20070295 Ver 6_5.01 SCM A - Wet Pond Design_20191220

Holding Village - North Lake STORMWATER CONTROL MEASURE A Maria Torres, E.I.
RAP-19000 SSFxn Above NP Daniel Gunter
12.16.2019
STAGE -STORAGE FUNCTION -ABOVE NORMAL POOL
Contour
(feet)
Stage
(feet)
Contour
Area
(SF)
Average
Contour
Area
(SF)
Incremental
Contour
Volume
(CF)
Accumulated
Contour
Volume
(CF)
Estimated
Stage
w/ S-S Fxn
(feet)
274.00
0.00
18,993
275.00
1.00
22,511
20752
20752
20752
1.00
276.00
2.00
24,354
23433
23433
44185
1.99
278.00
4.00
26,505
25430
50859
95044
3.98
280.00
6.00
28,243
27374
54748
149792
6.01
280.50
6.50
28,649
28446
14223
164015
6.52
Ks = 206S6
b = 1.1047

Holding Village - North Lake STORMWATER CONTROL MEASURE A
RAP-19000 SSFxn Main Pool
ION - MAIN POOL
Maria Torres, E.I.
Daniel Gunter
12.16.2019
Average
Incremental
Accumulated
Estimated
Contour
Contour
Contour
Contour
Stage
Contour
Stage
Area
Area
Volume
Volume
w/ S-S Fxn
(feet)
(feet)
(SF)
(SF)
i
(CF)
(CF)
(feet)
267.50
-1.00
8,899
Sediment Storage
268.50
0.00
9,739
269.00
0.50
10,168
9954
4977
4977
0.51
270.00
1.50
11,051
10610
10610
15586
1.46
272.00
3.50
12,888
11970
23939
39525
3.44
273.50
5.00
14,331
13610
20414
59940
5.04
274.00
5.50
1 14,824
14578
7289
67,228
5.61
*surface area and volume used for avg. depth calculation
Storage vs.
Stage
80000
70000
60000
v 50000
40000
R
30000
C0
20000
10000
0
0.00
1.00 2.00 3.00 4.00 5.00 6.00
Stage (feet)
Ks = 10351
b = 1.0853

Holding Village - North Lake STORMWATER CONTROL MEASURE A 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
270.50
-0.50
2,001
Sediment Storage
271.00
0.00
2,196
272.00
1.00
2,606 2401
2401 2401 1.00
273.50
2.50
3,268 2937
4406 6807 2.48
274.00
3.00
3,501 3385
1692 8499 3.02
Storage vs. Stage
9000
8000
y
= 2398.2x'1462
7000
R2 = 0.9999
6000
LL
v
5000
a
4000
0
in
3000
2000
1000
0
0.00
1.00 2.00 3.00 4.00
Stage (feet)
Ks = 2398.2
b = 1.1462

Holding Village - North Lake STORMWATER CONTROL MEASURE A
RAP-19000 Volume Calculation
67,228
cf
Volume of Main Pool below Normal Pool=
Volume of Forebay below Normal Pool=
8,499
cf
Total Volume Below Normal Pool =
75,727
cf
Total Volume Above Normal Pool=
164,015
cf
Total Volume of Facility =
239,742
cf
AGE OF PERMANENT POOL VOLUME
Per NCDEQ Minimum Design Criteria, the forebay volume should equal
approximately 15-20% of the main pool volume.
Total Main Pool Volume = 67,228
cf
Provided Forebay Volume = 8,499
cf
Provided Forebay Volume % = 13%
LVERAGE DEPTH OF MAIN POOL
Main Pool Volume at Normal Pool =
67,228
cf
Main Pool Area at Normal Pool =
14,824
sf
Average Depth =
4.54
ft
Maria Torres, E.I.
Daniel Gunter
12.16.2019

Holding Village - North Lake STORMWATER CONTROL MEASURE A 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 = 18.69 acres
Total impervious area to pond = 10.31 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 = 18.69 acres @ 55.2% impervious
Estimate the surface area required at pond normal pool elevation ==>
Wet Detention Basins are based on an minimum average depth of =
4.0
4.54
Lower Boundary => 50.0 1.51
Site % impervious => 55.2 1.64
1.51
Upper Boundary => 60.0 1.77
Therefore, SA/DA required =
1.51
Surface area required for main pool at normal pool =
12,333
=
0.28
Surface area provided for main pool at normal pool =
14,824
4.54 feet (Calculated)
5.0
1.31
1.40
1.49
ft2
acres
ft2

Holding Village - North Lake STORMWATER CONTROL MEASURE A 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 =
18.69
acres
Impervious area =
10.31
acres
Percent impervious cover, I =
55.2
Rainfall, P =
1.00
inches
Calculated values:
Rv =
0.55
WQv=
0.85
acre-ft
=
37068
cf.
�ED DEPTH
WQv=
37068 cf.
Stage/Storage Data:
Ks =
20656
b =
1.105
Zo =
274.00
Volume in 1" rainfall =
37068 cf.
Calculated values:
Depth of WQv in Basin = 1.70 ft
20.37 inches
Elevation = 275.70 ft

Holding Village - North Lake STORMWATER CONTROL MEASURE A
RAP-19000 WQV Drowdown Calculation
DESI
D orifice =
3 inch
# orifices =
1
Ks =
20656
b =
1.1047
Cd orifice =
0.60
Normal Pool Elevation =
274.00 feet
Volume @ Normal Pool =
0 cf
Orifice Invert =
274.00 feet
WSEL @ 1" Runoff Volume =
275.70 feet
WSEL
(feet)
Vol. Stored
(cf)
Orifice Flow
(cfs)
Avg. Flow
(cfs)
Incr. Vol.
(cf)
Incr. Time
(sec)
275.70
37068
0.296
275.55
33499
0.282
0.289
3569
12358
275.40
29966
0.267
0.274
3533
12892
275.25
26472
0.250
0.259
3494
13516
275.10
23022
0.233
0.242
3451
14262
274.95
19620
0.215
0.224
3402
15177
274.81
16273
0.195
0.205
3347
16341
274.66
12990
0.172
0.183
3282
17895
274.51
9785
0.146
0.159
3205
20139
274.36
6678
0.114
0.130
3107
23854
274.21
3707
0.065
0.090
2972
33138
Drawdown Time = 2.08 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 =
0.524 feet
Orifice composite loss coefficient =
0.600
Cross -sectional area of siphon =
0.049 sf
Q =
0.1711 cfs
Drawdown Time = Volume / Flowrate / 86400 (sec/day)
Drawdown Time = 2.51 days
Maria Torres, E.I.
Daniel Gunter
12.16.2019