Simulating Reservoir Leakage in Ground-Water Models

Leakage to ground water resulting from the expansion and contraction of reservoirs cannot be easily simulated by most ground‐water flow models. An algorithm, entitled the Reservoir Package, was developed for the United States Geological Survey (USGS) three‐dimensional finite‐difference modular ground‐water flow model MODFLOW. The Reservoir Package automates the process of specifying head‐dependent boundary cells, eliminating the need to divide a simulation into many stress periods while improving accuracy in simulating changes in ground‐water levels resulting from transient reservoir stage. Leakage between the reservoir and the underlying aquifer is simulated for each model cell corrresponding to the inundated area by multiplying the head difference between the reservoir and the aquifer with the hydraulic conductance of the reservoir‐bed sediments.