20070295 Ver 6_7.01 SCM C - Wet Pond Design_20191220

Holding Village - North Lake STORMWATER CONTROL MEASURE C Maria Torres, E.I.
RAP-19000 SSFxn Above NP Daniel Gunter
12.16.2019
STAGE -STORAGE FUNCTION - ABOVE NORMAL POOL
Average
Incremental
Accumulated
Estimated
Contour
Contour
Contour
Contour
Stage
Contour
Stage
Area
rera` '
t.iQA
Volume
Volume
w/ S-S Fxn
(feet)
(feet)
(SF)
(CF)
(CF) (feet)
312.00
0.00
10,254
313.00
1.00
12,376
11315
11315
11315
1.02
314.00
2.00
14,624
13500
13500
24815
1.96
316.00
4.00
17,821
16223
32445
57260
3.95
318.00
6.00
21,243
19532
39064
96324
6.11
Storage vs. Stage
120000
100000
y=11112x1.1936
80000 R2 = 0.9994
U
60000
;a
0) 40000
20000
0
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00
Stage (feet)
Ks = 11112
b = 1.1936

Holding Village - North Lake STORMWATER CONTROL MEASURE C Maria Torres, E.I.
RAP-19000 SSFxn Main Pool Daniel Gunter
12.16.2019
STAGE -STORAGE FUNCTION - MAIN POOL
Average
Incremental
Accumulated
Estimated
Contour
Contour
Contour
Contour
Stage
Contour
Stage
Area
Area
Volume
Volume
w/ S-S Fxn
(feet)
(feet)
(SF)
(SF)
(CF)
(CF)
(feet)
306.50
-0.50
2,823
Sediment
Storage
7
307.00
0.00
3,162
308.00
1.00
3,898
3530
3530
3530
1.01
310.00
3.00
5,602
4750
9500
13030
2.90
311.50
4.50
7,035
6319
9478
22508
4.52
312.00
5.00
1 7,528_1
7282
3641 1
26149 1
5.10
*surface area and volume used for avg. depth calculation
Storage vs. Stage
30000
25000 y = 3485.7x1 z373
R2 = 0.999
LL 20000
U
15000
;a
0) 10000
5000
0
0.00 1.00 2.00 3.00 4.00 5.00 6.00
Stage (feet)
Ks = 3486
b = 1.2373

Holding Village - North Lake STORMWATER CONTROL MEASURE C Maria Torres, E.I.
RAP-19000 SSFxn Foreboy Daniel Gunter
12.16.2019
REBAY
Average Incremental Accumulated Estimated
Contour Contour Contour Contour Stage
Contour Stage Area Area Volume Volume w/ S-S Fxn
308.50
-0.50
623
Sediment Storage
309.00
0.00
794
310.00
1.00
1,193 994
994 994 1.00
311.50
2.50
1,918 1556
2333 3327 2.48
312.00
3.00
2,170 2044
1022 4349 3.02
Storage vs. Stage
5000
4500
4000 y
= 991.31 x1.3358
R2 = 0.9998
3500
U
3000
2500
`0
2000
1500
1000
500
0
0.00
1.00 2.00 3.00 4.00
Stage (feet)
KS = 991.3
b = 1.3358

Holding Village - North Lake STORMWATER CONTROL MEASURE C
RAP-19000 Volume Calculation
TOTAL VOLUME OF FACILITY
Volume of Main Pool below Normal Pool=
26,149
cf
Volume of Forebay below Normal Pool=
4,349
cf
Total Volume Below Normal Pool =
30,497
cf
Total Volume Above Normal Pool=
96,324
cf
Total Volume of Facility =
126,821
cf
FOREBAY PERCENTAGE OF PERMANENT POOL -VOLUME
Per NCDEQ Minimum Design Criteria, the foreboy volume should equal
approximately 15-20% of the main pool volume.
Total Main Pool Volume = 26,149 cf
Provided Forebay Volume = 4,349 cf
Provided Forebay Volume % = 17%
AVERAGE DEPTH OF MAIN POOL
Main Pool Volume at Normal Pool =
26,149
cf
Main Pool Area at Normal Pool =
7,528
sf
Average Depth =
3.47
ft
Maria Torres, E.I.
Daniel Gunter
12.16.2019

