Rev = [(S)(Rv)(A)]/12
|
Where:
| ||||
Rev
|
=
|
Recharge volume (acre-feet)
| ||
S
|
=
|
Soil-specific recharge factor (inches); see table below
| ||
Rv
|
=
|
Volumetric runoff coefficient [0.05 + 0.009(I)], where I is
the impervious surface percentage (impervious area divided by total
project area) x 100%
| ||
A
|
=
|
Site area contributing to the recharge facility (acres)
|
Hydrologic Soil Group (HSG)
|
Soil Specific Recharge Factor(s)
(inches)
| |
---|---|---|
A
|
0.38
| |
B
|
0.25
| |
C
|
0.13
| |
D
|
0.06
|
If more than one hydrologic soil group is present at a site,
a composite recharge volume shall be computed based upon the proportion
of total site area within each hydrologic soil group.
|
Storm Event
|
Rainfall
(inches)
(source: NOAA)
| |
---|---|---|
2-year
|
2.45
| |
10-year
|
3.40
| |
25-year
|
4.00
| |
100-year
|
5.05
|
Table III-1
Acceptable Computation Methodologies for Stormwater Management
Plans
| |||
---|---|---|---|
Method
|
Method Developed By
|
Applicability
| |
TR-20 or commercial package based on TR-20
|
USDA-NRCS
|
When use of full model is desirable or necessary
| |
TR-55 or commercial package based on TR-55
|
USDA-NRCS
|
Applicable for plans within the models limitations
| |
HEC-1
|
U.S. Army Corps of Engineers
|
When full model is desirable or necessary
| |
PSRM
|
Penn State University
|
When full model is desirable or necessary
| |
Rational Method or commercial package based on rational method
|
Emil Kuiching (1889)
|
For sites less than 200 acres
| |
Other methods
|
Various
|
As approved by the Westmoreland County Conservation District
|
Table III-2
Soils Found in Landslide Susceptible Areas
| ||
---|---|---|
Abbreviation
|
Soil Name
| |
ErC
|
Ernest silt loam, 8-15% slopes
| |
FaD
|
Fairpoint very channery silt loam, 3-8% slopes
| |
GcB
|
Gilpin channery silt loam, 3-8% slopes
| |
GcC
|
Gilpin channery silt loam, 8-15% slopes
| |
GcD
|
Gilpin channery silt loam, 15-25% slopes
| |
GcF
|
Gilpin channery silt loam, 25-75% slopes
| |
GuB
|
Gilpin Upshur complex, 3-8% slopes
| |
GuC
|
Gilpin Upshur complex, 8-15% slopes
| |
GuD
|
Gilpin Upshur complex, 15-25% slopes
| |
GuF
|
Gilpin Upshur complex, 25-75% slopes
| |
GwF
|
Gilpin-Weikert channery loam, 25-75% slopes
| |
Ho
|
Holly silt loam
| |
MeD
|
Matewan channery loam, 15-25% slopes
| |
ShF
|
Shelocta-Gilpin channery silt loam, 25-75% slopes
| |
UwD
|
Urban land-Wharton complex, 8-25% slopes
| |
VaB
|
Vandergrift silt loam, 3-8% slopes
| |
VaC
|
Vandergrift silt loam, 8-15% slopes
| |
VaD
|
Vandergrift silt loam, 15-25% slopes
|