Buck CBE - Appendix C_20191230

Wood Environment & Infrastructure Solutions, Inc. Duke Energy Coal Combustion Residuals Management Program wood.
Buck Station Basin CAMA Closure Plan
APPENDIX C — Engineering Evaluations and
Analysis

Wood Environment & Infrastructure Solutions, Inc. Duke Energy Coal Combustion Residuals Management Program wood.
Buck Station Basin CAMA Closure Plan
Stormwater Peak Runoff and Volumes for 100-year Storm Event
Duke Energy, Buck Station
Stormwater
Rainfall Depth
Peak Runoff
Volume
Basin ID
(in)
(cfs)
(ac-ft)
Primary/Secondary Ash
7.17
545.24
68.129
Basin
Additional Primary Ash
7.17
382.38
63.001
Basin
Rev. 0
December 5, 2019

FINAL REPORT
Buck Steam Station
Full Probable Maximum Flood Evaluation
April 4, 2019
Mr. John Kwon, P.E.
Mr. Charlie Hiner, P.E.
Mr. Dale Smith, P.E.
Duke Energy
400 South Tryon Street
Charlotte, NC 28202
RE: Report for Full Probable Maximum Flood Evaluation
Ash Basin Dams, Buck Steam Station, Rowan County, NC
Gentlemen:
AECOM Technical Services, Inc. (AECOM) is pleased to submit this report for the task of Full
Probable Maximum Flood Evaluation according to regulatory requirements for the following
structures at Buck Steam Station:
1. Additional Primary Dam (ROWAN-068)
2. Basin 1 to Basin 2 Dam (ROWAN-069)
3. Basin 2 to Basin 3 Dam (ROWAN-070)
4. Divider Dam (ROWAN-071)
5. Main Dam (ROWAN-047)
The dams are classified by the North Carolina Department of Environmental Quality (NCDEQ)
as large size High Hazard (Class C) structures. This classification is driven by the potential
environmental effects of a failure of the Buck Steam Station ash pond dams. The High Hazard
classification is based upon the potential environmental impacts, not loss of life or property
resulting from a breach. As a high hazard dam, the Spillway Design Flood (SDF) that is required
by the previous NCDEQ Dam Regulations is the 3/a Probable Maximum Flood (PMF), based on
the size criteria. To meet the recent requirement by NCDEQ, the SDFs for all Buck ash ponds
have been elevated to Full PMF.
A HEC-HMS model was revised from the previous model for Hazard Potential Classification
task to evaluate the hydraulic performance of ash ponds at Buck Steam Station under the event of
Full PMF. The evaluation focused on the risk of flood water overtopping of embankments and
the required time to drain 80% of peak flood volume in the ponds.
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FINAL REPORT
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Full Probable Maximum Flood Evaluation
The results of the analysis performed herein by AECOM show that:
• Ash ponds in BUCK Steam Station can safely pass the Full PMF flow without overtopping
the dams. This is subject to the proposed water level reduction in Basin 2 by additional
removal of stoplogs facilitated by excavation of ash around the Basin 2 to 3 Dam outlet riser
to support this lowering.
• The outflow drainage system can drain 80% of peak PMF flood volume within 3.1 days
which is less than the maximum allowable 15 days.
Variable
Full
PIVIPStorm
Minimum Crest Elevation
(feet, NAVD88)
709.4
710.0
688.4
688.3
688.11
679.6
Initial WSEL (feet,
701.14
701.14
678.0
678.0
678.0
672.03
NAVD88)
(proposed)
(proposed)
(proposed)
Peak WSEL (feet, NAVD88)
708.81
708.81
687.48
687.48
687.48
677.78
Minimum Freeboard (feet)
0.59
1.19
0.92
0.82
0.63
1.82
Time Required to Drain 80%
of PMF Flood Volume (days)
1.43
1.43
0.70
0.70
0.70
2.07
If you have any questions or need additional information, please do not hesitate to call me at
301-820-3554. %`:�N'CAgO,,
pQ' *0ssi0 -.y
Sincerely, '�QQ� '��
i
= SEAL _
s 040145
Kenneth Ying, PhD,$ •• EP:' C?
Principal Water Resou��
AECOM
ACOM Page ii

FINAL REPORT
Buck Steam Station
Full Probable Maximum Flood Evaluation
FINAL REPORT
Full Probable Maximum Flood Evaluation
Buck Steam Station - Ash Ponds
Rowan County, North Carolina
Prepared for:
Duke Energy Corporation
400 South Tryon Street
Charlotte, North Carolina 28202
Prepared by:
AECOM
6000 Fairview Road Suite 200
Charlotte, NC 28210
A=COM
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eiH Y.
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FINAL REPORT
Buck Steam Station
Full Probable Maximum Flood Evaluation
Table of Contents
1.0.
Introduction.......................................................................................................................................4
2.0.
Review of Available Data...................................................................................................................6
3.0.
Hydrologic Parameter Calculation.....................................................................................................7
4.0.
Stage/Storage/Discharge Curve Development.................................................................................7
5.0.
Rainfall Data......................................................................................................................................8
6.0.
Hydrologic Model Simulation Results...............................................................................................8
7.0.
Conclusions........................................................................................................................................9
8.0.
References.........................................................................................................................................9
Figures
Figure 1: Aerial View of Buck Steam Plant Ash Basins.................................................................... 4
Tables
Table 1: Background Information — Buck Steam Station Ash Pond Dams ...................................... 5
Table 2: Comparison of NCDEQ and EPA Hazard Potential Classifications .................................... 6
Table 3: Model Simulation Results — Full PMP Storm for Existing Conditions ............................... 9
Appendices
Appendix A: Areal Topographic Survey of Buck Steam Station Ash Basins (2015)
Appendix B: Elevation -Discharge Curves
Appendix C: Hydrologic Simulation Results
COM Page ii

FINAL REPORT
Buck Steam Station
Full Probable Maximum Flood Evaluation
Acronyms and Abbreviations
CCR
Coal Combustion Residuals
DEC
Duke Energy Corporation
EPA
Environmental Protection Agency
GIS
Geographic Information System
HEC
Hydrologic Engineering Center
HMS
Hydrologic Modeling System
HPC
Hazard Potential Classification
IDF
Inflow Design Flood
LiDAR
Light Detection and Ranging
NAVD
North American Vertical Datum
NCDEQ
North Carolina Department of Environmental Quality
NGVD
National Geodetic Vertical Datum
PMF
Probable Maximum Flood
PMP
Probable Maximum Precipitation
SDF
Spillway Design Flood
COM Page iii

