Estimating The Fate of Precipitation From Stream Discharge: A Case Study in New Jersey

Precipitation that falls in a watershed undergoes three hydrological processes: evapotranspiration, groundwater recharge, and river runoff. Using the long-term average stream discharge of a watershed, one can estimate the long-term average evapotranspiration portion of the precipitation by using the precipitation minus the normalized river discharge. In addition, by partitioning the stream discharge into the runoff and groundwater basefl ow components, one can estimate the portion of the precipitation that recharges the groundwater and the portion that becomes direct runoff. The application variations of the two classical groundwater recharge calculation methods based on the stream discharge, i.e., seasonal recession and recession curve displacement, are discussed for this purpose. A water budget method developed by the New Jersey Geological Survey is also used in this paper for comparison. The calculation of the fate of precipitation from the average of nine watersheds shows that on average, approximately 50% of the annual precipitation is evapotranspired, 25% of the annual precipitation recharges the groundwater, and about 25% of the annual precipitation becomes runoff to area streams.