24 hrs Rainfall=2.75"
Runoff Area=95.000 ac
Runoff Volume=12.056 af
Runoff Depth=1.52"
Flow Length=4,625'
Tc=29.4 min
CN=87
126.66 cfs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 11HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Link 14L: Total Off-Site Runoff
Inflow Area = 155.490 ac, 14.24% Impervious, Inflow Depth = 1.13" for 1yr - 24 hrs event
Inflow = 143.32 cfs @ 12.25 hrs, Volume= 14.587 af
Primary = 143.32 cfs @ 12.25 hrs, Volume= 14.587 af, Atten= 0%, Lag= 0.0 min
Primary outflow = Inflow, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Link 14L: Total Off-Site Runoff
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
160
140
120
100
80
60
40
20
0
Inflow Area=155.490 ac
143.32 cfs143.32 cfs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 12HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 1S: PRE DA - 03
Runoff = 15.80 cfs @ 12.30 hrs, Volume= 1.858 af, Depth= 0.80"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"
Area (ac) CN Description
4.660 65 Woods/grass comb., Fair, HSG B
7.000 60 Woods, Fair, HSG B
* 2.190 88 Railbed - Gravel
0.830 85 Gravel roads, HSG B
13.240 69 Pasture/grassland/range, Fair, HSG B
27.920 68 Weighted Average
27.920 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
11.3 100 0.0100 0.15 Sheet Flow,
Range n= 0.130 P2= 3.32"
2.7 870 0.1100 5.34 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
0.3 135 0.0400 7.49 23.53 Pipe Channel, CMP_Round 24"
24.0" Round Area= 3.1 sf Perim= 6.3' r= 0.50'
n= 0.025 Corrugated metal
17.3 835 0.0260 0.81 Shallow Concentrated Flow,
Woodland Kv= 5.0 fps
31.6 1,940 Total
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 13HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Subcatchment 1S: PRE DA - 03
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
16
14
12
10
8
6
4
2
0
Type II 24-hr
2yr - 24hrs Rainfall=3.32"
Runoff Area=27.920 ac
Runoff Volume=1.858 af
Runoff Depth=0.80"
Flow Length=1,940'
Tc=31.6 min
CN=68
15.80 cfs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 14HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 2S: PRE DA - 02
Runoff = 17.50 cfs @ 12.34 hrs, Volume= 2.168 af, Depth= 0.80"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"
Area (ac) CN Description
4.290 65 Woods/grass comb., Fair, HSG B
9.010 60 Woods, Fair, HSG B
* 1.540 88 Railbed - Gravel
0.096 85 Gravel roads, HSG B
1.240 98 Paved roads w/curbs & sewers, HSG B
16.394 69 Pasture/grassland/range, Fair, HSG B
32.570 68 Weighted Average
31.330 96.19% Pervious Area
1.240 3.81% Impervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
17.9 100 0.0300 0.09 Sheet Flow,
Woods: Light underbrush n= 0.400 P2= 3.32"
2.4 160 0.0500 1.12 Shallow Concentrated Flow, Woods
Woodland Kv= 5.0 fps
2.3 246 0.0120 1.76 Shallow Concentrated Flow, Grass
Unpaved Kv= 16.1 fps
2.2 555 0.0468 4.24 31.82 Channel Flow, Grass Swale
Area= 7.5 sf Perim= 30.1' r= 0.25' n= 0.030
2.2 692 0.0810 5.23 39.25 Channel Flow, Rip Rap Swale
Area= 7.5 sf Perim= 30.1' r= 0.25' n= 0.032
6.4 395 0.0150 1.03 15.48 Channel Flow,
Area= 15.0 sf Perim= 60.0' r= 0.25' n= 0.070
0.6 200 0.0200 5.30 16.64 Pipe Channel, CMP_Round 24"
24.0" Round Area= 3.1 sf Perim= 6.3' r= 0.50'
n= 0.025 Corrugated metal
34.0 2,348 Total
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 15HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Subcatchment 2S: PRE DA - 02
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
18
16
14
12
10
8
6
4
2
0
Type II 24-hr
2yr - 24hrs Rainfall=3.32"
Runoff Area=32.570 ac
Runoff Volume=2.168 af
Runoff Depth=0.80"
Flow Length=2,348'
Tc=34.0 min
CN=68
17.50 cfs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 16HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 3S: PRE DA - 01
Runoff = 168.27 cfs @ 12.23 hrs, Volume= 16.003 af, Depth= 2.02"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"
Area (ac) CN Description
1.610 89 Gravel roads, HSG C
* 34.000 92 Ash, HSG B
20.900 98 Water Surface, HSG C
0.950 76 Woods/grass comb., Fair, HSG C
8.770 73 Woods, Fair, HSG C
28.770 79 Pasture/grassland/range, Fair, HSG C
95.000 87 Weighted Average
74.100 78.00% Pervious Area
20.900 22.00% Impervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
21.1 100 0.0200 0.08 Sheet Flow, Woods
Woods: Light underbrush n= 0.400 P2= 3.32"
2.3 225 0.1100 1.66 Shallow Concentrated Flow, Woods
Woodland Kv= 5.0 fps
0.8 290 0.1300 5.80 Shallow Concentrated Flow, Grass
Unpaved Kv= 16.1 fps
2.8 335 0.0150 1.97 Shallow Concentrated Flow, Ash
Unpaved Kv= 16.1 fps
2.4 3,675 25.38 Lake or Reservoir, Ash Ponds
Mean Depth= 20.00'
29.4 4,625 Total
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 17HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Subcatchment 3S: PRE DA - 01
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
180
160
140
120
100
80
60
40
20
0
Type II 24-hr
2yr - 24hrs Rainfall=3.32"
Runoff Area=95.000 ac
Runoff Volume=16.003 af
Runoff Depth=2.02"
Flow Length=4,625'
Tc=29.4 min
CN=87
168.27 cfs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 18HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Link 14L: Total Off-Site Runoff
Inflow Area = 155.490 ac, 14.24% Impervious, Inflow Depth = 1.55" for 2yr - 24hrs event
Inflow = 199.40 cfs @ 12.25 hrs, Volume= 20.029 af
Primary = 199.40 cfs @ 12.25 hrs, Volume= 20.029 af, Atten= 0%, Lag= 0.0 min
Primary outflow = Inflow, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Link 14L: Total Off-Site Runoff
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
220
200
180
160
140
120
100
80
60
40
20
0
Inflow Area=155.490 ac
199.40 cfs199.40 cfs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 19HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 1S: PRE DA - 03
Runoff = 39.28 cfs @ 12.28 hrs, Volume= 4.110 af, Depth= 1.77"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"
Area (ac) CN Description
4.660 65 Woods/grass comb., Fair, HSG B
7.000 60 Woods, Fair, HSG B
* 2.190 88 Railbed - Gravel
0.830 85 Gravel roads, HSG B
13.240 69 Pasture/grassland/range, Fair, HSG B
27.920 68 Weighted Average
27.920 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
11.3 100 0.0100 0.15 Sheet Flow,
Range n= 0.130 P2= 3.32"
2.7 870 0.1100 5.34 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
0.3 135 0.0400 7.49 23.53 Pipe Channel, CMP_Round 24"
24.0" Round Area= 3.1 sf Perim= 6.3' r= 0.50'
n= 0.025 Corrugated metal
17.3 835 0.0260 0.81 Shallow Concentrated Flow,
Woodland Kv= 5.0 fps
31.6 1,940 Total
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 20HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Subcatchment 1S: PRE DA - 03
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
40
35
30
25
20
15
10
5
0
Type II 24-hr
10yr - 24hrs Rainfall=4.84"
Runoff Area=27.920 ac
Runoff Volume=4.110 af
Runoff Depth=1.77"
Flow Length=1,940'
Tc=31.6 min
CN=68
39.28 cfs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 21HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 2S: PRE DA - 02
Runoff = 43.61 cfs @ 12.31 hrs, Volume= 4.795 af, Depth= 1.77"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"
Area (ac) CN Description
4.290 65 Woods/grass comb., Fair, HSG B
9.010 60 Woods, Fair, HSG B
* 1.540 88 Railbed - Gravel
0.096 85 Gravel roads, HSG B
1.240 98 Paved roads w/curbs & sewers, HSG B
16.394 69 Pasture/grassland/range, Fair, HSG B
32.570 68 Weighted Average
31.330 96.19% Pervious Area
1.240 3.81% Impervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
17.9 100 0.0300 0.09 Sheet Flow,
Woods: Light underbrush n= 0.400 P2= 3.32"
2.4 160 0.0500 1.12 Shallow Concentrated Flow, Woods
Woodland Kv= 5.0 fps
2.3 246 0.0120 1.76 Shallow Concentrated Flow, Grass
Unpaved Kv= 16.1 fps
2.2 555 0.0468 4.24 31.82 Channel Flow, Grass Swale
Area= 7.5 sf Perim= 30.1' r= 0.25' n= 0.030
2.2 692 0.0810 5.23 39.25 Channel Flow, Rip Rap Swale
Area= 7.5 sf Perim= 30.1' r= 0.25' n= 0.032
6.4 395 0.0150 1.03 15.48 Channel Flow,
Area= 15.0 sf Perim= 60.0' r= 0.25' n= 0.070
0.6 200 0.0200 5.30 16.64 Pipe Channel, CMP_Round 24"
24.0" Round Area= 3.1 sf Perim= 6.3' r= 0.50'
n= 0.025 Corrugated metal
34.0 2,348 Total
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 22HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Subcatchment 2S: PRE DA - 02
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
45
40
35
30
25
20
15
10
5
0
Type II 24-hr
10yr - 24hrs Rainfall=4.84"
Runoff Area=32.570 ac
Runoff Volume=4.795 af
Runoff Depth=1.77"
Flow Length=2,348'
Tc=34.0 min
CN=68
43.61 cfs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 23HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 3S: PRE DA - 01
Runoff = 281.98 cfs @ 12.23 hrs, Volume= 27.050 af, Depth= 3.42"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"
Area (ac) CN Description
1.610 89 Gravel roads, HSG C
* 34.000 92 Ash, HSG B
20.900 98 Water Surface, HSG C
0.950 76 Woods/grass comb., Fair, HSG C
8.770 73 Woods, Fair, HSG C
28.770 79 Pasture/grassland/range, Fair, HSG C
95.000 87 Weighted Average
74.100 78.00% Pervious Area
20.900 22.00% Impervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
21.1 100 0.0200 0.08 Sheet Flow, Woods
Woods: Light underbrush n= 0.400 P2= 3.32"
2.3 225 0.1100 1.66 Shallow Concentrated Flow, Woods
Woodland Kv= 5.0 fps
0.8 290 0.1300 5.80 Shallow Concentrated Flow, Grass
Unpaved Kv= 16.1 fps
2.8 335 0.0150 1.97 Shallow Concentrated Flow, Ash
Unpaved Kv= 16.1 fps
2.4 3,675 25.38 Lake or Reservoir, Ash Ponds
Mean Depth= 20.00'
29.4 4,625 Total
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 24HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Subcatchment 3S: PRE DA - 01
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
300
250
200
150
100
50
0
Type II 24-hr
10yr - 24hrs Rainfall=4.84"
Runoff Area=95.000 ac
Runoff Volume=27.050 af
Runoff Depth=3.42"
Flow Length=4,625'
Tc=29.4 min
CN=87
281.98 cfs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 25HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Link 14L: Total Off-Site Runoff
Inflow Area = 155.490 ac, 14.24% Impervious, Inflow Depth = 2.77" for 10yr - 24hrs event
Inflow = 361.79 cfs @ 12.24 hrs, Volume= 35.955 af
Primary = 361.79 cfs @ 12.24 hrs, Volume= 35.955 af, Atten= 0%, Lag= 0.0 min
Primary outflow = Inflow, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Link 14L: Total Off-Site Runoff
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
400
350
300
250
200
150
100
50
0
Inflow Area=155.490 ac
361.79 cfs361.79 cfs
Riverbend Ash Basin Closure Plan CALC-1.01-STORMWATER, Rev. 0
Amec Foster Wheeler Project No. 6226-14-0007 December, 2015
Reference 3

