Rev = (1/12) * (I)
|
Where:
| ||||
Rev
|
=
|
Recharge volume (cubic feet).
| ||
I
|
=
|
Impervious area within the limits of earth disturbance (square
feet).
|
An asterisk (*) in equations denotes multiplication.
|
Volume (cubic feet) = (2/12) * Impervious Surfaces (square feet)
|
Volume (cubic feet) = (1/12) * Impervious Surfaces (square feet)
|
Standards for managing runoff in the Pennypack Creek Watershed
for the two-, five-, ten-, twenty-five-, fifty-, and one-hundred-year
storm events are shown in Table 408.1. Development sites must control
proposed condition runoff rates to existing condition runoff rates
for the design storms in accordance with Table 408.1.
|
Table 408.1
| |||
---|---|---|---|
Peak Rate Control Standards in the Pennypack Creek Watershed
| |||
Proposed Condition Design Storm
|
Existing Condition Design Storm
| ||
1-year
|
1-year
| ||
2-year
|
Reduce to
|
1-year
| |
5-year
|
2-year
| ||
10-year
|
5-year
| ||
25-year
|
10-year
| ||
50-year
|
25-year
| ||
100-year
|
50-year
|
Table 409-1 summarizes acceptable computation methods, and the
method selected by the qualified person shall be based on the individual
limitations and suitability of each method for a particular site.
The Rational Method may be used to estimate peak discharges from drainage
areas that contain less than two acres. The Soil Complex Method shall
be used for drainage areas greater than two acres.
|
Table 409.1
| |||
---|---|---|---|
Acceptable Computation Methodologies For Stormwater Management
Plans
| |||
Method
|
Method Developed by
|
Applicability
| |
TR-20
|
USDA NRCS
|
Applicable where use of full hydrology computer model is desirable
or necessary
| |
TR-55
|
USDA NRCS
|
Applicable for land development plans within limitations described
in TR-55
| |
HEC-HMS
|
US Army Corps of Engineers
|
Applicable where use of full hydrologic computer model is desirable
or necessary
| |
Rational Method or commercial computer package based on Rational
Method
|
Emil Kuichling (1889)
|
For sites less than 2 acres or as approved by the municipality
and/or Municipal Engineer
| |
Other methods
|
Varies
|
Other computation methodologies approved by the municipality
and/or Municipal Engineer
|
*
|
NOTE: Successors to the above methods are also acceptable. These
successors include WinTR55 for TR-55 and WinTR20 for TR-20.
|