SW6180801_Calculations (Wet Pond #1)_20180829

Project #No Date
Project Name 1 8/29/2018
Date
1)Calculate percent impervious draining to pond.
Drainage Area =4.20 acres Road/Parking 0.63 ac
Impervious Area =2.40 acres Sidewalk 0.15 ac
Lots 1.45 ac
% Imperv. =57.20 %Driveways 0.18 ac
2)Find the volume of the 1.0" storm using the "Simple Method" (Schueler 1987):
Rv = 0.05 + 0.009 (I)
Rv = runoff coefficient (ratio of runoff to rainfall in inches)
I = percent impervious
Rv =0.565 in/in
Volume of 1.0" storm (must exceed 3630 cf):
WQv = 3630 x RD x Rv X A
WQv = volume of runoof gnerated from design storm
RD =Design storm =1 inch
Rv = Runoff Coef =0.565 inch/inch
A= Drainage Area = 4.20 acre
WQv =8,611 ft 3
3)Determine Surface Area to Drainage Area Ratio & Surface of Permanent Pool (Water Quality)
Desired Depth =3 ft
Imp. %Ratio
Lower Limit =50.00 1.49
Upper Limit =60.00 2.09 3,516 ft 2
Acutal =57.20 1.92
The volume of the 1" storm must be detained in the pond above the permanent pool and must be drawn down over a
period of two to five days.
Minimum SA Required =
Project Data Revisions
Description
State Stormwater Comments
WATER QUALITY & SURFACE AREA CALCUALTION
Wet Detention Pond #1
2018-002
Kathryn's Place
8/29/2018
Impervious
Project #No Date
Project Name 1 8/29/2018
Date
Stage Level Elevation (ft) Area (sf)
Stage Volume
(cf)
Cumulative Storage
(cf)
0 252 1452 0 0 Main Pool Vol = 14960 cf
1 253 1849 1651 1651 Main Pool SA = 4689 sf
2 254 2293 2071 3722
3 255 2780 2537 6258
4 256 3284 3032 9290
5 257 3808 3546 12836
5.5 257.5 4689 2124 14960
Stage Level Elevation (ft) Area (sf)
Stage Volume
(cf)
Cumulative Storage
(cf)Main Pool Vol = 14960 cf
0 255.5 896 0 0 Total Forebay Vol = 2751 cf
0.5 256 1108 501 501 Is Forebay ~ 15-20%YES 18%
1.5 257 1628 1368 1869
2 257.5 1901 882 2751
Stage Level Elevation (ft) Area (sf)
Stage Volume
(cf)
Cumulative Storage
(cf)WQ Volume = 8611 cf
0 257.5 6653 0 0 Temp. Pool Vol = 10146 cf
0.5 258 7921 3644 3644 Volume Enough YES
1.25 258.75 9420 6503 10146
Average Depth Calculation:
Vshelf = 201 cf
Dmax over shelf =0.5 ft
Peimeter =268 ft
Width =3 ft
VPP = 14960 cf
Abottom of shelf =3808 sf
Davg =3.88 ft
8/29/2018
POND VOLUMES
Wet Detention Pond #1
Total Main Pool
Permanent Pool Volume Check
Total Forebay Volume Forebay Volume Check
Temporary Pool Volume Temporary Pool Volume Check
Project Data Revisions
2018-002 Description
Kathryn's Place State Stormwater Comments
Project #No Date
Project Name 1 8/29/2018
Date
1)Input Orifice and Spillway Information
1.50 in
0.60
Volume Provided =10,146 cf
Number Orifices =1.00
Inv Orfice =257.50
Inv Primary Spillway =258.75
2)Calculate Area, Head and Discharge Flow
g=32.2 ft/s2
h= use h/3 to simulate decreasing head
A= cross section area of orifice
Q= discharge cfs
Q=discharge cfs
0.012 sf
0.417 feet
0.038 cfs
3)Calculate Drawn Down Time
Time =Volume/Flowrate
3.08 days
Check =OK
Project Data Revisions
2018-002 Description
Kathryn's Place State Stormwater Comments
8/29/2018
WATER QUALITY VOLUME DRAW DOWN CALCULATION
Wet Detention Pond #1
Drawdown Time =
Orifice Diameter =
Orfice Coefficent =
Orfice Cross Section Area =
Average head =
Discharge =
ghACQ20
Project #No Date
Project Name 1 8/29/2018
Date
Step 1.DETERMINE BOUYANT FORCES
Volume = Depth * Area
Depth = Riser Top Elev - Riser Bottom Elev
Riser Top Elev. =260 ft
Bottom of Riser Elev. =257.50 ft
Riser Wall Thickness =6.00 in
Diameter of Manhole =4.00 ft
Area = pi * diameter^2 / 4
Area (@ outside diam)=19.64 sf
Volume =49.09 cf
times wt of water 62.4 lbs/cf
Bouyant Force =3,063 lbs
Step 2.DETERMINE COUNTERWEIGHT REQUIREMENTS
Riser Top
Top Elevation =260
Thickness =0 inches
Outside Diam =5.00 ft
Volume =0.00 cf
Riser Walls
Inside Diam =4.00 ft
Wall Thickness =6.00 in
Height =2.50 ft
Volume =17.67 cf
Riser Bottom - Extended Base
Bottom Elevation =257.50
Diameter =0.00 ft
Thickness=6.00 in
Volume =0.00 cf
17.67 cf
150 lbs/cf
2,651 lbs
0.87
Y
1,331 lbs
Step 3.ADD CONCRETE BELOW INVERT IN RISER
12.57 sf
Volume Required =15.20 cf
1.21 ft
24 in
25.13 cf
2202 lb
1.58
Y
8/29/2018
RISER ANTI-FLOATATION
Wet Detention Pond #1
Project Data Revisions
2018-002 Description
Kathryn's Place State Stormwater Comments
Summary
Amount of Concrete Required =
Area of Riser (@inside diam) =
Factor of Safety > 1.30 (Y/N) =
Calculated Depth of Concrete =
Actual Depth Used =
Backcheck Volume =
Backcheck Weight of Added Conc
(150-62.4) =
Factor of Safety =
Total Volume =
x unit weight of reinforced conc.
CounterweIght =
Factor of Safety Provided (FSP) =
Additional Concrete Required (Y/N) =
Add minimum 24 inches below invert of
pond