ESTIMATES OF GROUND-WATER RECHARGE IN PENNSYLVANIA AVAILABLE ON THE WEB

Ground-water recharge rates were estimated from streamflow data for 197 watersheds throughout Pennsylvania by the use of computer programs RORA and PART. The RORA program uses a recession-curve displacement technique to estimate ground-water recharge from each storm period indicated on the streamflow hydrograph. The PART program uses a hydrograph-separation technique to derive base flow, which can provide a reasonable approximation of recharge for time periods of one year or more if losses of ground water from the watershed are minimal.

Recharge estimates were made using data collected during 1885-2001 at streamflow-gaging stations with at least 10 years of record. The watersheds were less than 500 square miles and were relatively unaffected by regulation. Estimates of (1) annual recharge, (2) mean-annual recharge for the period of streamflow record, and (3) mean-monthly recharge for the period of record were presented. Mean-annual recharge at the selected watersheds ranged from 5.8 to 29.3 inches; estimates from the RORA program were about 2 inches greater, on average, than from the PART program.

A web site http://pa.water.usgs.gov/recharge/index.html, developed in cooperation with the Pennsylvania Geological Survey, allows users to select watersheds by clicking on a map or selecting from a list and provides recharge rates from both estimation methods in tabular and graphic form. The web site illustrates some of the spatial and temporal variability of recharge in Pennsylvania.