FINAL REPORT
Buck Steam Station
Full Probable Maximum Flood Evaluation
1.0. Introduction
AECOM was contracted with Duke Energy Corporation (DEC) for the task of Probable Maximum Flood
(PMF) Evaluation of the ash ponds at Buck Steam Station. The scope of work for this study includes the
collection and review of relevant information and additional Hydrologic & Hydraulic (H&H) analyses to
evaluate whether the combined capacity of spillways can adequately manage flow during the peak
discharge from a PMF for Buck Steam Station ash ponds based on the high hazard potential (per NC
Rules) CCR surface impoundment classification. AECOM will also provide recommendation regarding
the management of PMF for the Buck Basin Dams.
Duke Energy's Buck Steam Station Plant is a retired coal-fired generating station located near Salisbury,
N.C. that began operation in 1926 and was retired in 2013. The facility is located on the Yadkin River
upstream of High Rock Lake and uses a wet -ash pond system consisting of three basins separated by a
system of five dams to store ash.
These dams are regulated by North Carolina Department of Environmental Quality (NCDEQ) and
include: the Main Dam (ROWAN-047), Divider Dam (ROWAN-071), and Basin 2 to Basin 3 Dam
(ROWAN-070), Basin 1 to Basin 2 Dam (ROWAN-069), and Additional Primary Dam (ROWAN-068).
Figure 1 shows the configuration of ponds and associated dams.
Figure 1: Aerial View of Buck Steam Plant Ash Basins
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FINAL REPORT
Buck Steam Station
Full Probable Maximum Flood Evaluation
In accordance with the U.S. Environmental Protection Agency's (EPA's) Final CCR Rule (effective date:
October 19, 2015) (Ref. 11), the inflow design flood is based on the hazard potential classification of the
impoundment as required by § 257.73 and § 257.74 of Final CCR rule. The inflow design floods for
specific hazard potential classifications are as follows: (1) The probable maximum flood (PMF) for high
hazard potential CCR surface impoundments; (2) the 1000-year flood for significant hazard potential CCR
surface impoundments; (3) the 100-year flood for low hazard potential CCR surface impoundments; and
(4) the 25-year flood for incised CCR surface impoundments. Based on the EPA CCR Rule, the Additional
Primary Dam classified as High Hazard and the rest of the dams were classified as Significant Hazard.
The dams are classified by the NCDEQ as large size High Hazard (Class C) structures. This classification is
driven by the potential environmental effects of a failure of the Buck Steam Station ash pond dams. The
High Hazard classification is based upon the potential environmental impacts, not loss of life or property
resulting from a breach. As a high hazard dam, the Spillway Design Flood (SDF) that is required by the
previous NCDEQ Dam Regulations is the % PMF when coupled with the size for the dam. To meet the
recent requirement by NCDEQ, the SDFs for all Buck ash ponds have been elevated to Full PMF.
The goal of this technical memorandum is to document the capacity of the spillway and outflow weirs
during a PMF event for the Buck station dams according to the guidance and criteria established by
NCDEQ. While DEC already demonstrated that the dams meet the EPA CCR Rule requirements as part
of the 2016 CCR certifications, these are covered herein again as well as a secondary goal.
Previous studies, including the Main Dam Spillway Replacement Investigation (Ref. 7) modeled and
classified the dams by the NCDEQ hazard classification system. Table 1 presents pertinent dam
characteristics collected from the previous studies.
Table 1: Background Information — Buck Steam Station Ash Pond Dams
General Dam
Information
Name
Additional
Basin 1 to
Basin 2 to
Divider
Main (Section
Main (Section
Primary
Basin 2
Basin 3
for Basin 2)
for Basin 3)
State ID
ROWAN-068
ROWAN-069
ROWAN-070
ROWAN-071
ROWAN-047
ROWAN-047
NCDEQ Hazard
High
High
High
High
High
High
Classification
Height (feet)
71
22
14
9
59
59
Minimum Crest
Elevation (feet,
709.4
710.0
688.4
688.3
688.11
679.6
NAVD88)
Notes: Based on most up to date topography including new bathymetric survey (Ref. 3).
The previous studies determined that all five Buck Steam Station ash pond dams are classified by NCDEQ
as large size High Hazard (Class C) structures. Inundation studies show that there is no probable loss of
life for all these dams, except Additional Primary, and the classification could be based on economic
damage due to potential environmental impacts.
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FINAL REPORT
Buck Steam Station
Full Probable Maximum Flood Evaluation
NCDEQ and EPA regulations use different classification systems to determine hazard risks associated
with a potential dam failure. The HPCs defined by NCDEQ are dependent on the effects of the failure
on environmental conditions downstream. EPA's HPC is defined based on whether the failure could
result in loss of life downstream. A comparison of NCDEQ HPCs and EPA HPCs is shown in Table 2.
Table 2: Comparison of NCDEQ and EPA Ilazard Potential Classifications
Classification
Defillition
Required
SDF
Very
Large
Full PMP
High Hazard
Probable loss of
Full PMP
human life
Probable loss of 1 or
Large
3/4 PMP
more human lives due to
No probable loss of
High
breached roadway or
(Class C)
bridge on or below the
Medium
�/2 PMP
human life, but
dam or economic damage
probable economic
greater than $200,000.
Significant
loss, environmental
1,000 Year
damage, or
Small
1;, PMP
disruption of lifeline
facilities.
Probable economic
Very
3/4 PMP
No probable loss of
damage between $30,000
Large
human life, low
Intermediate
and $200,000 or highway
Low
probability
orr
100 Year
Large
'/2 PMP
(Class B)
damage or service
economic
Medium
1/3 PMP
interruption affecting 25
environmental loss
to 250 vehicles a day.
(losses limited to
owner's property)
Small
100 Year
Very
y2 PMP
Probable economic
Large
damage less than $30,000
Dams which pose no
Large
1/, PMP
Low
or interruption of road
Less than Low
high, significant, or
25 Year
(Class A)
service affecting less than
low hazard potential.
Medium
100 Year
1
25 vehicles a day.
i
I
Small
50 Year
`
Note: All CCR Dams are classified from January 2019 by NCDEQ as high hazard with a required SDF of full PMP.
In previous studies, the design criteria applied the % PMF for each pond per the requirement for large
size Class C impoundments. The recent requirement from NC DEQ elevated the design criteria to Full
PMF. AECOM conducted a review of the available information and additional H&H analyses to support
the assessment of the capacity for the Buck CCR impoundments.
2.0. Review of Available Data
Duke Energy provided AECOM with available data for the Buck Steam Station systems. The data
provided by Duke Energy is summarized in Appendix C of the Phase 2 Report (Ref. 10). The same data
was used to complete this memorandum in addition to the supplementary hydrologic data and
information from the reports below:
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FINAL REPORT
Buck Steam Station
Full Probable Maximum Flood Evaluation
• AECOM, 2017: AECOM prepared report to NC DEQ for the new spillway design for Basin 3. This
spillway became operational in 2019 (Ref. 8).
• AECOM, 2016: AECOM prepared the report for the development of Hazard Potential
Classifications (HPCs) according to the definitions provided in the Coal Combustion Residuals
(CCR) Rule for the ash ponds at Buck Steam Station. (Ref. 15)
• AECOM, 2015: AECOM conducted a Spillway Replacement Analysis for Basin 3 (Secondary Pond)
in the Buck Steam Station dam system. This project studied investigated replacing the existing
riser. Updated hydrologic and hydraulic modelling was performed using HEC-HMS assuming
breach conditions to design the system for the % PMP storm event (Ref. 7).
• AECOM, 2014: AECOM conducted an H&H analysis of the existing conditions at the Buck Steam
Station to determine if the existing spillway systems for the dams could safely pass the % PMP
SDF without overtopping the embankment. The methodology and conclusions were submitted
in the Phase 2 Report, "Hydrologic and Hydraulic Analysis, Buck Steam Station — Ash Points,"
dated November 2014 (Ref. 10).
• ESP, 2012: ESP performed a dam breach analysis of the Buck Steam Station dams to determine
potential damage from failure events. The results indicated that significant damage to
properties other than that owned by DEC is not expected. Supporting information can be found
in the report "Dam Breach Analysis, Buck Steam Station", dated August 10, 2012 (Ref. 2).
• CHA, 2009: CHA performed an assessment of dam safety at the Buck Steam Station dams to
document the visual observations and stability analysis of the dams in this area. Survey
measurements of dam characteristics were documented. Additional information can be found
in the report, "Assessment of Dam Safety Coal Combustion Surface Impoundments (Task 3) Final
Report, Duke Energy Buck Steam Station", dated September 14, 2009 (Ref. 14). The supporting
computer models included the HEC-HMS model for the watershed and the EPA-SWMM Model
for the outfall pipeline.
3.0. Hydrologic Parameter Calculation
This hydrologic and hydraulic memorandum used hydrologic parameters calculated during preparation
of the HPC (Ref. 15).
During this memorandum update, no parameters were changed from the HPC Report (Ref. 15).
4.0. Stage/Storage/Discharge Curve Development
The stage/storage/discharge curves from HPC study were applied with proper modification to
incorporate the adjustment of stop -log outlet elevation.
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FINAL REPORT
Buck Steam Station
Full Probable Maximum Flood Evaluation
Stage/Storage Curve
The stage/storage curve for the ponds were adapted from the HPC report data (Ref. 15) and are listed in
Appendix B.
Stage/Discharge Curve
The stage -discharge rating curve adapted the data from HPC report for the Primary Pond. For Basin 2 to
Basin 3 Dam, initial water level and stop -log elevation were updated and the revised elevation -discharge
curve is shown in Appendix B. Other curves for each basin are also listed in Appendix B.
5.0. Rainfall Data
The probable maximum flood (PMF) is the flood that results from the probable maximum precipitation
(PMP). The PMP is defined as statistically the greatest amount of rainfall that can occur for a given
geographic area. The newly required design storm the Buck Steam Station Dams is the full PMF and the
ponds must pass at least 80% of peak PMF flood volume water stored within 15 days of the design
storm.
The rainfall amount and distribution for the Full PMP was calculated in the Phase 2 study using Hydro
meteorological Reports 51 (Ref. 4) and 52 (Ref. 5). The total rainfall depth for the full PMP was
calculated to be 29.49 inches for 6 hours. No updates to the Full PMP precipitation data were made for
this evaluation.
6.0. Hydrologic Model Simulation Results
Following calculation of the hydrologic parameters, Full PMP event, and stage/storage/discharge curves,
the hydrologic model was created. The United States Army Corps of Engineers (USACE) Hydrologic
Engineering Center (HEC) Hydrologic Modeling System (HMS) version 4.3 was used to model the study
area.
The control specifications of the model were set to run for 15 days following the start of the storm
events. This helped enabled that the majority of the full outflow hydrograph was captured. Starting
water surface elevation for the dams were entered into the HEC-HMS model based on normal pool
elevation of the reservoirs.
Tables 3 presents the results of the hydrologic analysis for the existing conditions of the dams. The HEC-
HMS simulations summary is shown in Appendix C. Note that the initial water surface elevations used
herein were selected based on the stop log elevations as provided by Duke for the spillway riser
structures for the dams. The calculated minimum freeboard will be different if stop log elevations are
changed.
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FINAL REPORT
Buck Steam Station
Full Probable Maximum Flood Evaluation
Cable 3: Model Simulation Results - Full PNIP Storm for Existing Conditions
Full PMP Storm
Variable
Additional
Basin 1 to
Basin 2 to
Divider
Main
Main
PrimaryBasin
Basin 2
3
(Section for
(Section for
Basin 2)
Basin 3)
Minimum Crest Elevation
709.4
710.0
688.4
688.3
688.11
679.6
(feet, NAVD88)
Initial WSEL (feet,
678.0
678.0
678.0
701.14
701.14
672.03
NAVD88)
(proposed)
(proposed)
(proposed)
Peak WSEL (feet, NAVD88)
708.81
708.81
687.48
687.48
687.48
677.78
Minimum Freeboard (feet)
0.59
1.19
0.92
0.82
0.63
1.82
Time Required to Drain 80%
of PMF Flood Volume (days)
1.43
1.43
0.70
0.70
0.70
2.07
7.0. Conclusions
The HEC-HMS model used in this analysis was developed using information obtained during the review
of available data. The developed model is deemed a reasonable estimation of the conditions for the
project area. The analysis was performed using conservative assumptions where appropriate for
hydrologic parameter calculation and hydraulic capacity of the outlet structures. The results of the
analysis are shown in Table 3, which presents the performance of dams under the design storms for
the designated HPCs for the dams at the Buck Steam Station based on the NCDEQ and the EPA Final
CCR Rule Classifications.
Through review of relevant information and additional H&H analyses, it was concluded that:
o The pond system can safely pass the Full PMF flow without overtopping the dams. This is
subject to the proposed water level reduction in Basin 2 by additional removal of stoplogs
facilitated by excavation of ash around the Basin 2 to 3 Dam outlet riser to support this
lowering.
o The outflow drainage system can drain 80% of PMF flood volume within 3.1 days which is less
than the maximum allowable 15 days.
Note that the outflow drainage system for the Main Dam includes an outfall pipeline which only
activates for flood larger than 100-year return period. Under the PMF condition, it is active until flood
elevation recedes below the 100-year flood level.
8.0. References
1. North Carolina Administrative Code - Title 15A Department of Environment and Natural
Resources of Subchapter 2K - Dam Safety. http://www.damsafetyaction.org/NC/about-
eaps/what.php
2. ESP Associates, P.A., Buck Steam Station Hydrologic Analysis - Calculation # BC -UNIT 5-6-0008,
April 20, 2012.
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FINAL REPORT
Buck Steam Station
Full Probable Maximum Flood Evaluation
3. Areal Topographic Survey of Buck Steam Station Ash Basins for Duke Energy Corporation.
Developed by WSP, February 2, 2015. Book No. BUCKBOOK01.
4. Probable Maximum Precipitation Estimates, United States East of the 105th Meridian.
Hydrometeorological Report No. 51. NOAA. June 1978.
5. http://www.nws.noaa.gov/oh/hdsc/studies/pmp.html#PMP-documents
6. Application of Probable Maximum Precipitation Estimates - United States East of the 105th
Meridian. Hydrometeorological Report No. 52. NOAA. August 1982.
7. http://www.nws.noaa.gov/oh/hdsc/studies/pmp.html#PMP_documents
8. NOAA, National Weather Service (2013) Precipitation -Frequency Atlas of the United Stated Point
Precipitation Frequency Estimates by NOAA Atlas 14, Volume 2, Version 3; (NOAA website:
http://hdsc.nws.noaa.gov/hdsc/pfds/pfds_map_cont.html?bkmrk=sc).
9. Design Report: Spillway Replacement, Basin 3 (Secondary Pond), Buck Steam Station (NCDEQ
State Dam ID: ROWAN-047). Salisbury, North Carolina. AECOM. July 31, 2015.
10. Design Report: New Spillway Replacement, Basin 3 (Secondary Pond), Buck Steam Station
(NCDEQ State Dam ID: ROWAN-047). Salisbury, North Carolina. AECOM. October, 2017.
11. U.S. Army Corps of Engineers (2013), Hydrologic Engineering Center, HEC-HMS, Hydrologic
Modeling System, Version 4.0, December 31, 2013.
12. AECOM, Buck Steam Station - Final Phase 2 Reconstitution of Ash Pond Design Report - Revision
4 - October 2017.
13. 40 C.F.R. § 257.261, Vol. 80 No. 74. April 17, 2015.
14. Froelich, D. C. (2008). "Embankment Dam Breach Parameters and Their Uncertainties." Journal
of Hydraulic Engineering, Vol. 134, No. 12, May, pgs. 1708-1720.
15. ESP Associates, N.C., Buck Steam Station Dam Breach Analysis- Calculation # BC -UNIT 5-6-0009,
August 10, 2012.
16. CHA, Assessment of Dam Safety Coal Combustion Surface Impoundments (Task 3) Final Report,
Duke Energy Buck Steam Station, September 14, 2009.
17. AECOM, Report for Determination of Hazard Potential Classifications - Buck Steam Station,
March 16, 2016.
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FINAL REPORT
Buck Steam Station
Full Probable Maximum Flood Evaluation
Appendix A
Areal Topographic Survey of Buck Steam Station Ash Basins (2015)
l0"
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AERA T?POGR!PW- SURVEY
.............. SP.......
_.
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FINAL REPORT
Buck Steam Station
Full Probable Maximum Flood Evaluation
Appendix B
Elevation -Discharge -Storage Curve Tables
Elevation -Discharge Rating Table for Basin 2 to Basin 3 Dam
Stop Log Elevation = 678 feet
(Primary Pond [Basin 21 in HEC-HMS Model)
Elevation
662
Discharge
0.0
664
0.0
666
0.0
668
0.0
670
0.0
672
0.0
674
0.0
676
0.0
678
0.0
678.27
5
679.27
45.0
680.27
103.5
681.27
171.2
682.27
234.1
683.27
257.8
684.27
279.5
684.77
289.8
685.27
299.7
685.77
309.2
686.77
327.5
687.77
344.9
688.77
529.0
689.27
759.8
690.27
1376.9
691.27
2155.1
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FINAL REPORT
Buck Steam Station
Full Probable Maximum Flood Evaluation
Elevation -Discharge Rating Table for Main Dam at Basin 3
(Secondary Pond [Basin 3] in HEC-HMS Model)
Elevation
r
658
Discharge
0
660
0
662
0
664
0
666
0
668
0
670
0
672
0
673
0
673.27
26
673.77
43
674.77
84
675.27
85
675.77
85
676.77
85
677.27
223
677.77
475
678.77
1188
679.27
1627
679.6
1942
681.27
6398
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FINAL REPORT
Buck Steam Station
Full Probable Maximum Flood Evaluation
Elevation -Discharge Rating Table for Additional Primary Basin
(Additional Primary Pond [Basin 1] in HEC-HMS Model)
Elevation
Discharge
.:
0.0
696
0.0
698
0.0
700
0.0
702
0.0
702.63
5.6
703.27
18.9
704
26.9
704.27
41.3
704.77
73.9
705.77
111.9
706.77
154.8
707.77
202.0
708.77
227.2
709.27
257.4
709.4
845.6
710
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FINAL REPORT
Buck Steam Station
Full Probable Maximum Flood Evaluation
Elevation -Storage Rating Table for Primary Pond (Basin 2)
(Primary Pond [Basin 21 in HEC-HMS Modell
Elevation
(Feet, NAVD88)
662
Volume (acre-foot)
0
664
0.00001
666
2.307
668
8.0763
670
17.072
672
29.202
674
44.515
676
63.217
678
85.407
678.27
88.698
679.27
101.39
680.27
114.88
681.27
129.31
682.27
145.69
683.27
166.93
684.27
193.55
684.77
211.88
685.27
233.33
685.77
257.25
686.77
310.84
687.77
367.82
688.77
428.55
689.27
459.96
690.27
524.71
691.27
592.21
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FINAL REPORT
Buck Steam Station
Full Probable Maximum Flood Evaluation
Elevation -Storage Rating Table for Secondary Pond (Basin 3)
(Secondary curve [Basin 3] in HEC-HMS Model)
Elevation
658
lVolurne ..t
0
660
2.1
662
8.9
664
19
666
31.8
668
47.2
670
66.3
672
89.3
672.2
91.9
673
102.4
673.2
105
673.27
105.9
673.77
113
674.77
128.5
675.27
136.8
675.77
145.3
676.77
163
677.27
172.2
677.77
181.6
678.77
201
679.27
210.9
679.6
217.4
681.27
252.8
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FINAL REPORT
Buck Steam Station
Full Probable Maximum Flood Evaluation
Elevation -Storage Rating Table for Additional Primary Basin (Basin 1)
(Additional Primary Pond [Basin 1] in HEC-HMS Model)
Elevation
D:foot)
696
Volume (acre-
0
698
0.01
700
0.81
702
7.68
702.63
19.81
703.27
32.13
704
46.19
704.27
54.07
704.77
72.65
705.77
126.08
706.77
194.89
707.77
268.98
708.77
346.45
709.27
386.09
709.4
396.48
710
444.91
AZCOM

