HomeMy WebLinkAbout20041488 Ver 6_Stormwater Info_200910060"h" "
DEPARTMENT OF PUBLIC UTILITIES
POST OFFICE Box 2263
SMITHFIELD, N.C. 27577
(919) 989-5075
September 21, 2009
The Stephens Center, Inc.
319 Chapanoke Road
Raleigh, NC 27603
Re: Winston Pointe Phase 1- Access Road to Active Recreation Site
Stormwater Management Statement and Plan
Dear Mr. Stephens:
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OCT _6 2009
DENR - WATER QUALITY
MM IM AND STORMWATER BRANCH
We have reviewed the Stormwater Management Plan and calculations submitted for Winston
Pointe Phase 1. Phase 1 consists of an active recreation site and an access road to the
recreation site. This road will also serve as a secondary access to the existing Winston
Pointe Phase lA and 1B. Based upon the information submitted, the stormwater management
plan has been approved with the following stipulations:
1. Please be advised that the culverts and storm sewer system located within the proposed
future public right-of-way has not been reviewed. It is the developer's and design
professional's responsibility to ensure that the system is designed adequately.
2. Please provide a copy of the recorded restrictive covenants noting who will be
responsible for maintenance of all drainage facilities located outside the proposed
NCDOT right of way.
3. Prior to recordation of the Final Plat, please provide a driveway culvert size chart
(8.5"x11") sealed by the engineer.
4. Prior to recordation of the Final Plat, please provide a stormwater certification stating that
all stormwater facilities were constructed in accordance with the approved stormwater
management plan.
5. Please indicate all drainage easements, access easements to stormwater BMPs, riparian
buffers, jurisdictional wetlands, and flood hazard areas on the Final Plat.
A copy of this letter will be forwarded to the Planning Office for their files. If you have any
questions or need additional information, please contact me at (919) 209-8333 or by email at
iamie.guerrero(a?iohnstonnc.com.
Sincerely,
/Ow- 9L- -r
Jamie Guerrero, PE
Stormwater Administrator
cc: Berry Gray -- Planner
Chandra Coats, PE - Utilities and Environmental Engineer
Michael Stewart, PE - Stewart-Proctor PLLC
Printed on reeyded paper
STORM WATER
MANAGEMENT
FOR
WINSTON POINTE
t-44.,
SEAL
22024
SUBDIVISION NAME: Winston Pointe
LOCATION: Between Winton Road (SR 1550) and Winston Pointe Drive.
P.U.D. zoning district (Clayton Township)
DEVELOPER: The Stephens Center, Inc
319 Chapanoke Road
Raleigh, NC 27603
CONSULTANT: STEWART-PROCTOR PLLC
319 Chapanoke Road, Suite 106
Raleigh. NC 27603
PHONE: (919) 779-1855
FAX: (919) 779-1661
GENERAL INFORMATION
The total area for Winston Pointe Phase 1 is 19.36 acres. The purpose for Phase 1 will be
for the construction of active recreation area as required by Town of Clayton. The
proposed road will connect the existing roads Winston Pointe Drive and Winston Road
S.R.1550. This in turn will provide another access for the existing subdivision as well as
access for future phases. Currently there is only one access now which is through Valley
Drive onto Guy Road S.R.1551.
IMPERVIOUS AREA
Approximately 4,035 linear feet of street will be created, with a Right of Way width of 50
feet. Grass lined ditches will be installed to direct drainage to easements. The expected
imperviousness is:
Roadway: 4035 IS x 20' = 80,700 sf
Total: 2.32 ac. = 12% total impervious area for Phase 1
Proposed impervious area = 2.32 ac./ 19.36 ac. = 12.0%
Allowable impervious area = 19.36 ac. x 12% = 2.32 ac. or 101,199 sf
The design will meet the maximum allowable design impervious surface limits.
However, voluntary measures will be implemented to improve the effect of
the future development on the surrounding drainageways. These include ending
constructed swales with vegetated level spreaders whenever possible, careful
limitation on clearing limits, and construction of retention pond for future
impervious area.
PEAK RUNNOFF REDUCTION
One pond area is shown on plans. This pond is designed to attenuate
the peak runoff of the future commercial impervious. See storm water
calculation.
LAND DEDICATION
Not required.
