SIMULATING RESERVOIR LEAKAGE IN GROUNDWATER MODELS

Leakage to ground water resulting from the expansion and contraction o f reservoirs cannot be easily simulated by most ground-water flow mode ls. An algorithm, entitled the Reservoir Package, was developed for th e United States Geological Survey (USGS) three-dimensional finite-diff erence modular ground-water flow model MODFLOW. The Reservoir Package automates the process of specifying head-dependent boundary cells, eli minating the need to divide a simulation into many stress periods whil e improving accuracy in simulating changes in ground-water levels resu lting from transient reservoir stage. Leakage between the reservoir an d the underlying aquifer is simulated for each model cell corrrespondi ng to the inundated area by multiplying the head difference between th e reservoir and the aquifer with the hydraulic conductance of the rese rvoir-bed sediments.