DURING-CONSTRUCTION HYDROCAD OUTPUT

4S
DURING
CONSTRUCTION DA -
01
5S
DURING
CONSTRUCTION DA -
02
6S
DURING
CONSTRUCTION DA -
03A
7S
DURING
CONSTRUCTION DA -
04
9S
DURING
CONSTRUCTION DA -
03B
18S
DURING
CONSTRUCTION DA -
01
19S
DURING
CONSTRUCTION DA -
02
25S
DURING
CONSTRUCTION DA -
04
26S
DURING
CONSTRUCTION DA -
03A
16P
SB-01
17P
SB-02
18P
SB-04
21P
SB-05 24P
SB-03
8L
Total
10L
Total
20L
Total 26L
Total
Routing Diagram for Riverbend Ash Pond Closure
Prepared by AMEC, Printed 11/5/2015
HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Subcat Reach Pond Link
Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 2HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Area Listing (selected nodes)
Area
(acres)
CN Description
(subcatchment-numbers)
1.130 85 Gravel roads, HSG B (9S)
73.000 86 Newly graded area, HSG B (6S, 7S, 25S, 26S)
173.600 91 Newly graded area, HSG C (4S, 5S, 18S, 19S)
4.740 69 Pasture/grassland/range, Fair, HSG B (9S)
1.230 98 Paved parking, HSG B (9S)
1.530 88 Railbed - Gravel (9S)
8.520 60 Woods, Fair, HSG B (9S)
3.220 65 Woods/grass comb., Fair, HSG B (9S)
266.970 88 TOTAL AREA
Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 3HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Soil Listing (selected nodes)
Area
(acres)
Soil
Group
Subcatchment
Numbers
0.000 HSG A
91.840 HSG B 6S, 7S, 9S, 25S, 26S
173.600 HSG C 4S, 5S, 18S, 19S
0.000 HSG D
1.530 Other 9S
266.970 TOTAL AREA
Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 4HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Ground Covers (selected nodes)
HSG-A
(acres)
HSG-B
(acres)
HSG-C
(acres)
HSG-D
(acres)
Other
(acres)
Total
(acres)
Ground
Cover
Subcatchment
Numbers
0.000 1.130 0.000 0.000 0.000 1.130 Gravel roads 9S
0.000 73.000 173.600 0.000 0.000 246.600 Newly graded area 4S,
5S,
6S,
7S,
18S,
19S,
25S,
26S
0.000 4.740 0.000 0.000 0.000 4.740 Pasture/grassland/range, Fair 9S
0.000 1.230 0.000 0.000 0.000 1.230 Paved parking 9S
0.000 0.000 0.000 0.000 1.530 1.530 Railbed - Gravel 9S
0.000 8.520 0.000 0.000 0.000 8.520 Woods, Fair 9S
0.000 3.220 0.000 0.000 0.000 3.220 Woods/grass comb., Fair 9S
0.000 91.840 173.600 0.000 1.530 266.970 TOTAL AREA
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 5HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 4S: DURING CONSTRUCTION DA - 01
Runoff = 164.35 cfs @ 12.05 hrs, Volume= 10.101 af, Depth= 1.84"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"
Area (ac) CN Description
65.900 91 Newly graded area, HSG C
65.900 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
4.5 100 0.0150 0.37 Sheet Flow,
Fallow n= 0.050 P2= 3.32"
8.4 1,150 0.0200 2.28 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
12.9 1,250 Total
Subcatchment 4S: DURING CONSTRUCTION DA - 01
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
180
160
140
120
100
80
60
40
20
0
Type II 24-hr
1yr - 24 hrs Rainfall=2.75"
Runoff Area=65.900 ac
Runoff Volume=10.101 af
Runoff Depth=1.84"
Flow Length=1,250'
Tc=12.9 min
CN=91
164.35 cfs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 6HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 5S: DURING CONSTRUCTION DA - 02
Runoff = 63.21 cfs @ 11.98 hrs, Volume= 3.204 af, Depth= 1.84"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"
Area (ac) CN Description
20.900 91 Newly graded area, HSG C
20.900 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
1.7 100 0.1600 0.96 Sheet Flow,
Fallow n= 0.050 P2= 3.32"
5.2 1,220 0.0600 3.94 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
6.9 1,320 Total
Subcatchment 5S: DURING CONSTRUCTION DA - 02
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
70
60
50
40
30
20
10
0
Type II 24-hr
1yr - 24 hrs Rainfall=2.75"
Runoff Area=20.900 ac
Runoff Volume=3.204 af
Runoff Depth=1.84"
Flow Length=1,320'
Tc=6.9 min
CN=91
63.21 cfs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 7HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 6S: DURING CONSTRUCTION DA - 03A
[49] Hint: Tc<2dt may require smaller dt
Runoff = 56.73 cfs @ 11.97 hrs, Volume= 2.708 af, Depth= 1.45"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"
Area (ac) CN Description
22.400 86 Newly graded area, HSG B
22.400 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
2.4 100 0.0700 0.69 Sheet Flow,
Fallow n= 0.050 P2= 3.32"
1.4 450 0.1100 5.34 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
1.8 750 0.0200 7.07 113.09 Channel Flow, Temporary Diversion
Area= 16.0 sf Perim= 29.0' r= 0.55' n= 0.020
5.6 1,300 Total
Subcatchment 6S: DURING CONSTRUCTION DA - 03A
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
60
55
50
45
40
35
30
25
20
15
10
5
0
Type II 24-hr
1yr - 24 hrs Rainfall=2.75"
Runoff Area=22.400 ac
Runoff Volume=2.708 af
Runoff Depth=1.45"
Flow Length=1,300'
Tc=5.6 min
CN=86
56.73 cfs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 8HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 7S: DURING CONSTRUCTION DA - 04
[49] Hint: Tc<2dt may require smaller dt
Runoff = 36.68 cfs @ 11.96 hrs, Volume= 1.704 af, Depth= 1.45"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"
Area (ac) CN Description
14.100 86 Newly graded area, HSG B
14.100 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
5.0 Direct Entry,
Subcatchment 7S: DURING CONSTRUCTION DA - 04
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
40
35
30
25
20
15
10
5
0
Type II 24-hr
1yr - 24 hrs Rainfall=2.75"
Runoff Area=14.100 ac
Runoff Volume=1.704 af
Runoff Depth=1.45"
Tc=5.0 min
CN=86
36.68 cfs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 9HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 9S: DURING CONSTRUCTION DA - 03B
Runoff = 8.52 cfs @ 12.22 hrs, Volume= 0.917 af, Depth= 0.54"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"
Area (ac) CN Description
8.520 60 Woods, Fair, HSG B
3.220 65 Woods/grass comb., Fair, HSG B
1.130 85 Gravel roads, HSG B
1.230 98 Paved parking, HSG B
* 1.530 88 Railbed - Gravel
4.740 69 Pasture/grassland/range, Fair, HSG B
20.370 69 Weighted Average
19.140 93.96% Pervious Area
1.230 6.04% Impervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
21.1 100 0.0200 0.08 Sheet Flow,
Woods: Light underbrush n= 0.400 P2= 3.32"
3.6 740 0.0460 3.45 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
24.7 840 Total
Subcatchment 9S: DURING CONSTRUCTION DA - 03B
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
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(
c
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9
8
7
6
5
4
3
2
1
0
Type II 24-hr
1yr - 24 hrs Rainfall=2.75"
Runoff Area=20.370 ac
Runoff Volume=0.917 af
Runoff Depth=0.54"
Flow Length=840'
Tc=24.7 min
CN=69
8.52 cfs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 10HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 18S: DURING CONSTRUCTION DA - 01
Runoff = 164.35 cfs @ 12.05 hrs, Volume= 10.101 af, Depth= 1.84"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"
Area (ac) CN Description
65.900 91 Newly graded area, HSG C
65.900 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
4.5 100 0.0150 0.37 Sheet Flow,
Fallow n= 0.050 P2= 3.32"
8.4 1,150 0.0200 2.28 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
12.9 1,250 Total
Subcatchment 18S: DURING CONSTRUCTION DA - 01
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
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(
c
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180
160
140
120
100
80
60
40
20
0
Type II 24-hr
1yr - 24 hrs Rainfall=2.75"
Runoff Area=65.900 ac
Runoff Volume=10.101 af
Runoff Depth=1.84"
Flow Length=1,250'
Tc=12.9 min
CN=91
164.35 cfs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 11HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 19S: DURING CONSTRUCTION DA - 02
Runoff = 63.21 cfs @ 11.98 hrs, Volume= 3.204 af, Depth= 1.84"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"
Area (ac) CN Description
20.900 91 Newly graded area, HSG C
20.900 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
1.7 100 0.1600 0.96 Sheet Flow,
Fallow n= 0.050 P2= 3.32"
5.2 1,220 0.0600 3.94 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
6.9 1,320 Total
Subcatchment 19S: DURING CONSTRUCTION DA - 02
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
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(
c
f
s
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70
60
50
40
30
20
10
0
Type II 24-hr
1yr - 24 hrs Rainfall=2.75"
Runoff Area=20.900 ac
Runoff Volume=3.204 af
Runoff Depth=1.84"
Flow Length=1,320'
Tc=6.9 min
CN=91
63.21 cfs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 12HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 25S: DURING CONSTRUCTION DA - 04
[49] Hint: Tc<2dt may require smaller dt
Runoff = 36.68 cfs @ 11.96 hrs, Volume= 1.704 af, Depth= 1.45"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"
Area (ac) CN Description
14.100 86 Newly graded area, HSG B
14.100 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
5.0 Direct Entry,
Subcatchment 25S: DURING CONSTRUCTION DA - 04
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
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(
c
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40
35
30
25
20
15
10
5
0
Type II 24-hr
1yr - 24 hrs Rainfall=2.75"
Runoff Area=14.100 ac
Runoff Volume=1.704 af
Runoff Depth=1.45"
Tc=5.0 min
CN=86
36.68 cfs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 13HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 26S: DURING CONSTRUCTION DA - 03A
[49] Hint: Tc<2dt may require smaller dt
Runoff = 56.73 cfs @ 11.97 hrs, Volume= 2.708 af, Depth= 1.45"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"
Area (ac) CN Description
22.400 86 Newly graded area, HSG B
22.400 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
2.4 100 0.0700 0.69 Sheet Flow,
Fallow n= 0.050 P2= 3.32"
1.4 450 0.1100 5.34 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
1.8 750 0.0200 7.07 113.09 Channel Flow, Temporary Diversion
Area= 16.0 sf Perim= 29.0' r= 0.55' n= 0.020
5.6 1,300 Total
Subcatchment 26S: DURING CONSTRUCTION DA - 03A
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
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60
55
50
45
40
35
30
25
20
15
10
5
0
Type II 24-hr
1yr - 24 hrs Rainfall=2.75"
Runoff Area=22.400 ac
Runoff Volume=2.708 af
Runoff Depth=1.45"
Flow Length=1,300'
Tc=5.6 min
CN=86
56.73 cfs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 14HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Pond 16P: SB-01
Inflow Area = 42.770 ac, 2.88% Impervious, Inflow Depth = 1.02" for 1yr - 24 hrs event
Inflow = 58.31 cfs @ 11.97 hrs, Volume= 3.625 af
Outflow = 0.00 cfs @ 0.00 hrs, Volume= 0.000 af, Atten= 100%, Lag= 0.0 min
Routing by Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Peak Elev= 674.23' @ 25.45 hrs Surf.Area= 43,380 sf Storage= 157,889 cf
Plug-Flow detention time= (not calculated: initial storage exceeds outflow)
Center-of-Mass det. time= (not calculated: no outflow)
Volume Invert Avail.Storage Storage Description
#1 670.00' 871,295 cf Custom Stage Data (Prismatic) Listed below (Recalc)
Elevation Surf.Area Inc.Store Cum.Store
(feet) (sq-ft) (cubic-feet) (cubic-feet)
670.00 31,595 0 0
672.00 36,915 68,510 68,510
674.00 42,640 79,555 148,065
676.00 49,120 91,760 239,825
678.00 58,856 107,976 347,801
680.00 74,771 133,627 481,428
682.00 95,853 170,624 652,052
684.00 123,390 219,243 871,295
Pond 16P: SB-01
Inflow
Hydrograph
Time (hours)
1201101009080706050403020100
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65
60
55
50
45
40
35
30
25
20
15
10
5
0
Inflow Area=42.770 ac
Peak Elev=674.23'
Storage=157,889 cf
58.31 cfs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 15HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Pond 17P: SB-02
Inflow Area = 14.100 ac, 0.00% Impervious, Inflow Depth = 1.45" for 1yr - 24 hrs event
Inflow = 36.68 cfs @ 11.96 hrs, Volume= 1.704 af
Outflow = 0.00 cfs @ 0.00 hrs, Volume= 0.000 af, Atten= 100%, Lag= 0.0 min
Routing by Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Peak Elev= 654.79' @ 24.35 hrs Surf.Area= 34,568 sf Storage= 74,239 cf
Plug-Flow detention time= (not calculated: initial storage exceeds outflow)
Center-of-Mass det. time= (not calculated: no outflow)
Volume Invert Avail.Storage Storage Description
#1 652.00' 195,565 cf Custom Stage Data (Prismatic) Listed below (Recalc)
Elevation Surf.Area Inc.Store Cum.Store
(feet) (sq-ft) (cubic-feet) (cubic-feet)
652.00 14,641 0 0
654.00 33,039 47,680 47,680
656.00 36,932 69,971 117,651
658.00 40,982 77,914 195,565
Pond 17P: SB-02
Inflow
Hydrograph
Time (hours)
1201101009080706050403020100
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40
35
30
25
20
15
10
5
0
Inflow Area=14.100 ac
Peak Elev=654.79'
Storage=74,239 cf
36.68 cfs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 16HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Pond 18P: SB-04
Inflow Area = 86.800 ac, 0.00% Impervious, Inflow Depth = 1.84" for 1yr - 24 hrs event
Inflow = 215.75 cfs @ 12.02 hrs, Volume= 13.305 af
Outflow = 2.26 cfs @ 11.85 hrs, Volume= 13.021 af, Atten= 99%, Lag= 0.0 min
Primary = 2.26 cfs @ 11.85 hrs, Volume= 13.021 af
Routing by Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Peak Elev= 675.09' @ 24.05 hrs Surf.Area= 185,155 sf Storage= 474,129 cf
Plug-Flow detention time= 2,014.8 min calculated for 13.015 af (98% of inflow)
Center-of-Mass det. time= 2,003.4 min ( 2,813.6 - 810.2 )
Volume Invert Avail.Storage Storage Description
#1 672.00' 1,435,854 cf Custom Stage Data (Prismatic) Listed below (Recalc)
Elevation Surf.Area Inc.Store Cum.Store
(feet) (sq-ft) (cubic-feet) (cubic-feet)
672.00 94,232 0 0
674.00 180,443 274,675 274,675
676.00 189,080 369,523 644,198
678.00 197,875 386,955 1,031,153
680.00 206,826 404,701 1,435,854
Device Routing Invert Outlet Devices
#1 Primary 672.00'24.0" Round CMP_Round 24"
L= 150.0' CMP, square edge headwall, Ke= 0.500
Inlet / Outlet Invert= 672.00' / 670.00' S= 0.0133 '/' Cc= 0.900
n= 0.025 Corrugated metal, Flow Area= 3.14 sf
#2 Device 1 676.00'16.0' long Sharp-Crested Rectangular Weir 2 End Contraction(s)
#3 Device 1 672.00'2.260 cfs Constant Flow/Skimmer
#4 Primary 677.00'Custom Weir/Orifice, Cv= 2.62 (C= 3.28)
Head (feet) 0.00 1.00 2.00
Width (feet) 20.00 25.00 30.00
Primary OutFlow Max=2.26 cfs @ 11.85 hrs HW=672.89' (Free Discharge)
1=CMP_Round 24" (Passes 2.26 cfs of 3.23 cfs potential flow)
2=Sharp-Crested Rectangular Weir ( Controls 0.00 cfs)
3=Constant Flow/Skimmer (Constant Controls 2.26 cfs)
4=Custom Weir/Orifice ( Controls 0.00 cfs)
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 17HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Pond 18P: SB-04
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
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(
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240
220
200
180
160
140
120
100
80
60
40
20
0
Inflow Area=86.800 ac
Peak Elev=675.09'
Storage=474,129 cf
215.75 cfs
2.26 cfs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 18HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Pond 21P: SB-05
Inflow Area = 86.800 ac, 0.00% Impervious, Inflow Depth = 1.84" for 1yr - 24 hrs event
Inflow = 215.75 cfs @ 12.02 hrs, Volume= 13.305 af
Outflow = 2.26 cfs @ 11.80 hrs, Volume= 13.080 af, Atten= 99%, Lag= 0.0 min
Primary = 2.26 cfs @ 11.80 hrs, Volume= 13.080 af
Routing by Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Peak Elev= 653.20' @ 24.05 hrs Surf.Area= 179,780 sf Storage= 472,920 cf
Plug-Flow detention time= 2,004.0 min calculated for 13.075 af (98% of inflow)
Center-of-Mass det. time= 1,995.2 min ( 2,805.4 - 810.2 )
Volume Invert Avail.Storage Storage Description
#1 650.00' 2,092,446 cf Custom Stage Data (Prismatic) Listed below (Recalc)
Elevation Surf.Area Inc.Store Cum.Store
(feet) (sq-ft) (cubic-feet) (cubic-feet)
650.00 100,077 0 0
652.00 165,087 265,164 265,164
654.00 189,476 354,563 619,727
656.00 214,653 404,129 1,023,856
658.00 261,346 475,999 1,499,855
660.00 331,245 592,591 2,092,446
Device Routing Invert Outlet Devices
#1 Primary 650.00'24.0" Round CMP_Round 24"
L= 150.0' CMP, square edge headwall, Ke= 0.500
Inlet / Outlet Invert= 650.00' / 646.00' S= 0.0267 '/' Cc= 0.900
n= 0.025 Corrugated metal, Flow Area= 3.14 sf
#2 Device 1 654.00'16.0' long Sharp-Crested Rectangular Weir 2 End Contraction(s)
#3 Device 1 650.00'2.260 cfs Constant Flow/Skimmer
#4 Primary 655.00'Custom Weir/Orifice, Cv= 2.62 (C= 3.28)
Head (feet) 0.00 1.00 2.00
Width (feet) 20.00 25.00 30.00
Primary OutFlow Max=2.26 cfs @ 11.80 hrs HW=650.76' (Free Discharge)
1=CMP_Round 24" (Passes 2.26 cfs of 3.27 cfs potential flow)
2=Sharp-Crested Rectangular Weir ( Controls 0.00 cfs)
3=Constant Flow/Skimmer (Constant Controls 2.26 cfs)
4=Custom Weir/Orifice ( Controls 0.00 cfs)
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 19HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Pond 21P: SB-05
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
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240
220
200
180
160
140
120
100
80
60
40
20
0
Inflow Area=86.800 ac
Peak Elev=653.20'
Storage=472,920 cf
215.75 cfs
2.26 cfs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 20HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Pond 24P: SB-03
Inflow Area = 36.500 ac, 0.00% Impervious, Inflow Depth = 1.45" for 1yr - 24 hrs event
Inflow = 93.32 cfs @ 11.96 hrs, Volume= 4.412 af
Outflow = 1.13 cfs @ 11.70 hrs, Volume= 4.404 af, Atten= 99%, Lag= 0.0 min
Primary = 1.13 cfs @ 11.70 hrs, Volume= 4.404 af
Routing by Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Peak Elev= 654.45' @ 19.88 hrs Surf.Area= 90,019 sf Storage= 141,880 cf
Plug-Flow detention time= 1,295.6 min calculated for 4.404 af (100% of inflow)
Center-of-Mass det. time= 1,294.6 min ( 2,120.2 - 825.6 )
Volume Invert Avail.Storage Storage Description
#1 652.00' 688,748 cf Custom Stage Data (Prismatic) Listed below (Recalc)
Elevation Surf.Area Inc.Store Cum.Store
(feet) (sq-ft) (cubic-feet) (cubic-feet)
652.00 20,697 0 0
653.00 47,259 33,978 33,978
654.00 88,689 67,974 101,952
655.00 91,666 90,178 192,130
656.00 94,682 93,174 285,304
657.00 97,737 96,210 381,513
658.00 100,832 99,285 480,798
659.00 103,965 102,399 583,196
660.00 107,139 105,552 688,748
Device Routing Invert Outlet Devices
#1 Primary 652.00'24.0" Round CMP_Round 24"
L= 200.0' CMP, square edge headwall, Ke= 0.500
Inlet / Outlet Invert= 652.00' / 650.00' S= 0.0100 '/' Cc= 0.900
n= 0.025 Corrugated metal, Flow Area= 3.14 sf
#2 Device 1 656.00'16.0' long Sharp-Crested Rectangular Weir 2 End Contraction(s)
#3 Device 1 652.00'1.130 cfs Constant Flow/Skimmer
#4 Primary 657.00'Custom Weir/Orifice, Cv= 2.62 (C= 3.28)
Head (feet) 0.00 1.00 2.00 3.00
Width (feet) 20.00 25.00 30.00 35.00
Primary OutFlow Max=1.13 cfs @ 11.70 hrs HW=652.58' (Free Discharge)
1=CMP_Round 24" (Passes 1.13 cfs of 1.21 cfs potential flow)
2=Sharp-Crested Rectangular Weir ( Controls 0.00 cfs)
3=Constant Flow/Skimmer (Constant Controls 1.13 cfs)
4=Custom Weir/Orifice ( Controls 0.00 cfs)
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 21HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Pond 24P: SB-03
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
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100
90
80
70
60
50
40
30
20
10
0
Inflow Area=36.500 ac
Peak Elev=654.45'
Storage=141,880 cf
93.32 cfs
1.13 cfs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 22HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Link 8L: Total
Inflow Area = 86.800 ac, 0.00% Impervious, Inflow Depth = 1.84" for 1yr - 24 hrs event
Inflow = 215.75 cfs @ 12.02 hrs, Volume= 13.305 af
Primary = 215.75 cfs @ 12.02 hrs, Volume= 13.305 af, Atten= 0%, Lag= 0.0 min
Primary outflow = Inflow, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Link 8L: Total
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
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(
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240
220
200
180
160
140
120
100
80
60
40
20
0
Inflow Area=86.800 ac
215.75 cfs215.75 cfs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 23HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Link 10L: Total
Inflow Area = 42.770 ac, 2.88% Impervious, Inflow Depth = 1.02" for 1yr - 24 hrs event
Inflow = 58.31 cfs @ 11.97 hrs, Volume= 3.625 af
Primary = 58.31 cfs @ 11.97 hrs, Volume= 3.625 af, Atten= 0%, Lag= 0.0 min
Primary outflow = Inflow, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Link 10L: Total
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
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(
c
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60
50
40
30
20
10
0
Inflow Area=42.770 ac
58.31 cfs58.31 cfs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 24HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Link 20L: Total
Inflow Area = 86.800 ac, 0.00% Impervious, Inflow Depth = 1.84" for 1yr - 24 hrs event
Inflow = 215.75 cfs @ 12.02 hrs, Volume= 13.305 af
Primary = 215.75 cfs @ 12.02 hrs, Volume= 13.305 af, Atten= 0%, Lag= 0.0 min
Primary outflow = Inflow, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Link 20L: Total
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
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(
c
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240
220
200
180
160
140
120
100
80
60
40
20
0
Inflow Area=86.800 ac
215.75 cfs215.75 cfs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 25HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Link 26L: Total
Inflow Area = 36.500 ac, 0.00% Impervious, Inflow Depth = 1.45" for 1yr - 24 hrs event
Inflow = 93.32 cfs @ 11.96 hrs, Volume= 4.412 af
Primary = 93.32 cfs @ 11.96 hrs, Volume= 4.412 af, Atten= 0%, Lag= 0.0 min
Primary outflow = Inflow, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Link 26L: Total
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
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(
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100
90
80
70
60
50
40
30
20
10
0
Inflow Area=36.500 ac
93.32 cfs93.32 cfs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 26HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 4S: DURING CONSTRUCTION DA - 01
Runoff = 209.60 cfs @ 12.04 hrs, Volume= 13.021 af, Depth= 2.37"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"
Area (ac) CN Description
65.900 91 Newly graded area, HSG C
65.900 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
4.5 100 0.0150 0.37 Sheet Flow,
Fallow n= 0.050 P2= 3.32"
8.4 1,150 0.0200 2.28 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
12.9 1,250 Total
Subcatchment 4S: DURING CONSTRUCTION DA - 01
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
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220
200
180
160
140
120
100
80
60
40
20
0
Type II 24-hr
2yr - 24hrs Rainfall=3.32"
Runoff Area=65.900 ac
Runoff Volume=13.021 af
Runoff Depth=2.37"
Flow Length=1,250'
Tc=12.9 min
CN=91
209.60 cfs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 27HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 5S: DURING CONSTRUCTION DA - 02
Runoff = 80.36 cfs @ 11.98 hrs, Volume= 4.130 af, Depth= 2.37"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"
Area (ac) CN Description
20.900 91 Newly graded area, HSG C
20.900 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
1.7 100 0.1600 0.96 Sheet Flow,
Fallow n= 0.050 P2= 3.32"
5.2 1,220 0.0600 3.94 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
6.9 1,320 Total
Subcatchment 5S: DURING CONSTRUCTION DA - 02
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
90
80
70
60
50
40
30
20
10
0
Type II 24-hr
2yr - 24hrs Rainfall=3.32"
Runoff Area=20.900 ac
Runoff Volume=4.130 af
Runoff Depth=2.37"
Flow Length=1,320'
Tc=6.9 min
CN=91
80.36 cfs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 28HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 6S: DURING CONSTRUCTION DA - 03A
[49] Hint: Tc<2dt may require smaller dt
Runoff = 75.27 cfs @ 11.96 hrs, Volume= 3.621 af, Depth= 1.94"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"
Area (ac) CN Description
22.400 86 Newly graded area, HSG B
22.400 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
2.4 100 0.0700 0.69 Sheet Flow,
Fallow n= 0.050 P2= 3.32"
1.4 450 0.1100 5.34 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
1.8 750 0.0200 7.07 113.09 Channel Flow, Temporary Diversion
Area= 16.0 sf Perim= 29.0' r= 0.55' n= 0.020
5.6 1,300 Total
Subcatchment 6S: DURING CONSTRUCTION DA - 03A
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
80
70
60
50
40
30
20
10
0
Type II 24-hr
2yr - 24hrs Rainfall=3.32"
Runoff Area=22.400 ac
Runoff Volume=3.621 af
Runoff Depth=1.94"
Flow Length=1,300'
Tc=5.6 min
CN=86
75.27 cfs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 29HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 7S: DURING CONSTRUCTION DA - 04
[49] Hint: Tc<2dt may require smaller dt
Runoff = 48.64 cfs @ 11.96 hrs, Volume= 2.279 af, Depth= 1.94"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"
Area (ac) CN Description
14.100 86 Newly graded area, HSG B
14.100 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
5.0 Direct Entry,
Subcatchment 7S: DURING CONSTRUCTION DA - 04
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
50
45
40
35
30
25
20
15
10
5
0
Type II 24-hr
2yr - 24hrs Rainfall=3.32"
Runoff Area=14.100 ac
Runoff Volume=2.279 af
Runoff Depth=1.94"
Tc=5.0 min
CN=86
48.64 cfs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 30HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 9S: DURING CONSTRUCTION DA - 03B
Runoff = 14.86 cfs @ 12.21 hrs, Volume= 1.440 af, Depth= 0.85"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"
Area (ac) CN Description
8.520 60 Woods, Fair, HSG B
3.220 65 Woods/grass comb., Fair, HSG B
1.130 85 Gravel roads, HSG B
1.230 98 Paved parking, HSG B
* 1.530 88 Railbed - Gravel
4.740 69 Pasture/grassland/range, Fair, HSG B
20.370 69 Weighted Average
19.140 93.96% Pervious Area
1.230 6.04% Impervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
21.1 100 0.0200 0.08 Sheet Flow,
Woods: Light underbrush n= 0.400 P2= 3.32"
3.6 740 0.0460 3.45 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
24.7 840 Total
Subcatchment 9S: DURING CONSTRUCTION DA - 03B
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
16
14
12
10
8
6
4
2
0
Type II 24-hr
2yr - 24hrs Rainfall=3.32"
Runoff Area=20.370 ac
Runoff Volume=1.440 af
Runoff Depth=0.85"
Flow Length=840'
Tc=24.7 min
CN=69
14.86 cfs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 31HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 18S: DURING CONSTRUCTION DA - 01
Runoff = 209.60 cfs @ 12.04 hrs, Volume= 13.021 af, Depth= 2.37"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"
Area (ac) CN Description
65.900 91 Newly graded area, HSG C
65.900 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
4.5 100 0.0150 0.37 Sheet Flow,
Fallow n= 0.050 P2= 3.32"
8.4 1,150 0.0200 2.28 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
12.9 1,250 Total
Subcatchment 18S: DURING CONSTRUCTION DA - 01
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
220
200
180
160
140
120
100
80
60
40
20
0
Type II 24-hr
2yr - 24hrs Rainfall=3.32"
Runoff Area=65.900 ac
Runoff Volume=13.021 af
Runoff Depth=2.37"
Flow Length=1,250'
Tc=12.9 min
CN=91
209.60 cfs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 32HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 19S: DURING CONSTRUCTION DA - 02
Runoff = 80.36 cfs @ 11.98 hrs, Volume= 4.130 af, Depth= 2.37"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"
Area (ac) CN Description
20.900 91 Newly graded area, HSG C
20.900 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