NITROGEN LOADING ESTIMATION
Use Method 2
(1) (2) (3) (4)
Type of Land Cover Area TN Export Coeff. TN Export from
(acres) (lbs/ac/yr) use
(lbs/yr)
Permanently preserved 2.09 0.6 1.25
Undisturbed open space
Permanently preserved 14.95 1.2 17.94
Managed open space
Impervious surface 2.32 21.2 49.18
TOTAL 19.36 - 68.39
The total N-loading from the site is (68.39 lbs/yr)/19.36ac = 3.53 lbs/ac. This
does not exceed the 3.6 lbs/ac limit: therefore nitrogen offset payment or water
quality BMP's will not be required.
EXISTING DRAINAGEWAYS
There are three internal drainage areas on this site all are unnamed tributaries
to White Oak Creek. These streams have been identified by NCDENR and
are shown on plans. There are 50' buffer placed on each side of the drainageways
and one intermitted crossing is planned.
UPSTREAM AND DOWNSTREAM DRAINAGE STRUCTURES
The majority of the drainage areas for the internal drainageways are contained
onsite as seen on the accompanying USGS Quad Map. The construction of the
roadway comprises an insignificant portion of the drainage of White Oak Creek
and therefore is not expected to have an impact on White Oak Creek or the FEMA
study associated with it.
STORM WATER SUPPLEMENT DEVICE #3
PURPOSE: TO RELEASE POST DEVELOPMENT RUNOFF AT A
RATE NOT TO EXCEED PRE-DEVELOPMENT RUNOFF. PROVIDE
STORAGE AND WATER SURFACE AREA TO PROVIDE FOR T.S.S.
AND NITROGEN LOADING REDUCTION.
PLAN: - COMPUTE SURFACE AREA NEEDED
- COMPUTE VOLUME OF I" FLUSH
- COMPUTE TARGET RUNOFF RATE.
-COMPUTE RUNOFF RATE WITH DESIGN PLAN.
-DESIGN FEATURES OR CONTROLS TO MEET
PURPOSE AND PROVIDE REQUIRED STORAGE.
OUTLET DEVICE #1
SURFACE AREA REQUIRED
ESTIMATED IMPERVIOUS SURFACE PERCENTAGE FOR TOTAL DRAINAGE
AREA TO THE STORAGE DEVICE IS 70%.
FOR A 5 FOOT DEEP PERMANT POOL THE SURFACE AREA REQUIRED
WOULD BE 2.07% OF THE TOTAL DRAINAGE AREA TO THE DEVICE.
IF:
D.A. TOTAL = 21.7 ACRE
THEN:
2.07% OF 21.7 ACRES = 19,567 SQUARE FEET
SURFACE AREA PROVIDED FOR PERMANENT POOL = 19,670 SQUARE FEET
VOLUME REQUIRED
VOLUME CALCULATED BY SIMPLE METHOD DESCRIBED BY THE NCDWQ
BMP DESIGN MANUAL.
Rv = 0.05 + 0.9 * Ia
la = 15.2ac imp / 21.7ac d.a. = 0.70
Rv=0.05+0.9 * 0.70=0.665
V = 3630 * 1" * 0.665 * 21.7 = 52,383Ft
VOLUME REQUIRED = 52,383FO
VOLUME PROVIDED = 54,093Ft3
STAGE 230' ABOVE WATER SURFACE
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RETENTION DEVICE #1
1" DRAWDOWN
TIME
INFLOW
STORAGE
STAGE
OUTFLOW R1.7511
outlet
MIN CFS CU. FT. FT CFS
0 0 73225 2.75 0.5 0.46
60 0.00 71560.52 2.6 0.4 0.45