FINAL REPORT
Buck Steam Station
Full Probable Maximum Flood Evaluation
Appendix C
Hydrologic Simulation Results
Full PMF Simulations
1. Additional Primary Dam & Basin 1 to 2 Dam
® Summary Results for Reservoir "Pond -Add -Prim" F-- F O C
Project: BUCK PMP HMS Simulation Run: PMP-BCDF
Reservoir: Pond Add Prim
Start of Run: 01Jan2012, 00:00 Basin Model: PROPOSED BCDF
End of Run: 163an2012, 00:00 Meteorologic Model: 6Hr PMP
Compute Time:l4Mar2D19, 18:14:18 Control Specifications:15-Day
Volume Units: o IN ACff
Computed Results
Peak Inflow: 3275.3 (CFS) Datetrime of Peak Inflow: 01]an2012, 03:23
Peak Disdarge: 204.10S) Date/Time of Peak Discharge:013an2D12, 06:15
Inflow Volume: 32.52 (IN) Peak Storage: 349.8 (AC+- )
Discharge Volume:31.05 ON Peak Elevation: 708.81(FT)
2. Basin 2 to 3 Dam, Divider Dam, and Main Dam (Section for Basin 2)
L Summary Results for Reservoir "Pond Primary" C p C
Project: BUCK PMP HMS Simulation Run: PMP-BCDF
Reservoir: Pond Primary
Startof Run: 011an2D12, 00:00 Basin Model: PROPOSED BCDF
End of Run: 16]an2D 12, 00:00 Meteorologic Model: 6Hr PMP
Compute Tiime:l4Mar2D19, 18:14:18 Control Specifications:l5-Day
Volume Units: o Cif AC -FT
Computed Results
Peak Inflow: 2989.1(CFS) Date/rime of Peak Inflow: 011an2012, 03:18
Peak Discharge: 339.8 (CFS) Date/rime of Peak Discharge:011an2012, 06:12
Inflow Volume: 28.96 (IN) Peak Storage: 351.1(AC+ )
Discharge Volume:28.86 (IN) Peak Elevation: 687.48 (FT)
A -COM

