20070295 Ver 6_6.01 SCM B - Wet Pond Design_20191220

Holding Village - North Lake STORMWATER CONTROL MEASURE B Maria Torres, E.I.
RAP-19000 SSFxn Above NP Daniel Gunter
12/16/2019
- BOVE NORMAL 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)
264.00
0.00
13,491
265.00
1.00
16,556
15024
15024
15024
1.00
266.00
2.00
18,086
17321
17321
32345
2.00
268.00
4.00
19,303
18695
37389
69734
4.00
270.00
6.00
20,501
19902
39804
109538
6.01
KS = 15012
b = 1.1086

Holding Village - North Lake STORMWATER CONTROL MEASURE B
Maria Torres, E.I.
RAP-19000
SSFxn Main Pool
Daniel Gunter
12/16/2019
N - MAIN POOL
Estimated
Average Incremental Accumulated
Contour
Contour Contour Contour
Stage
Contour Stage Area
Area Volume Volume
w/ S-S Fxn
(feet) (feet) (SF)
(SF) (CF) (CF)
(feet)
257.00
-0.50
4,791
Sediment Storage
257.50 0.00
5,088
258.00
0.50
5,392
5240
2620 2620
0.51
260.00
2.50
6,779
6086
12171 14791
2.38
262.00
4.50
8,253
7516
15032 29823
4.44
264.00
6.50
9,855 j
9054
18108
47,931
6.78
Isurtace area and volume used for avg. depth calculation
Ks = SS82
b = 1.1237

Holding Village - North Lake STORMWATER CONTROL MEASURE B Maria Torres, E.I.
RAP-19000 SSFxn Foreboy Daniel Gunter
12/16/2019
STAGE -STORAGE FUNCTION - FOREBAY
Average
Incremental
Accumulated
Estimated
Contour Contour
Contour
Contour
Stage
Contour Stage Area Area
Volume
Volume
w/ S-S Fxn
258.00
-0.50
713
Sediment Storage
258.50
0.00
842
260.00
1.50
1,254 1048
1572 1572 1.52
262.00
3.50
1,966 1610
3220 4792 3.38
264.00
5.50
2,950 2458
4916 9708 5.62
Storage vs. Stage
12000
10000
y = 880.13x13902
8000 R2 = 0.998
LL
U
6000
r
CO 4000
2000
0
0.00 1.00 2.00 3.00 4.00 5.00 6.00
Stage (feet)
Ks = 880.1
b = 1.3902

Holding Village - North Lake STORMWATER CONTROL MEASURE B
RAP-19000 Volume Calculation
47,931
cf
Volume of Main Pool below Normal Pool=
Volume of Forebay below Normal Pool=
9,708
cf
Total Volume Below Normal Pool =
57,639
cf
Total Volume Above Normal Pool=
109,538
cf
Total Volume of Facility =
167,177
cf
AGE OF PERMANENT POOL VOLUME
i
Per NCDEQ Minimum Design Criteria, the forebay volume should equal
approximately 15-20% of the main pool volume.
Total Main Pool Volume = 47,931
cf
Provided Forebay Volume = 9,708
cf
Provided Forebay Volume % = 20%
LVERAGE DEPTH OF MAIN POOL
Main Pool Volume at Normal Pool =
47,931
cf
Main Pool Area at Normal Pool =
9,855
sf
Average Depth =
4.86
ft
Maria Torres, E.I.
Daniel Gunter
12/16/2019

Holding Village - North Lake STORMWATER CONTROL MEASURE B 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 = 12.98 acres
Total impervious area to pond = 7.90 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 = 12.98 acres @ 60.9% impervious
Estimate the surface area required at pond normal pool elevation ==>
Wet Detention Basins are based on an minimum average depth of =
4.0
4.86
Lower Boundary => 60.0 1.77
Site % impervious => 60.9 1.80
1.55
Upper Boundary => 70.0 2.09
Therefore, SA/DA required =
1.55
Surface area required for main pool at normal pool =
8,791
=
0.20
Surface area provided for main pool at normal pool =
9,855
4.86 feet (Calculated)
5.0
1.49
1.52
1.80
ft2
acres
ft2

Holding Village - North Lake STORMWATER CONTROL MEASURE B Maria Torres, E.I.
RAP-19000 WQV Calculation Daniel Gunter
12/16/2019
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 =
12.98
acres
Impervious area =
7.90
acres
Percent impervious cover, I =
60.9
Rainfall, P =
1.00
inches
Calculated values:
Rv =
0.60
WQv=
0.65
acre-ft
=
28163
cf.
�ED DEPTH IN POND
WQv=
28163 cf.
Stage/Storage Data:
Ks =
15012
b =
1.109
Zo =
264.00
Volume in 1" rainfall =
28163 cf.
Calculated values:
Depth of WQv in Basin = 1.76 ft
21.17 inches
Elevation = 265.76 ft

Holding Village - North Lake STORMWATER CONTROL MEASURE B
RAP-19000 WQV Drowdown Calculation
DESI
D orifice =
2.5 inch
# orifices =
1
Ks =
15012
b =
1.1086
Cd orifice =
0.60
Normal Pool Elevation =
264.00 feet
Volume @ Normal Pool =
0 cf
Orifice Invert =
264.00 feet
WSEL @ 1" Runoff Volume =
265.76 feet
WSEL
(feet)
Vol. Stored
(cf)
Orifice Flow
(cfs)
Avg. Flow
(cfs)
Incr. Vol.
(cf)
Incr. Time
(sec)
265.76
28163
0.211
265.61
25445
0.201
0.206
2718
13186
265.46
22756
0.190
0.196
2689
13737
265.30
20097
0.179
0.185
2659
14380
265.15
17473
0.167
0.173
2624
15144
264.99
14887
0.154
0.161
2586
16075
264.84
12344
0.140
0.147
2543
17249
264.68
9851
0.125
0.133
2492
18797
264.53
7420
0.107
0.116
2431
20992
264.38
5065
0.085
0.096
2355
24501
264.22
2816
0.056
0.071
2249
31824
Drawdown Time = 2.15 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 =
0.553 feet
Orifice composite loss coefficient =
0.600
Cross -sectional area of siphon =
0.034 sf
Q =
0.1221 cfs
Drawdown Time = Volume / Flowrate / 86400 (sec/day)
Drawdown Time = 2.67 days
Maria Torres, E.I.
Daniel Gunter
12/16/2019