Rev = (1 inch/12 inches) * (I)
|
Where:
| ||
Rev
|
=
|
Recharge volume (cubic feet)
|
I
|
=
|
Impervious area (square feet) [per § 1241.401(e)]
|
An asterisk (*) in equations denotes multiplication.
|
Table 410.A.1
| ||
---|---|---|
Peak Rate Control Standards for All Sites in Lower Gwynedd Township
| ||
Proposed Condition Design Storm
|
Existing Condition Design Storm
| |
2-year
|
reduce to
|
1-year
|
5-year
|
reduce to
|
2-year
|
10-year
|
reduce to
|
5-year
|
25-year
|
reduce to
|
10-year
|
50-year
|
reduce to
|
25-year
|
100-year
|
reduce to
|
50-year
|
Q
|
=
|
Peak flow rate, cubic feet per second (CFS)
|
C
|
=
|
Runoff coefficient, dependent on land use/cover
|
I
|
=
|
Design rainfall intensity, inches per hour
|
A
|
=
|
Drainage area, acres.
|
Table 411.1
Acceptable Computation Methodologies for Stormwater Management
Plans
| ||
---|---|---|
Method
|
Method Developed By
|
Applicability
|
TR-20 (or commercial computer package based on TR-20)
|
USDA NRCS
|
Applicable where use of full hydrology computer model is desirable
or necessary
|
TR-55 (or commercial computer package based on TR-55)
|
USDA NRCS
|
Applicable for land development plans within limitations described
in TR-55
|
HEC-1/HEC-HMS
|
U.S. Army Corps of Engineers
|
Applicable where use of full hydrologic computer model is desirable
or necessary
|
PSRM
|
Penn State University
|
Applicable where use of full hydrologic computer model is desirable
or necessary; simpler than TR-20 or HEC-1
|
Rational Method (or commercial computer package based on Rational
Method)
|
Emil Kuichling (1889)
|
Peak discharge only for sites less than two acres or as approved
by the Township and/or Township Engineer
|
Other methods
|
Varies
|
Other computation methodologies approved by the Township and/or
Township Engineer
|