1.7 100 0.1600 0.96 Sheet Flow,
Fallow n= 0.050 P2= 3.32"
5.2 1,220 0.0600 3.94 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
6.9 1,320 Total
Subcatchment 19S: DURING CONSTRUCTION DA - 02
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
90
80
70
60
50
40
30
20
10
0
Type II 24-hr
2yr - 24hrs Rainfall=3.32"
Runoff Area=20.900 ac
Runoff Volume=4.130 af
Runoff Depth=2.37"
Flow Length=1,320'
Tc=6.9 min
CN=91
80.36 cfs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 33HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 25S: DURING CONSTRUCTION DA - 04
[49] Hint: Tc<2dt may require smaller dt
Runoff = 48.64 cfs @ 11.96 hrs, Volume= 2.279 af, Depth= 1.94"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"
Area (ac) CN Description
14.100 86 Newly graded area, HSG B
14.100 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
5.0 Direct Entry,
Subcatchment 25S: DURING CONSTRUCTION DA - 04
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
50
45
40
35
30
25
20
15
10
5
0
Type II 24-hr
2yr - 24hrs Rainfall=3.32"
Runoff Area=14.100 ac
Runoff Volume=2.279 af
Runoff Depth=1.94"
Tc=5.0 min
CN=86
48.64 cfs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 34HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 26S: DURING CONSTRUCTION DA - 03A
[49] Hint: Tc<2dt may require smaller dt
Runoff = 75.27 cfs @ 11.96 hrs, Volume= 3.621 af, Depth= 1.94"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"
Area (ac) CN Description
22.400 86 Newly graded area, HSG B
22.400 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
2.4 100 0.0700 0.69 Sheet Flow,
Fallow n= 0.050 P2= 3.32"
1.4 450 0.1100 5.34 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
1.8 750 0.0200 7.07 113.09 Channel Flow, Temporary Diversion
Area= 16.0 sf Perim= 29.0' r= 0.55' n= 0.020
5.6 1,300 Total
Subcatchment 26S: DURING CONSTRUCTION DA - 03A
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
80
70
60
50
40
30
20
10
0
Type II 24-hr
2yr - 24hrs Rainfall=3.32"
Runoff Area=22.400 ac
Runoff Volume=3.621 af
Runoff Depth=1.94"
Flow Length=1,300'
Tc=5.6 min
CN=86
75.27 cfs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 35HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Pond 16P: SB-01
Inflow Area = 42.770 ac, 2.88% Impervious, Inflow Depth = 1.42" for 2yr - 24hrs event
Inflow = 79.31 cfs @ 11.97 hrs, Volume= 5.061 af
Outflow = 0.00 cfs @ 0.00 hrs, Volume= 0.000 af, Atten= 100%, Lag= 0.0 min
Routing by Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Peak Elev= 675.60' @ 25.45 hrs Surf.Area= 47,824 sf Storage= 220,437 cf
Plug-Flow detention time= (not calculated: initial storage exceeds outflow)
Center-of-Mass det. time= (not calculated: no outflow)
Volume Invert Avail.Storage Storage Description
#1 670.00' 871,295 cf Custom Stage Data (Prismatic) Listed below (Recalc)
Elevation Surf.Area Inc.Store Cum.Store
(feet) (sq-ft) (cubic-feet) (cubic-feet)
670.00 31,595 0 0
672.00 36,915 68,510 68,510
674.00 42,640 79,555 148,065
676.00 49,120 91,760 239,825
678.00 58,856 107,976 347,801
680.00 74,771 133,627 481,428
682.00 95,853 170,624 652,052
684.00 123,390 219,243 871,295
Pond 16P: SB-01
Inflow
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
80
70
60
50
40
30
20
10
0
Inflow Area=42.770 ac
Peak Elev=675.60'
Storage=220,437 cf
79.31 cfs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 36HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Pond 17P: SB-02
Inflow Area = 14.100 ac, 0.00% Impervious, Inflow Depth = 1.94" for 2yr - 24hrs event
Inflow = 48.64 cfs @ 11.96 hrs, Volume= 2.279 af
Outflow = 0.00 cfs @ 0.00 hrs, Volume= 0.000 af, Atten= 100%, Lag= 0.0 min
Routing by Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Peak Elev= 655.50' @ 24.35 hrs Surf.Area= 35,951 sf Storage= 99,286 cf
Plug-Flow detention time= (not calculated: initial storage exceeds outflow)
Center-of-Mass det. time= (not calculated: no outflow)
Volume Invert Avail.Storage Storage Description
#1 652.00' 195,565 cf Custom Stage Data (Prismatic) Listed below (Recalc)
Elevation Surf.Area Inc.Store Cum.Store
(feet) (sq-ft) (cubic-feet) (cubic-feet)
652.00 14,641 0 0
654.00 33,039 47,680 47,680
656.00 36,932 69,971 117,651
658.00 40,982 77,914 195,565
Pond 17P: SB-02
Inflow
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
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(
c
f
s
)
50
45
40
35
30
25
20
15
10
5
0
Inflow Area=14.100 ac
Peak Elev=655.50'
Storage=99,286 cf
48.64 cfs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 37HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Pond 18P: SB-04
Inflow Area = 86.800 ac, 0.00% Impervious, Inflow Depth = 2.37" for 2yr - 24hrs event
Inflow = 275.29 cfs @ 12.02 hrs, Volume= 17.151 af
Outflow = 2.26 cfs @ 11.65 hrs, Volume= 16.702 af, Atten= 99%, Lag= 0.0 min
Primary = 2.26 cfs @ 11.65 hrs, Volume= 16.702 af
Routing by Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Peak Elev= 675.96' @ 24.11 hrs Surf.Area= 188,912 sf Storage= 636,856 cf
Plug-Flow detention time= 2,556.4 min calculated for 16.702 af (97% of inflow)
Center-of-Mass det. time= 2,540.5 min ( 3,343.5 - 803.0 )
Volume Invert Avail.Storage Storage Description
#1 672.00' 1,435,854 cf Custom Stage Data (Prismatic) Listed below (Recalc)
Elevation Surf.Area Inc.Store Cum.Store
(feet) (sq-ft) (cubic-feet) (cubic-feet)
672.00 94,232 0 0
674.00 180,443 274,675 274,675
676.00 189,080 369,523 644,198
678.00 197,875 386,955 1,031,153
680.00 206,826 404,701 1,435,854
Device Routing Invert Outlet Devices
#1 Primary 672.00'24.0" Round CMP_Round 24"
L= 150.0' CMP, square edge headwall, Ke= 0.500
Inlet / Outlet Invert= 672.00' / 670.00' S= 0.0133 '/' Cc= 0.900
n= 0.025 Corrugated metal, Flow Area= 3.14 sf
#2 Device 1 676.00'16.0' long Sharp-Crested Rectangular Weir 2 End Contraction(s)
#3 Device 1 672.00'2.260 cfs Constant Flow/Skimmer
#4 Primary 677.00'Custom Weir/Orifice, Cv= 2.62 (C= 3.28)
Head (feet) 0.00 1.00 2.00
Width (feet) 20.00 25.00 30.00
Primary OutFlow Max=2.26 cfs @ 11.65 hrs HW=672.82' (Free Discharge)
1=CMP_Round 24" (Passes 2.26 cfs of 2.75 cfs potential flow)
2=Sharp-Crested Rectangular Weir ( Controls 0.00 cfs)
3=Constant Flow/Skimmer (Constant Controls 2.26 cfs)
4=Custom Weir/Orifice ( Controls 0.00 cfs)
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 38HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Pond 18P: SB-04
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
300
250
200
150
100
50
0
Inflow Area=86.800 ac
Peak Elev=675.96'
Storage=636,856 cf
275.29 cfs
2.26 cfs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 39HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Pond 21P: SB-05
Inflow Area = 86.800 ac, 0.00% Impervious, Inflow Depth = 2.37" for 2yr - 24hrs event
Inflow = 275.29 cfs @ 12.02 hrs, Volume= 17.151 af
Outflow = 2.97 cfs @ 24.03 hrs, Volume= 16.802 af, Atten= 99%, Lag= 720.5 min
Primary = 2.97 cfs @ 24.03 hrs, Volume= 16.802 af
Routing by Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Peak Elev= 654.04' @ 24.03 hrs Surf.Area= 190,017 sf Storage= 627,883 cf
Plug-Flow detention time= 2,498.1 min calculated for 16.795 af (98% of inflow)
Center-of-Mass det. time= 2,486.9 min ( 3,289.9 - 803.0 )
Volume Invert Avail.Storage Storage Description
#1 650.00' 2,092,446 cf Custom Stage Data (Prismatic) Listed below (Recalc)
Elevation Surf.Area Inc.Store Cum.Store
(feet) (sq-ft) (cubic-feet) (cubic-feet)
650.00 100,077 0 0
652.00 165,087 265,164 265,164
654.00 189,476 354,563 619,727
656.00 214,653 404,129 1,023,856
658.00 261,346 475,999 1,499,855
660.00 331,245 592,591 2,092,446
Device Routing Invert Outlet Devices
#1 Primary 650.00'24.0" Round CMP_Round 24"
L= 150.0' CMP, square edge headwall, Ke= 0.500
Inlet / Outlet Invert= 650.00' / 646.00' S= 0.0267 '/' Cc= 0.900
n= 0.025 Corrugated metal, Flow Area= 3.14 sf
#2 Device 1 654.00'16.0' long Sharp-Crested Rectangular Weir 2 End Contraction(s)
#3 Device 1 650.00'2.260 cfs Constant Flow/Skimmer
#4 Primary 655.00'Custom Weir/Orifice, Cv= 2.62 (C= 3.28)
Head (feet) 0.00 1.00 2.00
Width (feet) 20.00 25.00 30.00
Primary OutFlow Max=2.73 cfs @ 24.03 hrs HW=654.04' (Free Discharge)
1=CMP_Round 24" (Passes 2.73 cfs of 21.37 cfs potential flow)
2=Sharp-Crested Rectangular Weir (Weir Controls 0.47 cfs @ 0.68 fps)
3=Constant Flow/Skimmer (Constant Controls 2.26 cfs)
4=Custom Weir/Orifice ( Controls 0.00 cfs)
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 40HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Pond 21P: SB-05
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
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(
c
f
s
)
300
250
200
150
100
50
0
Inflow Area=86.800 ac
Peak Elev=654.04'
Storage=627,883 cf
275.29 cfs
2.97 cfs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 41HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Pond 24P: SB-03
Inflow Area = 36.500 ac, 0.00% Impervious, Inflow Depth = 1.94" for 2yr - 24hrs event
Inflow = 123.80 cfs @ 11.96 hrs, Volume= 5.900 af
Outflow = 1.13 cfs @ 11.45 hrs, Volume= 5.887 af, Atten= 99%, Lag= 0.0 min
Primary = 1.13 cfs @ 11.45 hrs, Volume= 5.887 af
Routing by Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Peak Elev= 655.12' @ 24.00 hrs Surf.Area= 92,016 sf Storage= 202,791 cf
Plug-Flow detention time= 1,736.2 min calculated for 5.884 af (100% of inflow)
Center-of-Mass det. time= 1,736.4 min ( 2,553.6 - 817.3 )
Volume Invert Avail.Storage Storage Description
#1 652.00' 688,748 cf Custom Stage Data (Prismatic) Listed below (Recalc)
Elevation Surf.Area Inc.Store Cum.Store
(feet) (sq-ft) (cubic-feet) (cubic-feet)
652.00 20,697 0 0
653.00 47,259 33,978 33,978
654.00 88,689 67,974 101,952
655.00 91,666 90,178 192,130
656.00 94,682 93,174 285,304
657.00 97,737 96,210 381,513
658.00 100,832 99,285 480,798
659.00 103,965 102,399 583,196
660.00 107,139 105,552 688,748
Device Routing Invert Outlet Devices
#1 Primary 652.00'24.0" Round CMP_Round 24"
L= 200.0' CMP, square edge headwall, Ke= 0.500
Inlet / Outlet Invert= 652.00' / 650.00' S= 0.0100 '/' Cc= 0.900
n= 0.025 Corrugated metal, Flow Area= 3.14 sf
#2 Device 1 656.00'16.0' long Sharp-Crested Rectangular Weir 2 End Contraction(s)
#3 Device 1 652.00'1.130 cfs Constant Flow/Skimmer
#4 Primary 657.00'Custom Weir/Orifice, Cv= 2.62 (C= 3.28)
Head (feet) 0.00 1.00 2.00 3.00
Width (feet) 20.00 25.00 30.00 35.00
Primary OutFlow Max=1.13 cfs @ 11.45 hrs HW=652.58' (Free Discharge)
1=CMP_Round 24" (Passes 1.13 cfs of 1.21 cfs potential flow)
2=Sharp-Crested Rectangular Weir ( Controls 0.00 cfs)
3=Constant Flow/Skimmer (Constant Controls 1.13 cfs)
4=Custom Weir/Orifice ( Controls 0.00 cfs)
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 42HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Pond 24P: SB-03
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
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120
100
80
60
40
20
0
Inflow Area=36.500 ac
Peak Elev=655.12'
Storage=202,791 cf
123.80 cfs
1.13 cfs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 43HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Link 8L: Total
Inflow Area = 86.800 ac, 0.00% Impervious, Inflow Depth = 2.37" for 2yr - 24hrs event
Inflow = 275.29 cfs @ 12.02 hrs, Volume= 17.151 af
Primary = 275.29 cfs @ 12.02 hrs, Volume= 17.151 af, Atten= 0%, Lag= 0.0 min
Primary outflow = Inflow, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Link 8L: Total
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
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(
c
f
s
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300
250
200
150
100
50
0
Inflow Area=86.800 ac
275.29 cfs275.29 cfs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 44HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Link 10L: Total
Inflow Area = 42.770 ac, 2.88% Impervious, Inflow Depth = 1.42" for 2yr - 24hrs event
Inflow = 79.31 cfs @ 11.97 hrs, Volume= 5.061 af
Primary = 79.31 cfs @ 11.97 hrs, Volume= 5.061 af, Atten= 0%, Lag= 0.0 min
Primary outflow = Inflow, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Link 10L: Total
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
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(
c
f
s
)
80
70
60
50
40
30
20
10
0
Inflow Area=42.770 ac
79.31 cfs79.31 cfs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 45HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Link 20L: Total
Inflow Area = 86.800 ac, 0.00% Impervious, Inflow Depth = 2.37" for 2yr - 24hrs event
Inflow = 275.29 cfs @ 12.02 hrs, Volume= 17.151 af
Primary = 275.29 cfs @ 12.02 hrs, Volume= 17.151 af, Atten= 0%, Lag= 0.0 min
Primary outflow = Inflow, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Link 20L: Total
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
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(
c
f
s
)
300
250
200
150
100
50
0
Inflow Area=86.800 ac
275.29 cfs275.29 cfs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 46HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Link 26L: Total
Inflow Area = 36.500 ac, 0.00% Impervious, Inflow Depth = 1.94" for 2yr - 24hrs event
Inflow = 123.80 cfs @ 11.96 hrs, Volume= 5.900 af
Primary = 123.80 cfs @ 11.96 hrs, Volume= 5.900 af, Atten= 0%, Lag= 0.0 min
Primary outflow = Inflow, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Link 26L: Total
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
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(
c
f
s
)
120
100
80
60
40
20
0
Inflow Area=36.500 ac
123.80 cfs123.80 cfs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 47HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 4S: DURING CONSTRUCTION DA - 01
Runoff = 329.95 cfs @ 12.04 hrs, Volume= 21.016 af, Depth= 3.83"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"
Area (ac) CN Description
65.900 91 Newly graded area, HSG C
65.900 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
4.5 100 0.0150 0.37 Sheet Flow,
Fallow n= 0.050 P2= 3.32"
8.4 1,150 0.0200 2.28 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
12.9 1,250 Total
Subcatchment 4S: DURING CONSTRUCTION DA - 01
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
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(
c
f
s
)
350
300
250
200
150
100
50
0
Type II 24-hr
10yr - 24hrs Rainfall=4.84"
Runoff Area=65.900 ac
Runoff Volume=21.016 af
Runoff Depth=3.83"
Flow Length=1,250'
Tc=12.9 min
CN=91
329.95 cfs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 48HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 5S: DURING CONSTRUCTION DA - 02
Runoff = 125.90 cfs @ 11.98 hrs, Volume= 6.665 af, Depth= 3.83"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"
Area (ac) CN Description
20.900 91 Newly graded area, HSG C
20.900 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
1.7 100 0.1600 0.96 Sheet Flow,
Fallow n= 0.050 P2= 3.32"
5.2 1,220 0.0600 3.94 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
6.9 1,320 Total
Subcatchment 5S: DURING CONSTRUCTION DA - 02
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
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(
c
f
s
)
140
120
100
80
60
40
20
0
Type II 24-hr
10yr - 24hrs Rainfall=4.84"
Runoff Area=20.900 ac
Runoff Volume=6.665 af
Runoff Depth=3.83"
Flow Length=1,320'
Tc=6.9 min
CN=91
125.90 cfs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 49HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 6S: DURING CONSTRUCTION DA - 03A
[49] Hint: Tc<2dt may require smaller dt
Runoff = 125.81 cfs @ 11.96 hrs, Volume= 6.194 af, Depth= 3.32"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"
Area (ac) CN Description
22.400 86 Newly graded area, HSG B
22.400 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
2.4 100 0.0700 0.69 Sheet Flow,
Fallow n= 0.050 P2= 3.32"
1.4 450 0.1100 5.34 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
1.8 750 0.0200 7.07 113.09 Channel Flow, Temporary Diversion
Area= 16.0 sf Perim= 29.0' r= 0.55' n= 0.020
5.6 1,300 Total
Subcatchment 6S: DURING CONSTRUCTION DA - 03A
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
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(
c
f
s
)
140
120
100
80
60
40
20
0
Type II 24-hr
10yr - 24hrs Rainfall=4.84"
Runoff Area=22.400 ac
Runoff Volume=6.194 af
Runoff Depth=3.32"
Flow Length=1,300'
Tc=5.6 min
CN=86
125.81 cfs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 50HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 7S: DURING CONSTRUCTION DA - 04
[49] Hint: Tc<2dt may require smaller dt
Runoff = 81.22 cfs @ 11.95 hrs, Volume= 3.899 af, Depth= 3.32"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"
Area (ac) CN Description
14.100 86 Newly graded area, HSG B
14.100 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
5.0 Direct Entry,
Subcatchment 7S: DURING CONSTRUCTION DA - 04
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
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(
c
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)
90
80
70
60
50
40
30
20
10
0
Type II 24-hr
10yr - 24hrs Rainfall=4.84"
Runoff Area=14.100 ac
Runoff Volume=3.899 af
Runoff Depth=3.32"
Tc=5.0 min
CN=86
81.22 cfs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 51HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 9S: DURING CONSTRUCTION DA - 03B
Runoff = 35.47 cfs @ 12.19 hrs, Volume= 3.127 af, Depth= 1.84"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"
Area (ac) CN Description
8.520 60 Woods, Fair, HSG B
3.220 65 Woods/grass comb., Fair, HSG B
1.130 85 Gravel roads, HSG B
1.230 98 Paved parking, HSG B
* 1.530 88 Railbed - Gravel
4.740 69 Pasture/grassland/range, Fair, HSG B
20.370 69 Weighted Average
19.140 93.96% Pervious Area
1.230 6.04% Impervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
21.1 100 0.0200 0.08 Sheet Flow,
Woods: Light underbrush n= 0.400 P2= 3.32"
3.6 740 0.0460 3.45 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
24.7 840 Total
Subcatchment 9S: DURING CONSTRUCTION DA - 03B
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
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(
c
f
s
)
35
30
25
20
15
10
5
0
Type II 24-hr
10yr - 24hrs Rainfall=4.84"
Runoff Area=20.370 ac
Runoff Volume=3.127 af
Runoff Depth=1.84"
Flow Length=840'
Tc=24.7 min
CN=69
35.47 cfs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 52HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 18S: DURING CONSTRUCTION DA - 01
Runoff = 329.95 cfs @ 12.04 hrs, Volume= 21.016 af, Depth= 3.83"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"
Area (ac) CN Description
65.900 91 Newly graded area, HSG C
65.900 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
4.5 100 0.0150 0.37 Sheet Flow,
Fallow n= 0.050 P2= 3.32"
8.4 1,150 0.0200 2.28 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
12.9 1,250 Total
Subcatchment 18S: DURING CONSTRUCTION DA - 01
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
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(
c
f
s
)
350
300
250
200
150
100
50
0
Type II 24-hr
10yr - 24hrs Rainfall=4.84"
Runoff Area=65.900 ac
Runoff Volume=21.016 af
Runoff Depth=3.83"
Flow Length=1,250'
Tc=12.9 min
CN=91
329.95 cfs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 53HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 19S: DURING CONSTRUCTION DA - 02
Runoff = 125.90 cfs @ 11.98 hrs, Volume= 6.665 af, Depth= 3.83"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"
Area (ac) CN Description
20.900 91 Newly graded area, HSG C
20.900 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
1.7 100 0.1600 0.96 Sheet Flow,
Fallow n= 0.050 P2= 3.32"
5.2 1,220 0.0600 3.94 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
6.9 1,320 Total
Subcatchment 19S: DURING CONSTRUCTION DA - 02
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
140
120
100
80
60
40
20
0
Type II 24-hr
10yr - 24hrs Rainfall=4.84"
Runoff Area=20.900 ac
Runoff Volume=6.665 af
Runoff Depth=3.83"
Flow Length=1,320'
Tc=6.9 min
CN=91
125.90 cfs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 54HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 25S: DURING CONSTRUCTION DA - 04
[49] Hint: Tc<2dt may require smaller dt
Runoff = 81.22 cfs @ 11.95 hrs, Volume= 3.899 af, Depth= 3.32"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"
Area (ac) CN Description
14.100 86 Newly graded area, HSG B
14.100 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
5.0 Direct Entry,
Subcatchment 25S: DURING CONSTRUCTION DA - 04
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
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(
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90
80
70
60
50
40
30
20
10
0
Type II 24-hr
10yr - 24hrs Rainfall=4.84"
Runoff Area=14.100 ac
Runoff Volume=3.899 af
Runoff Depth=3.32"
Tc=5.0 min
CN=86
81.22 cfs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 55HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 26S: DURING CONSTRUCTION DA - 03A
[49] Hint: Tc<2dt may require smaller dt
Runoff = 125.81 cfs @ 11.96 hrs, Volume= 6.194 af, Depth= 3.32"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"
Area (ac) CN Description
22.400 86 Newly graded area, HSG B
22.400 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
2.4 100 0.0700 0.69 Sheet Flow,
Fallow n= 0.050 P2= 3.32"
1.4 450 0.1100 5.34 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
1.8 750 0.0200 7.07 113.09 Channel Flow, Temporary Diversion
Area= 16.0 sf Perim= 29.0' r= 0.55' n= 0.020
5.6 1,300 Total
Subcatchment 26S: DURING CONSTRUCTION DA - 03A
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
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(
c
f
s
)
140
120
100
80
60
40
20
0
Type II 24-hr
10yr - 24hrs Rainfall=4.84"
Runoff Area=22.400 ac
Runoff Volume=6.194 af
Runoff Depth=3.32"
Flow Length=1,300'
Tc=5.6 min
CN=86
125.81 cfs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 56HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Pond 16P: SB-01
Inflow Area = 42.770 ac, 2.88% Impervious, Inflow Depth = 2.61" for 10yr - 24hrs event
Inflow = 139.06 cfs @ 11.97 hrs, Volume= 9.320 af
Outflow = 0.00 cfs @ 0.00 hrs, Volume= 0.000 af, Atten= 100%, Lag= 0.0 min
Routing by Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Peak Elev= 678.93' @ 25.45 hrs Surf.Area= 66,256 sf Storage= 405,973 cf
Plug-Flow detention time= (not calculated: initial storage exceeds outflow)
Center-of-Mass det. time= (not calculated: no outflow)
Volume Invert Avail.Storage Storage Description
#1 670.00' 871,295 cf Custom Stage Data (Prismatic) Listed below (Recalc)
Elevation Surf.Area Inc.Store Cum.Store
(feet) (sq-ft) (cubic-feet) (cubic-feet)
670.00 31,595 0 0
672.00 36,915 68,510 68,510
674.00 42,640 79,555 148,065
676.00 49,120 91,760 239,825
678.00 58,856 107,976 347,801
680.00 74,771 133,627 481,428
682.00 95,853 170,624 652,052
684.00 123,390 219,243 871,295
Pond 16P: SB-01
Inflow
Hydrograph
Time (hours)
1201101009080706050403020100
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(
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140
120
100
80
60
40
20
0
Inflow Area=42.770 ac
Peak Elev=678.93'
Storage=405,973 cf
139.06 cfs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 57HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Pond 17P: SB-02
Inflow Area = 14.100 ac, 0.00% Impervious, Inflow Depth = 3.32" for 10yr - 24hrs event
Inflow = 81.22 cfs @ 11.95 hrs, Volume= 3.899 af
Outflow = 0.00 cfs @ 0.00 hrs, Volume= 0.000 af, Atten= 100%, Lag= 0.0 min
Routing by Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Peak Elev= 657.36' @ 24.35 hrs Surf.Area= 39,690 sf Storage= 169,822 cf
Plug-Flow detention time= (not calculated: initial storage exceeds outflow)
Center-of-Mass det. time= (not calculated: no outflow)
Volume Invert Avail.Storage Storage Description
#1 652.00' 195,565 cf Custom Stage Data (Prismatic) Listed below (Recalc)
Elevation Surf.Area Inc.Store Cum.Store
(feet) (sq-ft) (cubic-feet) (cubic-feet)
652.00 14,641 0 0
654.00 33,039 47,680 47,680
656.00 36,932 69,971 117,651
658.00 40,982 77,914 195,565
Pond 17P: SB-02
Inflow
Hydrograph
Time (hours)
1201101009080706050403020100
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90
80
70
60
50
40
30
20
10
0
Inflow Area=14.100 ac
Peak Elev=657.36'
Storage=169,822 cf
81.22 cfs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 58HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Pond 18P: SB-04
Inflow Area = 86.800 ac, 0.00% Impervious, Inflow Depth = 3.83" for 10yr - 24hrs event
Inflow = 433.67 cfs @ 12.02 hrs, Volume= 27.681 af
Outflow = 18.97 cfs @ 13.70 hrs, Volume= 27.188 af, Atten= 96%, Lag= 100.8 min
Primary = 18.97 cfs @ 13.70 hrs, Volume= 27.188 af
Routing by Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Peak Elev= 676.76' @ 13.70 hrs Surf.Area= 192,437 sf Storage= 789,804 cf
Plug-Flow detention time= 1,748.9 min calculated for 27.176 af (98% of inflow)
Center-of-Mass det. time= 1,739.3 min ( 2,529.0 - 789.7 )
Volume Invert Avail.Storage Storage Description
#1 672.00' 1,435,854 cf Custom Stage Data (Prismatic) Listed below (Recalc)
Elevation Surf.Area Inc.Store Cum.Store
(feet) (sq-ft) (cubic-feet) (cubic-feet)
672.00 94,232 0 0
674.00 180,443 274,675 274,675
676.00 189,080 369,523 644,198
678.00 197,875 386,955 1,031,153
680.00 206,826 404,701 1,435,854
Device Routing Invert Outlet Devices
#1 Primary 672.00'24.0" Round CMP_Round 24"
L= 150.0' CMP, square edge headwall, Ke= 0.500
Inlet / Outlet Invert= 672.00' / 670.00' S= 0.0133 '/' Cc= 0.900
n= 0.025 Corrugated metal, Flow Area= 3.14 sf
#2 Device 1 676.00'16.0' long Sharp-Crested Rectangular Weir 2 End Contraction(s)
#3 Device 1 672.00'2.260 cfs Constant Flow/Skimmer
#4 Primary 677.00'Custom Weir/Orifice, Cv= 2.62 (C= 3.28)
Head (feet) 0.00 1.00 2.00
Width (feet) 20.00 25.00 30.00
Primary OutFlow Max=18.97 cfs @ 13.70 hrs HW=676.76' (Free Discharge)
1=CMP_Round 24" (Barrel Controls 18.97 cfs @ 6.04 fps)
2=Sharp-Crested Rectangular Weir (Passes < 34.56 cfs potential flow)
3=Constant Flow/Skimmer (Passes < 2.26 cfs potential flow)
4=Custom Weir/Orifice ( Controls 0.00 cfs)
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 59HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Pond 18P: SB-04
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
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(
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450
400
350
300
250
200
150
100
50
0
Inflow Area=86.800 ac
Peak Elev=676.76'
Storage=789,804 cf
433.67 cfs
18.97 cfs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 60HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Pond 21P: SB-05
Inflow Area = 86.800 ac, 0.00% Impervious, Inflow Depth = 3.83" for 10yr - 24hrs event
Inflow = 433.67 cfs @ 12.02 hrs, Volume= 27.681 af
Outflow = 22.61 cfs @ 13.36 hrs, Volume= 27.318 af, Atten= 95%, Lag= 80.7 min
Primary = 22.61 cfs @ 13.36 hrs, Volume= 27.318 af
Routing by Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Peak Elev= 654.77' @ 13.36 hrs Surf.Area= 199,130 sf Storage= 768,740 cf
Plug-Flow detention time= 1,648.2 min calculated for 27.306 af (99% of inflow)
Center-of-Mass det. time= 1,641.6 min ( 2,431.3 - 789.7 )
Volume Invert Avail.Storage Storage Description
#1 650.00' 2,092,446 cf Custom Stage Data (Prismatic) Listed below (Recalc)
Elevation Surf.Area Inc.Store Cum.Store
(feet) (sq-ft) (cubic-feet) (cubic-feet)
650.00 100,077 0 0
652.00 165,087 265,164 265,164
654.00 189,476 354,563 619,727
656.00 214,653 404,129 1,023,856
658.00 261,346 475,999 1,499,855
660.00 331,245 592,591 2,092,446
Device Routing Invert Outlet Devices
#1 Primary 650.00'24.0" Round CMP_Round 24"
L= 150.0' CMP, square edge headwall, Ke= 0.500
Inlet / Outlet Invert= 650.00' / 646.00' S= 0.0267 '/' Cc= 0.900
n= 0.025 Corrugated metal, Flow Area= 3.14 sf
