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T-7 Retention Pond
Designer:
Company:
Date:
Project:
Location:
Design Procedure Form: Retention Pond (RP)
L. Gibson
BMP, Inc.
November 29, 2010
Subdivision B
NE Corner of 67th Ave. and 88th St.
Sheet 1 of 3
1. Baseflow
A) Is the permanent pool established by groundwater?
Choose One
YES
NO
2. Surcharge Volume
A) Effective Imperviousness of Tributary Area, I a I a = 80.0 %
B) Tributary Area's Imperviousness Ratio (i = I a / 100 ) i = 0.800
C) Contributing Watershed Area Area = 50.000 ac
D) For Watersheds Outside of the Denver Region, Depth of Average d 6 = in
Runoff Producing Storm
Choose One
E) Design Concept
(Select EURV when also designing for flood control)
Water Quality Capture Volume (WQCV)
Excess Urban Runoff Volume (EURV)
F) Water Quality Capture Volume (WQCV) V WQCV = 1.094 ac-ft
Based on 12-hour Drain Time
(V WQCV = (0.8 * (0.91 * i 3 - 1.19 * i 2 + 0.78 * i) / 12 * Area)
G) For Watersheds Outside of the Denver Region, V WQCV OTHER = ac-ft
Water Quality Capture Volume (WQCV)
(V WQCV OTHER = (d 6 *(V WQCV /0.43))
H) User Input of Water Quality Capture Volume (WQCV) V WQCV USER = ac-ft
(Only if a different WQCV Design Volume is desired)
I) Predominant Watershed NRCS Soil Group
Choose One
B
J) Excess Urban Runoff Volume (EURV) Design Volume
For HSG A: EURV A = (0.1878i - 0.0104)*Area
C / D
For HSG B: EURV B = (0.1178i - 0.0042)*Area
For HSG C/D: EURV C/D = (0.1043i - 0.0031)*Area EURV = 4.017 ac-f t
A
3. Basin Shape L : W = 3.0 : 1
(It is recommended to have a basin length to width ratio between 2:1 and 3:1)
4. Permanent Pool
A) Minimum Permanent Pool Volume V POOL = 1.313 ac-ft
B) Depth of the Safety Wetland Bench D LZ = 6 in
(Recommended to be 6 to 12 inches deep)
C) Depth of the Open Water Zone D OWZ = 12.0 ft
(Maximum depth of 12 feet)
5. Side Slopes
A) Maximum Side Slopes Above the Safety Wetland Bench Z PP = 5.00 ft / ft
(Horiz. dist. per unit vertical, should be no steeper than 4:1)
B) Maximum Side Slopes Below the Safety Wetland Bench Z OWZ = 3.00 ft / ft
(Horiz. dist. per unit vertical, should be no steeper than 3:1)
6. Inlet
Adequate tailwater during events exceeding the WQCV.
A) Describe means of providing energy dissipation at concentrated
inflow locations:
RP-10 Urban Drainage and Flood Control District November 2010
Urban Storm Drainage Criteria Manual Volume 3