At least the first one inch of runoff from new or replacement
impervious surfaces shall be infiltrated.
|
Revv = 1 (inch) * impervious area (square
feet) ÷ 12 (inches) = cubic feet (cf)
An asterisk (*) in equations denotes multiplication.
|
Wherever possible, infiltration facilities should be designed to accommodate infiltration of the entire water quality volume (WQv) (§ 384-17C), however, in all cases at least the first 0.5 inch of the WQv shall be infiltrated. The minimum infiltration volume (Rev) required would, therefore, be computed
as:
|
Rev = I * impervious area (square feet)
÷ 12 (inches) = cubic feet (cf)
An asterisk (*) in equations denotes multiplication.
| |
Where:
| |
I = The maximum equivalent infiltration amount (inches) that
the site can physically accept or 0.50 inch, whichever is greater.
|
The retention volume values derived from the methods in § 384-16C(2)(a), (b) or (c) is the minimum volume the applicant must control through an infiltration BMP facility. If site conditions preclude capture of runoff from portions of the impervious area, the infiltration volume for the remaining area should be increased an equivalent amount to offset the loss.
| |
Only if the minimum of 0.50 inch of infiltration requirement cannot be physically accomplished, a waiver from § 384-16, Infiltration volume requirements, is required from the Township.
|
Table 308.1
| ||||
---|---|---|---|---|
Peak Rate Control Standards in the Naamans Creek Watershed
| ||||
District
|
Proposed Condition Design Storm
|
(reduce to)
|
Existing Condition Design Storm
| |
Naamans Creek
|
2-year
|
2-year
| ||
5-year
|
2-year
| |||
10-year
|
5-year
| |||
25-year
|
25-year
| |||
50-year
|
50-year
| |||
100-year
|
100-year
|
Table 308.2
| ||
---|---|---|
Control Criteria for Chester Creek Watershed Stormwater
Management Districts
| ||
District
|
Control Criteria
| |
100%
|
Post-development peak discharge for all design storms must be
no greater than predevelopment peak discharges.
| |
75%
|
Post-development peak discharge for all design storms must be
no greater than 75% of the predevelopment peak discharges.
| |
50%
|
Post-development peak discharge for all design storms must be
no greater than 50% of the predevelopment peak discharges.
|
Table 309.1
| |||
---|---|---|---|
Acceptable Computation Methodologies for SWM Site Plans
| |||
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 with limitations described
in TR-55
| |
HEC-1/HEC-HMS
|
US Army Corps of Engineers
|
Applicable where use of a full hydrologic computer model is
desirable or necessary
| |
Rational Method (or commercial computer package based on Rational
Method)
|
Emil Kuichling (1889)
|
For sites up to 5 acres, or as approved by the Township and/or
Municipal Engineer
| |
Other methods
|
Varies
|
Other computation methodologies approved by the Township and/or
Municipal Engineer
|