FINAL REPORT
Buck Steam Station
Full Probable Maximum Flood Evaluation
3. Main Dam (Section for Basin 31
L71 Summary Results for Reservoir "Pond -Second" W C p C
Project: BUCK PMP HMS Simulation Run: PMP-BCDF
Reservoir: Pond Second
Startof Run: 013an2012, 00:00 Basin Model: PROPOSED BCDF
End of Run: 16]an2012, 00:00 Meteorologic Model: 6Hr PMP
Compute Time: l4Mar2019, 18:14:18 Control Specification: 15-0ay
Volume Units: o IN AC -FT
Computed Results
Peak Inflow: 1149.3 (CFS) Date/Time of Peak Inflow: Ol]an2012, 03:19
Peak Discharge: 483.5 (CPS) Date/Time of Peak Discharge:011an2012, 04:30
Inflow Volume: 28.48 (IN) Peak Storage: 181.8 (AC+-}
Discharge Volume:28.06 (IN) Peak Elevation: 677.78 (FT)
A=COM

wood.
October 14, 2019
Mr. Dale Smith
Project Manager
Duke Energy
526 South Church Street
Charlotte, North Carolina 28202
Subject: Hydrology and Hydraulics Analysis Summary Report
Buck Main Dam (ROWAN-047) and Additional Primary Dam (ROWAN-068)
Decommissioning
Duke Energy — Buck Steam Station
Rowan County, North Carolina
Wood Project No. 7812180092
Dear Mr. Smith,
As part of the decommissioning plan for the Main Dam (ROWAN-047) and the Additional Primary
Dam (ROWAN-068), Wood Environment & Infrastructure Solutions, Inc. (Wood) has prepared this
Hydraulic and Hydrologic analysis (H&H) summary report. This H&H summary represents the
Main Dam (ROWAN-047) and the Additional Primary Dam (ROWAN-068) in their proposed
decommissioned condition.
Background Information
The Main Dam (ROWAN-047) is classified by North Carolina Department of Environmental
Quality (NCDEQ) as a high hazard structure. The high -hazard classification is driven by the
potential environmental effects if a failure of the dam was to occur. The Main Dam was
constructed in 1957 and serves as the primary retention structure for the Primary Ash Basin
and the Secondary Ash Basin. The main characteristics of the dam are:
• Dam Length: 2,384 feet
• Structural Height: 70 feet
• Crest Width: 14 feet
• Upstream Slope: 3.5H:1V
• Downstream Slope: 3.5H:1 V
The Additional Primary Dam (ROWAN-068) is classified by NCDEQ as a high hazard dam.
This classification is driven by the potential environmental effects if a failure of the dam was to
occur. The Additional Primary Dam was constructed in 1982 and serves as the primary
Wood Environment & Infrastructure Solutions, Inc.
4021 Stirrup Creek Drive, Suite 100
Durham, North Carolina 27703
Tel [phone]
Fax [phone]
www.woodolc.com
Licensure: NC Engineering F-1253 NC Geology C-247