120 0.00 69950.63 2.5 0.4 0.44
180 0.00 68357.63 2.5 0.4 0.44
240 0 66781.54 2.4 0.4 0.43
300 0.00 65222.39 2.4 0.4 0.43
360 0.00 63680.21 2.3 0.4 0.42
420 0.00 62155.04 2.3 0.4 0.42
480 0 60646.90 2.2 0.4 0.41
540 0.00 59155.83 2.2 0.4 0.41
600 0.00 57681.86 2.1 0.4 0.40
660 0.00 56225.02 2.1 0.4 0.40
720 0 54785.34 2.0 0.4 0.40
780 0.00 53362.86 2.0 0.4 0.39
840 0.00 51957.62 1.9 0.4 0.39
900 0.00 50569.64 1.9 0.4 0.38
960 0 49198.97 1.8 0.4 0.38
1020 0.00 47845.63 1.8 0.4 0.37
1080 0.00 46509.68 1.7 0.4 0.37
1140 0.00 45191.14 1.7 0.4 0.36
1200 0 43890.05 1.6 0.4 0.36
1260 0.00 42606.45 1.6 0.4 0.35
1320 0.00 41340.39 1.5 0.3 0.35
1380 0.00 40091.90 1.5 0.3 0.34
1440 0 38861.02 1.5 0.3 0.34
1500 0.00 37647.79 1.4 0.3 0.33
1560 0.00 36452.27 1.4 0.3 0.33
1620 0.00 35274.48 1.3 0.3 0.32
1680 0 34114.49 1.3 0.3 0.32
1740 0.00 32972.32 1.3 0.3 0.31
1800 0.00 31848.04 1.2 0.3 0.31
1860 0.00 30741.68 1.2 0.3 0.30
1920 0 29653.30 1.1 0.3 0.30
1980 0.00 28582.95 1.1 0.3 0.29
2040 0.00 27530.67 1.1 0.3 0.29
2100 0.00 26496.52 1.0 0.3 0.28
2160 0 25480.55 1.0 0.3 0.28
2220 0.00 24482.83 1.0 0.3 0.27
2280 0.00 23503.40 0.9 0.3 0.27
2340 0.00 22542.32 0.9 0.3 0.26
2400 0 21599.65 0.8 0.3 0.26
2460 0.00 20675.46 0.8 0.3 0.25
2520 0.00 19769.80 0.8 0.2 0.25
2580 0.00 18882.75 0.7 0.2 0.24
2640 0 18014.36 0.7 0.2 0.24
2700 0.00 17164.71 0.7 0.2 0.23
2760 0.00 16333.87 0.7 0.2 0.23
2820 0.00 15521.91 0.6 0.2 0.22
2880 0 14728.90 0.6 0.2 0.21
2940 0.00 13954.94 0.6 0.2 0.21
3000 0.00 13200.08 0.5 0.2 0.20
3060 0.00 12464.43 0.5 0.2 0.20
3120 0 11748.07 0.5 0.2 0.19
3180 0.00 11051.08 0.5 0.2 0.19
3240 0.00 10373.57 0.4 0.2 0.18
3300 0.00 9715.63 0.4 0.2 0.18
3360 0 9077.37 0.4 0.2 0.17
3420 0.00 8458.89 0.4 0.2 0.17
3480 0.00 7860.30 0.3 0.2 0.16
3540 0.00 7281.72 0.3 0.2 0.16
3600 0 6723.28 0.3 0.1 0.15
3660 0.00 6185.11 0.3 0.1 0.14
3720 0.00 5667.34 0.2 0.1 0.14
3780 0.00 5170.13 0.2 0.1 0.13
3840 0 4693.63 0.2 0.1 0.13
3900 0.00 4238.00 0.2 0.1 0.12
3960 0.00 3803.43 0.2 0.1 0.11
4020 0.00 3390.11 0.2 0.1 0.11
4080 0 2998.24 0.1 0.1 0.1
4140 0.00 2628.04 0.1 0.1 0.1
4200 0.00 2279.78 0.1 0.1 0.1
4260 0.00 1953.71 0.1 0.1 0.1
4320 0 1650.15 0.1 0.1 0.1
4380 0.00 1369.44 0.1 0.1 0.1
4440 0.00 1111.96 0.1 0.1 0.1
4500 0.00 878.16 0.0 0.1 0.1
4560 0 668.58 0.0 0.1 0.1
4620 0.00 483.88 0.0 0.0 0.0
COMBINATION STORM WATER CALCULATIONS
I yr STORM
DETERMINE PRE DEVELOPMENTAL CONDITIONS:
DISCHARGE BY SCS METHOD AS DESRIBED IN THE Tr-55 MANUAL
Qp=quXAmXQ*
TIFTRRMTMF RXTRTTMft (n VAT.TTF. FOR OsTTF.
