HomeMy WebLinkAboutSW6230606_Stormwater Report_20231009 BENHA V EN EMERG ENC Y
S ER VICES 13
13151 NC HWY 27 W
BROADWAY, NC 27505
STORMWATER CALCULATION
FOURTH REVISION: 09 OCTOBER 2023
THIRD REVISION: 31 AUGUST 2023
SECOND REVISION: 27 JUNE 2023
FIRST REVISION: 20 DECEMBER 2022
DATE: 11 NOVEMBER 2022
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TELEPHONE 919 851 1980
FAX 919 851 1982
Drainage Area Run-off Summary
Benhaven Emergency Services 13 project description
This is a project to develop a 12,200 SF Emergency Service. The project is located at
13151 NC HWY 27 W, Broadway, NC 27505 on a lot of parcel size 2.49 ac. The site lies
within the jurisdiction of Harnett County with the zoning district of RA-20R.
The property is part of Falcon Crest Development. The project lies in FEMA Floodplain
Zone X, area of minimal flood hazard per FIRM Panel# 3710958600J dated Oct 3, 2006.
Neither USGS 7.5-minute quadrangle map (Olivia Quadrangle NC 7.5-Minute Series)
nor Soil Survey of Harnett County, North Carolina(Sheet 9 of 14)by USDA Soil
Conservation Service has jurisdictional features to the property. Also, S&EC (Soil &
Environmental Consultants, PA) of 8412 Falls of Neuse Road, Suite 104, Raleigh, NC
27615 believes that there are no jurisdictional features on property per site visit
conducted on 07/01/2022. The property lies in the Cape Fear River basin. The project lies
outside of a water supply watershed.
As part of the development, approximately 2.15-Acres of area will be disturbed with 0.73
acres of additional impervious (proposed building, parking spaces and sidewalk)will be
added to the existing development. The total disturbed area includes the 1.57 acres of
development area draining towards the Southwest side of the property along with 0.58
acres of area along Dunrovin Ln, where the improvement does not increase the runoff.
Thus, for the calculation purpose only 1.57-acre area as on Annex A are considered.
Drainage area
The site has a high spot near NE corner of the property. Most of the existing water
naturally flows towards the SW corner of the property. Two 1' deep and 3:1 side slope,
trapezoidal swales were proposed to collect the runoff for the treatment before releasing
near the SW corner of the property. A bioretention cell will serve the purpose of a
Stormwater Control Measure(SCM), by treating the runoff from the developed area (the
detail of the drainage area could be seen on Drainage Area Map, attached to this report).
The area is graded in such a way that the pre and post development drainage area remain
the same (1.57 acres)for a point near the outlet of the bioretention. This point is
considered as Point Of Analysis (POA)for the purpose of runoff calculations. Further, all
the impervious surface within the subject parcel is collected and treated to the SCM. The
SCM itself has a drainage area of 1.45 acres.
Below is the detail of the drainage area considered for the calculation of the pre-
development condition and post-development condition.
Pre-Development:
Ex. Impervious area(to remain) = 0.04 acres
Ex. Undeveloped area to be modified) = 1.53 acres
Total drainage area = 1.57 Acres
Post-Development:
New additional Impervious area = 0.73 acres
Ex. Impervious area(to remain) = 0.04 acres
Lawn with slope less than 5% = 0.26 acres
Lawn with slope more than 5% = 0.42 acres
Sub-total area to the SCM = 1.45 acres
Bypass area (not collected to SCM) = 0.12 acres
Total drainage area = 1.57 Acres
Bioretention Cell
A 2,850 SF Bioretention cell with IWS is proposed as a Stormwater Control Measure
(SCM). The bioretention cell is designed with 2.5' of media depth. PVC underdrain pipes
will be placed at the bottom of the cell and are connected to a 2'x2' concrete riser. The
riser will eventually discharge the collected water at the outlet pad via a 15" RCP pipe.
The proposed bioretention cell without IWS can achieve various pollutant removal. It can
reduce 40%total nitrogen, 45% of total phosphorus and 85% of suspended solids. A riser
with a 15" RCP outlet is proposed to discharge the outflow near the SW corner of the
property.
SHWT is identified at 43inch below surface during the storm water soil evaluation
carried out by "Soil & Environmental Consultants, PA" of 8412 Falls of Neuse Road,
Suite 104, Raleigh,NC 27615 (see included report), with a report titled "Detailed storm
water soils evaluation for Benhaven, 13151 NC Hwy 27, Broadway, NC.". Existing
ground elevation at the test location is 278', thus the existing SHWT is estimated at
274.42 fmsl, which is more than 2' below proposed bottom of bioretention cell (276.67').
Peak Runoff
The rational method is adopted to calculate the peak runoff and runoff volume. The peak
runoff calculation for 1-yr, 2-yr, 10-yr and 100-yr storms are presented under this
heading. Pre-development runoff at POA is compared to the post-development runoff at
the same location. The results of the calculations are presented here. The details of the
runoff calculations are annexed to the Hydraflow modelling report. All the time of
concentrations calculated were below 5 min. So, for the calculation purpose all the time
of concentrations for surface runoff were considered as 5-min. Below is the sample
calculation for time of concentration using Kirchoff's method.
Time of Concentration
The Kirpich Equation was used to analyze the time of concentration. A sample
calculation for the time of concentration from most remote point to POA is presented
below.
Kirpich Equation
Tc = L( 3 0.385
128
L=330 ft
H=11 ft
Tc = 3303/11 0.385
128
Tc= 2.52 min (5-min used)
Since, all the calculated time of concentrations were below 5 min, the minimum time of
concentration of 5 min is used for all drainage area.
Runoff Coefficients
Following runoff coefficients were used for the calculations.
Proposed Coefficient(C-Values)
Undistrurbed ground with grass cover(slope approx. 5%) =0.30
Improved lawn(slope less than 5%) =0.25
Improved lawn in slope (slope more than 5%) =0.35
Impervious roof =0.95
Impervious driveway, parking space and sidewalk =0.95
1-yr Peak Runoff
I- (1 yr) =4.48 in/hr(Tc-5min.)
Pre dev.: 0.32 (C-Value)x 4.48 x 1.57 ac = 2.24 cfs
Post dev.
SCM outflow: 0.65 (C-Value)x 4.48 x 1.45 ac = 0.06 cfs
Bypass Area: 0.35 (C-Value)x 4.48 x 0.12 ac = 0.19 cfs
Total (for POA) = 0.22 cfs
Post-Development-Combined post development peak flow accounts for difference in
Time of Concentrations from sub-basin run-off and SCM. See routing (Hydraflow report)
for details.
2-yr Peak Runoff
I- (2 yr) = 5.76 in/hr(Tc-5min.)
Pre dev.: 0.32 (C-Value)x 5.76 x 1.57 ac = 2.87 cfs
Post dev.
SCM outflow: 0.65 (C-Value)x 5.76 x 1.45 ac = 0.07 cfs
Bypass Area: 0.30 (C-Value)x 5.76 x 0.12 ac = 0.24 cfs
Total (for POA) = 0.28 cfs
Post-Development-Combined post development peak flow accounts for difference in
time of Concentrations from sub-basin run-off and SCM See routing (Hydraflow report)
for details.
10-yr Peak Runoff
I- (10 yr) =7.22 in/hr(Tc-5min.)
Pre dev.: 0.32 (C-Value)x 7.22 x 1.57 ac = 3.60 cfs
Post dev.
SCM outflow: 0.65 (C-Value)x 7.22 x 1.45 ac = 0.07 cfs
Bypass Area: 0.30 (C-Value)x 7.22 x 0.12 ac = 0.30 cfs
Total (for POA) = 0.35 cfs
Post-Development—Combined post development peak flow accounts for difference in
Time of Concentrations from sub-basin run-off and SCM. See routing (Hydraflow report)
for details.
