USING STREAMFLOW RECESSION TO ESTIMATE GROUND-WATER RECHARGE

From the time of Darcy, hydrologists have been aware of the connection between ground water and streamflow. By the late 1800s, hydrologists such as Boussinesq tried to develop methods to quantify the connection. During the early 1960s, hydrologists such as Rorabaugh, Meyboom, Knisel, and Glover, brought renewed effort to the development of quantitative methods for analyzing the interaction of ground water and surface water. As with Boussinesq, the one-dimensional analytical solutions they developed were of very simplified systems, where aquifers were isotropic and homogeneous and streams fully penetrated the aquifer. Furthermore, recharge was assumed to be uniform over the entire area of the aquifer. Rorabaugh developed two methods for estimating recharge, the instantaneous recharge method and the constant recharge method. For the instantaneous-recharge method, recharge is assumed to take place instantaneously, and recharge is calculated for each precipitation event. This method should be termed the Rorabaugh/Glover method because the method incorporates work by Glover for analyzing drainage from irrigated fields. For the constant recharge method, recharge is assumed to take place over a period of time, usually months, and a type curve solution is used to calculate a single value of recharge for that time period. For comparison of the two methods, analysis of a hydrograph of Indian Creek near Troy, Alabama, over a 5-month period of November through March, indicated 7.2 inches of recharge determined by the instantaneous recharge method and 6.7 inches of recharge determined by the constant recharge method. Although developed more than 40 years ago, hydrologists still find the Rorabaugh methods useful because of the widespread availability of stream-discharge data.