#2 Device 1 654.00'16.0' long Sharp-Crested Rectangular Weir 2 End Contraction(s)
#3 Device 1 650.00'2.260 cfs Constant Flow/Skimmer
#4 Primary 655.00'Custom Weir/Orifice, Cv= 2.62 (C= 3.28)
Head (feet) 0.00 1.00 2.00
Width (feet) 20.00 25.00 30.00
Primary OutFlow Max=22.61 cfs @ 13.36 hrs HW=654.77' (Free Discharge)
1=CMP_Round 24" (Barrel Controls 22.61 cfs @ 7.20 fps)
2=Sharp-Crested Rectangular Weir (Passes < 34.80 cfs potential flow)
3=Constant Flow/Skimmer (Passes < 2.26 cfs potential flow)
4=Custom Weir/Orifice ( Controls 0.00 cfs)
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 61HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Pond 21P: SB-05
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
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Inflow Area=86.800 ac
Peak Elev=654.77'
Storage=768,740 cf
433.67 cfs
22.61 cfs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 62HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Pond 24P: SB-03
Inflow Area = 36.500 ac, 0.00% Impervious, Inflow Depth = 3.32" for 10yr - 24hrs event
Inflow = 206.86 cfs @ 11.96 hrs, Volume= 10.092 af
Outflow = 5.54 cfs @ 14.47 hrs, Volume= 10.061 af, Atten= 97%, Lag= 150.8 min
Primary = 5.54 cfs @ 14.47 hrs, Volume= 10.061 af
Routing by Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Peak Elev= 656.19' @ 14.47 hrs Surf.Area= 95,264 sf Storage= 303,406 cf
Plug-Flow detention time= 1,899.5 min calculated for 10.057 af (100% of inflow)
Center-of-Mass det. time= 1,899.1 min ( 2,701.1 - 802.0 )
Volume Invert Avail.Storage Storage Description
#1 652.00' 688,748 cf Custom Stage Data (Prismatic) Listed below (Recalc)
Elevation Surf.Area Inc.Store Cum.Store
(feet) (sq-ft) (cubic-feet) (cubic-feet)
652.00 20,697 0 0
653.00 47,259 33,978 33,978
654.00 88,689 67,974 101,952
655.00 91,666 90,178 192,130
656.00 94,682 93,174 285,304
657.00 97,737 96,210 381,513
658.00 100,832 99,285 480,798
659.00 103,965 102,399 583,196
660.00 107,139 105,552 688,748
Device Routing Invert Outlet Devices
#1 Primary 652.00'24.0" Round CMP_Round 24"
L= 200.0' CMP, square edge headwall, Ke= 0.500
Inlet / Outlet Invert= 652.00' / 650.00' S= 0.0100 '/' Cc= 0.900
n= 0.025 Corrugated metal, Flow Area= 3.14 sf
#2 Device 1 656.00'16.0' long Sharp-Crested Rectangular Weir 2 End Contraction(s)
#3 Device 1 652.00'1.130 cfs Constant Flow/Skimmer
#4 Primary 657.00'Custom Weir/Orifice, Cv= 2.62 (C= 3.28)
Head (feet) 0.00 1.00 2.00 3.00
Width (feet) 20.00 25.00 30.00 35.00
Primary OutFlow Max=5.47 cfs @ 14.47 hrs HW=656.19' (Free Discharge)
1=CMP_Round 24" (Passes 5.47 cfs of 15.76 cfs potential flow)
2=Sharp-Crested Rectangular Weir (Weir Controls 4.34 cfs @ 1.43 fps)
3=Constant Flow/Skimmer (Constant Controls 1.13 cfs)
4=Custom Weir/Orifice ( Controls 0.00 cfs)
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 63HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Pond 24P: SB-03
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
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Inflow Area=36.500 ac
Peak Elev=656.19'
Storage=303,406 cf
206.86 cfs
5.54 cfs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 64HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Link 8L: Total
Inflow Area = 86.800 ac, 0.00% Impervious, Inflow Depth = 3.83" for 10yr - 24hrs event
Inflow = 433.67 cfs @ 12.02 hrs, Volume= 27.681 af
Primary = 433.67 cfs @ 12.02 hrs, Volume= 27.681 af, Atten= 0%, Lag= 0.0 min
Primary outflow = Inflow, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Link 8L: Total
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
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150
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Inflow Area=86.800 ac
433.67 cfs433.67 cfs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 65HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Link 10L: Total
Inflow Area = 42.770 ac, 2.88% Impervious, Inflow Depth = 2.61" for 10yr - 24hrs event
Inflow = 139.06 cfs @ 11.97 hrs, Volume= 9.320 af
Primary = 139.06 cfs @ 11.97 hrs, Volume= 9.320 af, Atten= 0%, Lag= 0.0 min
Primary outflow = Inflow, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Link 10L: Total
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
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120
100
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60
40
20
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Inflow Area=42.770 ac
139.06 cfs139.06 cfs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 66HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Link 20L: Total
Inflow Area = 86.800 ac, 0.00% Impervious, Inflow Depth = 3.83" for 10yr - 24hrs event
Inflow = 433.67 cfs @ 12.02 hrs, Volume= 27.681 af
Primary = 433.67 cfs @ 12.02 hrs, Volume= 27.681 af, Atten= 0%, Lag= 0.0 min
Primary outflow = Inflow, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Link 20L: Total
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
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400
350
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250
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150
100
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Inflow Area=86.800 ac
433.67 cfs433.67 cfs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 67HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Link 26L: Total
Inflow Area = 36.500 ac, 0.00% Impervious, Inflow Depth = 3.32" for 10yr - 24hrs event
Inflow = 206.86 cfs @ 11.96 hrs, Volume= 10.092 af
Primary = 206.86 cfs @ 11.96 hrs, Volume= 10.092 af, Atten= 0%, Lag= 0.0 min
Primary outflow = Inflow, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Link 26L: Total
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
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Inflow Area=36.500 ac
206.86 cfs206.86 cfs
6S
DURING
CONSTRUCTION DA -
03A
9S
DURING
CONSTRUCTION DA -
03B
16P
SB-01
10L
Total
Routing Diagram for Riverbend Ash Pond Closure
Prepared by AMEC, Printed 11/5/2015
HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Subcat Reach Pond Link
Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 2HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Area Listing (selected nodes)
Area
(acres)
CN Description
(subcatchment-numbers)
1.130 85 Gravel roads, HSG B (9S)
22.400 86 Newly graded area, HSG B (6S)
4.740 69 Pasture/grassland/range, Fair, HSG B (9S)
1.230 98 Paved parking, HSG B (9S)
1.530 88 Railbed - Gravel (9S)
8.520 60 Woods, Fair, HSG B (9S)
3.220 65 Woods/grass comb., Fair, HSG B (9S)
42.770 78 TOTAL AREA
Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 3HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Soil Listing (selected nodes)
Area
(acres)
Soil
Group
Subcatchment
Numbers
0.000 HSG A
41.240 HSG B 6S, 9S
0.000 HSG C
0.000 HSG D
1.530 Other 9S
42.770 TOTAL AREA
Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 4HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Ground Covers (selected nodes)
HSG-A
(acres)
HSG-B
(acres)
HSG-C
(acres)
HSG-D
(acres)
Other
(acres)
Total
(acres)
Ground
Cover
Subcatchment
Numbers
0.000 1.130 0.000 0.000 0.000 1.130 Gravel roads 9S
0.000 22.400 0.000 0.000 0.000 22.400 Newly graded area 6S
0.000 4.740 0.000 0.000 0.000 4.740 Pasture/grassland/range, Fair 9S
0.000 1.230 0.000 0.000 0.000 1.230 Paved parking 9S
0.000 0.000 0.000 0.000 1.530 1.530 Railbed - Gravel 9S
0.000 8.520 0.000 0.000 0.000 8.520 Woods, Fair 9S
0.000 3.220 0.000 0.000 0.000 3.220 Woods/grass comb., Fair 9S
0.000 41.240 0.000 0.000 1.530 42.770 TOTAL AREA
Type II 24-hr 25yr - 24hrs Rainfall=5.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 5HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 6S: DURING CONSTRUCTION DA - 03A
[49] Hint: Tc<2dt may require smaller dt
Runoff = 156.22 cfs @ 11.96 hrs, Volume= 7.788 af, Depth= 4.17"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 25yr - 24hrs Rainfall=5.75"
Area (ac) CN Description
22.400 86 Newly graded area, HSG B
22.400 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
2.4 100 0.0700 0.69 Sheet Flow,
Fallow n= 0.050 P2= 3.32"
1.4 450 0.1100 5.34 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
1.8 750 0.0200 7.07 113.09 Channel Flow, Temporary Diversion
Area= 16.0 sf Perim= 29.0' r= 0.55' n= 0.020
5.6 1,300 Total
Subcatchment 6S: DURING CONSTRUCTION DA - 03A
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
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Type II 24-hr
25yr - 24hrs Rainfall=5.75"
Runoff Area=22.400 ac
Runoff Volume=7.788 af
Runoff Depth=4.17"
Flow Length=1,300'
Tc=5.6 min
CN=86
156.22 cfs
Type II 24-hr 25yr - 24hrs Rainfall=5.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 6HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 9S: DURING CONSTRUCTION DA - 03B
Runoff = 49.40 cfs @ 12.19 hrs, Volume= 4.276 af, Depth= 2.52"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 25yr - 24hrs Rainfall=5.75"
Area (ac) CN Description
8.520 60 Woods, Fair, HSG B
3.220 65 Woods/grass comb., Fair, HSG B
1.130 85 Gravel roads, HSG B
1.230 98 Paved parking, HSG B
* 1.530 88 Railbed - Gravel
4.740 69 Pasture/grassland/range, Fair, HSG B
20.370 69 Weighted Average
19.140 93.96% Pervious Area
1.230 6.04% Impervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
21.1 100 0.0200 0.08 Sheet Flow,
Woods: Light underbrush n= 0.400 P2= 3.32"
3.6 740 0.0460 3.45 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
24.7 840 Total
Subcatchment 9S: DURING CONSTRUCTION DA - 03B
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
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50
45
40
35
30
25
20
15
10
5
0
Type II 24-hr
25yr - 24hrs Rainfall=5.75"
Runoff Area=20.370 ac
Runoff Volume=4.276 af
Runoff Depth=2.52"
Flow Length=840'
Tc=24.7 min
CN=69
49.40 cfs
Type II 24-hr 25yr - 24hrs Rainfall=5.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 7HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Pond 16P: SB-01
Inflow Area = 42.770 ac, 2.88% Impervious, Inflow Depth = 3.38" for 25yr - 24hrs event
Inflow = 176.02 cfs @ 11.97 hrs, Volume= 12.064 af
Outflow = 0.00 cfs @ 0.00 hrs, Volume= 0.000 af, Atten= 100%, Lag= 0.0 min
Routing by Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Peak Elev= 680.57' @ 25.45 hrs Surf.Area= 80,743 sf Storage= 525,482 cf
Plug-Flow detention time= (not calculated: initial storage exceeds outflow)
Center-of-Mass det. time= (not calculated: no outflow)
Volume Invert Avail.Storage Storage Description
#1 670.00' 871,295 cf Custom Stage Data (Prismatic) Listed below (Recalc)
Elevation Surf.Area Inc.Store Cum.Store
(feet) (sq-ft) (cubic-feet) (cubic-feet)
670.00 31,595 0 0
672.00 36,915 68,510 68,510
674.00 42,640 79,555 148,065
676.00 49,120 91,760 239,825
678.00 58,856 107,976 347,801
680.00 74,771 133,627 481,428
682.00 95,853 170,624 652,052
684.00 123,390 219,243 871,295
Pond 16P: SB-01
Inflow
Hydrograph
Time (hours)
1201101009080706050403020100
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160
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120
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Inflow Area=42.770 ac
Peak Elev=680.57'
Storage=525,482 cf
176.02 cfs
Type II 24-hr 25yr - 24hrs Rainfall=5.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 8HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Link 10L: Total
Inflow Area = 42.770 ac, 2.88% Impervious, Inflow Depth = 3.38" for 25yr - 24hrs event
Inflow = 176.02 cfs @ 11.97 hrs, Volume= 12.064 af
Primary = 176.02 cfs @ 11.97 hrs, Volume= 12.064 af, Atten= 0%, Lag= 0.0 min
Primary outflow = Inflow, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Link 10L: Total
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
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Inflow Area=42.770 ac
176.02 cfs176.02 cfs
4S
DURING
CONSTRUCTION DA -
01
5S
DURING
CONSTRUCTION DA -
02
18S
DURING
CONSTRUCTION DA -
01
19S
DURING
CONSTRUCTION DA -
02
25S
DURING
CONSTRUCTION DA -
04
26S
DURING
CONSTRUCTION DA -
03A
18P
SB-04
21P
SB-05 24P
SB-03
8L
Total
20L
Total 26L
Total
Routing Diagram for Riverbend Ash Pond Closure
Prepared by AMEC, Printed 11/5/2015
HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Subcat Reach Pond Link
Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 2HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Area Listing (selected nodes)
Area
(acres)
CN Description
(subcatchment-numbers)
36.500 86 Newly graded area, HSG B (25S, 26S)
173.600 91 Newly graded area, HSG C (4S, 5S, 18S, 19S)
210.100 90 TOTAL AREA
Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 3HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Soil Listing (selected nodes)
Area
(acres)
Soil
Group
Subcatchment
Numbers
0.000 HSG A
36.500 HSG B 25S, 26S
173.600 HSG C 4S, 5S, 18S, 19S
0.000 HSG D
0.000 Other
210.100 TOTAL AREA
Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 4HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Ground Covers (selected nodes)
HSG-A
(acres)
HSG-B
(acres)
HSG-C
(acres)
HSG-D
(acres)
Other
(acres)
Total
(acres)
Ground
Cover
Subcatchment
Numbers
0.000 36.500 173.600 0.000 0.000 210.100 Newly graded area 4S, 5S, 18S,
19S, 25S, 26S
0.000 36.500 173.600 0.000 0.000 210.100 TOTAL AREA
Type II 24-hr 100yr - 24hrs Rainfall=7.21"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 5HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 4S: DURING CONSTRUCTION DA - 01
Runoff = 515.36 cfs @ 12.04 hrs, Volume= 33.749 af, Depth= 6.15"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 100yr - 24hrs Rainfall=7.21"
Area (ac) CN Description
65.900 91 Newly graded area, HSG C
65.900 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
4.5 100 0.0150 0.37 Sheet Flow,
Fallow n= 0.050 P2= 3.32"
8.4 1,150 0.0200 2.28 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
12.9 1,250 Total
Subcatchment 4S: DURING CONSTRUCTION DA - 01
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
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550
500
450
400
350
300
250
200
150
100
50
0
Type II 24-hr
100yr - 24hrs Rainfall=7.21"
Runoff Area=65.900 ac
Runoff Volume=33.749 af
Runoff Depth=6.15"
Flow Length=1,250'
Tc=12.9 min
CN=91
515.36 cfs
Type II 24-hr 100yr - 24hrs Rainfall=7.21"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 6HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 5S: DURING CONSTRUCTION DA - 02
Runoff = 195.99 cfs @ 11.98 hrs, Volume= 10.703 af, Depth= 6.15"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 100yr - 24hrs Rainfall=7.21"
Area (ac) CN Description
20.900 91 Newly graded area, HSG C
20.900 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
1.7 100 0.1600 0.96 Sheet Flow,
Fallow n= 0.050 P2= 3.32"
5.2 1,220 0.0600 3.94 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
6.9 1,320 Total
Subcatchment 5S: DURING CONSTRUCTION DA - 02
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
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200
180
160
140
120
100
80
60
40
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0
Type II 24-hr
100yr - 24hrs Rainfall=7.21"
Runoff Area=20.900 ac
Runoff Volume=10.703 af
Runoff Depth=6.15"
Flow Length=1,320'
Tc=6.9 min
CN=91
195.99 cfs
Type II 24-hr 100yr - 24hrs Rainfall=7.21"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 7HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 18S: DURING CONSTRUCTION DA - 01
Runoff = 515.36 cfs @ 12.04 hrs, Volume= 33.749 af, Depth= 6.15"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 100yr - 24hrs Rainfall=7.21"
Area (ac) CN Description
65.900 91 Newly graded area, HSG C
65.900 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
4.5 100 0.0150 0.37 Sheet Flow,
Fallow n= 0.050 P2= 3.32"
8.4 1,150 0.0200 2.28 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
12.9 1,250 Total
Subcatchment 18S: DURING CONSTRUCTION DA - 01
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
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(
c
f
s
)
550
500
450
400
350
300
250
200
150
100
50
0
Type II 24-hr
100yr - 24hrs Rainfall=7.21"
Runoff Area=65.900 ac
Runoff Volume=33.749 af
Runoff Depth=6.15"
Flow Length=1,250'
Tc=12.9 min
CN=91
515.36 cfs
Type II 24-hr 100yr - 24hrs Rainfall=7.21"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 8HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 19S: DURING CONSTRUCTION DA - 02
Runoff = 195.99 cfs @ 11.98 hrs, Volume= 10.703 af, Depth= 6.15"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 100yr - 24hrs Rainfall=7.21"
Area (ac) CN Description
20.900 91 Newly graded area, HSG C
20.900 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
1.7 100 0.1600 0.96 Sheet Flow,
Fallow n= 0.050 P2= 3.32"
5.2 1,220 0.0600 3.94 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
6.9 1,320 Total
Subcatchment 19S: DURING CONSTRUCTION DA - 02
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
200
180
160
140
120
100
80
60
40
20
0
Type II 24-hr
100yr - 24hrs Rainfall=7.21"
Runoff Area=20.900 ac
Runoff Volume=10.703 af
Runoff Depth=6.15"
Flow Length=1,320'
Tc=6.9 min
CN=91
195.99 cfs
Type II 24-hr 100yr - 24hrs Rainfall=7.21"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 9HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 25S: DURING CONSTRUCTION DA - 04
[49] Hint: Tc<2dt may require smaller dt
Runoff = 132.14 cfs @ 11.95 hrs, Volume= 6.542 af, Depth= 5.57"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 100yr - 24hrs Rainfall=7.21"
Area (ac) CN Description
14.100 86 Newly graded area, HSG B
14.100 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
5.0 Direct Entry,
Subcatchment 25S: DURING CONSTRUCTION DA - 04
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
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(
c
f
s
)
140
120
100
80
60
40
20
0
Type II 24-hr
100yr - 24hrs Rainfall=7.21"
Runoff Area=14.100 ac
Runoff Volume=6.542 af
Runoff Depth=5.57"
Tc=5.0 min
CN=86
132.14 cfs
Type II 24-hr 100yr - 24hrs Rainfall=7.21"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 10HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 26S: DURING CONSTRUCTION DA - 03A
[49] Hint: Tc<2dt may require smaller dt
Runoff = 204.85 cfs @ 11.96 hrs, Volume= 10.393 af, Depth= 5.57"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 100yr - 24hrs Rainfall=7.21"
Area (ac) CN Description
22.400 86 Newly graded area, HSG B
22.400 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
2.4 100 0.0700 0.69 Sheet Flow,
Fallow n= 0.050 P2= 3.32"
1.4 450 0.1100 5.34 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
1.8 750 0.0200 7.07 113.09 Channel Flow, Temporary Diversion
Area= 16.0 sf Perim= 29.0' r= 0.55' n= 0.020
5.6 1,300 Total
Subcatchment 26S: DURING CONSTRUCTION DA - 03A
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
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(
c
f
s
)
220
200
180
160
140
120
100
80
60
40
20
0
Type II 24-hr
100yr - 24hrs Rainfall=7.21"
Runoff Area=22.400 ac
Runoff Volume=10.393 af
Runoff Depth=5.57"
Flow Length=1,300'
Tc=5.6 min
CN=86
204.85 cfs
Type II 24-hr 100yr - 24hrs Rainfall=7.21"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 11HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Pond 18P: SB-04
Inflow Area = 86.800 ac, 0.00% Impervious, Inflow Depth = 6.15" for 100yr - 24hrs event
Inflow = 677.69 cfs @ 12.01 hrs, Volume= 44.452 af
Outflow = 133.41 cfs @ 12.33 hrs, Volume= 43.947 af, Atten= 80%, Lag= 19.2 min
Primary = 133.41 cfs @ 12.33 hrs, Volume= 43.947 af
Routing by Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Peak Elev= 678.31' @ 12.33 hrs Surf.Area= 199,278 sf Storage= 1,093,411 cf
Plug-Flow detention time= 1,146.7 min calculated for 43.929 af (99% of inflow)
Center-of-Mass det. time= 1,141.3 min ( 1,918.4 - 777.1 )
Volume Invert Avail.Storage Storage Description
#1 672.00' 1,435,854 cf Custom Stage Data (Prismatic) Listed below (Recalc)
Elevation Surf.Area Inc.Store Cum.Store
(feet) (sq-ft) (cubic-feet) (cubic-feet)
672.00 94,232 0 0
674.00 180,443 274,675 274,675
676.00 189,080 369,523 644,198
678.00 197,875 386,955 1,031,153
680.00 206,826 404,701 1,435,854
Device Routing Invert Outlet Devices
#1 Primary 672.00'24.0" Round CMP_Round 24"
L= 150.0' CMP, square edge headwall, Ke= 0.500
Inlet / Outlet Invert= 672.00' / 670.00' S= 0.0133 '/' Cc= 0.900
n= 0.025 Corrugated metal, Flow Area= 3.14 sf
#2 Device 1 676.00'16.0' long Sharp-Crested Rectangular Weir 2 End Contraction(s)
#3 Device 1 672.00'2.260 cfs Constant Flow/Skimmer
#4 Primary 677.00'Custom Weir/Orifice, Cv= 2.62 (C= 3.28)
Head (feet) 0.00 1.00 2.00
Width (feet) 20.00 25.00 30.00
Primary OutFlow Max=133.11 cfs @ 12.33 hrs HW=678.31' (Free Discharge)
1=CMP_Round 24" (Barrel Controls 21.84 cfs @ 6.95 fps)
2=Sharp-Crested Rectangular Weir (Passes < 178.55 cfs potential flow)
3=Constant Flow/Skimmer (Passes < 2.26 cfs potential flow)
4=Custom Weir/Orifice (Weir Controls 111.27 cfs @ 3.64 fps)
Type II 24-hr 100yr - 24hrs Rainfall=7.21"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 12HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Pond 18P: SB-04
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
700
600
500
400
300
200
100
0
Inflow Area=86.800 ac
Peak Elev=678.31'
Storage=1,093,411 cf
677.69 cfs
133.41 cfs
Type II 24-hr 100yr - 24hrs Rainfall=7.21"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 13HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Pond 21P: SB-05
Inflow Area = 86.800 ac, 0.00% Impervious, Inflow Depth = 6.15" for 100yr - 24hrs event
Inflow = 677.69 cfs @ 12.01 hrs, Volume= 44.452 af
Outflow = 133.12 cfs @ 12.33 hrs, Volume= 44.080 af, Atten= 80%, Lag= 19.2 min
Primary = 133.12 cfs @ 12.33 hrs, Volume= 44.080 af
Routing by Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Peak Elev= 656.29' @ 12.33 hrs Surf.Area= 221,374 sf Storage= 1,086,617 cf
Plug-Flow detention time= 1,082.7 min calculated for 44.062 af (99% of inflow)
Center-of-Mass det. time= 1,079.1 min ( 1,856.2 - 777.1 )
Volume Invert Avail.Storage Storage Description
#1 650.00' 2,092,446 cf Custom Stage Data (Prismatic) Listed below (Recalc)
Elevation Surf.Area Inc.Store Cum.Store
(feet) (sq-ft) (cubic-feet) (cubic-feet)
650.00 100,077 0 0
652.00 165,087 265,164 265,164
654.00 189,476 354,563 619,727
656.00 214,653 404,129 1,023,856
658.00 261,346 475,999 1,499,855
660.00 331,245 592,591 2,092,446
Device Routing Invert Outlet Devices
#1 Primary 650.00'24.0" Round CMP_Round 24"
L= 150.0' CMP, square edge headwall, Ke= 0.500
Inlet / Outlet Invert= 650.00' / 646.00' S= 0.0267 '/' Cc= 0.900
n= 0.025 Corrugated metal, Flow Area= 3.14 sf
#2 Device 1 654.00'16.0' long Sharp-Crested Rectangular Weir 2 End Contraction(s)
#3 Device 1 650.00'2.260 cfs Constant Flow/Skimmer
#4 Primary 655.00'Custom Weir/Orifice, Cv= 2.62 (C= 3.28)
Head (feet) 0.00 1.00 2.00
Width (feet) 20.00 25.00 30.00
Primary OutFlow Max=132.83 cfs @ 12.33 hrs HW=656.29' (Free Discharge)
1=CMP_Round 24" (Barrel Controls 25.02 cfs @ 7.96 fps)
2=Sharp-Crested Rectangular Weir (Passes < 175.67 cfs potential flow)
3=Constant Flow/Skimmer (Passes < 2.26 cfs potential flow)
4=Custom Weir/Orifice (Weir Controls 107.81 cfs @ 3.61 fps)
Type II 24-hr 100yr - 24hrs Rainfall=7.21"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 14HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Pond 21P: SB-05
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
700
600
500
400
300
200
100
0
Inflow Area=86.800 ac
Peak Elev=656.29'
Storage=1,086,617 cf
677.69 cfs
133.12 cfs
Type II 24-hr 100yr - 24hrs Rainfall=7.21"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 15HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Pond 24P: SB-03
Inflow Area = 36.500 ac, 0.00% Impervious, Inflow Depth = 5.57" for 100yr - 24hrs event
Inflow = 336.74 cfs @ 11.96 hrs, Volume= 16.935 af
Outflow = 33.01 cfs @ 12.38 hrs, Volume= 16.904 af, Atten= 90%, Lag= 25.6 min
Primary = 33.01 cfs @ 12.38 hrs, Volume= 16.904 af
Routing by Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Peak Elev= 657.37' @ 12.38 hrs Surf.Area= 98,875 sf Storage= 417,663 cf
Plug-Flow detention time= 1,183.4 min calculated for 16.897 af (100% of inflow)
Center-of-Mass det. time= 1,184.0 min ( 1,971.5 - 787.5 )
Volume Invert Avail.Storage Storage Description
#1 652.00' 688,748 cf Custom Stage Data (Prismatic) Listed below (Recalc)
Elevation Surf.Area Inc.Store Cum.Store
(feet) (sq-ft) (cubic-feet) (cubic-feet)
652.00 20,697 0 0
653.00 47,259 33,978 33,978
654.00 88,689 67,974 101,952
655.00 91,666 90,178 192,130
656.00 94,682 93,174 285,304
657.00 97,737 96,210 381,513
658.00 100,832 99,285 480,798
659.00 103,965 102,399 583,196
660.00 107,139 105,552 688,748
Device Routing Invert Outlet Devices
#1 Primary 652.00'24.0" Round CMP_Round 24"
L= 200.0' CMP, square edge headwall, Ke= 0.500
Inlet / Outlet Invert= 652.00' / 650.00' S= 0.0100 '/' Cc= 0.900
n= 0.025 Corrugated metal, Flow Area= 3.14 sf
#2 Device 1 656.00'16.0' long Sharp-Crested Rectangular Weir 2 End Contraction(s)
#3 Device 1 652.00'1.130 cfs Constant Flow/Skimmer
#4 Primary 657.00'Custom Weir/Orifice, Cv= 2.62 (C= 3.28)
Head (feet) 0.00 1.00 2.00 3.00
Width (feet) 20.00 25.00 30.00 35.00
Primary OutFlow Max=32.95 cfs @ 12.38 hrs HW=657.37' (Free Discharge)
1=CMP_Round 24" (Barrel Controls 17.84 cfs @ 5.68 fps)
2=Sharp-Crested Rectangular Weir (Passes < 82.21 cfs potential flow)
3=Constant Flow/Skimmer (Passes < 1.13 cfs potential flow)
4=Custom Weir/Orifice (Weir Controls 15.11 cfs @ 1.97 fps)
Type II 24-hr 100yr - 24hrs Rainfall=7.21"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 16HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Pond 24P: SB-03
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
350
300
250
200
150
100
50
0
Inflow Area=36.500 ac
Peak Elev=657.37'
Storage=417,663 cf
336.74 cfs
33.01 cfs
Type II 24-hr 100yr - 24hrs Rainfall=7.21"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 17HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Link 8L: Total
Inflow Area = 86.800 ac, 0.00% Impervious, Inflow Depth = 6.15" for 100yr - 24hrs event
Inflow = 677.69 cfs @ 12.01 hrs, Volume= 44.452 af
Primary = 677.69 cfs @ 12.01 hrs, Volume= 44.452 af, Atten= 0%, Lag= 0.0 min
Primary outflow = Inflow, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Link 8L: Total
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
700
600
500
400
300
200
100
0
Inflow Area=86.800 ac
677.69 cfs677.69 cfs
Type II 24-hr 100yr - 24hrs Rainfall=7.21"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 18HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Link 20L: Total
Inflow Area = 86.800 ac, 0.00% Impervious, Inflow Depth = 6.15" for 100yr - 24hrs event
Inflow = 677.69 cfs @ 12.01 hrs, Volume= 44.452 af
Primary = 677.69 cfs @ 12.01 hrs, Volume= 44.452 af, Atten= 0%, Lag= 0.0 min
Primary outflow = Inflow, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Link 20L: Total
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
700
600
500
400
300
200
100
0
Inflow Area=86.800 ac
677.69 cfs677.69 cfs
Type II 24-hr 100yr - 24hrs Rainfall=7.21"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 19HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Link 26L: Total
Inflow Area = 36.500 ac, 0.00% Impervious, Inflow Depth = 5.57" for 100yr - 24hrs event
Inflow = 336.74 cfs @ 11.96 hrs, Volume= 16.935 af
Primary = 336.74 cfs @ 11.96 hrs, Volume= 16.935 af, Atten= 0%, Lag= 0.0 min
Primary outflow = Inflow, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Link 26L: Total
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
350
300
250
200
150
100
50
0
Inflow Area=36.500 ac
336.74 cfs336.74 cfs
Riverbend Ash Basin Closure Plan CALC-1.01-STORMWATER, Rev. 0
Amec Foster Wheeler Project No. 6226-14-0007 December, 2015
Reference 4