100-yr Peak Runoff
I- (100 yr) = 9.72 in/hr(Tc-5min.)
Pre dev.: 0.32 (C-Value)x 9.72 x 1.57 ac = 4.85 cfs
Post dev.
SCM outflow: 0.65 (C-Value)x 9.72 x 1.45 ac = 0.08 cfs
Bypass Area: 0.30 (C-Value)x 9.72 x 0.12 ac = 0.41 cfs
Total (for POA) = 0.48 cfs
Post-Development—Combined post development peak flow accounts for difference in
Time of Concentrations from sub-basin run-off and SCM. See routing (Hydraflow report)
for details.
Result
The results of the runoff calculations are summarized on table below.
Runoff in cfs
Return Period
Pre-Dev. Post-Dev.
1yr 2.24 0.22
2yr 2.87 0.28
10yr 3.60 0.35
100yr 4.85 0.48
Thus, the post development runoff for lyr, 2yr, l0yr and 100yr is less than the pre-
development runoff.
Supporting documents and calculations are annexed as below
Annex A: Drainage Area Maps
Annex B: Pre & Post-development Hydraflow Modeling and Report
Annex C: Drainage Swale Design
Annex D: Bioretention Cell Design
Annex E: SCM Operation & Maintenance Manual
Annex A:
Drainage Area Map
FM FM
PRE-DEVELOPMENT
EX. IMPERVIOUS M - I \ EX. IMPERVIOUS AREA: 0.04 AC
AREA: 0.04 AC
1 .53 AC
� - - - r � � � \ II \ � \ TOTALNAREALOPED AREA: 1 .57 AC
LEGEND
EX. IMPERVIOUS
290
\ STORM MANHOLE
- 29,
EX. UNDEVELOPED AREA: 1 .53 AC
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- -26°_ BENHAVEN EMERGENCY SERVICES 13
13151 NC HWY 27 W
_ - - 279- PRE-DEVELOPMENT BROADWAY, NC 27505 1"=30'@11X17
- \ BOBS TT DESIGN BUILD,INC.
600 GERMANTOWN ROAD
RALEIGH,NC 27607
PH.(919)651-1960
(999)661-9962
VDRAINAGE AREA ��'�� NAIL desi bbitt� � WWW aoBBITT COM
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Firm Lic#D-0191
POINT OF ANALYSIS i i 1 4 COPYRIGHT C 2022 BOBBITT DESIGN BUILD,INC.ALL RIGHTS RESERVED.
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Annex B :
Pre & Post-dev. Hydraflow Modeling
Report
Hydraflow Table of Contents Stormwater_Ben Have n_v4.gpw
Hydraflow Hydrographs Extension for Autodeskg Civil 3DO by Autodesk, Inc.v2023 Wednesday,08/30/2023
Watershed Model Schematic...................................................................................... 1
Hydrograph Return Period Recap............................................................................. 2
1 - Year
SummaryReport......................................................................................................................... 3
HydrographReports................................................................................................................... 4
Hydrograph No. 1, Rational, PreDev........................................................................................ 4
Hydrograph No. 2, Rational, Post.Dev..................................................................................... 5
Hydrograph No. 3, Rational, Post.Dev-Bypass........................................................................ 6
Hydrograph No. 4, Reservoir, Bioretention............................................................................... 7
Pond Report - BIORETENTION CELL................................................................................ 8
Hydrograph No. 5, Combine, PostDev_West (POA#2)............................................................ 9
2 - Year
SummaryReport....................................................................................................................... 10
HydrographReports................................................................................................................. 11
Hydrograph No. 1, Rational, PreDev...................................................................................... 11
Hydrograph No. 2, Rational, Post.Dev................................................................................... 12
Hydrograph No. 3, Rational, Post.Dev-Bypass...................................................................... 13
Hydrograph No. 4, Reservoir, Bioretention............................................................................. 14
Hydrograph No. 5, Combine, PostDev_West (POA#2).......................................................... 15
10 - Year
SummaryReport....................................................................................................................... 16
HydrographReports................................................................................................................. 17
Hydrograph No. 1, Rational, PreDev...................................................................................... 17
Hydrograph No. 2, Rational, Post.Dev................................................................................... 18
Hydrograph No. 3, Rational, Post.Dev-Bypass...................................................................... 19
Hydrograph No. 4, Reservoir, Bioretention............................................................................. 20
Hydrograph No. 5, Combine, PostDev_West (POA#2).......................................................... 21
100 - Year
SummaryReport....................................................................................................................... 22
HydrographReports................................................................................................................. 23
Hydrograph No. 1, Rational, PreDev...................................................................................... 23
Hydrograph No. 2, Rational, Post.Dev................................................................................... 24
Hydrograph No. 3, Rational, Post.Dev-Bypass...................................................................... 25
Hydrograph No. 4, Reservoir, Bioretention............................................................................. 26
