Ground-water recharge (GWR) is defined as the water that infiltrates the
ground and reaches the water table regardless of the underlying geology.
It supports aquifer recharge, stream baseflow and wetlands. It is estimated
in New Jersey using the methodology outlined in NJ Geological Survey Report
GSR-32, "A Method of Evaluating Ground-Water-Recharge Areas in New Jersey"
by E. G. Charles and others (1993). Application of this method using the
Arc/Info geographic information system (GIS) produced
19* county and 20* watershed
management area (WMA) ground-water recharge, GIS coverages. The county
recharge coverages were created by overlaying three coverages: 1) soils,
2) land use and land cover (LULC), and 3) municipalities. These three coverages
provided the following attributes: soil series names, land-use and land-cover
categories, and climate factors; respectively. These data were then used
to calculate ground-water recharge values using the following equation for
each area in the coverage:
ground-water recharge = (recharge factor x climate factor) - recharge
constant
The recharge factor and constant are determined by the cross tabulation of
LULC and soil series. The climate factor is determined
using zonal statistics and is a ratio of precipitation over
potential evapotranspiration.
The WMA coverages were created by combining all the county coverages of each
WMA and then "clipping" the result with the WMA boundary. Calculated
ground-water recharge values from each area in the coverages were rounded
to the nearest inch and ranked into 5 categories based upon the natural breaks
in the percentage of total volume, as shown in this
table
for Mercer Co. or this
table
for Watershed Management Area 8 (Upper Raritan).
Other attributes included in the coverages are soil symbols, hydrologic soil
group, hydric soil indication, soil descriptions (where found); LULC category
codes, climate factor, municipality and the statewide GWR rankings which
were generated by combining all of the county GWR coverages and ranking the
result.
* Recharge for Essex County has not been calculated at this time, and Hudson County's was not calculated due to the lack of current soil survey and soils coverage, therefore only parts of WMAs 4, 5, 6 , and 7 have recharge calculated.
