Estimates of Ground-Water Recharge Based on Streamflow-Hydrograph Methods: Pennsylvania

This study, completed by the U.S. Geological Survey (USGS) in cooperation with
the Pennsylvania Department of Conservation and Natural Resources, Bureau of
Topographic and Geologic Survey (T&GS), provides estimates of ground-water
recharge for watersheds throughout Pennsylvania computed by use of two
automated streamflow-hydrograph-analysis methods--PART and RORA. The PART
computer program uses a hydrograph-separation technique to divide the
streamflow hydrograph into components of direct runoff and base flow. Base flow
can be a useful approximation of recharge if losses and interbasin transfers of
ground water are minimal. The RORA computer program uses a recession-curve
displacement technique to estimate ground-water recharge from each storm period
indicated on the streamflow hydrograph.

Recharge estimates were made using streamflow records collected during
1885-2001 from 197 active and inactive streamflow-gaging stations in
Pennsylvania where streamflow is relatively unaffected by regulation. Estimates
of mean-annual recharge in Pennsylvania computed by the use of PART ranged from
5.8 to 26.6 inches; estimates from RORA ranged from 7.7 to 29.3 inches.
Estimates from the RORA program were about 2 inches greater than those derived
from the PART program.

Mean-monthly recharge was computed from the RORA program and was reported as a
percentage of mean-annual recharge. On the basis of this analysis, the major
ground-water recharge period in Pennsylvania typically is November through May;
the greatest monthly recharge typically occurs in March.

[Summary provided by the USGS.]