Hydrograph No. 5, Combine, PostDev_West (POA#2).......................................................... 27
1
Watershed Model Schematic Hydraflow Hydrographs Extension for Autodesk@ Civil 3D@ by Autodesk, Inc.v2023
Legend
5
Hyd. Origin Description
1 Rational PreDev
2 Rational Post.Dev
3 Rational Post.Dev-Bypass
4 Reservoir Bioretention
5 Combine PostDev_West(POA#2)
Project: Stormwater BenHaven_v4.gpw Wednesday, 08/30/2023
2
Hydrograph Return Period Recap
draflow Hydrographs Extension for Autodesk@ Civil 3D@ by Autodesk, Inc.v2023
Hyd. Hydrograph Inflow Peak Outflow(cfs) Hydrograph
No. type hyd(s) Description
(origin) 1-yr 2-yr 3-yr 5-yr 10-yr 25-yr 50-yr 100-yr
1 Rational ------ 2.236 2.872 ------- ------- 3.602 ------- ------- 4.852 PreDev
2 Rational ------ 4.222 5.422 ------- ------- 6.801 ------- ------- 9.161 Post.Dev
3 Rational ------ 0.188 0.242 ------- ------- 0.303 ------- ------- 0.408 Post.Dev-Bypass
4 Reservoir 2 0.061 0.074 ------- ------- 0.076 ------- ------- 0.080 Bioretention
5 Combine 3,4 0.219 0.281 ------- ------- 0.353 ------- ------- 0.475 PostDev_West(POA#2)
Proj. file: Stormwater BenHaven_v4.gpw Wednesday, 08/30/2023
1-yr Storm Runoff
3
Hydrograph Summary Report
Hydraflow Hydrographs Extension for Autodesk@ Civil 3DO by Autodesk, Inc.v2023
Hyd. Hydrograph Peak Time Time to Hyd. Inflow Maximum Total Hydrograph
No. type flow interval Peak volume hyd(s) elevation strge used Description
(origin) (cfs) (min) (min) (cuft) (ft) (cuft)
1 Rational 2.236 1 5 671 ------ ------ ------ PreDev
2 Rational 4.222 1 5 1,267 ------ ------ ------ Post.Dev
3 Rational 0.188 1 5 56 ------ ------ ------ Post.Dev-Bypass
4 Reservoir 0.061 1 10 1,246 2 280.91 1,248 Bioretention
5 Combine 0.219 1 5 1,303 3, 4 ------ ------ Post Dev_West(POA#2)
Stormwater BenHaven_v4.gpw Return Period: 1 Year Wednesday, 08/30/2023
4
Hydrograph Report
Hydraflow Hydrographs Extension for AUtodeskS Civil 3DO by Autodesk, Inc.v2023 Wednesday,08/30/2023
Hyd. No. 1
PreDev
Hydrograph type = Rational Peak discharge = 2.236 cfs
Storm frequency = 1 yrs Time to peak = 5 min
Time interval = 1 min Hyd. volume = 671 cuft
Drainage area = 1.560 ac Runoff coeff. = 0.32*
Intensity = 4.480 in/hr Tc by User = 5.00 min
OF Curve = mid NC IDF.IDF Asc/Rec limb fact = 1/1
Composite(Area/C)_[(1.520 x 0.30)+(0.040 x 0.95)]/1.560
PreDev
Q (cfs) Hyd. No. 1 -- 1 Year Q (cfs)
3.00 3.00
2.00 2.00
Oz
1.00 1.00
0.00 0.00
0 1 2 3 4 5 6 7 8 9 10
— Hyd No. 1 Time (min)
5
Hydrograph Report
Hydraflow Hydrographs Extension for AUtodeskS Civil 3DO by Autodesk, Inc.v2023 Wednesday,08/30/2023
Hyd. No. 2
Post.Dev
Hydrograph type = Rational Peak discharge = 4.222 cfs
Storm frequency = 1 yrs Time to peak = 5 min
Time interval = 1 min Hyd. volume = 1,267 cuft
Drainage area = 1.450 ac Runoff coeff. = 0.65*
Intensity = 4.480 in/hr Tc by User = 5.00 min
OF Curve = mid NC IDF.IDF Asc/Rec limb fact = 1/1
Composite(Area/C)_[(0.770 x 0.95)+(0.420 x 0.35)+(0.260 x 0.25)]/1.450
Post.Dev
Q (cfs) Hyd. No. 2 -- 1 Year Q (cfs)
5.00 5.00
4.00 4.00
3.00 3.00
2.00 2.00
1.00 1.00
0.00 0.00
0 1 2 3 4 5 6 7 8 9 10
— Hyd No. 2 Time (min)
6
Hydrograph Report
Hydraflow Hydrographs Extension for AUtodeskS Civil 3DO by Autodesk, Inc.v2023 Wednesday,08/30/2023
Hyd. No. 3
Post.Dev-Bypass
Hydrograph type = Rational Peak discharge = 0.188 cfs
Storm frequency = 1 yrs Time to peak = 5 min
Time interval = 1 min Hyd. volume = 56 cuft
Drainage area = 0.120 ac Runoff coeff. = 0.35*
Intensity = 4.480 in/hr Tc by User = 5.00 min
OF Curve = mid NC IDF.IDF Asc/Rec limb fact = 1/1
Composite(Area/C)_[(0.120 x 0.35)]/0.120
Post.Dev-Bypass
Q (cfs) Hyd. No. 3 -- 1 Year Q (cfs)
0.50 0.50
0.45 0.45
0.40 0.40
0.35 0.35
0.30 0.30
0.25 0.25
0.20 0.20
0.15 0.15
0.10 0.10
0.05 0.05
0.00 0.00
0 1 2 3 4 5 6 7 8 9 10
Hyd No. 3 Time (min)
7
Hydrograph Report
Hydraflow Hydrographs Extension for AUtodeskS Civil 3DO by Autodesk, Inc.v2023 Wednesday,08/30/2023
Hyd. No. 4
Bioretention
Hydrograph type = Reservoir Peak discharge = 0.061 cfs
Storm frequency = 1 yrs Time to peak = 10 min
Time interval = 1 min Hyd. volume = 1,246 cuft
Inflow hyd. No. = 2 - Post.Dev Max. Elevation = 280.91 ft
Reservoir name = BIORETENTION CELL Max. Storage = 1,248 cuft
Storage Indication method used. Outflow includes exfiltration.
Bioretention
Q (cfs) Hyd. No. 4 -- 1 Year Q (cfs)
5.00 5.00
4.00 4.00
3.00 3.00
2.00 2.00
1.00 1.00
0.00 - 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440
Time (min)
Hyd No. 4 Hyd No. 2 ® Total storage used = 1,248 cult
Pond Report 8
Hydraflow Hydrographs Extension for Autodesk@ Civil 3D@ by Autodesk, Inc.v2023 Wednesday,08/30/2023
Pond No. 1 - BIORETENTION CELL
Pond Data
Contours-User-defined contour areas.Average end area method used for volume calculation. Begining Elevation=280.50 ft
Stage/Storage Table
Stage(ft) Elevation(ft) Contour area(sqft) Incr.Storage(cuft) Total storage(cuft)
0.00 280.50 2,850 0 0
0.50 281.00 3,170 1,505 1,505
1.50 282.00 4,000 3,585 5,090
2.00 282.50 4,500 2,125 7,215
Culvert/Orifice Structures Weir Structures
[A] [B] [C] [PrFRsr] [A] [B] [C] [D]
Rise(in) = 15.00 Inactive Inactive Inactive Crest Len(ft) = 8.00 8.00 0.00 0.00
Span(in) = 15.00 4.00 0.00 0.00 Crest El.(ft) = 281.50 281.75 0.00 0.00
No.Barrels = 1 1 1 1 WeirCoeff. = 3.33 2.60 3.33 3.33
Invert El.(ft) = 276.85 281.50 0.00 0.00 Weir Type = 1 Broad --- ---
Length(ft) = 35.00 0.00 0.00 0.00 Multi-Stage = Yes No No No
Slope(%) = 1.00 1.00 0.00 n/a
N-Value = .013 .013 .013 n/a
Orifice Coeff. = 0.60 0.60 0.60 0.60 Exfil.(in/hr) = 1.000(by Contour)
Multi-Stage = n/a Yes Yes No TW Elev.(ft) = 0.00
Note:Culvert/Orifice outflows are analyzed under inlet(ic)and outlet(oc)control. Weir risers checked for orifice conditions(ic)and submergence(s).