CALCULATIONS FOR EROSION AND SEDIMENT CONTROL MEASURES

- SEDIMENT BASINS
- CLEAN WATER DIVERSION DITCHES
- RIP RAP APRONS

Riverbend Ash Basin Closure Plan CALC-1.01-STORMWATER, Rev. 0
Amec Foster Wheeler Project No. 6226-14-0007 December, 2015
SEDIMENT BASIN CALCULATIONS

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Riverbend Ash Basin Closure Plan CALC-1.01-STORMWATER, Rev. 0
Amec Foster Wheeler Project No. 6226-14-0007 December, 2015
CLEAN WATER DIVERSION DITCH CALCULATIONS

16S
CLEAN WATER
DIVERSION DITCH 1-
PHASE 1
17S
CLEAN WATER
DIVERSION DITCH 2
23S
DURING
CONSTRUCTION DA -
03B
24L
Phase 2 Clean Water
Diversion 2
Routing Diagram for Riverbend Ash Pond Closure
Prepared by AMEC, Printed 11/6/2015
HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Subcat Reach Pond Link
Riverbend Ash Pond Closure
Printed 11/6/2015Prepared by AMEC
Page 2HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Area Listing (selected nodes)
Area
(acres)
CN Description
(subcatchment-numbers)
1.490 85 Gravel roads, HSG B (17S, 23S)
0.280 89 Gravel roads, HSG C (16S)
5.715 69 Pasture/grassland/range, Fair, HSG B (17S, 23S)
4.460 79 Pasture/grassland/range, Fair, HSG C (16S)
1.640 98 Paved parking, HSG B (17S, 23S)
1.530 88 Railbed - Gravel (23S)
12.600 60 Woods, Fair, HSG B (17S, 23S)
3.600 73 Woods, Fair, HSG C (16S)
3.400 65 Woods/grass comb., Fair, HSG B (17S, 23S)
34.715 70 TOTAL AREA
Riverbend Ash Pond Closure
Printed 11/6/2015Prepared by AMEC
Page 3HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Soil Listing (selected nodes)
Area
(acres)
Soil
Group
Subcatchment
Numbers
0.000 HSG A
24.845 HSG B 17S, 23S
8.340 HSG C 16S
0.000 HSG D
1.530 Other 23S
34.715 TOTAL AREA
Riverbend Ash Pond Closure
Printed 11/6/2015Prepared by AMEC
Page 4HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Ground Covers (selected nodes)
HSG-A
(acres)
HSG-B
(acres)
HSG-C
(acres)
HSG-D
(acres)
Other
(acres)
Total
(acres)
Ground
Cover
Subcatchment
Numbers
0.000 1.490 0.280 0.000 0.000 1.770 Gravel roads 16S,
17S,
23S
0.000 5.715 4.460 0.000 0.000 10.175 Pasture/grassland/range, Fair 16S,
17S,
23S
0.000 1.640 0.000 0.000 0.000 1.640 Paved parking 17S,
23S
0.000 0.000 0.000 0.000 1.530 1.530 Railbed - Gravel 23S
0.000 12.600 3.600 0.000 0.000 16.200 Woods, Fair 16S,
17S,
23S
0.000 3.400 0.000 0.000 0.000 3.400 Woods/grass comb., Fair 17S,
23S
0.000 24.845 8.340 0.000 1.530 34.715 TOTAL AREA
Type II 24-hr 25yr - 24hrs Rainfall=5.75"Riverbend Ash Pond Closure
Printed 11/6/2015Prepared by AMEC
Page 5HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 16S: CLEAN WATER DIVERSION DITCH 1- PHASE 1
Runoff = 27.16 cfs @ 12.17 hrs, Volume= 2.267 af, Depth= 3.26"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 25yr - 24hrs Rainfall=5.75"
Area (ac) CN Description
3.600 73 Woods, Fair, HSG C
0.280 89 Gravel roads, HSG C
4.460 79 Pasture/grassland/range, Fair, HSG C
8.340 77 Weighted Average
8.340 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
21.1 100 0.0200 0.08 Sheet Flow,
Woods: Light underbrush n= 0.400 P2= 3.32"
2.3 225 0.1100 1.66 Shallow Concentrated Flow,
Woodland Kv= 5.0 fps
0.5 175 0.1600 6.44 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
23.9 500 Total
Subcatchment 16S: CLEAN WATER DIVERSION DITCH 1- PHASE 1
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
30
25
20
15
10
5
0
Type II 24-hr
25yr - 24hrs Rainfall=5.75"
Runoff Area=8.340 ac
Runoff Volume=2.267 af
Runoff Depth=3.26"
Flow Length=500'
Tc=23.9 min
CN=77
27.16 cfs
Type II 24-hr 25yr - 24hrs Rainfall=5.75"Riverbend Ash Pond Closure
Printed 11/6/2015Prepared by AMEC
Page 6HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 17S: CLEAN WATER DIVERSION DITCH 2
Runoff = 13.63 cfs @ 12.17 hrs, Volume= 1.129 af, Depth= 2.26"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 25yr - 24hrs Rainfall=5.75"
Area (ac) CN Description
0.180 65 Woods/grass comb., Fair, HSG B
4.080 60 Woods, Fair, HSG B
0.360 85 Gravel roads, HSG B
0.410 98 Paved parking, HSG B
0.975 69 Pasture/grassland/range, Fair, HSG B
6.005 66 Weighted Average
5.595 93.17% Pervious Area
0.410 6.83% Impervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
17.9 100 0.0300 0.09 Sheet Flow,
Woods: Light underbrush n= 0.400 P2= 3.32"
2.4 160 0.0500 1.12 Shallow Concentrated Flow,
Woodland Kv= 5.0 fps
2.3 246 0.0120 1.76 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
22.6 506 Total
Subcatchment 17S: CLEAN WATER DIVERSION DITCH 2
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
14
12
10
8
6
4
2
0
Type II 24-hr
25yr - 24hrs Rainfall=5.75"
Runoff Area=6.005 ac
Runoff Volume=1.129 af
Runoff Depth=2.26"
Flow Length=506'
Tc=22.6 min
CN=66
13.63 cfs
Type II 24-hr 25yr - 24hrs Rainfall=5.75"Riverbend Ash Pond Closure
Printed 11/6/2015Prepared by AMEC
Page 7HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 23S: DURING CONSTRUCTION DA - 03B
Runoff = 49.40 cfs @ 12.19 hrs, Volume= 4.276 af, Depth= 2.52"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 25yr - 24hrs Rainfall=5.75"
Area (ac) CN Description
8.520 60 Woods, Fair, HSG B
3.220 65 Woods/grass comb., Fair, HSG B
1.130 85 Gravel roads, HSG B
1.230 98 Paved parking, HSG B
* 1.530 88 Railbed - Gravel
4.740 69 Pasture/grassland/range, Fair, HSG B
20.370 69 Weighted Average
19.140 93.96% Pervious Area
1.230 6.04% Impervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
21.1 100 0.0200 0.08 Sheet Flow,
Woods: Light underbrush n= 0.400 P2= 3.32"
3.6 740 0.0460 3.45 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
24.7 840 Total
Subcatchment 23S: DURING CONSTRUCTION DA - 03B
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
55
50
45
40
35
30
25
20
15
10
5
0
Type II 24-hr
25yr - 24hrs Rainfall=5.75"
Runoff Area=20.370 ac
Runoff Volume=4.276 af
Runoff Depth=2.52"
Flow Length=840'
Tc=24.7 min
CN=69
49.40 cfs
Type II 24-hr 25yr - 24hrs Rainfall=5.75"Riverbend Ash Pond Closure
Printed 11/6/2015Prepared by AMEC
Page 8HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Link 24L: Phase 2 Clean Water Diversion 2
Inflow Area = 26.375 ac, 6.22% Impervious, Inflow Depth = 2.46" for 25yr - 24hrs event
Inflow = 62.88 cfs @ 12.18 hrs, Volume= 5.405 af
Primary = 62.88 cfs @ 12.18 hrs, Volume= 5.405 af, Atten= 0%, Lag= 0.0 min
Primary outflow = Inflow, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Link 24L: Phase 2 Clean Water Diversion 2
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
70
60
50
40
30
20
10
0
Inflow Area=26.375 ac
62.88 cfs62.88 cfs
Tensar International Corporation
5401 St. Wendel-Cynthiana Road
Poseyville, Indiana 47633
Tel. [phone]
Fax [phone]
www.nagreen.com
Erosion Control Materials Design Software
Version 5.0
Project Name: Riverbend
Project Number: 52592
Project Location: Charlotte, NC
Channel Name: Clean Water Diversion 1 - (Stability)
Discharge 27.16
Peak Flow Period 12.5
Channel Slope 0.0288
Channel Bottom Width 2
Left Side Slope 3
Right Side Slope 3
Low Flow Liner
Retardance Class C
Vegtation Type Bunch Type
Vegetation Density Fair 50-75%
Soil Type Loam
C125
Phase Reach Discharge Velocity Normal
Depth
Mannings
N
Permissible
Shear Stress
Calculated
Shear Stress
Safety
Factor
Remarks Staple
Pattern
C125
Unvegetated
Straight 27.16
cfs
7.75
ft/s
0.8 ft 0.02 2.25 lbs/ft2 1.43 lbs/ft2 1.57 STABLE D
Unreinforced Vegetation - Class C - Bunch Type - Fair 50-75%
Phase Reach DischargeVelocity Normal
Depth
Mannings
N
Permissible
Shear Stress
Calculated
Shear Stress
Safety
Factor
Remarks Staple
Pattern
Unreinforced
Vegetation
Straight 27.16
cfs
3.67
ft/s
1.27 ft 0.056 4.2 lbs/ft2 2.29 lbs/ft2 1.84 STABLE --
Underlying
Substrate
Straight 27.16
cfs
3.67
ft/s
1.27 ft -- 0.04 lbs/ft2 0.106 lbs/ft2 0.33 UNSTABLE --
Page 1 of 2
11/9/2015http://www.ecmds.com/print/analysis/52592/57089
Tensar International Corporation
5401 St. Wendel-Cynthiana Road
Poseyville, Indiana 47633
Tel. [phone]
Fax [phone]
www.nagreen.com
Erosion Control Materials Design Software
Version 5.0
Project Name: Riverbend
Project Number: 52592
Project Location: Charlotte, NC
Channel Name: Clean Water Diversion 1 - (Capacity)
Discharge 27.16
Peak Flow Period 12.5
Channel Slope 0.005
Channel Bottom Width 2
Left Side Slope 3
Right Side Slope 3
Low Flow Liner
Retardance Class C
Vegtation Type Bunch Type
Vegetation Density Fair 50-75%
Soil Type Loam
C125
Phase Reach Discharge Velocity Normal
Depth
Mannings
N
Permissible
Shear Stress
Calculated
Shear Stress
Safety
Factor
Remarks Staple
Pattern
C125
Unvegetated
Straight 27.16
cfs
4.35
ft/s
1.15 ft 0.019 2.25 lbs/ft2 0.36 lbs/ft2 6.29 STABLE D
Unreinforced Vegetation - Class C - Bunch Type - Fair 50-75%
Phase Reach Discharge Velocity Normal
Depth
Mannings
N
Permissible
Shear Stress
Calculated
Shear Stress
Safety
Factor
Remarks Staple
Pattern
Unreinforced
Vegetation
Straight 27.16
cfs
1.69
ft/s
2 ft 0.066 4.2 lbs/ft2 0.63 lbs/ft2 6.71 STABLE --
Underlying
Substrate
Straight 27.16
cfs
1.69
ft/s
2 ft -- 0.04 lbs/ft2 0.021 lbs/ft2 1.67 STABLE --
Page 1 of 2
11/9/2015http://www.ecmds.com/print/analysis/52592/80147
Tensar International Corporation
5401 St. Wendel-Cynthiana Road
Poseyville, Indiana 47633
Tel. [phone]
Fax [phone]
www.nagreen.com
Erosion Control Materials Design Software
Version 5.0
Project Name: Riverbend
Project Number: 52592
Project Location: Charlotte, NC
Channel Name: Clean Water Diversion 2 - Phase 1 (Stability)
Discharge 13.63
Peak Flow Period 12.5
Channel Slope 0.032
Channel Bottom Width 2
Left Side Slope 3
Right Side Slope 3
Low Flow Liner
Retardance Class C
Vegtation Type Bunch Type
Vegetation Density Fair 50-75%
Soil Type Loam
C125
Phase Reach Discharge Velocity Normal
Depth
Mannings
N
Permissible
Shear Stress
Calculated
Shear Stress
Safety
Factor
Remarks Staple
Pattern
C125
Unvegetated
Straight 13.63
cfs
6.43
ft/s
0.57 ft 0.022 2.25 lbs/ft2 1.14 lbs/ft2 1.97 STABLE D
Unreinforced Vegetation - Class C - Bunch Type - Fair 50-75%
Phase Reach DischargeVelocity Normal
Depth
Mannings
N
Permissible
Shear Stress
Calculated
Shear Stress
Safety
Factor
Remarks Staple
Pattern
Unreinforced
Vegetation
Straight 13.63
cfs
2.77
ft/s
0.99 ft 0.068 4.2 lbs/ft2 1.98 lbs/ft2 2.12 STABLE --
Underlying
Substrate
Straight 13.63
cfs
2.77
ft/s
0.99 ft -- 0.04 lbs/ft2 0.063 lbs/ft2 0.56 UNSTABLE --
Page 1 of 2
11/9/2015http://www.ecmds.com/print/analysis/52592/57092
Tensar International Corporation
5401 St. Wendel-Cynthiana Road
Poseyville, Indiana 47633
Tel. [phone]
Fax [phone]
www.nagreen.com
Erosion Control Materials Design Software
Version 5.0
Project Name: Riverbend
Project Number: 52592
Project Location: Charlotte, NC
Channel Name: Clean Water Diversion 2 - Phase 1 (Capacity)
Discharge 13.63
Peak Flow Period 12.5
Channel Slope 0.005
Channel Bottom Width 2
Left Side Slope 3
Right Side Slope 3
Low Flow Liner
Retardance Class C
Vegtation Type Bunch Type
Vegetation Density Fair 50-75%
Soil Type Loam
C125
Phase Reach Discharge Velocity Normal
Depth
Mannings
N
Permissible
Shear Stress
Calculated
Shear Stress
Safety
Factor
Remarks Staple
Pattern
C125
Unvegetated
Straight 13.63
cfs
3.44
ft/s
0.86 ft 0.02 2.25 lbs/ft2 0.27 lbs/ft2 8.35 STABLE D
Unreinforced Vegetation - Class C - Bunch Type - Fair 50-75%
Phase Reach DischargeVelocity Normal
Depth
Mannings
N
Permissible
Shear Stress
Calculated
Shear Stress
Safety
Factor
Remarks Staple
Pattern
Unreinforced
Vegetation
Straight 13.63
cfs
1.2 ft/s 1.64 ft 0.083 4.2 lbs/ft2 0.51 lbs/ft2 8.21 STABLE --
Underlying
Substrate
Straight 13.63
cfs
1.2 ft/s 1.64 ft -- 0.04 lbs/ft2 0.011 lbs/ft2 3.2 STABLE --
Page 1 of 2
11/9/2015http://www.ecmds.com/print/analysis/52592/80165
Tensar International Corporation
5401 St. Wendel-Cynthiana Road
Poseyville, Indiana 47633
Tel. [phone]
Fax [phone]
www.nagreen.com
Erosion Control Materials Design Software
Version 5.0
Project Name: Riverbend
Project Number: 52592
Project Location: Charlotte, NC
Channel Name: Clean Water Diversion 2 - Phase 2 (Stability)
Discharge 62.9
Peak Flow Period 12.5
Channel Slope 0.015
Channel Bottom Width 2
Left Side Slope 3
Right Side Slope 3
Low Flow Liner
Retardance Class C
Vegtation Type Bunch Type
Vegetation Density Fair 50-75%
Soil Type Loam
C125
Phase Reach DischargeVelocity Normal
Depth
Mannings
N
Permissible
Shear Stress
Calculated
Shear Stress
Safety
Factor
Remarks Staple
Pattern
C125
Unvegetated
Straight62.9 cfs 8.37
ft/s
1.28 ft 0.018 2.25 lbs/ft2 1.2 lbs/ft2 1.87 STABLE D
Unreinforced Vegetation - Class C - Bunch Type - Fair 50-75%
Phase Reach DischargeVelocity Normal
Depth
Mannings
N
Permissible
Shear Stress
Calculated
Shear Stress
Safety
Factor
Remarks Staple
Pattern
Unreinforced
Vegetation
Straight62.9 cfs 4.01
ft/s
1.98 ft 0.048 4.2 lbs/ft2 1.85 lbs/ft2 2.27 STABLE --
Underlying
Substrate
Straight62.9 cfs 4.01
ft/s
1.98 ft -- 0.04 lbs/ft2 0.118 lbs/ft2 0.3 UNSTABLE --
Page 1 of 2
11/9/2015http://www.ecmds.com/print/analysis/52592/57095
Tensar International Corporation
5401 St. Wendel-Cynthiana Road
Poseyville, Indiana 47633
Tel. [phone]
Fax [phone]
www.nagreen.com
Erosion Control Materials Design Software
Version 5.0
Project Name: Riverbend
Project Number: 52592
Project Location: Charlotte, NC
Channel Name: Clean Water Diversion 2 - Phase 2 (Capacity)
Discharge 62.9
Peak Flow Period 12.5
Channel Slope .005
Channel Bottom Width 2
Left Side Slope 3
Right Side Slope 3
Low Flow Liner
Retardance Class C
Vegtation Type Bunch Type
Vegetation Density Fair 50-75%
Soil Type Loam
C125
Phase Reach DischargeVelocity Normal
Depth
Mannings
N
Permissible
Shear Stress
Calculated
Shear Stress
Safety
Factor
Remarks Staple
Pattern
C125
Unvegetated
Straight62.9 cfs 5.95
ft/s
1.57 ft 0.016 2.25 lbs/ft2 0.49 lbs/ft2 4.58 STABLE D
Unreinforced Vegetation - Class C - Bunch Type - Fair 50-75%
Phase Reach DischargeVelocity Normal
Depth
Mannings
N
Permissible
Shear Stress
Calculated
Shear Stress
Safety
Factor
Remarks Staple
Pattern
Unreinforced
Vegetation
Straight62.9 cfs 2.48
ft/s
2.59 ft 0.052 4.2 lbs/ft2 0.81 lbs/ft2 5.19 STABLE --
Underlying
Substrate
Straight62.9 cfs 2.48
ft/s
2.59 ft -- 0.04 lbs/ft2 0.043 lbs/ft2 0.81 UNSTABLE --
Page 1 of 2
11/9/2015http://www.ecmds.com/print/analysis/52592/80291
Riverbend Ash Basin Closure Plan CALC-1.01-STORMWATER, Rev. 0
Amec Foster Wheeler Project No. 6226-14-0007 December, 2015
RIP RAP APRON CALCULATIONS

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Project Description
Friction Method Manning Formula
Solve For Normal Depth
Input Data
Roughness Coefficient 0.020
Channel Slope 0.02900 ft/ft
Left Side Slope 3.00 ft/ft (H:V)
Right Side Slope 3.00 ft/ft (H:V)
Bottom Width 2.00 ft
Discharge 27.20 ft³/s
Results
Normal Depth 0.79 ft
Flow Area 3.45 ft²
Wetted Perimeter 6.99 ft
Hydraulic Radius 0.49 ft
Top Width 6.73 ft
Critical Depth 1.10 ft
Critical Slope 0.00701 ft/ft
Velocity 7.89 ft/s
Velocity Head 0.97 ft
Specific Energy 1.76 ft
Froude Number 1.95
Flow Type Supercritical
GVF Input Data
Downstream Depth 0.00 ft
Length 0.00 ft
Number Of Steps 0
GVF Output Data
Upstream Depth 0.00 ft
Profile Description
Profile Headloss 0.00 ft
Downstream Velocity Infinity ft/s
Upstream Velocity Infinity ft/s
Normal Depth 0.79 ft
Critical Depth 1.10 ft
Channel Slope 0.02900 ft/ft
Worksheet for Clean Water Diversion Ditch - 1 (Apron Design)
11/9/2015 8:56:50 AM
Bentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03]
27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA [phone]of1Page
Worksheet for Clean Water Diversion Ditch - 1 (Apron Design)
GVF Output Data
Critical Slope 0.00701 ft/ft
11/9/2015 8:56:50 AM
Bentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03]
27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA [phone]of2Page
Project Description
Friction Method Manning Formula
Solve For Normal Depth
Input Data
Roughness Coefficient 0.020
Channel Slope 0.03200 ft/ft
Left Side Slope 3.00 ft/ft (H:V)
Right Side Slope 3.00 ft/ft (H:V)
Discharge 62.88 ft³/s
Results
Normal Depth 1.43 ft
Flow Area 6.13 ft²
Wetted Perimeter 9.04 ft
Hydraulic Radius 0.68 ft
Top Width 8.58 ft
Critical Depth 1.94 ft
Critical Slope 0.00632 ft/ft
Velocity 10.26 ft/s
Velocity Head 1.64 ft
Specific Energy 3.06 ft
Froude Number 2.14
Flow Type Supercritical
GVF Input Data
Downstream Depth 0.00 ft
Length 0.00 ft
Number Of Steps 0
GVF Output Data
Upstream Depth 0.00 ft
Profile Description
Profile Headloss 0.00 ft
Downstream Velocity Infinity ft/s
Upstream Velocity Infinity ft/s
Normal Depth 1.43 ft
Critical Depth 1.94 ft
Channel Slope 0.03200 ft/ft
Critical Slope 0.00632 ft/ft
Worksheet for Clean Water Diversion Ditch - 2 (Apron Design)
11/9/2015 8:58:51 AM
Bentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03]
27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA [phone]of1Page
Riverbend Ash Basin Closure Plan CALC-1.01-STORMWATER, Rev. 0
Amec Foster Wheeler Project No. 6226-14-0007 December, 2015
Reference 5

POST-CONSTRUCTION HYDROCAD OUTPUT

11S
POST DA - 01
12S
POST DA - 02
13S
POST DA - 03
15L
Total Off-Site Runoff
Routing Diagram for Riverbend Ash Pond Closure
Prepared by AMEC, Printed 11/5/2015
HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Subcat Reach Pond Link
Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 2HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Area Listing (selected nodes)
Area
(acres)
CN Description
(subcatchment-numbers)
0.700 85 Gravel roads, HSG B (13S)
47.220 69 Pasture/grassland/range, Fair, HSG B (13S)
99.200 79 Pasture/grassland/range, Fair, HSG C (11S, 12S)
1.240 98 Paved parking, HSG B (13S)
8.510 60 Woods, Fair, HSG B (13S)
5.800 73 Woods, Fair, HSG C (11S, 12S)
3.030 65 Woods/grass comb., Fair, HSG B (13S)
165.700 75 TOTAL AREA
Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 3HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Soil Listing (selected nodes)
Area
(acres)
Soil
Group
Subcatchment
Numbers
0.000 HSG A
60.700 HSG B 13S
105.000 HSG C 11S, 12S
0.000 HSG D
0.000 Other
165.700 TOTAL AREA
Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 4HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Ground Covers (selected nodes)
HSG-A
(acres)
HSG-B
(acres)
HSG-C
(acres)
HSG-D
(acres)
Other
(acres)
Total
(acres)
Ground
Cover
Subcatchment
Numbers
0.000 0.700 0.000 0.000 0.000 0.700 Gravel roads 13S
0.000 47.220 99.200 0.000 0.000 146.420 Pasture/grassland/range, Fair 11S,
12S,
13S
0.000 1.240 0.000 0.000 0.000 1.240 Paved parking 13S
0.000 8.510 5.800 0.000 0.000 14.310 Woods, Fair 11S,
12S,
13S
0.000 3.030 0.000 0.000 0.000 3.030 Woods/grass comb., Fair 13S
0.000 60.700 105.000 0.000 0.000 165.700 TOTAL AREA
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 5HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 11S: POST DA - 01
Runoff = 62.52 cfs @ 12.31 hrs, Volume= 6.896 af, Depth= 1.01"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"
Area (ac) CN Description
78.940 79 Pasture/grassland/range, Fair, HSG C
3.060 73 Woods, Fair, HSG C
82.000 79 Weighted Average
82.000 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
21.1 100 0.0200 0.08 Sheet Flow,
Woods: Light underbrush n= 0.400 P2= 3.32"
2.3 225 0.1100 1.66 Shallow Concentrated Flow,
Woodland Kv= 5.0 fps
10.8 2,300 0.0490 3.56 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
34.2 2,625 Total
Subcatchment 11S: POST DA - 01
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
70
60
50
40
30
20
10
0
Type II 24-hr
1yr - 24 hrs Rainfall=2.75"
Runoff Area=82.000 ac
Runoff Volume=6.896 af
Runoff Depth=1.01"
Flow Length=2,625'
Tc=34.2 min
CN=79
62.52 cfs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 6HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 12S: POST DA - 02
Runoff = 17.64 cfs @ 12.27 hrs, Volume= 1.829 af, Depth= 0.95"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"
Area (ac) CN Description
2.740 73 Woods, Fair, HSG C
20.260 79 Pasture/grassland/range, Fair, HSG C
23.000 78 Weighted Average
23.000 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
21.1 100 0.0200 0.08 Sheet Flow,
Woods: Light underbrush n= 0.400 P2= 3.32"
3.2 260 0.0730 1.35 Shallow Concentrated Flow,
Woodland Kv= 5.0 fps
6.5 1,530 0.0590 3.91 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
30.8 1,890 Total
Subcatchment 12S: POST DA - 02
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
18
16
14
12
10
8
6
4
2
0
Type II 24-hr
1yr - 24 hrs Rainfall=2.75"
Runoff Area=23.000 ac
Runoff Volume=1.829 af
Runoff Depth=0.95"
Flow Length=1,890'
Tc=30.8 min
CN=78
17.64 cfs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 7HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 13S: POST DA - 03
Runoff = 17.10 cfs @ 12.40 hrs, Volume= 2.540 af, Depth= 0.50"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"
Area (ac) CN Description
8.510 60 Woods, Fair, HSG B
3.030 65 Woods/grass comb., Fair, HSG B
1.240 98 Paved parking, HSG B
0.700 85 Gravel roads, HSG B
47.220 69 Pasture/grassland/range, Fair, HSG B
60.700 68 Weighted Average
59.460 97.96% Pervious Area
1.240 2.04% Impervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
27.8 100 0.0100 0.06 Sheet Flow,
Woods: Light underbrush n= 0.400 P2= 3.32"
8.9 2,220 0.0660 4.14 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
36.7 2,320 Total
Subcatchment 13S: POST DA - 03
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
18
16
14
12
10
8
6
4
2
0
Type II 24-hr
1yr - 24 hrs Rainfall=2.75"
Runoff Area=60.700 ac
Runoff Volume=2.540 af
Runoff Depth=0.50"
Flow Length=2,320'
Tc=36.7 min
CN=68
17.10 cfs
Type II 24-hr 1yr - 24 hrs Rainfall=2.75"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 8HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Link 15L: Total Off-Site Runoff
Inflow Area = 165.700 ac, 0.75% Impervious, Inflow Depth = 0.82" for 1yr - 24 hrs event
Inflow = 96.08 cfs @ 12.32 hrs, Volume= 11.265 af
Primary = 96.08 cfs @ 12.32 hrs, Volume= 11.265 af, Atten= 0%, Lag= 0.0 min
Primary outflow = Inflow, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Link 15L: Total Off-Site Runoff
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
100
90
80
70
60
50
40
30
20
10
0
Inflow Area=165.700 ac
96.08 cfs96.08 cfs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 9HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 11S: POST DA - 01
Runoff = 90.72 cfs @ 12.31 hrs, Volume= 9.754 af, Depth= 1.43"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"
Area (ac) CN Description
78.940 79 Pasture/grassland/range, Fair, HSG C
3.060 73 Woods, Fair, HSG C
82.000 79 Weighted Average
82.000 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
21.1 100 0.0200 0.08 Sheet Flow,
Woods: Light underbrush n= 0.400 P2= 3.32"
2.3 225 0.1100 1.66 Shallow Concentrated Flow,
Woodland Kv= 5.0 fps
10.8 2,300 0.0490 3.56 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
34.2 2,625 Total
Subcatchment 11S: POST DA - 01
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
100
90
80
70
60
50
40
30
20
10
0
Type II 24-hr
2yr - 24hrs Rainfall=3.32"
Runoff Area=82.000 ac
Runoff Volume=9.754 af
Runoff Depth=1.43"
Flow Length=2,625'
Tc=34.2 min
CN=79
90.72 cfs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 10HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 12S: POST DA - 02
Runoff = 25.92 cfs @ 12.27 hrs, Volume= 2.610 af, Depth= 1.36"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"
Area (ac) CN Description
2.740 73 Woods, Fair, HSG C
20.260 79 Pasture/grassland/range, Fair, HSG C
23.000 78 Weighted Average
23.000 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
21.1 100 0.0200 0.08 Sheet Flow,
Woods: Light underbrush n= 0.400 P2= 3.32"
3.2 260 0.0730 1.35 Shallow Concentrated Flow,
Woodland Kv= 5.0 fps
6.5 1,530 0.0590 3.91 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
30.8 1,890 Total
Subcatchment 12S: POST DA - 02
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
25
20
15
10
5
0
Type II 24-hr
2yr - 24hrs Rainfall=3.32"
Runoff Area=23.000 ac
Runoff Volume=2.610 af
Runoff Depth=1.36"
Flow Length=1,890'
Tc=30.8 min
CN=78
25.92 cfs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 11HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 13S: POST DA - 03
Runoff = 30.89 cfs @ 12.37 hrs, Volume= 4.040 af, Depth= 0.80"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"
Area (ac) CN Description
8.510 60 Woods, Fair, HSG B
3.030 65 Woods/grass comb., Fair, HSG B
1.240 98 Paved parking, HSG B
0.700 85 Gravel roads, HSG B
47.220 69 Pasture/grassland/range, Fair, HSG B
60.700 68 Weighted Average
59.460 97.96% Pervious Area
1.240 2.04% Impervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
27.8 100 0.0100 0.06 Sheet Flow,
Woods: Light underbrush n= 0.400 P2= 3.32"
8.9 2,220 0.0660 4.14 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
36.7 2,320 Total
Subcatchment 13S: POST DA - 03
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
30
25
20
15
10
5
0
Type II 24-hr
2yr - 24hrs Rainfall=3.32"
Runoff Area=60.700 ac
Runoff Volume=4.040 af
Runoff Depth=0.80"
Flow Length=2,320'
Tc=36.7 min
CN=68
30.89 cfs
Type II 24-hr 2yr - 24hrs Rainfall=3.32"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 12HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Link 15L: Total Off-Site Runoff
Inflow Area = 165.700 ac, 0.75% Impervious, Inflow Depth = 1.19" for 2yr - 24hrs event
Inflow = 146.02 cfs @ 12.31 hrs, Volume= 16.405 af
Primary = 146.02 cfs @ 12.31 hrs, Volume= 16.405 af, Atten= 0%, Lag= 0.0 min
Primary outflow = Inflow, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Link 15L: Total Off-Site Runoff
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
160
140
120
100
80
60
40
20
0
Inflow Area=165.700 ac
146.02 cfs146.02 cfs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 13HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 11S: POST DA - 01
Runoff = 173.08 cfs @ 12.30 hrs, Volume= 18.207 af, Depth= 2.66"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"
Area (ac) CN Description
78.940 79 Pasture/grassland/range, Fair, HSG C
3.060 73 Woods, Fair, HSG C
82.000 79 Weighted Average
82.000 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
21.1 100 0.0200 0.08 Sheet Flow,
Woods: Light underbrush n= 0.400 P2= 3.32"
2.3 225 0.1100 1.66 Shallow Concentrated Flow,
Woodland Kv= 5.0 fps
10.8 2,300 0.0490 3.56 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
34.2 2,625 Total
Subcatchment 11S: POST DA - 01
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
180
160
140
120
100
80
60
40
20
0
Type II 24-hr
10yr - 24hrs Rainfall=4.84"
Runoff Area=82.000 ac
Runoff Volume=18.207 af
Runoff Depth=2.66"
Flow Length=2,625'
Tc=34.2 min
CN=79
173.08 cfs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 14HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 12S: POST DA - 02
Runoff = 50.29 cfs @ 12.26 hrs, Volume= 4.938 af, Depth= 2.58"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"
Area (ac) CN Description
2.740 73 Woods, Fair, HSG C
20.260 79 Pasture/grassland/range, Fair, HSG C
23.000 78 Weighted Average
23.000 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
21.1 100 0.0200 0.08 Sheet Flow,
Woods: Light underbrush n= 0.400 P2= 3.32"
3.2 260 0.0730 1.35 Shallow Concentrated Flow,
Woodland Kv= 5.0 fps
6.5 1,530 0.0590 3.91 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
30.8 1,890 Total
Subcatchment 12S: POST DA - 02
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
55
50
45
40
35
30
25
20
15
10
5
0
Type II 24-hr
10yr - 24hrs Rainfall=4.84"
Runoff Area=23.000 ac
Runoff Volume=4.938 af
Runoff Depth=2.58"
Flow Length=1,890'
Tc=30.8 min
CN=78
50.29 cfs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 15HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 13S: POST DA - 03
Runoff = 77.12 cfs @ 12.35 hrs, Volume= 8.936 af, Depth= 1.77"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"
Area (ac) CN Description
8.510 60 Woods, Fair, HSG B
3.030 65 Woods/grass comb., Fair, HSG B
1.240 98 Paved parking, HSG B
0.700 85 Gravel roads, HSG B
47.220 69 Pasture/grassland/range, Fair, HSG B
60.700 68 Weighted Average
59.460 97.96% Pervious Area
1.240 2.04% Impervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
27.8 100 0.0100 0.06 Sheet Flow,
Woods: Light underbrush n= 0.400 P2= 3.32"
8.9 2,220 0.0660 4.14 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
36.7 2,320 Total
Subcatchment 13S: POST DA - 03
Runoff
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
o
w

(
c
f
s
)
80
70
60
50
40
30
20
10
0
Type II 24-hr
10yr - 24hrs Rainfall=4.84"
Runoff Area=60.700 ac
Runoff Volume=8.936 af
Runoff Depth=1.77"
Flow Length=2,320'
Tc=36.7 min
CN=68
77.12 cfs
Type II 24-hr 10yr - 24hrs Rainfall=4.84"Riverbend Ash Pond Closure
Printed 11/5/2015Prepared by AMEC
Page 16HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Link 15L: Total Off-Site Runoff
Inflow Area = 165.700 ac, 0.75% Impervious, Inflow Depth = 2.32" for 10yr - 24hrs event
Inflow = 298.11 cfs @ 12.30 hrs, Volume= 32.081 af
Primary = 298.11 cfs @ 12.30 hrs, Volume= 32.081 af, Atten= 0%, Lag= 0.0 min
Primary outflow = Inflow, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Link 15L: Total Off-Site Runoff
Inflow
Primary
Hydrograph
Time (hours)
1201101009080706050403020100
Fl
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(
c
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s
)
300
250
200
150
100
50
0
Inflow Area=165.700 ac
298.11 cfs298.11 cfs
Dam Breach Stormwater Calculation Primary and Secondary Dam Decommissioning Plan
❑uke Energy— Riverbend Steam Station
Calculation Title:
Stormwater Analysis of Final Grades with Dam Breach Openings
Summary:
Dam breach openings were designed to convey stormwater for the 50-year, 24-hour design storm event
considering final conditions after breaching of the primary and secondary ash basin dams.
The primary ash basin dam (GASTO-097) breach utilizes 2 channels to convey the stormwater runoff.
Both channels were designed for capacity and stabilization for the 50-year, 24-hour storm event.
The secondary ash basin dam (GASTO-98) breach utilizes 2 low flow channels to convey smaller storm
events while larger events will discharge through the approximately 350 feet wide breach opening.
Notes:
Revision Log:.
No.
Description
Originator
Verifier
Technical Reviewer
0
Initial Submittal
Chad Brown
Josh Bell
Richard, Hiner
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Amec Foster Wheeler Project No. 7810-16-0625 1 of 6
10/18/2016 (Initial Submittal) amec
foster
wheeler

Dam Breach Stormwater Calculation Primary and Secondary Dam Decommissioning Plan
Duke Energy – Riverbend Steam Station

Amec Foster Wheeler Project No. 7810-16-0625 2 of 6
10/18/2016 (Initial Submittal)

OBJECTIVE:
The objective of these calculations is to support the design of stormwater conveyance measures
based on final conditions following the decommissioning of the primary and secondary ash basin
dams (GASTO-097 and GASTO-098).
METHOD:
Stormwater flow rates were calculated using the SCS method. The hydraulic capacity of proposed
stormwater conveyances was evaluated using Manning’s equation within HydroCAD and HEC-RAS
modeling software.
DEFINITION OF VARIABLES:
W = shear;
A = area;
b = bottom width;
CN = curve number;
d = flow depth;
D = channel depth;
i = rainfall intensity;
L = length;
n = Manning’s n;
P = wetted perimeter;
Q = flow rate;
R = hydraulic radius;
S = longitudinal slope;
t = time
T = top width;
Tc = time of concentration;
V = velocity; and
Z = channel side slope.
CALCULATIONS:
1.0 Design Dam Breach Conveyances
The final grades of the ash stack and the ash basin areas will convey stormwater runoff to the
proposed dam breach locations and ultimately discharge to Mountain Island Lake along the
northeastern edge of the property.