Duke Energy
October 14, 2019
Page 2
Buck Steam Station
Hydrology and Hydraulics Analysis Summary Report
Wood Project No. 7812-18-0092
retention structure for the Additional Primary Ash Basin. The main characteristics of the dam
are:
• Dam Length: 2,000 feet
• Structural Height: 72 feet
• Crest Width: 20 feet
• Upstream Slope: 2.5H:1V
• Downstream Slope: 2.5H:1 V
H&H Evaluation Criteria
The computer program HydroCAD was used to perform the Hydrologic and Hydraulic calculations
to determine the flow depth and velocity through the breach section for the proposed
decommissioned condition. The Main Dam (ROWAN-047), in the decommissioned conditions,
will have a trapezoidal opening (breach) in the western dam section. The breach opening is
designed to have approximately a 150 foot bottom width, 10:1 side slopes, and is cut to an
elevation of approximately 643 feet at the inside face of the dam. The Additional Primary Dam
(ROWAN-068), in the decommissioned conditions, will have a trapezoidal opening (breach) in the
eastern dam section. The breach opening is designed to have approximately a 50 foot bottom
width, 10:1 side slopes, and is cut to an elevation of approximately 666 feet at the inside face of
the dam.
The design storm for the decommissioned condition is the 100-year, 24-hour storm event, which
equates to 7.17 inches of rainfall for a twenty-four (24) hour period.
H&H Summary
A summary of the H&H modeling is provided in Table 1 below.
Table 1 - H&H Results
Results for Decommissioned
Condition
Main Dam
(ROWAN-047)
Additional Primary
Dam (ROWAN-068)
Peak Discharge Rate (ft3/s)
545
382
Breach Opening Bottom Width (ft)
50
150
Breach Opening Side Slope
10:1
10:1
Flow Depth in Breach (ft)
0.96
0.95
Slope of Breach Channel (ft/ft)
0.0213
0.0704
Peak Velocity (ft/s)
5.15
6.67

Duke Energy
October 14, 2019
Page 3
Conclusion
Buck Steam Station
Hydrology and Hydraulics Analysis Summary Report
Wood Project No. 7812-18-0092
Based on the results of this H&H analysis, Wood concludes that the breaches in the Main Dam
(ROWAN-047) and the Additional Primary Dam (ROWAN-068) will safely pass the 100-year storm
event without overtopping the remaining dike remnants. Furthermore, the discharge velocity
through the dike opening should not cause erosive conditions across the breach section or
adjacent dike slopes (the breach opening/channel for the Additional Primary Dam (ROWAN-068)
will be lined with riprap due to the steeper slope and higher velocity).
Closing
Wood appreciates the opportunity to offer our services on this project. If you have any
questions concerning this response, please contact us.
Sincerely,
Wood Environment & Infrastructure Solutions, Inc...
Y • Q V.V
r
SEAL
Richard L. Hiner, PE, CPESC = 29185 Joshua M. Bell, PE
Senior Associate Engineer 4:; Senior Engineer
���� ✓/ l/ d d l l l l l l l l l l�\\\\
Attachments H&H Calculations — Decommissioned Conditions

1S
Final C nditions -
Addition I Primary
Ba in DA
Dam Breach Channel
M
Dukeville Road Culvert
Subcat Reach on Link
2S
Final Co ditions -
Primary/ econdary
Basi DA
7R
Dam Breach Channel

Buck Ash Basin Breaches - 100-year
Final Conditions -Full PMP
Prepared by AMEC Printed 10/11/2019
HvdroCAD® 10.00-24 s/n 05847 © 2018 HvdroCAD Software Solutions LLC Paae 2
Area Listing (all nodes)
Area CN Description
(acres) (subcatchment-numbers)
172.776 86 Newly graded area, HSG B (1 S, 2S)
189.614 65 Woods/grass comb., Fair, HSG B (1S, 2S)
362.390 75 TOTAL AREA

Buck Ash Basin Breaches - 100-year
Final Conditions -Full PMP
Prepared by AMEC Printed 10/11/2019
HydroCAD® 10.00-24 s/n 05847 © 2018 HydroCAD Software Solutions LLC Page 3
Soil Listing (all nodes)
Area Soil Subcatchment
(acres) Group Numbers
0.000 HSG A
362.390 HSG B 1 S, 2S
0.000 HSG C
0.000 HSG D
0.000 Other
362.390 TOTAL AREA

Buck Ash Basin Breaches - 100-year
Final Conditions -Full PMP
Prepared by AMEC Printed 10/11/2019
HydroCADO 10.00-24 s/n 05847 © 2018 HydroCAD Software Solutions LLC Page 4
Ground Covers (all nodes)
HSG-A HSG-B HSG-C HSG-D Other Total Ground Subcatchment
(acres) (acres) (acres) (acres) (acres) (acres) Cover Numbers
0.000
172.776
0.000
0.000
0.000
172.776
Newly graded area 1 S, 2S
0.000
189.614
0.000
0.000
0.000
189.614
Woods/grass comb., Fair 1 S, 2S
0.000
362.390
0.000
0.000
0.000
362.390
TOTAL AREA

Buck Ash Basin Breaches - 100-year
Final Conditions -Full PMP Type 1124-hr 100-yr Rainfall=7.17"
Prepared by AMEC Printed 10/11/2019
HvdroCAD® 10.00-24 s/n 05847 © 2018 HvdroCAD Software Solutions LLC Paae 5
Time span=0.00-200.00 hrs, dt=0.05 hrs, 4001 points
Runoff by SCS TR-20 method, UH=SCS, Split Pervious/Imperv.
Reach routing by Dyn-Stor-Ind method - Pond routing by Dyn-Stor-Ind method
Subcatchment 1 S: Final Conditions - Runoff Area=167.300 ac 0.00% Impervious Runoff Depth=4.52"
Flow Length=2,025' Tc=64.7 min CN=77/0 Runoff=382.38 cfs 63.001 of
Subcatchment2S: Final Conditions - Runoff Area=195.090 ac 0.00% Impervious Runoff Depth=4.19"
Flow Length=1,100' Tc=44.0 min CN=74/0 Runoff=545.24 cfs 68.129 of
Reach 6R: Dam Breach Channel Avg. Flow Depth=0.95' Max Vet=6.67 fps Inflow=382.38 cfs 63.001 of
n=0.055 L=355.0' S=0.0704'/' Capacity=4,106,525.71 cfs Outflow=382.14 cfs 63.001 of
Reach 7R: Dam Breach Channel Avg. Flow Depth =0.96' Max Vet=5.15 fps Inflow=545.24 cfs 68.129 of
n=0.040 L=470.0' S=0.0213 '/' Capacity=1,856,073.24 cfs Outflow=544.30 cfs 68.129 of
Reach 8R: Dukeville Road Culvert Avg. Flow Depth =0.98' Max Vet=7.78 fps Inflow=382.14 cfs 63.001 of
600.0" x 48.0" Box Pipe n=0.013 L=100.0' S=0.0050 '/' Capacity=2,437.78 cfs Outflow=382.28 cfs 63.001 of
Total Runoff Area = 362.390 ac Runoff Volume = 131.130 of Average Runoff Depth = 4.34"
100.00% Pervious = 362.390 ac 0.00% Impervious = 0.000 ac