Stage(ft) Stage/ Discharge Elev(ft)
2.00 282.50
1.80 282.30
1.60 282.10
1.40 281.90
1.20 281.70
1.00 281.50
0.80 281.30
0.60 281.10
0.40 280.90
0.20 280.70
0.00 280.50
0.00 3.00 6.00 9.00 12.00 15.00 18.00 21.00 24.00 27.00
Total Q Discharge(cfs)
9
Hydrograph Report
Hydraflow Hydrographs Extension for AUtodeskS Civil 3DO by Autodesk, Inc.v2023 Wednesday,08/30/2023
Hyd. No. 5
PostDev West(POA#2)
Hydrograph type = Combine Peak discharge = 0.219 cfs
Storm frequency = 1 yrs Time to peak = 5 min
Time interval = 1 min Hyd. volume = 1,303 cuft
Inflow hyds. = 3, 4 Contrib. drain. area = 0.120 ac
PostDev_West (POA#2)
Q (cfs) Hyd. No. 5 -- 1 Year Q (cfs)
0.50 0.50
0.45 0.45
0.40 0.40
0.35 0.35
0.30 0.30
0.25 0.25
0.20 0.20
0.15 0.15
0.10 0.10
0.05 0.05
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200
Time (min)
Hyd No. 5 Hyd No. 3 Hyd No. 4
2-yr Storm Runoff
10
Hydrograph Summary Report
Hydraflow Hydrographs Extension for Autodesk@ Civil 3DO by Autodesk, Inc.v2023
Hyd. Hydrograph Peak Time Time to Hyd. Inflow Maximum Total Hydrograph
No. type flow interval Peak volume hyd(s) elevation strge used Description
(origin) (cfs) (min) (min) (cuft) (ft) (cuft)
1 Rational 2.872 1 5 862 ------ ------ ------ PreDev
2 Rational 5.422 1 5 1,627 ------ ------ ------ Post.Dev
3 Rational 0.242 1 5 72 ------ ------ ------ Post.Dev-Bypass
4 Reservoir 0.074 1 10 1,606 2 281.03 1,603 Bioretention
5 Combine 0.281 1 5 1,679 3, 4 ------ ------ Post Dev_West(POA#2)
Stormwater BenHaven_v4.gpw Return Period: 2 Year Wednesday, 08/30/2023
11
Hydrograph Report
Hydraflow Hydrographs Extension for AUtodeskS Civil 3DO by Autodesk, Inc.v2023 Wednesday,08/30/2023
Hyd. No. 1
PreDev
Hydrograph type = Rational Peak discharge = 2.872 cfs
Storm frequency = 2 yrs Time to peak = 5 min
Time interval = 1 min Hyd. volume = 862 cuft
Drainage area = 1.560 ac Runoff coeff. = 0.32*
Intensity = 5.753 in/hr Tc by User = 5.00 min
OF Curve = mid NC IDF.IDF Asc/Rec limb fact = 1/1
Composite(Area/C)_[(1.520 x 0.30)+(0.040 x 0.95)]/1.560
PreDev
Q (cfs) Hyd. No. 1 --2 Year Q (cfs)
3.00 3.00
2.00 2.00
1.00 1.00
0.00 0.00
0 1 2 3 4 5 6 7 8 9 10
— Hyd No. 1 Time (min)
12
Hydrograph Report
Hydraflow Hydrographs Extension for AUtodeskS Civil 3DO by Autodesk, Inc.v2023 Wednesday,08/30/2023
Hyd. No. 2
Post.Dev
Hydrograph type = Rational Peak discharge = 5.422 cfs
Storm frequency = 2 yrs Time to peak = 5 min
Time interval = 1 min Hyd. volume = 1,627 cuft
Drainage area = 1.450 ac Runoff coeff. = 0.65*
Intensity = 5.753 in/hr Tc by User = 5.00 min
OF Curve = mid NC IDF.IDF Asc/Rec limb fact = 1/1
Composite(Area/C)_[(0.770 x 0.95)+(0.420 x 0.35)+(0.260 x 0.25)]/1.450
Post.Dev
Q (cfs) Hyd. No. 2 --2 Year Q (cfs)
6.00 6.00
5.00 5.00
4.00 4.00
3.00 3.00
2.00 2.00
1.00 1.00
0.00 0.00
0 1 2 3 4 5 6 7 8 9 10
— Hyd No. 2 Time (min)
13
Hydrograph Report
Hydraflow Hydrographs Extension for AUtodeskS Civil 3DO by Autodesk, Inc.v2023 Wednesday,08/30/2023
Hyd. No. 3
Post.Dev-Bypass
Hydrograph type = Rational Peak discharge = 0.242 cfs
Storm frequency = 2 yrs Time to peak = 5 min
Time interval = 1 min Hyd. volume = 72 cuft
Drainage area = 0.120 ac Runoff coeff. = 0.35*
Intensity = 5.753 in/hr Tc by User = 5.00 min
OF Curve = mid NC IDF.IDF Asc/Rec limb fact = 1/1
Composite(Area/C)_[(0.120 x 0.35)]/0.120
Post.Dev-Bypass
Q (cfs) Hyd. No. 3 --2 Year Q (cfs)
0.50 0.50
0.45 0.45
0.40 0.40
0.35 0.35
0.30 0.30
0.25 0.25
0.20 0.20
0.15 0.15
0.10 0.10
0.05 0.05
0.00 0.00
0 1 2 3 4 5 6 7 8 9 10
Hyd No. 3 Time (min)
14
Hydrograph Report
Hydraflow Hydrographs Extension for AUtodeskS Civil 3DO by Autodesk, Inc.v2023 Wednesday,08/30/2023
Hyd. No. 4
Bioretention
Hydrograph type = Reservoir Peak discharge = 0.074 cfs
Storm frequency = 2 yrs Time to peak = 10 min
Time interval = 1 min Hyd. volume = 1,606 cuft
Inflow hyd. No. = 2 - Post.Dev Max. Elevation = 281.03 ft
Reservoir name = BIORETENTION CELL Max. Storage = 1,603 cuft
Storage Indication method used. Outflow includes exfiltration.
Bioretention
Q (cfs) Hyd. No. 4 --2 Year Q (cfs)
6.00 6.00
5.00 5.00
4.00 4.00
3.00 3.00
2.00 2.00
1.00 1.00
0.00 - 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Time (min)
Hyd No. 4 — Hyd No. 2 Total storage used = 1,603 cult
15
Hydrograph Report
Hydraflow Hydrographs Extension for AUtodeskS Civil 3DO by Autodesk, Inc.v2023 Wednesday,08/30/2023
Hyd. No. 5
PostDev West(POA#2)
Hydrograph type = Combine Peak discharge = 0.281 cfs
Storm frequency = 2 yrs Time to peak = 5 min
Time interval = 1 min Hyd. volume = 1,679 cuft
Inflow hyds. = 3, 4 Contrib. drain. area = 0.120 ac
PostDev_West (POA#2)
Q (cfs) Hyd. No. 5 --2 Year Q (cfs)
0.50 0.50
0.45 0.45
0.40 0.40
0.35 0.35
0.30 0.30
0.25 0.25
0.20 0.20
0.15 0.15
0.10 0.10
0.05 0.05
0.00 - 0.00
0 120 240 360 480 600 720 840 960 1080 1200
Time (min)
Hyd No. 5 Hyd No. 3 Hyd No. 4
10-yr Storm Runoff
16
Hydrograph Summary Report
Hydraflow Hydrographs Extension for Autodesk@ Civil 3DO by Autodesk, Inc.v2023
Hyd. Hydrograph Peak Time Time to Hyd. Inflow Maximum Total Hydrograph
No. type flow interval Peak volume hyd(s) elevation strge used Description
(origin) (cfs) (min) (min) (cuft) (ft) (cuft)
1 Rational 3.602 1 5 1,081 ------ ------ ------ PreDev
2 Rational 6.801 1 5 2,040 ------ ------ ------ Post.Dev
3 Rational 0.303 1 5 91 ------ ------ ------ Post.Dev-Bypass
4 Reservoir 0.076 1 10 2,020 2 281.14 2,014 Bioretention
5 Combine 0.353 1 5 2,111 3, 4 ------ ------ Post Dev_West(POA#2)
Stormwater BenHaven_v4.gpw Return Period: 10 Year Wednesday, 08/30/2023
17
Hydrograph Report
Hydraflow Hydrographs Extension for AUtodeskS Civil 3DO by Autodesk, Inc.v2023 Wednesday,08/30/2023
Hyd. No. 1
PreDev
Hydrograph type = Rational Peak discharge = 3.602 cfs
Storm frequency = 10 yrs Time to peak = 5 min
Time interval = 1 min Hyd. volume = 1,081 cuft
Drainage area = 1.560 ac Runoff coeff. = 0.32*
Intensity = 7.216 in/hr Tc by User = 5.00 min
OF Curve = mid NC IDF.IDF Asc/Rec limb fact = 1/1
Composite(Area/C)_[(1.520 x 0.30)+(0.040 x 0.95)]/1.560
PreDev
Q (cfs) Hyd. No. 1 -- 10 Year Q (cfs)
4.00 4.00
3.00 3.00
2.00 2.00
1.00 1.00
0.00 0.00
0 1 2 3 4 5 6 7 8 9 10
Hyd No. 1 Time (min)
18
Hydrograph Report
Hydraflow Hydrographs Extension for AUtodeskS Civil 3DO by Autodesk, Inc.v2023 Wednesday,08/30/2023
Hyd. No. 2
Post.Dev
Hydrograph type = Rational Peak discharge = 6.801 cfs
Storm frequency = 10 yrs Time to peak = 5 min
Time interval = 1 min Hyd. volume = 2,040 cuft
Drainage area = 1.450 ac Runoff coeff. = 0.65*
Intensity = 7.216 in/hr Tc by User = 5.00 min
OF Curve = mid NC IDF.IDF Asc/Rec limb fact = 1/1
Composite(Area/C)_[(0.770 x 0.95)+(0.420 x 0.35)+(0.260 x 0.25)]/1.450
Post.Dev
Q (cfs) Hyd. No. 2 -- 10 Year Q (cfs)
7.00 7.00
6.00 6.00
5.00 5.00
4.00 4.00
3.00 3.00
2.00 2.00
1.00 1.00
0.00 0.00
0 1 2 3 4 5 6 7 8 9 10
— Hyd No. 2 Time (min)
19
Hydrograph Report
Hydraflow Hydrographs Extension for AUtodeskS Civil 3DO by Autodesk, Inc.v2023 Wednesday,08/30/2023
Hyd. No. 3
Post.Dev-Bypass
Hydrograph type = Rational Peak discharge = 0.303 cfs
Storm frequency = 10 yrs Time to peak = 5 min
Time interval = 1 min Hyd. volume = 91 cuft
Drainage area = 0.120 ac Runoff coeff. = 0.35*
Intensity = 7.216 in/hr Tc by User = 5.00 min
OF Curve = mid NC IDF.IDF Asc/Rec limb fact = 1/1
Composite(Area/C)_[(0.120 x 0.35)]/0.120
Post.Dev-Bypass
Q (cfs) Hyd. No. 3 -- 10 Year Q (cfs)
0.50 0.50
0.45 0.45
0.40 0.40
0.35 0.35
0.30 0.30
0.25 0.25
0.20 0.20
21
0.15 0.15
0.10 0.10
0.05 0.05
0.00 0.00
0 1 2 3 4 5 6 7 8 9 10
— Hyd No. 3 Time (min)
20
Hydrograph Report
Hydraflow Hydrographs Extension for AUtodeskS Civil 3DO by Autodesk, Inc.v2023 Wednesday,08/30/2023
Hyd. No. 4
Bioretention
Hydrograph type = Reservoir Peak discharge = 0.076 cfs
Storm frequency = 10 yrs Time to peak = 10 min
Time interval = 1 min Hyd. volume = 2,020 cuft
Inflow hyd. No. = 2 - Post.Dev Max. Elevation = 281.14 ft
Reservoir name = BIORETENTION CELL Max. Storage = 2,014 cuft
Storage Indication method used. Outflow includes exfiltration.