Holding Village - North Lake STORMWATER CONTROL MEASURE C Maria Torres, E.I.
RAP-19000 Surface Area Calculation Daniel Gunter
12.16.2019
WET DETENTION BASIN SUMMARY
Enter the drainage area characteristics =_>
Total drainage area to pond = 9.45 acres
Total impervious area to pond = 5.07 acres
Note The basin must be sized to treat all impervious surface runoff draining into the pond, not just the impervious
surface from on -site development.
Drainage area = 9.45 acres @ 53.6% impervious
Estimate the surface area required at pond normal pool elevation ==>
Wet Detention Basins are based on an minimum average depth of
= 3.47
3.0
3.47
4.0
Lower Boundary => 50.0 1.79
1.51
Site % impervious => 53.6 1.90
1.76
1.60
Upper Boundary => 60.0 2.09
1.77
Therefore, SA/DA required =
1.76
Surface area required for main pool at normal pool =
7,243
ft2
=
0.17
acres
Surface area provided for main pool at normal pool =
7,528
ft2
feet (Calculated)

Holding Village - North Lake STORMWATER CONTROL MEASURE C
RAP-19000 WQV Calculation
DETERMINATION OF WATER QUALITY VOLUME
WQ v = (P)(R v)(A)/12
where,
WQv= water quality volume (in acre-ft)
Rv= 0.05+0.009(I) where I is percent impervious cover
A = area in acres
P = rainfall (in inches)
Input data:
Total area, A =
9.45
acres
Impervious area =
5.07
acres
Percent impervious cover, I =
53.6
%
Rainfall, P =
1.00
inches
Calculated values:
Rv=
0.53
WQV=
0.42
acre-ft
=
18273
cf.
ASSOCIATED DEPTH IN POND
WQV= 18273 cf.
Stage/Storage Data:
Ks =
11112
b =
1.194
Zo =
312.00
Volume in 1" rainfall =
18273 cf.
Calculated values:
Depth of WQv in Basin = 1.52 ft
= 18.20 inches
Elevation = 313.52 ft
Maria Torres, E.I.
Daniel Gunter
12.16.2019

Holding Village - North Lake STORMWATER CONTROL MEASURE C Maria Torres, E.I.
RAP-19000 WQV Drawdown Calculation Daniel Gunter
12.16.2019
DRAWDOWN ORIFICE DESIGN
D orifice =
2.25 inch
# orifices =
1
Ks =
11112
b =
1.1936
Cd orifice =
0.60
Normal Pool Elevation =
312.00 feet
Volume @ Normal Pool =
0 cf
Orifice Invert =
312.00 feet
WSEL @ 1" Runoff Volume =
313.52 feet
WSEL
(feet)
Vol. Stored
(cf)
Orifice Flow
(cfS)
Avg. Flow
(cfS)
Incr. Vol.
(cf)
Incr. Time
(sec)
313.52
18273
0.158
313.39
16425
0.151
0.155
1848
11952
313.26
14609
0.143
0.147
1815
12341
313.13
12830
0.135
0.139
1779
12792
313.00
11090
0.126
0.131
1740
13322
312.87
9393
0.117
0.122
1697
13960
312.74
7745
0.107
0.112
1648
14751
312.61
6152
0.095
0.101
1593
15776
312.48
4624
0.082
0.089
1528
17192
312.35
3174
0.067
0.075
1449
19369
312.22
1827
0.047
0.057
1347
23541
Drawdown Time = 1.79 days
By comparison, if calculated by the average head over the orifice
(assuming average head is one-third the total depth), the result would be:
Average driving head on orifice = 0.474 feet
Orifice composite loss coefficient = 0.600
Cross -sectional area of siphon = 0.028 sf
Q = 0.0916 cfs
Drawdown Time = Volume / Flowrate / 86400 (sec/day)
Drawdown Time = 2.31 days