Buck Ash Basin Breaches - 100-year
Final Conditions -Full PMP Type // 24-hr 100-yr Rainfall=7.17"
Prepared by AMEC Printed 10/11/2019
HvdroCADO 10.00-24 s/n 05847 © 2018 HvdroCAD Software Solutions LLC Paae 6
Summary for Subcatchment 1S: Final Conditions - Additional Primary Basin DA
Runoff = 382.38 cfs @ 12.68 hrs, Volume= 63.001 af, Depth= 4.52"
Runoff by SCS TR-20 method, UH=SCS, Split Pervious/Imperv., Time Span= 0.00-200.00 hrs, dt= 0.05 hrs
Type II 24-hr 100-yr Rainfall=7.17"
Area (ac) CN Description
74.400 65 Woods/grass comb., Fair, HSG B
92.900 86 Newly graded area, HSG B
167.300 77 Weighted Average
167.300 77 100.00% Pervious Area
Tc Length
Slope
Velocity
Capacity Description
(min) (feet)
(ft/ft)
(ft/sec)
(cfs)
27.7 100
0.0100
0.06
Sheet Flow,
Woods: Light underbrush n= 0.400 P2= 3.34"
37.0 1,925
0.0300
0.87
Shallow Concentrated Flow,
Woodland Kv= 5.0 fps
64.7 2,025 Total
Subcatchment 1S: Final Conditions - Additional Primary Basin DA
Hydrograph
382.38 cfs @ 12.68 hrs
R6noff=312.38 cfs @ 12.i8 hrs
350 1 Type 124-hr
Ra 100-yr infall 7.17"
300 Runoff Area=167.�00 ac
Runoff Volume=63-.001-af
250 Runoff Deptht4.52"
3 200 Flow Length=2,025'
_o Tc=64,7 min
u_ 150 - CN=77/0
100
50 /
0 20 40 60 80 100 120 140 160 180 200
Time (hours)
0 Runoff

Buck Ash Basin Breaches - 100-year
Final Conditions -Full PMP Type // 24-hr 100-yr Rainfall=7.17"
Prepared by AMEC Printed 10/11/2019
HvdroCADO 10.00-24 s/n 05847 © 2018 HvdroCAD Software Solutions LLC Paae 7
Summary for Subcatchment 2S: Final Conditions - Primary/Secondary Basin DA
Runoff = 545.24 cfs @ 12.42 hrs, Volume= 68.129 af, Depth= 4.19"
Runoff by SCS TR-20 method, UH=SCS, Split Pervious/Imperv., Time Span= 0.00-200.00 hrs, dt= 0.05 hrs
Type II 24-hr 100-yr Rainfall=7.17"
Area (ac)
CN
Description
56.943
86
Newly graded area, HSG B
87.553
65
Woods/grass comb., Fair, HSG B
22.933
86
Newly graded area, HSG B
27.661
65
Woods/grass comb., Fair, HSG B
195.090
74
Weighted Average
195.090
74
100.00% Pervious Area
Tc Length
Slope
Velocity
Capacity Description
(min) (feet)
(ft/ft)
(ft/sec)
(cfs)
27.7 100
0.0100
0.06
Sheet Flow,
Woods: Light underbrush n= 0.400 P2= 3.34"
16.3 1,000
0.0420
1.02
Shallow Concentrated Flow,
Woodland Kv= 5.0 fDs
44.0 1,100 Total
Subcatchment 2S: Final Conditions - Primary/Secondary Basin DA
545.24 cfs
500
450
400
350
3 300
,° 250
200
150
100
50
0
I
Hydrograph
12.42 hrs 0 Runoff
Runoff=5�5.24 cfs @ 12.42 hrs
�Type 124-hr
�10�yr RainfalT�717"
F —1 F Ruof-Are�a=19y190c
Runoff Volume=68.129 of
L Runof�Depth�4.19"
Flow Length=1,100'
�Tc=44'0 min
CN=74/0
20 40 60 80 100 120 140 160 180 200
Time (hours)

Buck Ash Basin Breaches - 100-year
Final Conditions -Full PMP Type 1124-hr 100-yr Rainfall=7.17"
Prepared by AMEC Printed 10/11/2019
HvdroCAD® 10.00-24 s/n 05847 © 2018 HvdroCAD Software Solutions LLC Paae 8
Summary for Reach 6R: Dam Breach Channel
Inflow Area = 167.300 ac, 0.00% Impervious, Inflow Depth = 4.52" for 100-yr event
Inflow = 382.38 cfs @ 12.68 hrs, Volume= 63.001 of
Outflow = 382.14 cfs @ 12.69 hrs, Volume= 63.001 af, Atten= 0%, Lag= 0.4 min
Routing by Dyn-Stor-Ind method, Time Span= 0.00-200.00 hrs, dt= 0.05 hrs
Max. Velocity= 6.67 fps, Min. Travel Time= 0.9 min
Avg. Velocity = 5.27 fps, Avg. Travel Time= 1.1 min
Peak Storage= 20,347 cf @ 12.69 hrs
Average Depth at Peak Storage= 0.95'
Bank -Full Depth= 70.00' Flow Area= 52,500.0 sf, Capacity= 4,106,525.71 cfs
50.00' x 70.00' deep channel, n= 0.055
Side Slope Z-value= 10.0 7' Top Width= 1,450.00'
Length= 355.0' Slope= 0.0704 7'
Inlet Invert= 665.00', Outlet Invert= 640.00'
Reach 6R: Dam Breach Channel
Hydrograph
❑ Inflow
❑ Outflow
i%
Avg. Flow Depth=0.95'
11 /�Max Vel=6.67
'
11 ��Capacity=4,106,525.71 cfs
1
1 iiii�iiiiiiiiiiiiii�iiiiiiiiiiiiiii�iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii�

Buck Ash Basin Breaches - 100-year
Final Conditions -Full PMP Type/1 24-hr 100-yr Rainfall=7.17"
Prepared by AMEC Printed 10/11/2019
HvdroCADO 10.00-24 s/n 05847 © 2018 HvdroCAD Software Solutions LLC Paae 9
7
[01
5
a�
4
a 3
d
0
2
1
7
0
6i
2
1
Reach 6R: Dam Breach Channel
Stage -Discharge
0 1,000,000 2,000,000 3,000,000 4,000,000
Discharge (cfs)
Reach 6R: Dam Breach Channel
Stage -Storage
0 5,000,000 10,000,000 15,000,000
Storage (cubic -feet)
❑ Primary
❑ Storage