Bioretention
Q (cfs) Hyd. No. 4 -- 10 Year Q (cfs)
7.00 7.00
6.00 6.00
5.00 5.00
4.00 4.00
3.00 3.00
2.00 2.00
1.00 1.00
0.00 - 0.00
0 180 360 540 720 900 1080 1260 1440 1620
Time (min)
Hyd No. 4 Hyd No. 2 ® Total storage used = 2,014 cult
21
Hydrograph Report
Hydraflow Hydrographs Extension for AUtodeskS Civil 3DO by Autodesk, Inc.v2023 Wednesday,08/30/2023
Hyd. No. 5
PostDev West(POA#2)
Hydrograph type = Combine Peak discharge = 0.353 cfs
Storm frequency = 10 yrs Time to peak = 5 min
Time interval = 1 min Hyd. volume = 2,111 cuft
Inflow hyds. = 3, 4 Contrib. drain. area = 0.120 ac
PostDev_West (POA#2)
Q (cfs) Hyd. No. 5 -- 10 Year Q (cfs)
0.50 0.50
0.45 0.45
0.40 0.40
0.35 0.35
0.30 0.30
0.25 0.25
0.20 0.20
0.15 0.15
0.10 0.10
0.05 0.05
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200
Time (min)
Hyd No. 5 Hyd No. 3 Hyd No. 4
100-yr Storm Runoff
22
Hydrograph Summary Report
Hydraflow Hydrographs Extension for Autodesk@ Civil 3DO by Autodesk, Inc.v2023
Hyd. Hydrograph Peak Time Time to Hyd. Inflow Maximum Total Hydrograph
No. type flow interval Peak volume hyd(s) elevation strge used Description
(origin) (cfs) (min) (min) (cuft) (ft) (cuft)
1 Rational 4.852 1 5 1,456 ------ ------ ------ PreDev
2 Rational 9.161 1 5 2,748 ------ ------ ------ Post.Dev
3 Rational 0.408 1 5 122 ------ ------ ------ Post.Dev-Bypass
4 Reservoir 0.080 1 10 2,728 2 281.34 2,718 Bioretention
5 Combine 0.475 1 5 2,850 3, 4 ------ ------ PostDev_West(POA#2)
Stormwater BenHaven_v4.gpw Return Period: 100 Year Wednesday, 08/30/2023
23
Hydrograph Report
Hydraflow Hydrographs Extension for AUtodeskS Civil 3DO by Autodesk, Inc.v2023 Wednesday,08/30/2023
Hyd. No. 1
PreDev
Hydrograph type = Rational Peak discharge = 4.852 cfs
Storm frequency = 100 yrs Time to peak = 5 min
Time interval = 1 min Hyd. volume = 1,456 cuft
Drainage area = 1.560 ac Runoff coeff. = 0.32*
Intensity = 9.720 in/hr Tc by User = 5.00 min
OF Curve = mid NC IDF.IDF Asc/Rec limb fact = 1/1
Composite(Area/C)_[(1.520 x 0.30)+(0.040 x 0.95)]/1.560
PreDev
Q (cfs) Hyd. No. 1 -- 100 Year Q (cfs)
5.00 5.00
4.00 4.00
3.00 3.00
2.00 2.00
1.00 1.00
0.00 0.00
0 1 2 3 4 5 6 7 8 9 10
— Hyd No. 1 Time (min)
24
Hydrograph Report
Hydraflow Hydrographs Extension for AUtodeskS Civil 3DO by Autodesk, Inc.v2023 Wednesday,08/30/2023
Hyd. No. 2
Post.Dev
Hydrograph type = Rational Peak discharge = 9.161 cfs
Storm frequency = 100 yrs Time to peak = 5 min
Time interval = 1 min Hyd. volume = 2,748 cuft
Drainage area = 1.450 ac Runoff coeff. = 0.65*
Intensity = 9.720 in/hr Tc by User = 5.00 min
OF Curve = mid NC IDF.IDF Asc/Rec limb fact = 1/1
Composite(Area/C)_[(0.770 x 0.95)+(0.420 x 0.35)+(0.260 x 0.25)]/1.450
Post.Dev
Q (cfs) Hyd. No. 2-- 100 Year Q (cfs)
10.00 10.00
8.00 8.00
6.00 6.00
4.00 4.00
2.00 2.00
0.00 0.00
0 1 2 3 4 5 6 7 8 9 10
— Hyd No. 2 Time (min)
25
Hydrograph Report
Hydraflow Hydrographs Extension for AUtodeskS Civil 3DO by Autodesk, Inc.v2023 Wednesday,08/30/2023
Hyd. No. 3
Post.Dev-Bypass
Hydrograph type = Rational Peak discharge = 0.408 cfs
Storm frequency = 100 yrs Time to peak = 5 min
Time interval = 1 min Hyd. volume = 122 cuft
Drainage area = 0.120 ac Runoff coeff. = 0.35*
Intensity = 9.720 in/hr Tc by User = 5.00 min
OF Curve = mid NC IDF.IDF Asc/Rec limb fact = 1/1
Composite(Area/C)_[(0.120 x 0.35)]/0.120
Post.Dev-Bypass
Q (cfs) Hyd. No. 3-- 100 Year Q (cfs)
0.50 0.50
0.45 0.45
0.40 0.40
0.35 0.35
0.30 0.30
0.25 NIL 0.25
0.20 0.20
0.15 z X0.15
0.10 0.10
0.05 0.05
0.00 0.00
0 1 2 3 4 5 6 7 8 9 10
— Hyd No. 3 Time (min)
26
Hydrograph Report
Hydraflow Hydrographs Extension for AUtodeskS Civil 3DO by Autodesk, Inc.v2023 Wednesday,08/30/2023
Hyd. No. 4
Bioretention
Hydrograph type = Reservoir Peak discharge = 0.080 cfs
Storm frequency = 100 yrs Time to peak = 10 min
Time interval = 1 min Hyd. volume = 2,728 cuft
Inflow hyd. No. = 2 - Post.Dev Max. Elevation = 281.34 ft
Reservoir name = BIORETENTION CELL Max. Storage = 2,718 cuft
Storage Indication method used. Outflow includes exfiltration.