The design criteria used for the breach openings was determined by first estimating the peak flow to
the conveyances using the SCS method, then evaluating the capacity using Manning’s equation.
The conveyances were designed for capacity and stability for the 50-year, 24 hour design storm
[Ref 1]. The precipitation frequency table is presented in Appendix 1.

Dam Breach Stormwater Calculation Primary and Secondary Dam Decommissioning Plan
Duke Energy – Riverbend Steam Station

Amec Foster Wheeler Project No. 7810-16-0625 3 of 6
10/18/2016 (Initial Submittal)

1.1 Estimate drainage areas
Drainage area delineation was based on the proposed final conditions after closure by removal of
the existing ash basins and ash stack. The drainage areas are defined in Drawing
RVB_C901.004.053 and are summarized in the following table:

Drainage
Area ID
Drainage Area
{A}
(ac)
Soil Class
Curve
Number
(CN)
DA-097-1 14.83 B69
DA-097-2 7.08 B69
DA-098-1 71.00 B69
Table 1: Summary of Drainage Areas

1.2 Calculate Time-of-Concentration
The time-of-concentration (Tc) is the amount of time needed for water to travel from the
hydrologically most distant point in a drainage area to the drainage area outlet. The estimated flow
paths for the drainage areas are shown in Drawing RVB_C901.004.053.

The total time-of-concentration for a catchment generally consists of the following three
components: sheet flow, shallow concentrated flow and channel flow [Ref 2]. Details of the
calculation method are presented in Appendix 2. In general, sheet flow was assumed for the first
100 feet of the flow path then shallow concentrated flow to the proposed conveyance channels.
The remaining flow path within the contributing drainage areas was analyzed as channel flow.
HydroCAD software was used to estimate time of concentration based on the SCS method [Ref. 2]
and the input parameters summarized in the following tables:

Drainage
Area ID
Flow Length
{L}
(ft.)
Surface
Description
Manning No.
{n}
Land Slope
(ft/ft)
Time of
Concentration
{Tc,sheet}
(min)
DA-097-1 100 Range 0.130 0.090 4.7
DA-097-2 100 Range 0.130 0.100 4.5
DA-098-1 100 Range 0.130 0.020 8.6
Table 2: Time of Concentration from Sheet Flow

Drainage
Area ID
Flow Length
{L}
(ft.)
Surface Description Land Slope
(ft/ft)
Time of
Concentration
{Tc,scf}
(min)
DA-097-1 890 Unpaved 0.080 3.3
DA-097-2 435 Unpaved 0.080 1.6
DA-098-1 480 Unpaved 0.100 1.6
Table 3: Time of Concentration from Shallow Concentrated Flow

Dam Breach Stormwater Calculation Primary and Secondary Dam Decommissioning Plan
Duke Energy – Riverbend Steam Station

Amec Foster Wheeler Project No. 7810-16-0625 4 of 6
10/18/2016 (Initial Submittal)

Drainage
Area ID
Flow Length
{L}
(ft.)
Channel
Velocity
{V}
(ft/s)
Time of
Concentration
{Tc,channel}
(min)
DA-097-1 750 9.37 1.3
DA-097-2 410 11.35 0.6
DA-098-1 1,475 5.83 4.2
Table 4: Time of Concentration from Channel Flow

Drainage
Area ID
Time of
Concentration
{Tc,sheet}
(min)
Time of
Concentration
{Tc,scf}
(min)
Time of
Concentration
{Tc,channel}
(min)
Total Time of
Concentration
{Tc,total}
(min)
DA-097-1 4.7 3.3 1.3 9.3
DA-097-2 4.5 1.6 0.6 6.7
DA-098-1 8.6 1.6 4.2 14.4
Table 5: Total Time of Concentration

1.3 Describe land use conditions
Land use conditions were estimated based on anticipated long-term conditions as shown in
Drawing RVB_C901.004.053. Site soils information for calculations were assigned based on soils
maps showing the site primarily consists of hydrologic soil group B soils [Ref 3]. The soils map is
presented in Appendix 3. Given the site’s soils and the final conditions the land use was assumed
to consist of fair condition grass with a CN value of 69.

HydroCAD software [Ref. 4] was used to estimate final condition stormwater flows for drainage
areas for the 50-year, 24-hour storm event based on the SCS method. Table 6 summarizes the
peak flows into each of the proposed breach conveyance channels based on the delineated
drainage areas. HydroCAD output is presented in Appendix 4.

Drainage
Area ID
Peak Flow
{Q50}
(cfs)
DA-097-1 71.26
DA-097-2 37.30
DA-098-1 286.47
Table 6: Peak Flow

1.4 Stormwater channel capacity and stability
1.4.1 GASTO-097 Breach Opening
The GASTO-097 breach opening utilizes two channels that were designed to convey stormwater
runoff. The GASTO-097 Breach Channel 1 is a 2-foot deep trapezoidal ditch with a 4-foot bottom
width and 3H:1V side slopes. GASTO-097 Breach Channel 2 is a 2-foot deep trapezoidal ditch with
a 2-foot bottom width and 3H:1V side slopes. The breach channels were modeled using HEC-RAS
with stations starting at the downstream confluence with an existing swale located at the toe of the
existing dam that discharges to existing wetlands before ultimately discharging to Mountain Island
Dam Breach Stormwater Calculation Primary and Secondary Dam Decommissioning Plan
Duke Energy – Riverbend Steam Station

Amec Foster Wheeler Project No. 7810-16-0625 5 of 6
10/18/2016 (Initial Submittal)

Lake. Sections were spaced at 50 feet along the channel lengths. The capacity of the proposed
GASTO-097 breach channels were evaluated using HEC-RAS [Ref. 5] along with the stability for
lining based on the computed shear forces. Flow depth, velocity, and shear forces for the breach
opening channels during the 50-year peak discharge can be found in the included HEC-RAS output
(Appendix 5).

The permissible velocity for a channel with grass lining (tall fescue), slope of 0% to 5%, and easily
erodible soils is 4.5 feet per second [Ref. 7]. Originally, the GASTO-097 breach channels were
analyzed as grass lined channels using North America Green’s web application [Ref 6]. The web
application was used to determine the type of erosion control matting needed within the channel
prior to establishment of vegetation and to determine the Manning’s n values for the channels in the
vegetated condition. Manning’s n values of 0.047 and 0.053 for Breach Channels 1 and 2 were
calculated (Appendix 6) and input into the HEC-RAS model for each channel. The HEC-RAS
models showed the four most down-gradient sections (Sections 0+00 – 1+50) for both channels
proved to have velocities more than the permissible velocity for grass lining of 4.5 feet per second,
thus the channel required armoring in these sections. In these steeper sloped sections of the
channels 6-inch riprap with a Manning’s n value of 0.069 was then analyzed. The calculated shear
forces exceeded the permissible shear force of 2.00 lb/ft2 reported in the North Carolina Erosion
and Sedimentation Control Planning and Design Manual [Ref 7] and therefore, channel lining of
Class B grouted riprap was chosen for these sections [Ref 8]. Tables of allowable velocities and
shear forces for the design of stable channels and diversion are presented in Appendix 7. The
North Carolina Department of Transportation (NCDOT) acceptance criteria table for riprap and
stone for erosion control is presented in Appendix 8.

1.4.2 GASTO-098 Breach Opening

The GASTO-098 breach opening is approximately 350-foot wide with two small 1-foot deep base
flows channels located along both edges of the breach opening. The GASTO-098 breach opening
was modeled using HEC-RAS [Ref. 5] with stations starting at the confluence with existing wetlands
before discharging to Mountain Island Lake. Sections were spaced at 50 feet along the breach
opening. The capacity and stability of the proposed GASTO-098 breach opening was evaluated
using HEC-RAS. Flow depth, velocity and shear forces for the breach opening channel during the
50-year peak discharge can be found in the included HEC-RAS output (Appendix 5).

The permissible velocity for a channel with grass lining (tall fescue), slope of 0% to 5%, and easily
erodible soils is 4.5 feet per second. The breach opening was analyzed as a grass lined channel
with a Manning’s n of 0.035. Every section proved to have velocities less than the permissible
velocity for grass lining of 4.5 feet per second thus the channel does not require armoring [Ref 7].

DISCUSSION:
The results from the analysis show that the proposed GASTO-097 Breach Channels 1 and 2, and
the GASTO-098 breach opening have flow capacity and lining stability to convey the stormwater
runoff from the 50-yr, 24-hr storm event.

Dam Breach Stormwater Calculation Primary and Secondary Dam Decommissioning Plan
Duke Energy – Riverbend Steam Station

Amec Foster Wheeler Project No. 7810-16-0625 6 of 6
10/18/2016 (Initial Submittal)

In comments regarding previous submittals, North Carolina Department of Environmental Quality
Dam Safety personnel suggested consideration of armoring vegetated channels to the 25-year
water surface elevation. Given the accessibility and size of the proposed vegetated sections of the
breach channels, vegetation appears to be maintainable and is an acceptable long-term lining.

DRAWINGS:
1. Drawing RVB_C901.004.053 Dam Breach Cross-Section Locations

REFERENCES:
1. Bonnin, G.M. et. al., “NOAA Atlas 14, Volume 2, Version 3, Point Precipitation Frequency
Estimates”, NOAA National Weather Service, obtained September 15, 2014.

2. United States Department of Agriculture, “Urban Hydrology for Small Watersheds”, Technical
Release 55, June 1986.

3. USDA-FSA-APFO NAIP MrSID Mosaic for Gaston County, North Carolina, dated 2010; NRCS
Soil Survey for Gaston County, dated 2013.

4. HydroCAD 10.00 (build 9), HydroCAD Software Solutions LLC, 2013.

5. HEC-RAS 4.1.0, U.S. Army Corps of Engineers – Hydrologic Engineering Center, January
2010.

6. North American Green Tensar, Erosion Control Materials Design Software – ECMDS Version
5.0, 2011.

7. North Carolina Department of Environment and Natural Resources, “Erosion and Sediment
Control Planning and Design Manual”, Revised May 2013.

8. “Standard Specification for Roads and Structures”, North Carolina Department of
Transportation, Raleigh, January 2012.

APPENDICES:
1. Precipitation Frequency [Ref. 1]
2. Time of Concentration Calculation Method [Ref. 2]
3. Soil Survey [Ref. 3]
4. HydroCAD Output
5. HEC-RAS Output
6. ECMDS Output
7. Design of Stable Channels and Diversions [Ref. 7]
8. Riprap and Stone for Erosion Control [Ref. 8]

DRAWING

RVB_C901.004.053 Dam Breach Cross-Section Locations
10 20 30TENTHSINCHES123
DWG SIZE REVISION
FOR
DRAWING NO.
TITLE
FILENAME:
DWG TYPE:
JOB NO:
DATE:
SCALE: DES:
DFTR:
CHKD:
ENGR:
APPD:
A
F
E
D
C
B
2345 786
45 789106
A
F
C
B
22"x34"
ANSI D
Environment &
Infrastructure
SEAL
REV DATE JOB NO. PROJECT TYPE DES DFTR CHKD ENGR APPD DESCRIPTION
N
NC GEOLOGY: C-247
NC ENG: F-1253
LICENSURE:
FAX: [phone]
TEL: [phone]
CHARLOTTE, NC 28208
SUITE 100
2801 YORKMONT ROAD
10/18/2016
6226-14-0007
DWG
AS SHOWN
KRD
KRD
TBM
CNB
CNB
.053 DAM BREACH CROSS-SECTION ALIGNMENTS.dwg
0
0
.
0
5
3
RVB_C901.004.053
PERMIT ISSUE - NOT FOR CONSTRUCTION
DAM BREACH CROSS-SECTION LOCATIONS
RIVERBEND STEAM STATION
ASH POND CCR REMOVAL GRADING PLAN
0 10/18/2016 7810160625 CLOSURE PLAN CNB TBM KRD KRD PERMIT ISSUE

0.053
EXISTING GRADE INDEX CONTOUR (10')
EXISTING GRADE INTERMEDIATE CONTOUR (2')
FINAL GRADE INDEX CONTOUR (10')
FINAL GRADE INTERMEDIATE CONTOUR (2')
DRAINAGE AREA BOUNDARY
DIVERSION CHANNEL
TIME OF CONCENTRATION FLOW PATH
WETLAND AREAS
WETLAND STREAM
LEGEND
01:44:35 PM 10-18-2016 (-04'00' GMT)

APPENDIX 1

Precipitation Frequency [Ref. 1]

NOAA Atlas 14, Volume 2, Version 3
Location name: Mount Holly, North Carolina, US*
Latitude: 35.3674°, Longitude: -80.9637°
Elevation: 719 ft*
* source: Google Maps
POINT PRECIPITATION FREQUENCY ESTIMATES
G.M. Bonnin, D. Martin, B. Lin, T. Parzybok, M.Yekta, and D. Riley
NOAA, National Weather Service, Silver Spring, Maryland
PF_tabular | PF_graphical | Maps_&_aerials
PF tabular
PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches)1
Duration Average recurrence interval (years)
1 2 5 10 25 50 100 200 500 1000
5-min 0.391
(0.361-0.424)
0.462
(0.427-0.503)
0.539
(0.497-0.586)
0.595
(0.547-0.645)
0.659
(0.602-0.713)
0.704
(0.640-0.762)
0.745
(0.673-0.806)
0.781
(0.701-0.847)
0.822
(0.730-0.894)
0.851
(0.748-0.929)
10-min 0.625
(0.577-0.677)
0.739
(0.683-0.804)
0.864
(0.796-0.938)
0.952
(0.874-1.03)
1.05
(0.960-1.14)
1.12
(1.02-1.21)
1.18
(1.07-1.28)
1.24
(1.11-1.34)
1.30
(1.15-1.42)
1.34
(1.18-1.46)
15-min 0.782
(0.721-0.846)
0.930
(0.858-1.01)
1.09
(1.01-1.19)
1.20
(1.11-1.30)
1.33
(1.22-1.44)
1.42
(1.29-1.54)
1.50
(1.35-1.62)
1.56
(1.40-1.69)
1.64
(1.45-1.78)
1.68
(1.48-1.84)
30-min 1.07
(0.989-1.16)
1.28
(1.19-1.40)
1.55
(1.43-1.69)
1.75
(1.60-1.89)
1.97
(1.80-2.13)
2.14
(1.94-2.31)
2.29
(2.07-2.48)
2.43
(2.18-2.64)
2.61
(2.31-2.83)
2.72
(2.40-2.97)
60-min 1.34
(1.23-1.45)
1.61
(1.49-1.75)
1.99
(1.83-2.16)
2.27
(2.09-2.46)
2.63
(2.40-2.84)
2.90
(2.63-3.13)
3.16
(2.85-3.41)
3.41
(3.06-3.70)
3.74
(3.32-4.07)
3.98
(3.50-4.34)
2-hr 1.55
(1.42-1.69)
1.87
(1.71-2.05)
2.33
(2.13-2.54)
2.67
(2.44-2.92)
3.12
(2.83-3.41)
3.47
(3.13-3.78)
3.81
(3.42-4.16)
4.15
(3.69-4.54)
4.60
(4.05-5.04)
4.94
(4.30-5.43)
3-hr 1.66
(1.52-1.82)
2.00
(1.83-2.19)
2.50
(2.28-2.74)
2.88
(2.63-3.16)
3.40
(3.09-3.72)
3.82
(3.44-4.18)
4.23
(3.79-4.63)
4.66
(4.14-5.11)
5.25
(4.58-5.76)
5.71
(4.92-6.28)
6-hr 2.02
(1.86-2.21)
2.43
(2.24-2.66)
3.04
(2.80-3.33)
3.52
(3.22-3.84)
4.17
(3.79-4.54)
4.69
(4.24-5.10)
5.21
(4.67-5.68)
5.75
(5.11-6.27)
6.50
(5.68-7.10)
7.09
(6.12-7.76)
12-hr 2.40
(2.21-2.61)
2.89
(2.67-3.16)
3.63
(3.34-3.96)
4.21
(3.86-4.58)
5.01
(4.56-5.44)
5.66
(5.11-6.14)
6.33
(5.66-6.85)
7.02
(6.21-7.60)
7.99
(6.95-8.64)
8.76
(7.52-9.49)
24-hr 2.75
(2.56-2.95)
3.32
(3.10-3.57)
4.17
(3.88-4.48)
4.84
(4.50-5.19)
5.75
(5.32-6.16)
6.47
(5.98-6.93)
7.21
(6.65-7.72)
7.96
(7.32-8.54)
8.99
(8.23-9.65)
9.79
(8.94-10.5)
2-day 3.23
(3.01-3.46)
3.88
(3.63-4.17)
4.84
(4.52-5.19)
5.59
(5.21-6.00)
6.61
(6.14-7.08)
7.42
(6.88-7.94)
8.24
(7.62-8.82)
9.08
(8.38-9.72)
10.2
(9.40-11.0)
11.1
(10.2-11.9)
3-day 3.43
(3.20-3.67)
4.12
(3.85-4.41)
5.11
(4.77-5.46)
5.88
(5.48-6.29)
6.94
(6.45-7.42)
7.78
(7.21-8.32)
8.64
(7.99-9.23)
9.51
(8.78-10.2)
10.7
(9.84-11.5)
11.6
(10.7-12.4)
4-day 3.63
(3.39-3.88)
4.35
(4.07-4.66)
5.37
(5.01-5.74)
6.17
(5.75-6.59)
7.27
(6.76-7.77)
8.15
(7.55-8.69)
9.03
(8.36-9.64)
9.94
(9.17-10.6)
11.2
(10.3-12.0)
12.1
(11.1-13.0)
7-day 4.18
(3.93-4.44)
4.98
(4.69-5.29)
6.06
(5.70-6.44)
6.92
(6.49-7.34)
8.10
(7.57-8.59)
9.03
(8.43-9.59)
9.98
(9.29-10.6)
11.0
(10.2-11.7)
12.3
(11.4-13.1)
13.3
(12.3-14.2)
10-day 4.78
(4.51-5.09)
5.69
(5.36-6.05)
6.84
(6.43-7.27)
7.73
(7.27-8.22)
8.94
(8.38-9.50)
9.88
(9.25-10.5)
10.8
(10.1-11.5)
11.8
(11.0-12.5)
13.1
(12.2-13.9)
14.1
(13.1-15.0)
20-day 6.42
(6.09-6.78)
7.58
(7.18-8.00)
8.94
(8.47-9.44)
10.0
(9.48-10.6)
11.5
(10.8-12.1)
12.6
(11.9-13.3)
13.7
(12.9-14.5)
14.9
(13.9-15.7)
16.4
(15.3-17.4)
17.6
(16.4-18.7)
30-day 7.92
(7.54-8.33)
9.32
(8.86-9.79)
10.8
(10.3-11.4)
12.0
(11.4-12.6)
13.5
(12.8-14.2)
14.7
(13.9-15.5)
15.9
(15.0-16.7)
17.0
(16.0-17.9)
18.6
(17.4-19.6)
19.7
(18.4-20.8)
45-day 9.95
(9.53-10.4)
11.6
(11.1-12.2)
13.3
(12.7-13.9)
14.6
(13.9-15.2)
16.2
(15.4-16.9)
17.4
(16.6-18.2)
18.6
(17.7-19.5)
19.8
(18.8-20.8)
21.3
(20.2-22.4)
22.4
(21.2-23.6)
60-day 11.8
(11.4-12.4)
13.8
(13.2-14.4)
15.6
(14.9-16.2)
17.0
(16.2-17.7)
18.7
(17.9-19.5)
20.1
(19.2-20.9)
21.3
(20.4-22.3)
22.6
(21.5-23.6)
24.2
(23.0-25.3)
25.4
(24.1-26.6)
1 Precipitation frequency (PF) estimates in this table are based on frequency analysis of partial duration series (PDS).
Numbers in parenthesis are PF estimates at lower and upper bounds of the 90% confidence interval. The probability that precipitation frequency estimates (for a
given duration and average recurrence interval) will be greater than the upper bound (or less than the lower bound) is 5%. Estimates at upper bounds are not
checked against probable maximum precipitation (PMP) estimates and may be higher than currently valid PMP values.
Please refer to NOAA Atlas 14 document for more information.
Back to Top
PF graphical
Page 1 of 4Precipitation Frequency Data Server
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Back to Top
Maps & aerials
Small scale terrain
Map data ©2014 GoogleReport a map error50 km  
Page 2 of 4Precipitation Frequency Data Server
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Large scale terrain
Large scale map
Large scale aerial
Back to Top
US Department of Commerce
National Oceanic and Atmospheric Administration
National Weather Service
Office of Hydrologic Development
1325 East West Highway
Silver Spring, MD 20910
Map data © 2014 GoogleReport a map error2 km
Map data © 2014 GoogleReport a map error2 km
Imagery ©2014 TerraM etricsReport a map error2 km  
Page 3 of 4Precipitation Frequency Data Server
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APPENDIX 2

Time of Concentration Calculation Method [Ref. 2]