SOIL CLASS USE AREA ac) Cn
B FAIR PASTURE 3.60 69
B FAIR WOODS 18.1 60
[(3.60 X 69) + (18.1 X 60)) / 21.7 = 62
Cn PRE = 62
DETERMINE RUNOFF DEPTH AND PEAK FLOW FOR EXISTING CONDITIONS
FOR THE I yr / 3" EVENT
P - 3"
A = 21.7ac - 0.034mi2
S = [1000/Cn]-10
= 6.13
Q* = [(P-0.2S)2] / (P +0.8S)
Q* = 0.40"
Ia = 1.226
IaA/P = 0.41
Tp = CALC DETAILS ATTACHED
SHEET FLOW = 0.87hr
SHALLOW FLOW = 0.07hr
CHANNEL FLOW = 0.02hr
Tp = 0.96hr
Qu = 245 (EXHIBIT 4-II)
Qp = 245(0.034)0.40 = 3.33 cfs
PEAK FLOW FOR THE 1 YEAR EVENT = 3.33 cfs
DETERMINE POST DEVELOPMENTAL CONDITIONS:
DISCHARGE BY SCS METHOD AS DESRIBED IN THE Tr-55 MANUAL
3" EVENT
Qp=quXAmXQ*
DETERMINE PROPOSED Cn VALUE FOR SITE
SOIL CLASS USE AREA ac Cn
B FAIR PASTURE 4.50 69
B IMPERVIOUS 15.19 98
B FAIR WOODS 2.01 60
[(4.50 X 69) + (15.19 X 98) + (2.01 X 60)] / 21.7 = 89
Cn POST = 89
DETERMINE RUNOFF DEPTH AND PEAK FLOW FOR PROPOSED CONDITIONS
FOR THE 1 yr / 3" EVENT
P = 3"
A = 21.7ac - 0.034mi2
S = [1000/Cn]-10
= 1.24
Q* = [(P-0.2S)2] / (P +0.8S)
Q* = 1.90"
la = 0.248
IaA/P = 0.083
Tp - CALC DETAILS ATTACHED
SHEET FLOW = 0.87hr
SHALLOW FLOW = 0.07hr
CHANNEL FLOW = 0.02hr
Qu = 375 (EXHIBIT 4-II)
Tp = 0.96hr
Qp = 375(0.034)1.90 = 24.23 cfs
PEAK FLOW FOR THE 1 YEAR EVENT = 24.23 cfs
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COMBINATION STORM WATER CALCULATIONS
l0yr STORM
DETERMINE PRE DEVELOPMENTAL CONDITIONS:
DISCHARGE BY SCS METHOD AS DESRIBED IN THE Tr-55 MANUAL
Qp=quXAmXQ*
T)FTF.RMTNF. F.XTRTTNCT C'n VA1.1 TF, FOR SITE
SOIL CLASS USE AREA ac Cn
B FAIR PASTURE 3.60 69
B FAIR WOODS 18.1 60
[(3.60 X 69) + (18.1 X 60)] / 21.7 = 62
Cn PRE = 62
DETERMINE RUNOFF DEPTH AND PEAK FLOW FOR EXISTING CONDITIONS
FOR THE IOyr / 5.38" EVENT
P = 5.38"
A = 21.7ac - 0.034mi2
S = [1000/Cn]-10
= 6.13
Q* = [(P-0.25)2] / (P +0.8S)
Q* = 1.68"
Ia = 1.226
IaA/P = 0.23
Tp = CALC DETAILS ATTACHED
SHEET FLOW = 0.87hr
SHALLOW FLOW = 0.07hr
CHANNEL FLOW = 0.02hr
Tp = 0.96hr
Qu = 340 (EXHIBIT 4-II)
Qp = 340(0.034)1.68 = 19.42 cfs
PEAK FLOW FOR THE 10 YEAR EVENT = 19.42 cfs
DETERMINE POST DEVELOPMENTAL CONDITIONS:
DISCHARGE BY SCS METHOD AS DESRIBED IN THE Tr-55 MANUAL
5.38" EVENT
Qp=quXAmXQ*
rnFTFRMTNF PRnPO4FIn C:n VALITF. FOR SITF_,
SOIL CLASS USE AREA ac Cn
B FAIR PASTURE 4.50 69
B IMPERVIOUS 15.19 98
B FAIR WOODS 2.01 60
[(4.50 X 69) + (15.19 X 98) + (2.01 X 60)1/ 21.7 = 89
Cn POST = 89
DETERMINE RUNOFF DEPTH AND PEAK FLOW FOR PROPOSED CONDITIONS
FOR THE IOyr / 5.38" EVENT
P = 5.38"
A = 21.7ac - 0.024mi2
S = [1000/Cn]-10
= 1.24
Q* = [(P-0.25)2] / (P +0.8S)
Q* = 4.13"
la = 0.248
IaA/P = 0.05
Tp = CALC DETAILS ATTACHED
SHEET FLOW = 0.87hr