Bioretention
Q (cfs) Hyd. No. 4-- 100 Year Q (cfs)
10.00 10.00
8.00 8.00
6.00 6.00
4.00 4.00
2.00 2.00
0.00 - 0.00
0 180 360 540 720 900 1080 1260 1440 1620 1800
Time (min)
Hyd No. 4 - Hyd No. 2 ® Total storage used = 2,718 cult
27
Hydrograph Report
Hydraflow Hydrographs Extension for AUtodeskS Civil 3DO by Autodesk, Inc.v2023 Wednesday,08/30/2023
Hyd. No. 5
PostDev West(POA#2)
Hydrograph type = Combine Peak discharge = 0.475 cfs
Storm frequency = 100 yrs Time to peak = 5 min
Time interval = 1 min Hyd. volume = 2,850 cuft
Inflow hyds. = 3, 4 Contrib. drain. area = 0.120 ac
PostDev_West (POA#2)
Q (cfs) Hyd. No. 5-- 100 Year Q (cfs)
0.50 0.50
0.45 0.45
0.40 0.40
0.35 0.35
0.30 0.30
0.25 0.25
0.20 0.20
0.15 0.15
0.10 0.10
0.05 0.05
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320
Time (min)
Hyd No. 5 Hyd No. 3 Hyd No. 4
Annex C:
Drainage Swale Design
Benhaven Emergency Services 13
Channel Design Sheet
Swale ID#1
Solve depth of flow for given discharge, shape and slope of channel
C 0.73
A 0.48
Input 7.22
Discharge, Q 2.51
Input
Discharge 2.51 cfs
Bed slope 0.0263
Shape Trapezoidal
Bottom width 1 ft
Side slope 3 H to 1V
Mannings Coeff. 0.025
Depth of flow (assumed) 0.347 Ft
Calculation
Flow area 0.71 SF
wetted perimeter 3.20 Ft
hydraulic radius 0.22 Ft
velocity 3.54 ft/s
Calculated Discharge 2.51 CFS
Depth of Flow (calculated) 0.35 Ft
(see separate channel lining calculation using North American Green Erosion Control
Materials Design Software ECMDS Version 7.0)
Benhaven Emergency Services 13
Channel Design Sheet
Swale ID#2
Solve depth of flow for given discharge, shape and slope of channel
C 0.61
A 0.97
Input 7.22
Discharge, Q 4.30
Input
Discharge 4.30 cfs
Bed slope 0.06
Shape Trapezoidal
Bottom width 1 ft
Side slope 3 H to 1V
Mannings Coeff. 0.025
Depth of flow (assumed) 0.369 Ft
Calculation
Flow area 0.78 SF
wetted perimeter 3.33 Ft
hydraulic radius 0.23 Ft
velocity 5.53 ft/s
Calculated Discharge 4.30 CFS
Depth of Flow (calculated) 0.37 Ft
(see separate channel lining calculation using North American Green Erosion Control
Materials Design Software ECMDS Version 7.0)
NORTH North American Green
AMER�CAN 5401 St. Wendel-Cynthiana Rd.
Poseyville, Indiana 47633
GREEN Tel. 800.772.2040
>Fax 812.867.0247
www.nagreen.com
ECMDS v7.0
CHANNEL ANALYSIS
>>>BENHAVEN E.S. 13 Swale ID#1
Name BENHAVEN E.S. 13 Swale
ID#1
Discharge 2.51
Channel Slope 0.0263
Channel Bottom Width 1
Left Side Slope 3
Right Side Slope 3
Low Flow Liner
Retardence Class E<2 in
Vegetation Type None
Vegetation Density None
Soil Type Silt Loam(SM)
C125
Phase Reach Discharge Velocity
Normal Mannings N Permissible Calculated Safety Remarks Sple
Depth Shear Stress Shear Stress Factor Pattatern
C125 Straight 2.51 cfs 3.53 ft/s 0.35 ft 0.025 2.3 Ibs/ft2 0.57 Ibs/ft2 4.04 STABLE D
Unvegetated
Underlying Straight 2.51 cfs 3.53 ft/s 0.35 ft 0.025 1.68 Ibs/ft2 0.36 Ibs/ft2 4.63 STABLE D
Substrate
NORTH North American Green
AMER�CAN 5401 St. Wendel-Cynthiana Rd.
Poseyville, Indiana 47633
GREEN Tel. 800.772.2040
>Fax 812.867.0247
www.nagreen.com
ECMDS v7.0
CHANNEL ANALYSIS
>>>BENHAVEN E.S. 13 Swale#2
Name BENHAVEN E.S. 13
Swale#2
Discharge 4.3
Channel Slope 0.06
Channel Bottom Width 1
Left Side Slope 3
Right Side Slope 3
Low Flow Liner
Retardence Class C 6-12 in
Vegetation Type None
Vegetation Density None
Soil Type Silt Loam(SM)
C125
Phase Reach Discharge Velocity
Normal Mannings N Permissible Calculated Safety Remarks Sple
Depth Shear Stress Shear Stress Factor Pattatern
C125 Straight 4.3 cfs 5.52 ft/s 0.37 ft 0.025 2.3 Ibs/ft2 1.38 Ibs/ft2 1.66 STABLE D
Unvegetated
Underlying Straight 4.3 cfs 5.52 ft/s 0.37 ft 0.025 1.68 Ibs/ft2 0.87 Ibs/ft2 1.93 STABLE D
Substrate
BENHAVEN EMERGENCY SERVICES 13
STORM DRAINAGE CALCULATIONS
n=0.012(RCP) n=0.010(HDPE) STORM FREQUENCY-10 YR Al-AREA INLET MH-MANHOLE
RCP-REINFORCED CONCRETE PIPE DI-DROP INLET FES-FLARED END SECTION
HDPE-HIGH DENSITY POLYETHELENE SMOOTH CORE,DOUBLE WALLED PIPE Cl-CURB INLET 1B-JUNCTION BOX
INCREMENTAL GRATE
STRUCTURE DESIGN FLOW-10YR STORM SEWER DESIGN STORM PIPE INVERTS HEADWATER COMMENTS
INLET AREA ELEV.
