SW6180801_Calculations (Wet Pond #2)_20180829

Project #No Date
Project Name 1 8/29/2018
Date
1)Calculate percent impervious draining to pond.
Drainage Area =16.90 acres Road/Parking 2.23 ac
Impervious Area =9.70 acres Sidewalk 0.65 ac
Lots 5.62 ac
% Imperv. =57.42 %Driveways 0.70 ac
Amenity 0.50 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 =0.567 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 =0.567 inch/inch
A= Drainage Area = 16.90 acre
WQv =34,772 ft 3
3)Determine Surface Area to Drainage Area Ratio & Surface of Permanent Pool (Water Quality)
Desired Depth =5 ft
Imp. %Ratio
Lower Limit =50.00 1.31
Upper Limit =60.00 1.49 10,627 ft 2
Acutal =57.42 1.44
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 #2
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)
0 247.5 5544 0 0 Main Pool Vol = 49583 cf
0.5 248 5829 2843 2843 Main Pool SA = 9102 sf
1.5 249 6429 6129 8972
2.5 250 7054 6742 15714
3.5 251 7708 7381 23095
4.5 252 8391 8050 31144
5.5 253 9102 8747 39891
6 253.5 9467 4642 44533
6.5 254 10732 5050 49583
Stage Level Elevation (ft) Area (sf)
Stage Volume
(cf)
Cumulative Storage
(cf)Total Main Pool Vol = 49583 cf
0 251 1265 0 0 Total Forebay Vol = 7569 cf
1 252 2003 1634 1634 Is Forebay ~ 15-20%YES 15%
2 253 2900 2452 4086
3 254 4066 3483 7569
Stage Level Elevation (ft) Area (sf)
Stage Volume
(cf)
Cumulative Storage
(cf)WQ Volume = 34772 cf
0 254 14798 0 0 Temp. Pool Vol = 35123 cf
0.5 254.5 16325 7781 7781 Volume Enough YES
1 255 17578 8476 16257
2 256 20154 18866 35123
Average Depth Calculation:
Vshelf = 276 cf
Dmax over shelf =0.5 ft
Peimeter =368 ft
Width =3 ft
VPP = 49583 cf
Abottom of shelf =9467 sf
Davg =5.21 ft
Project Data Revisions
2018-002 Description
Kathryn's Place State Stormwater Comments
8/29/2018
POND VOLUMES
Wet Detention Pond #2
Total Main Pool
Permanent Pool Volume Check
Total Forebay Volume Forebay Volume Check
Temporary Pool Volume Temporary Pool Volume Check
Project #No Date
Project Name 1 8/29/2018
Date
1)Input Orifice and Spillway Information
2.50 in
0.60
Volume Provided =35,123 cf
Number Orifices =1.00
Inv Orfice =254.00
Inv Primary Spillway =256.00
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
0.034 sf
0.667 feet
0.134 cfs
3)Calculate Drawn Down Time
Time =Volume/Flowrate
3.03 days
Check =OK
Drawdown Time =
Orifice Diameter =
Orfice Coefficent =
Orfice Cross Section Area =
Average head =
Discharge =
8/29/2018
WATER QUALITY VOLUME DRAW DOWN CALCULATION
Wet Detention Pond #2
Project Data Revisions
2018-002 Description
Kathryn's Place State Stormwater Comments
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. =258 ft
Bottom of Riser Elev. =254.00 ft
Riser Wall Thickness =6.00 in
Diameter of Manhole =6.00 ft
Area = pi * diameter^2 / 4
Area (@ outside diam)=38.48 sf
Volume =153.94 cf
times wt of water 62.4 lbs/cf
Bouyant Force =9,606 lbs
Step 2.DETERMINE COUNTERWEIGHT REQUIREMENTS
Riser Top
Top Elevation =258
Thickness =0 inches
Outside Diam =7.00 ft
Volume =0.00 cf
Riser Walls
Inside Diam =6.00 ft
Wall Thickness =6.00 in
Height =4.00 ft
Volume =40.84 cf
Riser Bottom - Extended Base
Bottom Elevation =254.00
Diameter =0.00 ft
Thickness=6.00 in
Volume =0.00 cf
40.84 cf
150 lbs/cf
6,126 lbs
0.64
Y
6,361 lbs
Step 3.ADD CONCRETE BELOW INVERT IN RISER
28.27 sf
Volume Required =72.62 cf
2.57 ft
32 in
75.40 cf
6605 lb
1.33
Y
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 32 inches below invert of
pond
8/29/2018
RISER ANTI-FLOATATION
Wet Detention Pond #2
Project Data Revisions
2018-002 Description
Kathryn's Place State Stormwater Comments