A finite-element model for simulating hydraulic interchange of surface and ground water

A model was developed to be useful for predicting changes in streamflow as a result of groundwater pumping. The stream aquifer model is especially useful for simulating streams that flow intermittently owing to leakage to the aquifer or diversion for irrigation or streams that become perched owing to declining hydraulic head in the aquifer. The model couples the equation of two-dimensional groundwater flow with the kinematic equations of one-dimensional open-channel flow. Darcy 's law for vertical flow through a semipermeable streambed is used to couple the groundwater flow and streamflow equations. The equations of flow are approximated numerically by the finite-element method. A listing of the Fortran program that solves the equations of flow , and a description of data-input formats are given in the report. The program can simulate a variety of hydrologic characteristics including perched streams, streamflow diversions , springs, recharge from irrigated acreage, and evapotranspiration from the water table and phreatophytes. Time-dependent boundary conditions can be simulated. The program can be modified easily to simulate unconfined aquifers and aquifers with variable directions of anisotropy. (USGS)