SW3210401_Design Calculations_20210810

Wet Pond Design
Project Name: Waxhaw-Nixon
Job Number: 18244
Step 1: Compute the water quality volume (WQV).
WQv (Ft3) = (3630) X (RD) X (Rv) X (AD)
Where:
WQV = Water Quality Volume (Ft)
AD = Drainage Area to Wet Pond (acres).
Rv = Volumetric Runoff Coefficient = 0.05 + 0.9 (% Impervious)
Rp = Design Storm Rainfall Depth (in). Typically 1.0".
Percent Impervious = 60%
AD = 17.96 acres
Rp = 1.0 in
Rv = 0.59
WQv = 38,465 Ft"

Step 2: Determine Surface Area Requirements.
Average Permanent Pool Depth = 5.28 Feet
Percent Impervious = 60%
SA / DA Ratio = 1.71
Required Surface Area = 13,378 Ft2
Step 3: Preliminary Temporary Water Quality Drawdown Calculations
Pond Height above Orifice
= 2.9
feet
Orifice Invert Elevation
= 0.0
feet
Pond Surface Area at Height Above Orifice
= 24,925
square feet
Pond Surface Area at Orifice Invert Elevation
= 13,378
square feet
Orifice Diameter (D)
= 3.50
inches = 0.29 feet
Orifice Area (a)
= 0.0668
square feet
Average Surface Area (A)
= 19,152
square feet
Gravitational Constatnt (g)
= 32.2
fft/sec2
Head (H)
= 2.75
feet
Discharge Coefficient (C)
= 0.6
Time (t)
= 197,598
seconds = 2.29 days
Note:
The above calculation is based on the Bernoulli Equation where:
-2xA
t _ - )0,5 X (0 - H0.5)
C x a x (2g)
Step 4: Compute Site Hydraulic Input Parameters.
Condition
Area (Ac)
CN
Tc (hours)
Pre -developed
29.60
58
0.348
Post -developed
29.60
88
0.0833
Results
Condition
Q2-year
Q10-year
Q25-year
Q50-year
Pre -developed
10.15
34.94
54.52
71.52
Post -developed
4.89
16.27
32.72
50.21

POND 1 STAGE STORAGE CALCULATION
Area Calculation - Forebay
Contour
Area
Volume (ac-ft)
Volume
sq. It
AC
Inc
Accum.
cu. It
537
430
0.0099
0.0000
0.0000
0
538
706
0.0162
0.0129
0.0129
562
539
1012
0.0232
0.0196
0.0325
1417
540
1348
0.0309
0.0270
0.0595
2593
541
1716
0.0394
0.0351
0.0946
4121
542
2113
0.0485
0.0439
0.1385
6032
543
2542
0.0584
0.0534
0.1918
8356
544
3002
0.0689
0.0636
0.2554
11125
544.5
3703
0.0850
0.0384
0.2938
12798
Area Calculation - Main Pond
Contour
Area
Volume ac-ft
Volume
sq. It
AC
Inc
Accum.
cu. It
537
6730
0.1545
0.0000
0.0000
0
538
7463
0.1713
0.1628
0.1628
7093
539
8225
0.1888
0.1800
0.3428
14934
540
9014
0.2069
0.1978
0.5407
1 23551
541
9831
0.2257
0.2162
0.7569
32970
542
10675
0.2451
0.2353
0.9922
43220
543
11546
0.2651
0.2550
1.2472
54328
544
12445
0.2857
0.2753
1.5225
66321
544.5
13796
0.3167
1 0.1505
1.6731
72878
Ave. Permanent Pool Depth 5.28
Volume Calculation - Permanent Pool
Contour
Area
Volume ac-ft
Volume
sq. It
AC
Inc
Accum.
cu. It
537
7160
0.1644
0.0000
0.0000
0
538
8169
0.1875
0.1758
0.1758
7659
539
9237
0.2121
0.1997
0.3755
16356
540
10362
0.2379
0.2248
0.6003
1 26151
541
11547
0.2651
0.2514
0.8517
37100
542
12788
0.2936
0.2792
1.1309
49262
543
14088
0.3234
0.3084
1.4393
62695
544
15447
0.3546
0.3389
1.7782
77457
544.5
17499
0.4017
0.1890
1.9671
85688
Volume Calculation - Temporary Pool
Contour
Area
Volume ac-ft
Volume
sq. It
AC
Inc
Accum.
cu. It
544.5
17499
0.4017
0.0000
0.0000
0
545
20064
0.4606
0.2154
0.2154
9383
546
22032
0.5058
0.4830
0.6984
30424
547
24099
0.5532
0.5293
1.2278
1 53482
548
26165
0.6007
0.5768
1.8046
78606
549
28501
0.6543
0.6273
2.4318
105931
550
30387
0.6976
0.6758
3.1077
135370
551
32547
0.7472
0.7222
3.8299
166831
552
34706
0.7967
0.7718
4.6017
200452
552.5
36129
0.8294
0.4065
5.0082
218159
553
37551
0.8621
0.4228
5.4311
236578
554
40927
0.9396
0.9005
6.3316
275805