FROM TO TYPE C. AREA AVG. AREA I Q LENGTH DIA. SLOPE DEPTH OF VELOCITY CAPACITY INV.IN INV.OUT (FT) REQ'D AVAIL. -
.C' (CFS) (ft.) (in.) I%) FLOW(ft) (F/S) FULL(CFS)
5 - DI 0.81 0.48 - - - - - - - - - - - - 289.50 1.45 1.50 15"NYLOPLAST CATCH BASIN W/LIGHT-DUTY GRATE INLINE WITH
PROPOSED ROOF DRAIN.CONNECT ROOF LEADER W/'WYE'CONNECTOR
5 4 HDPE - - 0.81 0.48 7.22 2.79 152.00 12 0.99 0.56 6.15 4.61 1 287.50 286.00 - - - 6"ROOF DRAIN LEADER AT 1%SLOPE
4 MH 290.50 2.45 4.17
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
4 3 HDPE - - 0.81 0.48 7.22 2.79 57.00 12 3.04 0.40 9.35 8.09 285.83 284.10 - - - -
2 - RISER 0.58 0.97 - - - - - - - - - - - - 281.00 1.92 4.15 -
2 1 RCP 0.66 1.45 7.22 0.50 35.00 15 2.43 0.18 4.52 10.94 276.85 276.00 Q=0.5 CFS IS 10-YR SCM DISCHARGE BASED ON HYDRAFLOW MODEL
1 FES
ROOF DRAIN(SEE PLAN FOR SIZES,LOCATIONS AND SLOPE) NOTE:
6"HDPE ROOF DRAIN-APPROX.250 LF 8"HDPE ROOF DRAIN-APPROX 240 LF HDPE PIPE SHALL ADHERE TO THE SPECIFICATIONS OF ASTM D2321 AND BE CERTIFIED BY AN ENGINEER ACCORDING TO HARNETT COUNTY STANDARDS
Annex D :
Bioretention Cell Design
Benhaven Emergency Services
Bioretention Design Sheet
Design Volume (DV) Calculation Using Simple Method
Drainage area, A 62984 SF
Impervious area 34022 SF
R = 0.06 + 0.9 * I�
'10,hCIe Rv = Runoff coefficient(unitless)
1A = Impervious fraction (unitless)
IA 54 %
R 0.54
DV = 3630 # Rc * Rv ` A
Where: DV = Design volume (cu ft)
RD = Design storm depth (in)
A - Drainage area (ac)
A 1.45 Ac
Rp 1 Inch
DV 2834 CF Also called Water Quality Volume (WQV)
Bioretention Design
Ponding depth, H 12.0 inch (12" max)
Depth of filter media, df 2.5 ft (min. depth with IWS)
filtration rate (min. assumed), IR 1.0 in/hr
Required Provided
Surface Area (S.A.), DV/H 2834 2850 SF
Underdrain Design
Infiltration to underdrain,Qf(S.A.x/R) 237.5 ft3/hr [(ie. 2850 SF * 1 in* 1/12 (in/ft)]
=0.066 cfs De. 237.5 ft^3/hr * 1/3600 (hr/sec)]
Underdrain design flow, Q 0.66 cfs [Q= 10 X infiltration]
Roughness factor, n 0.011
Slope of underdrain pipe, S 0.005 ft/ft
Diameter of underdrain, D 6.81 inch D= I S*
Number of Pipes Kequired in the Underdrain JJ
If D is less than #of 4"pipes If D is less than #of 6" pipes
5.13 2 7.84 2
5.95 3 9M 3
6_66 4 10,13 4
7_22 5
7.75 6
8_2D
Provide (5) rows of 4" SCH 40 perforated (4 rows of 3/8" perforations@6" O.C.) PVC pipe @ 0.5%slope
DESIGN OF - - - OUTLET PROTECTION
New York DOT Dissipator Method For Use in Defined Channels
(Source: "Bank and cliaiuiel lining procedures',New York Depanmew of
Transportation_Division of Design and Constnuction_ 1971.)
Guide to Color Key: jUserinputData I Calculated Value lReference Data
Designed By: N Nyaupane Date: 8/30/2023
Checked By: B. Pittman Date: 8/30/2023
Company: Bobbitt Construction Inc.
Project Name: Benhanve Emergency Services 13
Project No.: 22-0011
Site Location (City/Town) Broadway
Culvert Id. 101
Estimation of Stone Size and Dimensions For Culvert Aprons
Step 1) Compute flow velocity V.at culvert or paved channel outlet.
Step 2) For pipe culverts Do is diameter_
For pipe arch, arch and box culverts, and paved channel outlets,
Do=A.where A.=cross-sectional area of flow at outlet.
For multiple culverts,use Do= 1.25 x Do of single culvert_
Velocity(ft/s) 4.52
Opening type Pipe Culvert
Single or multiple openings? Single
Outlet pipe diameter, Do (ft) 1.25
NOTE 1: If opening type is anything other than"Pipe Culvert", Do=Ao
(Cross-sectional area of flow at outlet).
NOTE 2: If multiple openings, Do=1.25 x Do of single culvert.
Step 3) For apron grades of 10%or steeper,use recomniendation�
For next higher zone. (Zones 1 through 6)_
Zone 1 Figure 8.06c
Will apron have >/=10% grade? No
NOTE: For apron slopes equal to or greater than 10%, use next higher Zone in Figure 8.06d to
determine apron length.
Apron length (ft) 5 Figure 8.06d
Determination of Stone Sizes For Dumped Stone Channel Linings
and Revetments
Stone size required(as per NCDOT Riprap Stone Class) Class A(Min. 2", Midrange 4", &Max 6")
Calculations provides minimal appron size, for better protection provide a 6'X8'X18" NCDOT Class B rip rap
Figure 8.06c: Zone Determiniation for Apron Material
25
1
1 1 I I I I 1 1 • 1 • { I 1 1
1 . 6 1 1
I I I I t 1 1 I V I
20 1 1 1 S I 1 # 1111
1 1 1 1 1 • I • I l • 1 1 1 I _ I I I I
1 1 1I 1 1 1 1 1 1 1 11 1 1 1
• 1 1 1 1 1 1 1 1 • 1 1 I f 1 I I I I I I
1 loll 1
I I I 1 11 1 I I I I
1 1 11 1 1 1 1 1 1
�l•� 15CL
1 1
LIL-
ON I
• 1 1 1 _ 7 __ _ 1 1 1 1 1 1 1
' 1 1 1 � 1 ' 1 1 1 ; t • f . I I � 1 I _ � I 1 1 1 1 1 1
� 1 I I I , 1 1 I ••7 1 : 1 1 1 1 I 1 1 1 1 1 1 1 I
Lrr 1 1 I 1 I 1 1 11 I I I
U 1 1 1 1 1 1 1
J 1 Q / 1 k l 1 1 1 =
LU 1 • I 1 1 1 1 1 I 1
1 • 1 1 1 1 1 1 I 1
1 1 1 I I I I Y I 1 1 • I I
1 ! 1 1 1 I I 1 1 1
1 1 I I 1 1 d l • 1 1 1
1 1 1 1 1 1 I 1 1 1 1 I I i 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 3 1 , 1 1 1 1 1 1 1 • 1 1 1 1 1 1 1 1 1 1
I I 1 • 1 1 1 1 1 11 1 1 , 1 1 � 1 1 1 1 1 1 1 1 1 1
1 . 1 ' • 1 � 1 1 1 1 I • I 1 1 1 1 1 � 1 1
1 1 1 • 1 1 1 V I • 1 I 1 1 1 1 1 1 ' ! 1 l i
1 1 1 1 I 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
. 1 1 • 1 . 1 1 1 1 1 1 / l 1 1 1 1 1 1 1 1 ! 1 1
1 I 11 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 I l f 1
O 1 1 1 1 1 1 1 1 1 1 / V 1 1 1 1 1 I 1 1 1 • 1 I I 1
k a' or it.r Or I ( I
0 5' 10, 15, 20' 257
DIAMETER (Ft,)
Figure 8.06c
Figure 8.06d: Length of Apron
LENGTH OF APRON
Z
TO PROTECT TO PREVENT SCOUR
p APRON MATERIAL CULVERT HOLE USE L2ALWAYS
N L2
L1
1 STONE FILLING(FINE) CL.A 3 X D, 4 x D.
2 STONE FILLING(LIGHT) CL.B 3 X Da 6 x De
3 STONE FILLING(MEDIUM) CL. 1 4 X Do 8 x Do
4 STONE FILLING(HEAVY) CL. 1 4 X Do 8 x Do
5 STONE FILLING(HEAVY) CL. 2 5 X Do 10 x D.
6 STONE FILLING(HEAVY) CL 2 6 X Do 10 x D.
7 SPECIAL STUDY REQUIRED(ENERGY DISSIPATORS,STILLING
BASIN OR LARGER SIZE STONE).