Chapter 3
3–1(210-VI-TR-55, Second Ed., June 1986)
Technical Release 55
Urban Hydrology for Small Watersheds
Time of Concentration and Travel TimeChapter 3 Time of Concentration and
Travel Time
Travel time ( Tt ) is the time it takes water to travel
from one location to another in a watershed. Tt is a
component of time of concentration ( T c ), which is
the time for runoff to travel from the hydraulically
most distant point of the watershed to a point of
interest within the watershed. Tc is computed by
summing all the travel times for consecutive compo-
nents of the drainage conveyance system.
Tc influences the shape and peak of the runoff
hydrograph. Urbanization usually decreases Tc,
thereby increasing the peak discharge. But Tc can be
increased as a result of (a) ponding behind small or
inadequate drainage systems, including storm drain
inlets and road culverts, or (b) reduction of land slope
through grading.
Factors affecting time of concen-
tration and travel time
Surface roughness
One of the most significant effects of urban develop-
ment on flow velocity is less retardance to flow. That
is, undeveloped areas with very slow and shallow
overland flow through vegetation become modified by
urban development: the flow is then delivered to
streets, gutters, and storm sewers that transport runoff
downstream more rapidly. Travel time through the
watershed is generally decreased.
Channel shape and flow patterns
In small non-urban watersheds, much of the travel
time results from overland flow in upstream areas.
Typically, urbanization reduces overland flow lengths
by conveying storm runoff into a channel as soon as
possible. Since channel designs have efficient hydrau-
lic characteristics, runoff flow velocity increases and
travel time decreases.
Slope
Slopes may be increased or decreased by urbanization,
depending on the extent of site grading or the extent
to which storm sewers and street ditches are used in
the design of the water management system. Slope will
tend to increase when channels are straightened and
decrease when overland flow is directed through
storm sewers, street gutters, and diversions.
Computation of travel time and
time of concentration
Water moves through a watershed as sheet flow,
shallow concentrated flow, open channel flow, or
some combination of these. The type that occurs is a
function of the conveyance system and is best deter-
mined by field inspection.
Travel time ( Tt ) is the ratio of flow length to flow
velocity:
T L
Vt=
3600
[eq. 3-1]
where:
Tt = travel time (hr)
L = flow length (ft)
V = average velocity (ft/s)
3600 = conversion factor from seconds to hours.
Time of concentration ( Tc ) is the sum of Tt values for
the various consecutive flow segments:
TT T Tct t tm=++12K [eq. 3-2]
where:
Tc = time of concentration (hr)
m = number of flow segments
Technical Release 55
Urban Hydrology for Small Watersheds
Time of Concentration and Travel TimeChapter 3
3–2 (210-VI-TR-55, Second Ed., June 1986)
Figure 3-1 Average velocities for estimating travel time for shallow concentrated flow
10 20
Average velocity (ft/sec)
Wa
t
e
r
c
o
u
r
s
e

s
l
o
p
e

(
f
t
/
f
t
)
.20
.50
Un
p
a
v
e
d
Pa
v
e
d
.06
.04
.02
.10
.01
.005
1 2 4 6
Chapter 3
3–3(210-VI-TR-55, Second Ed., June 1986)
Technical Release 55
Urban Hydrology for Small Watersheds
Time of Concentration and Travel Time
Sheet flow
Sheet flow is flow over plane surfaces. It usually
occurs in the headwater of streams. With sheet flow,
the friction value (Manning’s n) is an effective rough-
ness coefficient that includes the effect of raindrop
impact; drag over the plane surface; obstacles such as
litter, crop ridges, and rocks; and erosion and trans-
portation of sediment. These n values are for very
shallow flow depths of about 0.1 foot or so. Table 3-1
gives Manning’s n values for sheet flow for various
surface conditions.
For sheet flow of less than 300 feet, use Manning’s
kinematic solution (Overtop and Meadows 1976) to
compute Tt:
T nL
Ps
t =()
()
0 007
08
2
05 04
..
..[eq. 3-3]
where:
Tt = travel time (hr),
n = Manning’s roughness coefficient (table 3-1)
L = flow length (ft)
P2 = 2-year, 24-hour rainfall (in)
s = slope of hydraulic grade line
(land slope, ft/ft)
This simplified form of the Manning’s kinematic solu-
tion is based on the following: (1) shallow steady
uniform flow, (2) constant intensity of rainfall excess
(that part of a rain available for runoff), (3) rainfall
duration of 24 hours, and (4) minor effect of infiltra-
tion on travel time. Rainfall depth can be obtained
from appendix B.
Shallow concentrated flow
After a maximum of 300 feet, sheet flow usually be-
comes shallow concentrated flow. The average veloc-
ity for this flow can be determined from figure 3-1, in
which average velocity is a function of watercourse
slope and type of channel. For slopes less than 0.005
ft/ft, use equations given in appendix F for figure 3-1.
Tillage can affect the direction of shallow concen-
trated flow. Flow may not always be directly down the
watershed slope if tillage runs across the slope.
After determining average velocity in figure 3-1, use
equation 3-1 to estimate travel time for the shallow
concentrated flow segment.
Open channels
Open channels are assumed to begin where surveyed
cross section information has been obtained, where
channels are visible on aerial photographs, or where
blue lines (indicating streams) appear on United States
Geological Survey (USGS) quadrangle sheets.
Manning’s equation or water surface profile informa-
tion can be used to estimate average flow velocity.
Average flow velocity is usually determined for bank-
full elevation.
Table 3-1 Roughness coefficients (Manning’s n) for
sheet flow
Surface description n
1/
Smooth surfaces (concrete, asphalt,
gravel, or bare soil) .......................................... 0.011
Fallow (no residue).................................................. 0.05
Cultivated soils:
Residue cover ≤20% ......................................... 0.06
Residue cover >20% ......................................... 0.17
Grass:
Short grass prairie............................................ 0.15
Dense grasses 2/................................................ 0.24
Bermudagrass . ................................................. 0.41
Range (natural)......................................................... 0.13
Woods:3/
Light underbrush .............................................. 0.40
Dense underbrush ............................................ 0.80
1 The n values are a composite of information compiled by Engman
(1986).
2 Includes species such as weeping lovegrass, bluegrass, buffalo
grass, blue grama grass, and native grass mixtures.
3 When selecting n , consider cover to a height of about 0.1 ft. This
is the only part of the plant cover that will obstruct sheet flow.
Technical Release 55
Urban Hydrology for Small Watersheds
Time of Concentration and Travel TimeChapter 3
3–4 (210-VI-TR-55, Second Ed., June 1986)
Manning’s equation is:
V rs
n
=149
2
3
1
2.[eq. 3-4]
where:
V = average velocity (ft/s)
r = hydraulic radius (ft) and is equal to a/pw
a = cross sectional flow area (ft
2)
pw = wetted perimeter (ft)
s = slope of the hydraulic grade line (channel
slope, ft/ft)
n = Manning’s roughness coefficient for open
channel flow.
Manning’s n values for open channel flow can be
obtained from standard textbooks such as Chow
(1959) or Linsley et al. (1982). After average velocity is
computed using equation 3-4, Tt for the channel seg-
ment can be estimated using equation 3-1.
Reservoirs or lakes
Sometimes it is necessary to estimate the velocity of
flow through a reservoir or lake at the outlet of a
watershed. This travel time is normally very small and
can be assumed as zero.
Limitations
• Manning’s kinematic solution should not be used
for sheet flow longer than 300 feet. Equation 3-3
was developed for use with the four standard
rainfall intensity-duration relationships.
• In watersheds with storm sewers, carefully identify
the appropriate hydraulic flow path to estimate Tc.
Storm sewers generally handle only a small portion
of a large event. The rest of the peak flow travels
by streets, lawns, and so on, to the outlet. Consult a
standard hydraulics textbook to determine average
velocity in pipes for either pressure or nonpressure
flow.
• The minimum Tc used in TR-55 is 0.1 hour.
• A culvert or bridge can act as a reservoir outlet if
there is significant storage behind it. The proce-
dures in TR-55 can be used to determine the peak
flow upstream of the culvert. Detailed storage
routing procedures should be used to determine
the outflow through the culvert.
Example 3-1
The sketch below shows a watershed in Dyer County,
northwestern Tennessee. The problem is to compute
Tc at the outlet of the watershed (point D). The 2-year
24-hour rainfall depth is 3.6 inches. All three types of
flow occur from the hydraulically most distant point
(A) to the point of interest (D). To compute Tc, first
determine Tt for each segment from the following
information:
Segment AB: Sheet flow; dense grass; slope (s) = 0.01
ft/ft; and length (L) = 100 ft. Segment BC: Shallow
concentrated flow; unpaved; s = 0.01 ft/ft; and
L = 1,400 ft. Segment CD: Channel flow; Manning’s
n = .05; flow area (a) = 27 ft2; wetted perimeter
(pw) = 28.2 ft; s = 0.005 ft/ft; and L = 7,300 ft.
See figure 3-2 for the computations made on
worksheet 3.
A B C D
7,300 ft1,400 ft100 ft
(Not to scale)

APPENDIX 3

Soil Survey [Ref. 3]

PREPARED
BY
DATE CHECKED
BY
DATE JOB NUMBER FIGURE
0 1,000 2,000 3,000 4,000500
Feet
2
Source: USDA-FSA-APFO NAIP MrSID Mosaic for Gaston County, North Carolina, dated 2010; NRCS Soil Survey for Gaston County, dated 2013.
PaD2
Ud
WeD
WkF
VaB
PaD2
W
CfB
Ur
PaE
ApB
WnB
PaD2
LdB2
ChA
ChA
CfB
CeD2
PaD2
PaE
CoA
PaE
PaD2
CeB2
CeD2
ChA
WnD
ApB LdB2
WeD CeB2
PaD2
ChA
ChA
W
PaD2
CeB2
W
PaD2
CeB2
WeD
CfD
W
PaE
PaD2
ChA
PaE
NC OneMap, NC Center for Geographic Information and Analysis, NC 911
Board
NRCS SOIL SURVEY
RIVERBEND STEAM STATION
GASTON COUNTY, NORTH CAROLINA
r
Soil Symbol Description
Hydrologic Soil
Group
CeB2 Cecil sandy clay loam, 2 to 8 percent slopes, moderately eroded B
CeD2 Cecil sandy clay loam, 8 to 15 percent slopes, moderately eroded B
CfB Cecil-Urban land complex, 2 to 8 percent slopes B
ChA Chewacla loam, 0 to 2 percent slopes, frequently flooded B/D
CoA Congaree loam, 0 to 2 percent slopes, occasionally flooded C
LdB2 Lloyd sandy clay loam, 2 to 8 percent slopes, moderately eroded B
PaD2 Pacolet sandy clay loam, 8 to 15 percent slopes, moderately eroded B
PaE Pacolet sandy loam, 15 to 25 percent slopes B
Ud Udorthents, loamy C
Ur Urban land NA
W Water NA
WeD Wedowee sandy loam, 6 to 15 percent slopes B
WkF Wilkes loam, 15 to 30 percent slopes D
WnB Winnsboro loam, 2 to 8 percent slopes C
7810-15-0348JMS 12/4/15 12/4/15CB
Project Boundary Soil Type Boundary
Do
c
u
m
e
n
t

P
a
t
h
:

F
:
\
A
M
E
C
_
P
r
o
j
e
c
t
s
\
2
0
1
5
\
7
8
1
0
-
1
5
-
0
3
8
4

R
i
v
e
r
b
e
n
d
\
G
I
S
\
M
X
D
s
\
F
i
g
-
2
_
S
o
i
l
s
.
m
x
d

APPENDIX 4

HydroCAD Output

2S
DA-098-1
3S
DA-097-1
4S
DA-097-2
Routing Diagram for GASTO-097 and 098 Dam Breach
Prepared by AMEC, Printed 10/17/2016
HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Subcat Reach Pond Link
GASTO-097 and 098 Dam Breach
Printed 10/17/2016Prepared by AMEC
Page 2HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Area Listing (selected nodes)
Area
(acres)
CN Description
(subcatchment-numbers)
92.910 69 50-75% Grass cover, Fair, HSG B (2S, 3S, 4S)
92.910 69 TOTAL AREA
GASTO-097 and 098 Dam Breach
Printed 10/17/2016Prepared by AMEC
Page 3HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Soil Listing (selected nodes)
Area
(acres)
Soil
Group
Subcatchment
Numbers
0.000 HSG A
92.910 HSG B 2S, 3S, 4S
0.000 HSG C
0.000 HSG D
0.000 Other
92.910 TOTAL AREA
GASTO-097 and 098 Dam Breach
Printed 10/17/2016Prepared by AMEC
Page 4HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Ground Covers (selected nodes)
HSG-A
(acres)
HSG-B
(acres)
HSG-C
(acres)
HSG-D
(acres)
Other
(acres)
Total
(acres)
Ground
Cover
Subcatchment
Numbers
0.000 92.910 0.000 0.000 0.000 92.910 50-75% Grass cover, Fair 2S, 3S,
4S
0.000 92.910 0.000 0.000 0.000 92.910 TOTAL AREA
Type II 24-hr 50yr - 24hrs Rainfall=6.47"GASTO-097 and 098 Dam Breach
Printed 10/17/2016Prepared by AMEC
Page 5HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Time span=0.00-72.00 hrs, dt=0.05 hrs, 1441 points
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN
Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method
Runoff Area=71.000 ac 0.00% Impervious Runoff Depth=3.08"Subcatchment 2S: DA-098-1
Flow Length=2,055' Tc=14.4 min CN=69 Runoff=286.47 cfs 18.249 af
Runoff Area=14.830 ac 0.00% Impervious Runoff Depth=3.08"Subcatchment 3S: DA-097-1
Flow Length=1,740' Tc=9.3 min CN=69 Runoff=71.26 cfs 3.812 af
Runoff Area=7.080 ac 0.00% Impervious Runoff Depth=3.08"Subcatchment 4S: DA-097-2
Flow Length=945' Tc=6.7 min CN=69 Runoff=37.30 cfs 1.820 af
Total Runoff Area = 92.910 ac Runoff Volume = 23.880 af Average Runoff Depth = 3.08"
100.00% Pervious = 92.910 ac 0.00% Impervious = 0.000 ac
Type II 24-hr 50yr - 24hrs Rainfall=6.47"GASTO-097 and 098 Dam Breach
Printed 10/17/2016Prepared by AMEC
Page 6HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 2S: DA-098-1
Runoff = 286.47 cfs @ 12.07 hrs, Volume= 18.249 af, Depth= 3.08"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.05 hrs
Type II 24-hr 50yr - 24hrs Rainfall=6.47"
Area (ac) CN Description
71.000 69 50-75% Grass cover, Fair, HSG B
71.000 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
8.6 100 0.0200 0.19 Sheet Flow,
Range n= 0.130 P2= 3.32"
1.6 480 0.1000 5.09 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
4.2 1,475 0.0200 5.83 17.48 Channel Flow,
Area= 3.0 sf Perim= 6.3' r= 0.48'
n= 0.022 Earth, clean & straight
14.4 2,055 Total
Subcatchment 2S: DA-098-1
Runoff
Hydrograph
Time (hours)
7065605550454035302520151050
Fl
o
w

(
c
f
s
)
300
250
200
150
100
50
0
Type II 24-hr
50yr - 24hrs Rainfall=6.47"
Runoff Area=71.000 ac
Runoff Volume=18.249 af
Runoff Depth=3.08"
Flow Length=2,055'
Tc=14.4 min
CN=69
286.47 cfs
Type II 24-hr 50yr - 24hrs Rainfall=6.47"GASTO-097 and 098 Dam Breach
Printed 10/17/2016Prepared by AMEC
Page 7HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 3S: DA-097-1
Runoff = 71.26 cfs @ 12.01 hrs, Volume= 3.812 af, Depth= 3.08"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.05 hrs
Type II 24-hr 50yr - 24hrs Rainfall=6.47"
Area (ac) CN Description
14.830 69 50-75% Grass cover, Fair, HSG B
14.830 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
4.7 100 0.0900 0.35 Sheet Flow,
Range n= 0.130 P2= 3.32"
3.3 890 0.0800 4.55 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
1.3 750 0.0150 9.37 187.34 Channel Flow,
Area= 20.0 sf Perim= 16.6' r= 1.20'
n= 0.022 Earth, clean & straight
9.3 1,740 Total
Subcatchment 3S: DA-097-1
Runoff
Hydrograph
Time (hours)
7065605550454035302520151050
Fl
o
w

(
c
f
s
)
70
60
50
40
30
20
10
0
Type II 24-hr
50yr - 24hrs Rainfall=6.47"
Runoff Area=14.830 ac
Runoff Volume=3.812 af
Runoff Depth=3.08"
Flow Length=1,740'
Tc=9.3 min
CN=69
71.26 cfs
Type II 24-hr 50yr - 24hrs Rainfall=6.47"GASTO-097 and 098 Dam Breach
Printed 10/17/2016Prepared by AMEC
Page 8HydroCAD® 10.00 s/n 08086 © 2013 HydroCAD Software Solutions LLC
Summary for Subcatchment 4S: DA-097-2
Runoff = 37.30 cfs @ 11.98 hrs, Volume= 1.820 af, Depth= 3.08"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.05 hrs
Type II 24-hr 50yr - 24hrs Rainfall=6.47"
Area (ac) CN Description
7.080 69 50-75% Grass cover, Fair, HSG B
7.080 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
4.5 100 0.1000 0.37 Sheet Flow,
Range n= 0.130 P2= 3.32"
1.6 435 0.0800 4.55 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
0.6 410 0.0250 11.35 181.63 Channel Flow,
Area= 16.0 sf Perim= 14.6' r= 1.10'
n= 0.022 Earth, clean & straight
6.7 945 Total
Subcatchment 4S: DA-097-2
Runoff
Hydrograph
Time (hours)
7065605550454035302520151050
Fl
o
w

(
c
f
s
)
40
35
30
25
20
15
10
5
0
Type II 24-hr
50yr - 24hrs Rainfall=6.47"
Runoff Area=7.080 ac
Runoff Volume=1.820 af
Runoff Depth=3.08"
Flow Length=945'
Tc=6.7 min
CN=69
37.30 cfs

APPENDIX 5

HEC-RAS Output

HEC-RAS Plan: Plan 03 River: GASTO-097 BC 1 Reach: GASTO-097 BC 1 Profile: PF 1
Reach River Sta Profile Q Total Min Ch El W.S. Elev Crit W.S. E.G. Elev E.G. Slope Vel Chnl Flow Area Top Width Mann Wtd Chnl Froude # Chl Shear Chan Shear Total Max Chl Dpth
(cfs) (ft) (ft) (ft) (ft) (ft/ft) (ft/s) (sq ft) (ft) (lb/sq ft) (lb/sq ft) (ft)
GASTO-097 BC 1 750 PF 1 71.26 683.23 685.13 684.72 685.36 0.012485 3.87 18.42 15.47 0.047 0.62 0.89 0.89 1.90
GASTO-097 BC 1 700 PF 1 71.26 682.60 684.48 684.72 0.013035 3.94 18.10 15.28 0.047 0.64 0.93 0.93 1.88
GASTO-097 BC 1 650 PF 1 71.26 681.95 683.88 684.10 0.011549 3.76 18.93 15.61 0.047 0.60 0.84 0.84 1.93
GASTO-097 BC 1 600 PF 1 71.26 681.37 683.25 683.49 0.013110 3.92 18.16 15.49 0.047 0.64 0.92 0.92 1.88
GASTO-097 BC 1 550 PF 1 71.26 680.71 682.58 682.82 0.013413 3.98 17.91 15.20 0.047 0.65 0.95 0.95 1.87
GASTO-097 BC 1 500 PF 1 71.26 680.04 681.93 682.16 0.012811 3.91 18.22 15.33 0.047 0.63 0.91 0.91 1.89
GASTO-097 BC 1 450 PF 1 71.26 679.40 681.29 681.53 0.012538 3.88 18.36 15.38 0.047 0.63 0.90 0.90 1.89
GASTO-097 BC 1 400 PF 1 71.26 678.77 680.66 680.89 0.012748 3.90 18.25 15.35 0.047 0.63 0.91 0.91 1.89
GASTO-097 BC 1 350 PF 1 71.26 678.13 680.05 680.27 0.011938 3.81 18.69 15.50 0.047 0.61 0.86 0.86 1.92
GASTO-097 BC 1 300 PF 1 71.26 677.53 679.41 679.65 0.013037 3.94 18.10 15.28 0.047 0.64 0.93 0.93 1.88
GASTO-097 BC 1 250 PF 1 71.26 676.88 678.77 679.01 0.012561 3.88 18.38 15.44 0.047 0.63 0.90 0.90 1.89
GASTO-097 BC 1 200 PF 1 71.26 676.25 678.12 678.36 0.013221 3.95 18.03 15.30 0.047 0.64 0.94 0.94 1.87
GASTO-097 BC 1 150 PF 1 71.26 675.67 677.16 677.16 677.65 0.014158 5.65 12.61 12.94 0.030 1.01 0.83 0.83 1.49
GASTO-097 BC 1 100 PF 1 71.26 674.70 676.01 676.19 676.74 0.023646 6.82 10.45 11.91 0.030 1.28 1.25 1.25 1.31
GASTO-097 BC 1 50 PF 1 71.26 673.01 674.17 674.49 675.21 0.038885 8.18 8.71 10.99 0.030 1.62 1.86 1.86 1.16
GASTO-097 BC 1 0 PF 1 71.26 668.00 668.82 669.49 671.61 0.151671 13.39 5.32 8.94 0.030 3.06 5.48 5.48 0.82
HEC-RAS Plan: Plan 01 River: GASTO-097 BC 2 Reach: GASTO-097 BC 2 Profile: PF 1
Reach River Sta Profile Q Total Min Ch El W.S. Elev Crit W.S. E.G. Elev E.G. Slope Vel Chnl Flow Area Top Width Mann Wtd Chnl Froude # Chl Shear Chan Shear Total Max Chl Dpth
(cfs) (ft) (ft) (ft) (ft) (ft/ft) (ft/s) (sq ft) (ft) (lb/sq ft) (lb/sq ft) (ft)
GASTO-097 BC 2 550 PF 1 37.30 682.83 684.38 684.11 684.59 0.020077 3.63 10.28 11.27 0.053 0.67 1.09 1.09 1.55
GASTO-097 BC 2 500 PF 1 37.30 681.84 683.39 683.59 0.019951 3.62 10.31 11.31 0.053 0.67 1.09 1.09 1.55
GASTO-097 BC 2 450 PF 1 37.30 680.85 682.41 682.61 0.019292 3.57 10.44 11.37 0.053 0.66 1.06 1.06 1.56
GASTO-097 BC 2 400 PF 1 37.30 679.88 681.44 681.64 0.019094 3.56 10.48 11.40 0.053 0.65 1.05 1.05 1.56
GASTO-097 BC 2 350 PF 1 37.30 678.92 680.49 680.68 0.018863 3.54 10.52 11.41 0.053 0.65 1.04 1.04 1.57
GASTO-097 BC 2 300 PF 1 37.30 677.98 679.54 679.74 0.019325 3.58 10.43 11.37 0.053 0.66 1.06 1.06 1.56
GASTO-097 BC 2 250 PF 1 37.30 677.05 678.66 678.84 0.016579 3.37 11.05 11.70 0.053 0.61 0.94 0.94 1.61
GASTO-097 BC 2 200 PF 1 37.30 676.13 677.63 677.41 677.86 0.023353 3.84 9.72 10.97 0.053 0.72 1.24 1.24 1.50
GASTO-097 BC 2 150 PF 1 37.30 675.24 676.51 676.51 676.91 0.015476 5.03 7.42 9.66 0.030 1.01 0.71 0.71 1.27
GASTO-097 BC 2 100 PF 1 37.30 674.02 675.09 675.29 675.78 0.033107 6.67 5.59 8.44 0.030 1.44 1.32 1.32 1.07
GASTO-097 BC 2 50 PF 1 37.30 666.34 666.93 667.61 671.38 0.416223 16.94 2.20 5.52 0.030 4.72 10.03 10.03 0.59
GASTO-097 BC 2 0 PF 1 37.30 650.00 650.64 651.27 654.01 0.284471 14.73 2.53 5.87 0.030 3.95 7.40 7.40 0.64
HEC-RAS Plan: Plan 01 River: GASTO-098 BREACH Reach: GASTO-098 BREACH Profile: PF 1
Reach River Sta Profile Q Total Min Ch El W.S. Elev Crit W.S. E.G. Elev E.G. Slope Vel Chnl Flow Area Top Width Mann Wtd Chnl Froude # Chl Shear Chan Shear Total Max Chl Dpth
(cfs) (ft) (ft) (ft) (ft) (ft/ft) (ft/s) (sq ft) (ft) (lb/sq ft) (lb/sq ft) (ft)
GASTO-098 BREACH 400 PF 1 286.47 656.96 658.23 658.23 658.36 0.040580 2.95 97.24 480.36 0.035 1.15 0.51 0.51 1.27
GASTO-098 BREACH 350 PF 1 286.47 655.77 657.08 657.05 657.17 0.020403 2.41 118.66 471.74 0.035 0.85 0.32 0.32 1.31
GASTO-098 BREACH 300 PF 1 286.47 654.58 655.87 655.86 655.98 0.028358 2.69 106.53 461.17 0.035 0.99 0.41 0.41 1.29
GASTO-098 BREACH 250 PF 1 286.47 653.39 654.71 654.66 654.80 0.019824 2.44 117.60 451.40 0.035 0.84 0.32 0.32 1.32
GASTO-098 BREACH 200 PF 1 286.47 652.21 653.50 653.49 653.62 0.028659 2.78 102.99 427.14 0.035 1.00 0.43 0.43 1.29
GASTO-098 BREACH 150 PF 1 286.47 651.04 652.34 652.30 652.44 0.019540 2.54 112.98 403.97 0.035 0.84 0.34 0.34 1.30
GASTO-098 BREACH 100 PF 1 286.47 649.88 651.14 651.13 651.27 0.028526 2.91 98.39 379.96 0.035 1.01 0.46 0.46 1.26
GASTO-098 BREACH 50 PF 1 286.47 648.79 649.73 649.73 649.88 0.027171 3.09 92.82 316.65 0.035 1.00 0.50 0.50 0.94
GASTO-098 BREACH 0 PF 1 286.47 646.59 647.31 647.46 647.81 0.067520 5.64 50.77 138.74 0.035 1.64 1.54 1.54 0.72

APPENDIX 6

ECMDS Output

10/17/2016 www.ecmds.com/print/analysis/103585/103590
http://www.ecmds.com/print/analysis/103585/103590 1/1
Tensar International Corporation
5401 St. Wendel-Cynthiana Road
Poseyville, Indiana 47633
Tel. [phone]
Fax [phone]
www.nagreen.com
Erosion Control Materials Design Software
Version 5.0
Project Name: Riverbend Dam Decommissioning
Project Number: 103585
Channel Name: GASTO-097 Breach Channel 1
Discharge 71.26
Peak Flow Period 12
Channel Slope 0.013
Channel Bottom Width 4
Left Side Slope 3
Right Side Slope 3
Low Flow Liner
Retardance Class C
Vegtation Type Mix (Sod & Bunch)
Vegetation Density Fair 50-75%
Soil Type Loam
C125
Phase Reach DischargeVelocity Normal
Depth
Mannings
N
Permissible Shear
Stress
Calculated Shear
Stress
Safety
Factor
Remarks Staple
Pattern
C125
Unvegetated
Straight 71.26
cfs
7.87
ft/s
1.19 ft 0.018 2.25 lbs/ft2 0.97 lbs/ft2 2.32 STABLE D
Unreinforced Vegetation - Class C - Mix (Sod & Bunch) - Fair 50-75%
Phase Reach DischargeVelocity Normal
Depth
Mannings
N
Permissible Shear
Stress
Calculated Shear
Stress
Safety
Factor
Remarks Staple
Pattern
Unreinforced
Vegetation
Straight 71.26
cfs
3.9
ft/s
1.89 ft 0.047 4.2 lbs/ft2 1.53 lbs/ft2 2.74 STABLE --
Underlying
Substrate
Straight 71.26
cfs
3.9
ft/s
1.89 ft -- 0.04 lbs/ft2 0.066 lbs/ft2 0.53 UNSTABLE --
10/17/2016 www.ecmds.com/print/analysis/103585/103595
http://www.ecmds.com/print/analysis/103585/103595 1/1
Tensar International Corporation
5401 St. Wendel-Cynthiana Road
Poseyville, Indiana 47633
Tel. [phone]
Fax [phone]
www.nagreen.com
Erosion Control Materials Design Software
Version 5.0
Project Name: Riverbend Dam Decommissioning
Project Number: 103585
Channel Name: GASTO-097 Breach Channel 2
Discharge 37.30
Peak Flow Period 12
Channel Slope 0.022
Channel Bottom Width 2
Left Side Slope 3
Right Side Slope 3
Low Flow Liner
Retardance Class C
Vegtation Type Mix (Sod & Bunch)
Vegetation Density Fair 50-75%
Soil Type Loam
C125
Phase Reach DischargeVelocity Normal
Depth
Mannings
N
Permissible Shear
Stress
Calculated Shear
Stress
Safety
Factor
Remarks Staple
Pattern
C125
Unvegetated
Straight37.3 cfs 7.89
ft/s
0.97 ft 0.02 2.25 lbs/ft2 1.33 lbs/ft2 1.7 STABLE D
Unreinforced Vegetation - Class C - Mix (Sod & Bunch) - Fair 50-75%
Phase Reach DischargeVelocity Normal
Depth
Mannings
N
Permissible Shear
Stress
Calculated Shear
Stress
Safety
Factor
Remarks Staple
Pattern
Unreinforced
Vegetation
Straight37.3 cfs 3.77
ft/s
1.51 ft 0.053 4.2 lbs/ft2 2.08 lbs/ft2 2.02 STABLE --
Underlying
Substrate
Straight37.3 cfs 3.77
ft/s
1.51 ft -- 0.04 lbs/ft2 0.073 lbs/ft2 0.48 UNSTABLE --

APPENDIX 7

Design of Stable Channels and Diversions [Ref. 7]