SHALLOW FLOW = 0.07hr
CHANNEL FLOW = 0.02hr
Qu = 375 (EXHIBIT 4-II)
Tp = 0.96hr
Qp = 375(0.034)4.13 = 52.66 cfs
PEAK FLOW FOR THE 10 YEAR EVENT = 52.66 cfs
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COMBINATION STORM WATER CALCULATIONS
100yr STORM
DETERMINE PRE DEVELOPMENTAL CONDITIONS:
DISCHARGE BY SCS METHOD AS DESRIBED IN THE Tr-55 MANUAL
Qp=quXAmXQ*
DETERMINE EXISTING Cn VALUE FOR SITE
SOIL CLASS USE AREA (ac) Cn
B FAIR PASTURE 3.60 69
B FAIR WOODS 18.1 60
[(3.60 X 69) + (18.1 X 60)1/ 21.7 = 62
Cn PRE = 62
DETERMINE RUNOFF DEPTH AND PEAK FLOW FOR EXISTING CONDITIONS
FOR THE 100yr / 8" EVENT
P = 811
A = 15.5ac - 0.034mi2
S = [1000/Cn]-10
= 6.13
Q* = [(P-0.2S)2] / (P +0.8S)
Q* = 3.56"
Ia = 1.226
IaA/P = 0.15
Tp = CALC DETAILS ATTACHED
SHEET FLOW = 0.87hr
SHALLOW FLOW = 0.07hr
CHANNEL FLOW = 0.02hr
Tp = 0.96hr
Qu = 350 (EXHIBIT 4-II)
Qp = 350(0.034)3.56 = 42.36 cfs
PEAK FLOW FOR THE 100 YEAR EVENT = 42.36 cfs
DETERMINE POST DEVELOPMENTAL CONDITIONS:
DISCHARGE BY SCS METHOD AS DESRIBED IN THE Tr-55 MANUAL
8" EVENT
Qp=quXAmXQ*
DETERMINE PROPOSED Cn VALUE FOR SITE
SOIL CLASS USE AREA ac Cn
B FAIR PASTURE 4.50 69
B IMPERVIOUS 15.19 98
B FAIR WOODS 2.01 60
[(4.50 X 69) + (15.19 X 98) + (2.01 X 60)] / 21.7 = 89
Cn POST = 89
DETERMINE RUNOFF DEPTH AND PEAK FLOW FOR PROPOSED CONDITIONS
FOR THE 100yr / 8" EVENT
P = 8„
A = 21.7ac - 0.034mi2
S = [1000/Cn]-10
= 1.24
Q* = [(P-0.2S)2] / (P +0.8S)
Q* = 6.68"
Ia = 0.248
IaA/P = 0.03
Tp = CALC DETAILS ATTACHED
SHEET FLOW = 0.87hr
SHALLOW FLOW = 0.07hr
CHANNEL FLOW = 0.02hr
Qu = 375 (EXHIBIT 4-II)
Tp = 0.96hr
Qp = 375(0.034)6.68 = 85.17 cfs
PEAK FLOW FOR THE 100 YEAR EVENT = 85.17 cfs
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SUMMARY DEVICE #I
OUTLET WILL CONSEST OF ONE 72in DIAMETER H.D.P.E.
OUTLET RISER PIPE WITH HOLES BORED INTO IT. EVERY HALF
FOOT VERTICALY THERE WILL BE A ROW OF 20 X 1 inch RADIUS
HOLES SET ROUGHLY 7.5inchs ON CENTER. THE ROWS WILL BE
STAGGARED. THE OUTLET BARRELL WILL BE A 36inch H.D.P.E.
PEAK FLOWS FROM THE STORMS:
1 YEAR:
PRE: 3.33 cfs
POST: 24.23 cfs
DEVICE: 3.2 cfs
10 YEAR:
PRE: 19.42 cfs
POST: 52.66 cfs
DEVICE: 8.1 cfs
THE 100 YEAR STORM IS PASSED THROUGH A DESIGNED
SPILLWAY TO CARRY THE 100 YEAR FLOW AWAY FROM THE
DEVICE.
EMERGENCY SPILLWAY DESIGN
Qioo = 85.17 cfs
Q = CLH32
SOLVING FOR L LEAVES L= Q/(CH3')
L = 85.17/(3)1'-'= 28.39
MAKE L = 29'
EMERGENCY SPILLWAY IS 1' HIGH WITH AN OPENING 29' WIDE.
ELEVATIONS:
PERMENANT POOL: FROM 291' TO 296'
1" RAINFALL EVENT STOARAGE: FROM 296' TO 298.5'
STORMWATER EVENT STORAGE: FROM 298.5' TO 299.5'
SPILLWAY ELEVATIONS FROM 301.0' TO 302.0'
TOP OF DAM: 302.0'
GeD