Buck Ash Basin Breaches - 100-year
Final Conditions -Full PMP Type 1124-hr 100-yr Rainfall=7.17"
Prepared by AMEC Printed 10/11/2019
HvdroCAD® 10.00-24 s/n 05847 © 2018 HvdroCAD Software Solutions LLC Paae 10
Stage -Area -Storage for Reach 6R: Dam Breach Channel
Elevation
End -Area
Storage
(feet)
(sq-ft)
(cubic -feet)
665.00
0.0
0
665.75
43.5
15,425
666.50
98.1
34,826
667.25
163.9
58,202
668.00
241.0
85,555
668.75
329.3
116,884
669.50
428.7
152,189
670.25
539.4
191,469
671.00
661.2
234,726
671.75
794.3
281,959
672.50
938.5
333,168
673.25
1,094.0
388,352
674.00
1,260.6
447,513
674.75
1,438.4
510,650
675.50
1,627.5
577,763
676.25
1,828.5
649,100
677.00
2,040.6
724,413
677.75
2,263.9
803,702
678.50
2,498.5
886,968
679.25
2,744.3
974,209
680.00
3,001.2
1,065,426
680.75
3,269.3
1,160,619
681.50
3,548.7
1,259,788
682.25
3,839.3
1,362,934
683.00
4,141.0
1,470,055
683.75
4,453.9
1,581,152
684.50
4,778.1
1,696,226
685.25
5,113.4
1,815,275
686.00
5,460.0
1,938,300
686.75
5,818.4
2,065,550
687.50
6,188.1
2,196,776
688.25
6,568.9
2,331,977
689.00
6,961.0
2,471,155
689.75
7,364.3
2,614,309
690.50
7,778.7
2,761,439
691.25
8,204.4
2,912,544
692.00
8,641.2
3,067,626
692.75
9,089.3
3,226,684
693.50
9,548.5
3,389,718
694.25
10,019.0
3,556,727
695.00
10,500.6
3,727,713
695.75
10,993.5
3,902,675
696.50
11,497.5
4,081,612
697.25
12,013.4
4,264,775
698.00
12,540.6
4,451,913
698.75
13,079.0
4,643,027
699.50
13,628.5
4,838,118
700.25
14,189.3
5,037,184
701.00
14,761.2
5,240,226
701.75
15,344.4
5,447,244
702.50
15,938.7
5,658,239
703.25
16,544.3
5,873,209
Elevation
End -Area
Storage
(feet)
(sq-ft)
(cubic -feet)
704.00
17,161.0
6,092,155
704.75
17,789.0
6,315,077
705.50
18,428.1
6,541,976
706.25
19,078.5
6,772,850
707.00
19,740.0
7,007,700
707.75
20,413.4
7,246,775
708.50
21,098.1
7,489,826
709.25
21,794.0
7,736,852
710.00
22,501.0
7,987,855
710.75
23,219.3
8,242,834
711.50
23,948.7
8,501,789
712.25
24,689.3
8,764,719
713.00
25,441.2
9,031,626
713.75
26,204.3
9,302,509
714.50
26,978.5
9,577,368
715.25
27,764.0
9,856,202
716.00
28,560.6
10,139,013
716.75
29,368.5
10,425,800
717.50
30,187.5
10,716,563
718.25
31,018.5
11,011,550
719.00
31,860.6
11,310,513
719.75
32,714.0
11,613,452
720.50
33,578.5
11,920,368
721.25
34,454.3
12,231,259
722.00
35,341.2
12,546,126
722.75
36,239.4
12,864,969
723.50
37,148.7
13,187, 789
724.25
38,069.3
13,514,584
725.00
39,001.0
13,845,355
725.75
39,943.9
14,180,102
726.50
40,898.1
14,518,826
727.25
41,863.5
14,861,525
728.00
42,840.0
15,208,200
728.75
43,828.4
15,559,100
729.50
44,828.1
15,913,976
730.25
45,839.0
16,272,827
731.00
46,861.0
16,635,655
731.75
47,894.3
17,002,459
732.50
48,938.7
17,373,239
733.25
49,994.3
17,747,994
734.00
51,061.2
18,126,726
734.75
52,139.3
18,509,434

Buck Ash Basin Breaches - 100-year
Final Conditions -Full PMP Type 1124-hr 100-yr Rainfall=7.17"
Prepared by AMEC Printed 10/11/2019
HvdroCAD® 10.00-24 s/n 05847 © 2018 HvdroCAD Software Solutions LLC Paae 11
Summary for Reach 7R: Dam Breach Channel
Inflow Area = 195.090 ac, 0.00% Impervious, Inflow Depth = 4.19" for 100-yr event
Inflow = 545.24 cfs @ 12.42 hrs, Volume= 68.129 of
Outflow = 544.30 cfs @ 12.44 hrs, Volume= 68.129 af, Atten= 0%, Lag= 1.0 min
Routing by Dyn-Stor-Ind method, Time Span= 0.00-200.00 hrs, dt= 0.05 hrs
Max. Velocity= 5.15 fps, Min. Travel Time= 1.5 min
Avg. Velocity = 3.57 fps, Avg. Travel Time= 2.2 min
Peak Storage= 49,667 cf @ 12.44 hrs
Average Depth at Peak Storage= 0.96'
Bank -Full Depth= 55.00' Flow Area= 35,750.0 sf, Capacity= 1,856,073.24 cfs
100.00' x 55.00' deep channel, n= 0.040
Side Slope Z-value= 10.0 7' Top Width= 1,200.00'
Length= 470.0' Slope= 0.0213 7'
Inlet Invert= 640.00', Outlet Invert= 630.00'
Reach 7R: Dam Breach Channel
Hydrograph
❑ Inflow
❑ Outflow
11 !/ . .. 12.44 hrs
Avg. Flow i
�•Max Vel=5.15 fps
1 //
11 �� Capacity=1,856,073.24 cfs
1, Ili
11

Buck Ash Basin Breaches - 100-year
Final Conditions -Full PMP Type/1 24-hr 100-yr Rainfall=7.17"
Prepared by AMEC Printed 10/11/2019
HvdroCADO 10.00-24 s/n 05847 © 2018 HvdroCAD Software Solutions LLC Paae 12
5
5
4
4
3
3
�
a 2
d 2
0
1
1
5
5
4
4
3
93
� 2
a
0 2
1
1
Reach 7R: Dam Breach Channel
Stage -Discharge
0 500,000 1,000,000 1,500,000
Discharge (cfs)
Reach 7R: Dam Breach Channel
Stage -Storage
0 5,000,000 10,000,000 15,000,000
Storage (cubic -feet)
❑ Primary
❑ Storage

Buck Ash Basin Breaches - 100-year
Final Conditions -Full PMP Type 1124-hr 100-yr Rainfall=7.17"
Prepared by AMEC Printed 10/11/2019
HvdroCAD® 10.00-24 s/n 05847 © 2018 HvdroCAD Software Solutions LLC Paae 13
Stage -Area -Storage for Reach 7R: Dam Breach Channel
Elevation
End -Area
Storage
(feet)
(sq-ft)
(cubic -feet)
640.00
0.0
0
640.55
58.0
27,272
641.10
122.1
57,387
641.65
192.2
90,346
642.20
268.4
126,148
642.75
350.6
164,794
643.30
438.9
206,283
643.85
533.2
250,616
644.40
633.6
297,792
644.95
740.0
347,812
645.50
852.5
400,675
646.05
971.0
456,382
646.60
1,095.6
514,932
647.15
1,226.2
576,326
647.70
1,362.9
640,563
648.25
1,505.6
707,644
648.80
1,654.4
777,568
649.35
1,809.2
850,336
649.90
1,970.1
925,947
650.45
2,137.0
1,004,402
651.00
2,310.0
1,085,700
651.55
2,489.0
1,169,842
652.10
2,674.1
1,256,827
652.65
2,865.2
1,346,656
653.20
3,062.4
1,439,328
653.75
3,265.6
1,534,844
654.30
3,474.9
1,633,203
654.85
3,690.2
1,734,406
655.40
3,911.6
1,838,452
655.95
4,139.0
1,945,342
656.50
4,372.5
2,055,075
657.05
4,612.0
2,167,652
657.60
4,857.6
2,283,072
658.15
5,109.2
2,401,336
658.70
5,366.9
2,522,443
659.25
5,630.6
2,646,394
659.80
5,900.4
2,773,188
660.35
6,176.2
2,902,826
660.90
6,458.1
3,035,307
661.45
6,746.0
3,170,632
662.00
7,040.0
3,308,800
662.55
7,340.0
3,449,812
663.10
7,646.1
3,593,667
663.65
7,958.2
3,740,366
664.20
8,276.4
3,889,908
664.75
8,600.6
4,042,294
665.30
8,930.9
4,197,523
665.85
9,267.2
4,355,596
666.40
9,609.6
4,516,512
666.95
9,958.0
4,680,272
667.50
10,312.5
4,846,875
668.05
10,673.0
5,016,322
Elevation
End -Area
Storage
(feet)
(sq-ft)
(cubic -feet)
668.60
11,039.6
5,188,612
669.15
11,412.2
5,363,746
669.70
11,790.9
5,541,723
670.25
12,175.6
5,722,544
670.80
12,566.4
5,906,208
671.35
12,963.2
6,092,716
671.90
13, 366.1
6,282,067
672.45
13,775.0
6,474,262
673.00
14,190.0
6,669,300
673.55
14,611.0
6,867,182
674.10
15, 038.1
7,067,907
674.65
15,471.2
7,271,476
675.20
15,910.4
7,477,888
675.75
16,355.6
7,687,144
676.30
16,806.9
7,899,243
676.85
17,264.2
8,114,186
677.40
17,727.6
8,331,972
677.95
18,197.0
8,552,602
678.50
18,672.5
8,776,075
679.05
19,154.0
9,002,392
679.60
19,641.6
9,231,552
680.15
20,135.2
9,463,556
680.70
20,634.9
9,698,403
681.25
21,140.6
9,936,094
681.80
21,652.4
10,176,628
682.35
22,170.2
10,420,006
682.90
22,694.1
10,666,227
683.45
23,224.0
10,915,292
684.00
23,760.0
11,167,200
684.55
24,302.0
11,421,952
685.10
24,850.1
11,679,547
685.65
25,404.2
11,939,986
686.20
25,964.4
12,203,268
686.75
26,530.6
12,469,394
687.30
27,102.9
12,738,363
687.85
27,681.2
13,010,176
688.40
28,265.6
13,284,832
688.95
28,856.0
13,562,332
689.50
29,452.5
13,842,675
690.05
30,055.0
14,125,862
690.60
30,663.6
14,411,892
691.15
31,278.2
14,700,766
691.70
31,898.9
14,992,483
692.25
32,525.6
15,287,044
692.80
33,158.4
15,584,448
693.35
33,797.2
15,884,696
693.90
34,442.1
16,187,787
694.45
35,093.0
16,493,722
695.00
35,750.0
16,802,500