Appendices
This section addresses the design of stable conveyance channels and
diversions using flexible linings. A stable channel is defined as a channel
which is nonsilting and nonscouring. To minimize silting in the channel, flow
velocities should remain constant or increase slightly throughout the channel
length. This is especially important in designing diversion channels and can
be accomplished by adjusting channel grade. Procedures presented in this
section address the problems of erosion and scour. More advanced procedures
for permanent, unlined channels may be found elsewhere. (References: Garde
and Ranga Raju, 1980)
Diversions are channels usually with a supporting ridge on the lower side.
They are generally located to divert flows across a slope and are designed
following the same procedures as other channels. Design tables for vegetated
diversions and waterways are included at the end of this section.
Flexible channel linings are generally preferred to rigid linings from an
erosion control standpoint because they conform to changes in channel shape
without failure and are less susceptible to damage from frost heaving, soil
swelling and shrinking, and excessive soil pore water pressure from lack of
drainage. Flexible linings also are generally less expensive to construct, and
when vegetated, are more natural in appearance. On the other hand, flexible
linings generally have higher roughness and require a larger cross section for
the same discharge.
EROSION CONTROL CRITERIA
The minimum design criteria for conveyance channels require that two
primary conditions be satisfied: the channel system must have capacity for
the peak flow expected from the 10-year storm and the channel lining must be
resistant to erosion for the design velocity. In some cases, out-of-bank flow
may be considered a functional part of the channel system. In these cases,
flow capacities and design velocities should be considered separately for out-
of-bank flows and channel flows.
Both the capacity of the channel and the velocity of flow are functions of the
channel lining, cross-sectional area and slope. The channel system must carry
the design flow, fit site conditions, and be stable.
STABLE CHANNEL DESIGN METHODS
Two accepted procedures for designing stable channels with flexible linings
are: (1) the permissible velocity approach; and (2) the tractive force approach.
Under the permissible velocity approach, the channel is considered stable if the
design, mean velocity is lower than the maximum permissible velocity. Under
the tractive force approach, erosive stress evaluated at the boundary between
flowing water and lining materials must be less than the minimum unit tractive
force that will cause serious erosion of material from a level channel bed.
8.05 DESIGN OF STABLE CHANNELS AND DIVERSIONS
8.05.1
8
8.05.2
The permissible velocity procedure is recommended for the design of vegetative
channels because of common usage and the availability of reliable design
tables. The tractive force approach is recommended for design of channels
with temporary synthetic liners or riprap liners. The tractive force procedure
is described in full in the U.S. Department of Transportation, Federal Highway
Administration Bulletin, Design of Roadside Channels with Flexible Linings.
Permissible Velocity
Procedure
The permissible velocity procedure uses two equations to calculate flow:
Manning’s equation,
9   R S n
where:
V = average velocity in the channel in ft/sec.
n = Manning’s roughness coefficient, based upon the lining of the
channel
R = hydraulic radius, wetted cross-sectional area/wetted perimeter
in ft
S = slope of the channel in ft/ft
and the continuity equation,
4 $9
where:
Q = flow in the channel in cfs
A = cross-sectional area of flow within the channel in ft2
V = average velocity in the channel in ft/sec.
Manning’s equation and the continuity equation are used together to determine
channel capacity and flow velocity. A nomograph for solving Manning’s
equation is given in Figure 8.05a.
6HOHFWLQJ3HUPDQHQW
Channel Lining
Channel lining materials include such flexible materials as grass, riprap and
gabions, as well as rigid materials such as paving blocks, flag stone, gunite,
asphalt, and concrete. The design of concrete and similar rigid linings
is generally not restricted by flow velocities. However, flexible channel
linings do have maximum permissible flow velocities beyond which they are
susceptible to erosion. The designer should select the type of liner that best
fits site conditions.
Table 8.05a lists maximum permissible velocities for established grass linings
and soil conditions. Before grass is established, permissible velocity is
determined by the choice of temporary liner. Permissible velocities for riprap
linings are higher than for grass and depend on the stone size selected.
Appendices
8.05.3
8
8.05.4
Table 8.05a
Maximum Allowable Design Velocities1
for Vegetated Channels
Typical
Channel Slope
Application
Soil
Characteristics2
Grass Lining Permissible Velocity
3
for Established Grass
Lining (ft/sec)
0-5% Easily Erodible
Non-plastic
(Sands & Silts)
Bermudagrass
Tall fescue
Bahiagrass
Kentucky bluegrass
Grass-legume mixture
5.0
4.5
4.5
4.5
3.5
Erosion Resistant
Plastic
(Clay mixes)
Bermudagrass
Tall fescue
Bahiagrass
Kentucky bluegrass
Grass-legume mixture
6.0
5.5
5.5
5.5
4.5
5-10% Easily Erodible
Non-plastic
(Sands & Silts)
Bermudagrass
Tall fescue
Bahiagrass
Kentucky bluegrass
Grass-legume mixture
4.5
4.0
4.0
4.0
3.0
Erosion Resistant
Plastic
(Clay mixes)
Bermudagrass
Tall fescue
Bahiagrass
Kentucky bluegrass
Grass-legume mixture
5.5
5.0
5.0
5.0
3.5
>10% Easily Erodible
Non-plastic
(Sands & Silts)
Bermudagrass
Tall fescue
Bahiagrass
Kentucky bluegrass
3.5
2.5
2.5
2.5
Erosion Resistant
Plastic
(Clay mixes)
Bermudagrass
Tall fescue
Bahiagrass
Kentucky bluegrass
4.5
3.5
3.5
3.5
6RXUFH86'$6&60RGL¿HG
NOTE:1Permissible Velocity based on 10-year storm peak runoff
26RLOHURGLELOLW\EDVHGRQUHVLVWDQFHWRVRLOPRYHPHQWIURPFRQFHQWUDWHGÀRZLQJZDWHU
3Before grass is established, permissible velocity is determined by the type of temporary liner used.
Selecting Channel
Cross-Section
Geometry
To calculate the required size of an open channel, assume the design flow is
uniform and does not vary with time. Since actual flow conditions change
throughout the length of a channel, subdivide the channel into design reaches,
and design each reach to carry the appropriate capacity.
The three most commonly used channel cross-sections are “V”-shaped,
parabolic, and trapezoidal. Figure 8.05b gives mathematical formulas for the
area, hydraulic radius and top width of each of these shapes.
Appendices
8.05.5
8
8.05.6 Rev. 12/93
Design Procedure-
Permissible Velocity
The following is a step-by-step procedure for designing a runoff conveyance
channel using Manning’s equation and the continuity equation:
Step 1. Determine the required flow capacity, Q, by estimating peak runoff
rate for the design storm (Appendix 8.03).
Step 2. Determine the slope and select channel geometry and lining.
Step 3. Determine the permissible velocity for the lining selected, or the
desired velocity, if paved. (see Table 8.05a, page 8.05.4)
Step 4. Make an initial estimate of channel size—divide the required Q by the
permissible velocity to reach a “first try” estimate of channel flow area. Then
select a geometry, depth, and top width to fit site conditions.
Step 5. Calculate the hydraulic radius, R, from channel geometry (Figure
8.05b, page 8.05.5).
Step 6. Determine roughness coefficient n.
Structural Linings—see Table 8.05b, page 8.05.6.
Grass Lining:
a. Determine retardance class for vegetation from Table 8.05c, page
8.05.8. To meet stability requirement, use retardance for newly
mowed condition (generally C or D). To determine channel capacity,
use at least one retardance class higher.
b. Determine n from Figure 8.05c, page 8.05.7.
Step 7. Calculate the actual channel velocity, V, using Manning’s equation
(Figure 8.05a, pg. 8.05.3), and calculate channel capacity, Q, using the
continuity equation.
Step 8. Check results against permissible velocity and required design
capacity to determine if design is acceptable.
Step 9. If design is not acceptable, alter channel dimensions as appropriate.
For trapezoidal channels, this adjustment is usually made by changing the
bottom width.
Table 8.05b
Manning’s n for Structural
Channel Linings
Channel Lining
Recommended
n values
Asphaltic concrete, machine placed
Asphalt, exposed prefabricated
Concrete
Metal, corrugated
Plastic
Shotcrete
Gabion
Earth
0.014
0.015
0.015
0.024
0.013
0.017
0.030
0.020
6RXUFH$PHULFDQ6RFLHW\RI&LYLO(QJLQHHUVPRGL¿HG
Appendices
Rev. 12/93 8.05.7
Step 10. For grass-lined channels once the appropriate channel dimensions
have been selected for low retardance conditions, repeat steps 6 through 8
using a higher retardance class, corresponding to tall grass. Adjust capacity of
the channel by varying depth where site conditions permit.
NOTE 1: If design velocity is greater than 2.0 ft/sec., a temporary lining
may be required to stabilize the channel until vegetation is established.
The temporary liner may be designed for peak flow from the 2-year storm.
If a channel requires a temporary lining, the designer should analyze
shear stresses in the channel to select the liner that provides protection
and promotes establishment of vegetation. For the design of temporary
liners, use tractive force procedure.
NOTE 2: Design Tables—Vegetated Channels and Diversions at the end
of this section may be used to design grass-lined channels with parabolic
cross-sections.
Step 11. Check outlet for carrying capacity and stability. If discharge
velocities exceed allowable velocities for the receiving stream, an outlet
protection structure will be required (Table 8.05d, page 8.05.9).
Sample Problem 8.05a illustrates the design of a grass-lined channel.
8
8.05.8
Table 8.05c
Retardance Classification for Vegetal Covers
Retardance Cover Condition
A Reed canarygrass
Weeping lovegrass
Excellent stand, tall (average 36”)
Excellent stand, tall (average 30”)
B Tall fescue
Bermudagrass
Grass-legume mixture
(tall fescue,red
fescue, sericea
lespedeza)
Grass mixture
(timothy, smooth
bromegrass or
orchardgrass)
Sericea lespedeza
Reed canarygrass
Alfalfa
Good stand, uncut, (average 18”)
Good stand, tall (average 12”)
Good stand, uncut
Good stand, uncut (average 20”)
*RRGVWDQGQRWZRRG\WDOODYHUDJH´
Good stand, cut, (average 12-15”)
Good stand, uncut (average 11”)
C Tall fescue
Bermudagrass
Bahiagrass
Grass-legume mixture--
summer (orchardgrass,
redtop and annual
lespedeza)
Centipedegrass
Kentucky bluegrass
Redtop
Good stand (8-12”)
Good stand, cut (average 6”)
Good stand, uncut (6-8”)
Good stand, uncut (6-8”)
Very dense cover (average 6”)
Good stand, headed (6-12”)
Good stand, uncut (15-20”)
D Tall fescue
Bermudagrass
Bahiagrass
Grass-legume mixture--
fall-spring (orchardgrass,
redtop, and
annual lespedeza)
Red fescue
Centipedegrass
Kentucky bluegrass
Good stand, cut (3-4”)
Good stand, cut (2.5”)
Good stand, cut (3-4”)
Good stand, uncut (4-5”)
Good stand, uncut (12-18”)
Good stand, cut (3-4”)
Good stand, cut (3-4”)
E Bermudagrass
Bermudagrass
Good stand, cut (1.5”)
Burned stubble
0RGL¿HGIURP86'$6&6(QJLQHHULQJ)LHOG0DQXDO
Appendices
8.05.9
Table 8.05d
Maximum Permissible
Velocities for Unprotected
Soils in Existing Channels.
Materials
Maximum Permissible
Velocities (fps)
)LQH6DQGQRQFROORLGDO
Sand Loam (noncolloidal)
Silt Loam (noncolloidal)
2UGLQDU\)LUP/RDP
)LQH*UDYHO
Stiff Clay (very colloidal)
Graded, Loam to Cobbles (noncolloidal)
Graded, Silt to Cobbles (colloidal)
Alluvial Silts (noncolloidal)
Alluvial Silts (colloidal)
Coarse Gravel (noncolloidal)
Cobbles and Shingles
2.5
2.5
3.0
3.5
5.0
5.0
5.0
5.5
3.5
5.0
6.0
5.5
Sample Problem 8.05a
Design of a
Grass-lined Channel.
Given:
Design Q10 = 16.6 cfs
Proposed channel grade = 2%
Proposed vegetation: Tall fescue
Soil: Creedmoor (easily erodible)
Permissible velocity, Vp = 4.5 ft/s (Table 8.05a)
Retardance class: “B” uncut, “D” cut (Table 8.05c).
Trapezoidal channel dimensions:
GHVLJQLQJIRUORZUHWDUGDQFHFRQGLWLRQUHWDUGDQFHFODVV'
design to meet Vp.
Find:
Channel dimensions
Solution:
Make an initial estimate of channel size
$ 49FIVIWVHF IW2
7U\ERWWRPZLGWK IWZVLGHVORSHVRI
Z = 3
A = bd + Zd2
P = b + 2d Z2 + 1
R = AP
An iterativeVROXWLRQXVLQJ)LJXUHDWRUHODWHÀRZGHSWKWR0DQQLQJ¶Vn
SURFHHGVDVIROORZV0DQQLQJ¶VHTXDWLRQLVXVHGWRFKHFNYHORFLWLHV

)URP)LJFSJ5HWDUGDQFH&ODVVG95 [ 
d (ft) A (ft
2) R (ft) *n Vt (fps) Q (cfs) Comments
0.8 4.32 0.54 0.043 3.25 14.0 V<Vp OK,
Q<Q10
(too small, try deeper channel)
5.13 0.042 3.53 18.10 V<Vp, OK,
Q>Q10, OK
1RZGHVLJQIRUKLJKUHWDUGDQFHFODVV%
)RUWKHHDVHRIFRQVWUXFWLRQDQGPDLQWHQDQFHDVVXPHDQG
try d = 1.5 ft and trial velocity Vt = 3.0 ft/sec
d (ft) A (ft
2) R (ft)Vt (fps)n V (fps) Q (cfs) Comments
1.5 11.25 3.0
2.0
1.6
**1.5
0.08
0.11
0.12
0.13
2.5
1.8
1.6
1.5
28
20
18
17
reduce Vtreduce Vt
Q>Q10 OK
** These assumptions = actual V (fps.) (chart continued on next page)
8
8.05.10 Rev. 12/93
(continued)
Sample Problem 8.05a
Design of a
Grass-lined Channel.
Channel summary:
Trapezoidal shape, Z = 3, b = 3 ft, d = 1.5 ft, grade = 2%
1RWH,Q6DPSOH3UREOHPDWKH³QYDOXH´LV¿UVWFKRVHQEDVHGRQD
permissible velocity and not a design velocity criteria. Therefore, the use of
7DEOHFPD\QRWEHDVDFFXUDWHDVLQGLYLGXDOUHWDUGDQFHFODVVFKDUWVZKHQ
a design velocity is the determining factor.
Tractive Force
Procedure
The design of riprap-lined channels and temporary channel linings is based on
analysis of tractive force.
127(7KLVSURFHGXUHLVIRUXQLIRUPÀRZLQFKDQQHOVDQGLVnot to be
used for design of deenergizing devices and may not be valid for larger
channels.
To calculate the required size of an open channel, assume the design flow is
uniform and does not vary with time. Since actual flow conditions change
through the length of a channel, subdivide the channel into design reaches as
appropriate.
PERMISSIBLE SHEAR STRESS
The permissible shear stress, Td, is the force required to initiate movement of
the lining material. Permissible shear stress for the liner is not related to the
erodibility of the underlying soil. However, if the lining is eroded or broken,
the bed material will be exposed to the erosive force of the flow.
COMPUTING NORMAL DEPTH
7KH¿UVWVWHSLQVHOHFWLQJDQDSSURSULDWHOLQLQJLVWRFRPSXWHWKHGHVLJQ
ÀRZGHSWKWKHQRUPDOGHSWKDQGGHWHUPLQHWKHVKHDUVWUHVV
Normal depths can be calculated by Manning’s equation as shown for
trapezoidal channels in Figure 8.05d. Values of the Manning’s roughness
coefficient for different ranges of depth are provided in Table 8.05e for
temporary linings and Table 8.05f for riprap. The coefficient of roughness
generally decreases with increasing flow depth.
n value for Depth Ranges*
Table 8.05e
Manning’s Roughness
Coefficients for Temporary
Lining Materials
0-0.5 ft 0.5-2.0 ft >2.0 ft
Lining Type
Woven Paper Net
Jute Net
)LEHUJODVV5RYLQJ
6WUDZZLWK1HW
Curled Wood Mat
Synthetic Mat
0.016
0.028
0.028
0.065
0.066
0.036
0.015
0.022
0.021
0.033
0.035
0.025
0.015


0.025
0.028
0.021
* Adapted from: FHWA-HEC 15, Pg. 37 - April 1988
Appendices
Rev. 12/93 8.05.11
8
8.05.12 Rev. 12/93
Table 8.05f Manning’s Roughness Coefficient
n - value
n value for Depth Ranges
Lining Category Lining Type 0-0.5 ft
(0-15 cm)
0.5-2.0 ft
(15-60 cm)
2.0 ft
(>60 cm)
Rigid Concrete
Grouted Riprap
Stone Masonry
Soil Cement
Asphalt
0.015
0.040
0.042
0.025
0.018
0.013
0.030
0.032
0.022
0.016
0.013
0.028
0.030
0.020
0.016
Unlined Bare Soil
Rock Cut
0.023
0.045
0.020
0.035
0.020
0.025
Gravel Riprap 1-inch (2.5-cm) D502-inch (5-cm) D50
0.044
0.066
0.033
0.041
0.030
0.034
Rock Riprap 6-inch (15-cm) D5012-inch (30-cm) D50
0.104
--

0.078
0.035
0.040
Note: Values listed are representative values for the respective depth ranges. Manning’s roughness coefficients, n, vary with the flow depth.
DETERMINING SHEAR STRESS
Shear stress, T, at normal depth is computed for the lining by the following
equation:
T = yds
Td = Permissible shear stress
where:
T = shear stress in lb/ft2
y = unit weight of water, 62.4 lb/ft3
d = flow depth in ft
s = channel gradient in ft/ft
If the permissible shear stress, Td, given in Table 8.05g is greater than the
computed shear stress, the riprap or temporary lining is considered acceptable.
If a lining is unacceptable, select a lining with a higher permissible shear stress
and repeat the calculations for normal depth and shear stress. In some cases it
may be necessary to alter channel dimensions to reduce the shear stress.
Computing tractive force around a channel bend requires special considerations
because the change in flow direction imposes higher shear stress on the channel
bottom and banks. The maximum shear stress in a bend, Tb, is given by the
following equation:
Tb = KbT
where:
Tb = bend shear stress in lb/ft2
kb = bend factor
T = computed stress for straight channel in lb/ft2
The value of kb is related to the radius of curvature of the channel at its center
line, Rc, and the bottom width of the channel, B, Figure 8.05e. The length of
channel requiring protection downstream from a bend, Lp, is a function of the
roughness of the lining material and the hydraulic radius as shown in Figure
8.05f.
Appendices
Rev. 12/93 8.05.13
Table 8.05g
Permissible Shear Stresses
for Riprap and Temporary
Liners
Permissible Unit Shear Stress, Td
Lining Category Lining Type (lb/ft
2)
Temporary Woven Paper Net
Jute Net
)LEHUJODVV5RYLQJ
Single
Double
6WUDZZLWK1HW
Curled Wood mat
Synthetic Mat
0.15
0.45
0.60
0.85
1.45
1.55
2.00
d50 Stone Size (inches)
Gravel Riprap 1
2
0.33
0.67
Rock Riprap 6

12
15
18
21
24
2.00
3.00
4.00
5.00
6.00
7.80
8.00
Adapted From: FHWA, HEC-15, April 1983, pgs. 17 & 37.
Design Procedure-
Temporary Liners
The following is a step-by-step procedure for designing a temporary liner for
a channel. Because temporary liners have a short period of service, the design
Q may be reduced. For liners that are needed for six months or less, the 2-year
frequency storm is recommended.
Step 1. Select a liner material suitable for site conditions and application.
Determine roughness coefficient from manufacturer’s specifications or Table
8.05e, page 8.05.10.
Step 2. Calculate the normal flow depth using Manning’s equation (Figure
8.05d). Check to see that depth is consistent with that assumed for selection of
Manning’s n in Figure 8.05d, page 8.05.11. For smaller runoffs Figure 8.05d
is not as clearly defined. Recommended solutions can be determined by using
the Manning equation.
Step 3. Calculate shear stress at normal depth.
Step 4. Compare computed shear stress with the permissible shear stress for
the liner.
Step 5. If computed shear is greater than permissible shear, adjust channel
dimensions to reduce shear, or select a more resistant lining and repeat steps
1 through 4.
Design of a channel with temporary lining is illustrated in Sample Problem
8.05b, page 8.05.14.
8
8.05.14 Rev. 12/93
Sample Problem 8.05b
Design of a Temporary Liner
for a Vegetated Channel
Given:
Q2 = 16.6 cfs
%RWWRPZLGWK IW
Z = 3
n = 0.02 (Use basic n value for channels cut in earth (Table 8.05b)
Vp IWVHFPD[LPXPDOORZDEOHYHORFLW\IRUEDUHVRLOSJ
Channel gradient = 2%
Find:
Suitable temporary liner material
Solution:
8VLQJ0DQQLQJ¶VHTXDWLRQ
b(ft) d(ft) A(ft
2) R(ft) V(fps) Q(cfs) Comments
3.0 2.82 0.42 5.88 16.60 V>Vp,
(needs protection)
Q Q 2, OK
9HORFLW\!ISVFKDQQHOUHTXLUHVWHPSRUDU\OLQHU

&DOFXODWHFKDQQHOGHVLJQZLWKVWUDZZLWKQHWDVWHPSRUDU\OLQHU
n = 0.033 (Table 8.05e). Td = 1.45 (Table 8.05g, pg. 8.05.13)
b(ft) d(ft) A(ft
2) R(ft) V(fps) Q(cfs) Comments
3.0 0.76 4.05 4.10 16.60 V<Td, OK
Calculate shear stress for Q2 conditions:
7 \GV ZKHUH \ XQLWZHLJKWRIZDWHUOEIW
3)
   G ÀRZGHSWKLQIW
s = channel gradient in ft/ft
7  77d, OK
7HPSRUDU\OLQHUVWUDZZLWKQHW
*In some cases the solution is not as clearly defined; the use of a more conservative material is
recommended.
DESIGN OF RIPRAP LINING-MILD GRADIENT
The mild gradient channel procedure is applicable for channel grades less than
10%. The method assumes that the channel cross section has been designed
properly, including undercut and that the remaining problem is to provide a
stable riprap lining.
Side slope stability. As the angle of the side slope approaches the angle of
repose of the channel lining, the lining material becomes less stable. The
stability of a side slope is given by the tractive force ratio, K2, a function of the
side slope and the angle of repose of the rock lining material.
The rock size to be used for the channel lining can be determined by comparing
the tractive force ratio, an indicator of side slope stability, to the shear stress
on the sides and shear stress on the bottom of the channel. The angle of
repose for different rock shapes and sized is shown in Figure 8.05g. The
required rock size (mean diameter of the gradation, d50) for the side slopes is
determined from the following equation:
d50 (sides) = K1 d50 (bottom) K2where:
K1 = ratio of shear stress on the sides, Ts, and bottom, T, of a
trapezoidal channel (Figure 8.05h),
K2 = tractive force ratio (Figure 8.05i).
Appendices
Rev. 12/93 8.05.15
8
8.05.16 Rev. 12/93
Appendices
Rev. 12/93 8.05.17
Selection of riprap gradation and thickness. Riprap gradation should
have a smooth size distribution curve. The largest stone size in the
gradation should not exceed 1.5 times the d50 size. The most important
criterion is that interstices formed by larger stones be filled with smaller sizes
in an interlocking fashion, preventing the formation of open pockets. These
gradation requirements apply regardless of the type of filter design used.
In general, riprap constructed with angular stone performs best. Round stones
are acceptable as riprap provided they are not placed on side slopes steeper than
3:1. Flat, slab-like stones should be avoided since they are easily dislodged by
the flow. An approximate guide to stone shape is that neither the breadth nor
the thickness of a single stone be less than one-third its length.
The thickness of a riprap lining should equal 1.5 times the diameter of the
largest rock size in the gradation.
Filter design: When rock riprap is used, an appropriate underlying filter
material must be selected. The filter material may be either a granular, gravel
or sand filter blanket, or a geotextile fabric.
8
8.05.18 Rev. 12/93
For a granular filter blanket, the following criteria must be met:
d15¿OWHU
d85 base < 5
5 <d15¿OWHU
d15 base < 40
d50¿OWHU
d50 base < 40
Where “filter” refers to the overlying riprap or gravel and “base” refers to
the underlying soil, sand or gravel. The relationship must hold between the
filter blanket and base material and between the riprap and filter blanket.
The minimum thickness for a filter blanket should not be less than 6
inches.
In selecting a filter fabric, the fabric should have a permeability at least
equal to the soil and a pore structure that will hold back the base soil. The
following properties are essential to assure performance under riprap:
• For filter fabric covering a base with granular particles containing 50
percent or less (by weight) of fine particles (less than U.S. Standard
Sieve No. 200):
a. d85 base (mm)/EOS* filter cloth (mm) > 1.
b. Total open area of filter is less than 36%.
• Filter fabric covering other soils:
a. EOS less than U.S. Standard Sieve No. 70.
b. Total open area of filter less than 10%.
*EOS - Equivalent Opening Size to a U.S. Standard Sieve Size
Design Procedure-
Riprap Lining, Mild
Gradient
The following is a step-by-step procedure for designing a riprap channel
lining with mild gradients. This procedure is designed for smaller channels
that are generally used as erosion control measures, and is not intended for
conveyance channels.
Additional design information for lined channels may be obtained from the
National Technical Information Services (NTIS) by obtaining a copy of the
National Cooperative Highway Research Program Report No. 108, titled
“Tentative Design Procedure for Riprap - Lined Channels”.
Step 1. Select a riprap size, and look up the Manning’s n value (Table 8.05f)
and permissible shear stress, Td (Table 8.05g).
Step 2. Calculate the normal flow depth in the channel, using Manning’s
equation (Figure 8.05d). Check that the n value for the calculated normal
depth is consistent with that determined in step 1.
Step 3. Calculate shear stress at normal depth.

APPENDIX 8

Riprap and Stone for Erosion Control [Ref. 8]

Section 1043

10-62
All stone shall meet the approval of the Engineer. While no specific gradation is required, 1
there shall be equal distribution of the various sizes of the stone within the required size 2
range. The size of an individual stone particle will be determined by measuring its long 3
dimension. 4
Stone or broken concrete for rip rap shall meet Table 1042-1 for the class and size 5
distribution. 6
TABLE 1042-1
ACCEPTANCE CRITERIA FOR RIP RAP AND STONE FOR EROSION CONTROL
Required Stone Sizes, inches Class Minimum Midrange Maximum
A 2 4 6
B 5 8 12
1 5 10 17
2 9 14 23
No more than 5.0% of the material furnished can be less than the minimum size specified nor 7
no more than 10.0% of the material can exceed the maximum size specified. 8
SECTION 1043 9
AGGREGATE FROM CRUSHED CONCRETE 10
1043-1 GENERAL 11
Aggregate from crushed concrete is a recycled product made by crushing concrete obtained 12
from concrete truck clean out, demolition of existing concrete structures or pavement, or 13
similar sources and transported from a crushing facility. It does not include concrete 14
pavements that are rubblelized, broken or otherwise crushed in place on the roadway. 15
The crushed material must meet all sources approval requirements described in Sections 1005 16
and 1006 with the exception of the sodium sulfate test requirement. Deleterious materials 17
shall not be more than 3%. 18
Sampling and acceptance for the determination of gradaction, LL and PI will be performed as 19
described in the Aggregate QC/QA Program Manual and the Aggregate Sampling Manual. 20
1043-2 AGGREGATE BASE COURSE 21
The material shall meet the ABC gradation. The LL of the material shall be raised 5 points to 22
no more than 35. 23
1043-3 AGGREGATE SHOULDER BORROW 24
The material shall meet Section 1019. 25
1043-4 CLEAN COARSE AGGREGATE FOR ASPHALT 26
The material shall meet the gradation of a standard size in Table 1005-1. Use of the material 27
shall be approved by the Engineer, and the mix shall meet all requirements. 28
1043-5 CLEAN COARSE AGGREGATE FOR CONCRETE 29
The material shall meet the gradation of a standard size in Table 1005-1. Use of the material 30
is restricted to Class B concrete mixes only. Use of the material shall be approved by the 31
Engineer, and the concrete shall meet all requirements. 32
SECTION 1044 33
SUBSURFACE DRAINAGE MATERIALS 34
1044-1 SUBDRAIN FINE AGGREGATE 35
Subdrain fine aggregate shall meet No. 2S or 2MS in Table 1005-2. 36
NCDOT 2012 Standard Specifications