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)
|
TABLE 408.1
| ||||
---|---|---|---|---|
Peak Rate Control Standards by Stormwater Management District
in the Wissahickon Creek Watershed
| ||||
District
|
Proposed Condition Design Storm
|
Existing Condition Design Storm
| ||
A
|
2-year
|
Reduce to
|
1-year
| |
5-year
|
5-year
| |||
10-year
|
10-year
| |||
25-year
|
25-year
| |||
50-year
|
50-year
| |||
100-year
|
100-year
| |||
B
|
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
| |||
C*
|
Conditional direct discharge district
|
NOTES:
| |
---|---|
In District C, development sites that can discharge directly
to the Wissahickon Creek Main Channel and to the Schuylkill River
main channel without use of City infrastructure may do so without
control of proposed conditions peak rate of runoff.
| |
Projects that are required to obtain a NPDES permit for stormwater
discharges associated with construction activities are required to
show no increase in peaks from existing conditions.
| |
When adequate capacity in the downstream system does not exist
and will not be provided through improvements, the proposed conditions
peak rate of runoff must be controlled to the predevelopment conditions
peak rate as required in District A provisions for the specified design
storms. The predevelopment condition for new development is the existing
condition. For redevelopment purposes in Philadelphia County, the
predevelopment condition shall be determined according to the procedures
found in the Philadelphia Stormwater Guidance Manual.
|
TABLE 409.1
| |||
---|---|---|---|
Acceptable Computation Methodologies For Stormwater Management
Plans
| |||
Montgomery County Portion of the Watershed
| |||
Method
|
Method Developed By
|
Applicability
| |
WINTR-20
|
USDA NRCS
|
Applicable where use of full hydrology computer model is desirable
or necessary
| |
WINTR-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 200 acres and with times of concentration
less than 60 minutes (tc < 60 min), or as approved by the municipality
| |
Other methods
|
Varies
|
Other computation methodologies approved by the municipality
and/or Municipal Engineer
|
NOTE:
| ||
---|---|---|
*
|
Successors to the above methods are also acceptable.
|