Figure 8.06d
.Lidth=3 times pipe dia.(Ed-)
NOTE: For apron slopes equal to or greater than 10%, use next
higher Zone to determine Apron Length.
Annex E :
SCM Operation & Maintenance Manual
OPERATIONS & MAINTENANCE MANUAL
Project. BENHEVEN EMERGENCY SERVICES 13
STORMWATER CONTROL STRUCTURE
BIO-RETENTION AREA
Broadway , NC
Owners:
Address:
Phone Number:
Prepared by:
Date:
Project: BENHEVEN EMERGENCY SERVICES 13
Date Constructed:
Location:
Contractor: (List below)
Landscape Contractor
Grading Contractor
OPERATIONS AND MAINTENANCE MANUAL
BENHEVEN EMERGENCY SERVICES 13 ORMWATER BIO-RETENTION AREA
This manual establishes procedures for maintenance and operation of the [project
name] Bio-retention area (s) in accordance with the Harnett County guidelines as set forth
in the LDO Section 4.4.6
MAINTENANCE OF BIO-RETENTION AREAS
Vegetation—The drainage areas have a ground cover of warm season grasses or
fescue, which if properly maintained will prevent erosion of the embankment and
provide an easy surface for inspection. The grass will be most difficult to obtain in the
area subject to water level fluctuation.
Re-Seeding—Periodic re-seeding may be required to establish grass on areas where
seed did not take or have been destroyed. Before seeding, a one time fertilizer
Rev 1/2011 1
application (12-12-12) should be applied at a minimum rate of 12 to 15 pounds per
1 ,000 SF. The seed should be evenly sown at a rate of three pounds per 1 ,000 SF.
The seed should be covered with soil to the depth of approximately Y4". Immediately
following the planting, the area should be mulched with straw and tacked.
Trees and Shrubs—Trees, shrubs and other landscape vegetation should be permitted
only as shown on the approved planting plan. The vegetation should be kept healthy
and vibrant. If a tree or shrub dies it should be removed and replaced with another tree
or shrub from the same species (attach plant list).
Mowing—Grass mowing, brush cutting and removal of weed vegetation will be
necessary for the proper maintenance of the areas. All area slopes and vegetation
should be mowed when the grass exceeds 8" in height. Acceptable methods include
the use of weed whips or power brush cutters and mowers.
Erosion—Erosion occurs when the water concentrates causing failure of the vegetation
or when vegetation dies and sets up the environment for rill erosion and eventually
gullies from the stormwater runoff. The areas should be inspected. Proper care of
vegetative areas that develop erosion is required to prevent more serious damage to
the site. Rills and gullies should be filled with suitable soil compacted and then seeded.
Methods described earlier on vegetation should be used to properly establish the grass
surface. Where eroded areas are detected, the cause of the erosion should be
addressed to prevent a continued maintenance problem. Frequently, problems result
from the concentration of runoff to one point of the bio-retention area instead of a
uniform distribution of runoff usually on slopes and at the inflow points. This can be
corrected by reshaping, to more evenly distribute the runoff to areas not experiencing
erosion problems.
Rodent Control—Generally in this urban environment, rodents are not a problem.
Rodents such as groundhogs, muskrats and moles are attracted to moist, wet areas
and can be quite dangerous to structural integrity and proper performance of the
earthwork and drainage. Groundhogs and muskrats thrive on burrowing into the
manmade earthwork, which become pathways for seepage. In the event that burrows
are detected within the bio-retention area, the rodents should be dealt with by removal.
Trash and Debris--Trash acts as a barrier to stormwater infiltration and attracts
unwanted pests. The bio-retention area should be kept clear of debris such as loose
bottles, cans, food containers and other forms of rubbish. The area should be cleared
of debris as needed.
MAINTENANCE OF SPILLWAYS AND CONTROL STRUCTURE
Inspection of Conduits--Conduits should be inspected thoroughly once a year. Conduits
should be visually inspected at the joints. Pipes should be inspected for proper
alignment (sagging), elongation and displacement at joints, cracks, leaks, surface wear,
loss of protective coating, corrosion and blocking. Problems with conduits most often
occur at joints and special attention should be given to them during inspection. Joints
should be checked for gaps caused by elongation or settlement and loss of joint filler
material. Open joints can permit erosion of the earthwork and possibly the piping of soil
Rev 1/2011 2
material through the joints. A depression in the soil surface over the pipe may be signs
that soil is being removed from around the pipe. The underdrains should be inspected to
ensure that they are functional and allowing the bioretention area to drain.
OPERATION
Record Keeping--Operation of bio-retention area should include recording of the
following:
Annual Inspection Reports--A collection of written inspection reports should be
kept on record. Inspection by a qualified professional is required annually.
Copies should be provided to the Harnett County Stormwater Management Section
of the Engineering Department on the approved form.
Observations--All observations should be recorded.
Maintenance--Written records of maintenance and/or repairs should be recorded.
Other Operational Procedures--The owner should maintain a complete and up-to-date
set of plans (as-built drawings) and all changes made to the bio-retention area over time
should be recorded on the as-builts. Do not pile snow on top of bioretention area.
Sedimentation and Dredging--Sedimentation from on-site and off-site soils will
eventually result in the clogging of drainage conduits and will have to be removed. The
frequency of this sediment removal can be reduced by ensuring that the site areas
around the building be stabilized with a vegetative ground cover such that it restrains
erosion. Do not drive heavy equipment into the bioretention area. Remove and replace
vegetation, sediment, mulch, etc. by hand or have equipment that can reach from edge
of bioretention area.
Example Maintenance Schedule for Bio-retention Areas
Description Method Frequency Time of year
SOIL
Inspect and repair erosion Visual Monthly All year
ORGANIC LAYER
Remulch any void area By hand As needed As needed
Remove previous mulch By hand Once every Spring
layer before applying new 2-3 years
layer (optional)
Any additional mulch added By hand As needed As needed
PLANTS
Removal and replacement See planting Twice a year As directed by
of all dead and diseased specifications landscaper
vegetation considered
beyond treatment
Treat all diseased trees Mechanical N/A Varies, dependent
and shrubs or by hand on insect or disease
Rev 1/2011 3
infestation
Removal of cattails and By hand or As needed As needed
other invasive species through hand
application of
herbicide
Watering of plant material By hand Daily Immediately after
shall take place at the end completion of project
of each day for fourteen
consecutive days and after
planting is completed
Remove support stakes and By hand As needed As needed
wires within 6 months of
establishment
Detail of Planting Guide for each Bio-Retention Basin
BIO-RETENTION INSPECTION CHECKLIST
Date:
Rev 1/2011 4
Time:
BENHEVEN EMERGENCY SERVICES 13 _ Broadway NC
Check/Circle Condition Observations Actin — [Action — Action --
Noted Re air Monitor Investig ative
U/S Sloe Type:
Vegetation/Riprap
Rodent burrows
Crest Type:
Ruts/erosion
Cracks/settlement
Poor alignment
D/S Sloe Type:
Vegetation/erosion
Rodent burrows
Sloughs/slides/cracks
Seepage/wetness
Pool Type:
Ground cover
Sedimentation
Abutment Type:
Vegetation/erosion
Slough/slides/cracks
Seepage/wetness
General Comments, Sketches & Field Measurements
Rev 1/2011 5
PERODIC INSPECTION, OPERATION & MAINTENANCE RECORDS
BENHEVEN EMERGENCY SERVICES 13 Broadway , NC
Date Time Rain Weather General Observations Recorded By
Conditions or Comments
Date Maintenance Performed Comments Recorded
By
Date Equipment Operated Comments Recorded
By
Rev 1/2011 6