Buck Ash Basin Breaches - 100-year
Final Conditions -Full PMP Type/1 24-hr 100-yr Rainfall=7.17"
Prepared by AMEC Printed 10/11/2019
HvdroCAD® 10.00-24 s/n 05847 © 2018 HvdroCAD Software Solutions LLC Paae 14
Summary for Reach 8R: Dukeville Road Culvert
Inflow Area = 167.300 ac, 0.00% Impervious, Inflow Depth = 4.52" for 100-yr event
Inflow = 382.14 cfs @ 12.69 hrs, Volume= 63.001 of
Outflow = 382.28 cfs @ 12.69 hrs, Volume= 63.001 af, Atten= 0%, Lag= 0.2 min
Routing by Dyn-Stor-Ind method, Time Span= 0.00-200.00 hrs, dt= 0.05 hrs
Max. Velocity= 7.78 fps, Min. Travel Time= 0.2 min
Avg. Velocity = 2.42 fps, Avg. Travel Time= 0.7 min
Peak Storage= 4,910 cf @ 12.69 hrs
Average Depth at Peak Storage= 0.98'
Bank -Full Depth= 4.00' Flow Area= 200.0 sf, Capacity= 2,437.78 cfs
600.0" W x 48.0" H Box Pipe
n= 0.013
Length= 100.0' Slope= 0.0050 T
Inlet Invert= 640.00', Outlet Invert= 639.50'
Reach 8R: Dukeville Road Culvert
Hydrograph
382.28 cfs
@ 12.69
hrs
Inflow Arlea=167.300 ac
Inflow=382.14 cfs @ 12.69 hrs
350
Outflow=482.28 cfs @ 12.169 hrs
Avg. Flow Depth=0.98'
300
Max Vet=7.78 fps
600.0" x-48.0"
`Lo 250
Box Pipe
_LL
n �013
200 /
L
L UT
g=0.0050
U_ 150
apaciM=2,437.78 cfs
��
100 t,
50
1 i-
0 20 40 60 80 100 120 140 160 180 11
Inflow
❑ Outflow

Buck Ash Basin Breaches - 100-year
Final Conditions -Full PMP Type/1 24-hr 100-yr Rainfall=7.17"
Prepared by AMEC Printed 10/11/2019
HvdroCADO 10.00-24 s/n 05847 © 2018 HvdroCAD Software Solutions LLC Paae 15
0
3
2
a
a)
0
1
we
2
3
1
Reach 8R: Dukeville Road Culvert
Stage -Discharge
1,000 2,000 3,000
Discharge (cfs)
Reach 8R: Dukeville Road Culvert
Stage -Storage
5,000 10,000 15,000 20,000
Storage (cubic -feet)
❑ Primary
❑ Storage

Buck Ash Basin Breaches - 100-year
Final Conditions -Full PMP Type 1124-hr 100-yr Rainfall=7.17"
Prepared by AMEC Printed 10/11/2019
HvdroCAD® 10.00-24 s/n 05847 © 2018 HvdroCAD Software Solutions LLC Paae 16
Stage -Area -Storage for Reach 8R: Dukeville Road Culvert
Elevation
End -Area
Storage
(feet)
(sq-ft)
(cubic -feet)
640.00
0.0
0
640.05
2.5
250
640.10
5.0
500
640.15
7.5
750
640.20
10.0
1,000
640.25
12.5
1,250
640.30
15.0
1,500
640.35
17.5
1,750
640.40
20.0
2,000
640.45
22.5
2,250
640.50
25.0
2,500
640.55
27.5
2,750
640.60
30.0
3,000
640.65
32.5
3,250
640.70
35.0
3,500
640.75
37.5
3,750
640.80
40.0
4,000
640.85
42.5
4,250
640.90
45.0
4,500
640.95
47.5
4,750
641.00
50.0
5,000
641.05
52.5
5,250
641.10
55.0
5,500
641.15
57.5
5,750
641.20
60.0
6,000
641.25
62.5
6,250
641.30
65.0
6,500
641.35
67.5
6,750
641.40
70.0
7,000
641.45
72.5
7,250
641.50
75.0
7,500
641.55
77.5
7,750
641.60
80.0
8,000
641.65
82.5
8,250
641.70
85.0
8,500
641.75
87.5
8,750
641.80
90.0
9,000
641.85
92.5
9,250
641.90
95.0
9,500
641.95
97.5
9,750
642.00
100.0
10,000
642.05
102.5
10,250
642.10
105.0
10,500
642.15
107.5
10,750
642.20
110.0
11,000
642.25
112.5
11,250
642.30
115.0
11,500
642.35
117.5
11,750
642.40
120.0
12,000
642.45
122.5
12,250
642.50
125.0
12,500
642.55
127.5
12,750
Elevation
End -Area
Storage
(feet)
(sq-ft)
(cubic -feet)
642.60
130.0
13,000
642.65
132.5
13,250
642.70
135.0
13,500
642.75
137.5
13,750
642.80
140.0
14,000
642.85
142.5
14,250
642.90
145.0
14,500
642.95
147.5
14,750
643.00
150.0
15,000
643.05
152.5
15,250
643.10
155.0
15,500
643.15
157.5
15,750
643.20
160.0
16,000
643.25
162.5
16,250
643.30
165.0
16,500
643.35
167.5
16,750
643.40
170.0
17,000
643.45
172.5
17,250
643.50
175.0
17,500
643.55
177.5
17,750
643.60
180.0
18,000
643.65
182.5
18,250
643.70
185.0
18,500
643.75
187.5
18,750
643.80
190.0
19,000
643.85
192.5
19,250
643.90
195.0
19,500
643.95
197.5
19,750
644.00
200.0
20,000