Users manual for the University of Idaho ground-water flow model and recharge program

This manual documents two computer programs. The first is a finite difference ground-water flow model which has been applied to several areas in southern Idaho since its conception in 1970. The second program, titled RECHARGE, calculates and sums several factors contributing to aquifer recharge and discharge, for each cell of a rectangular model grid. The model simulates two-dimensional flow under anisotropic and heterogeneous aquifer conditions. Head values are calculated by application of the alternating-direction procedure to the backward-difference form of the finite -difference equation. The model is capable of calculating flow to or from a single overlying or underlying aquifer under transient or steady-state conditions, for confined and unconfined aquifers. [...] The RECHARGE program calculates aquifer recharge and discharge from precipitation, ground-water and surface-water irrigation, canal seepage, river gains and losses, ground-water pumping, and boundary underflow. These factors are summed for each grid cell and timestep for input to a ground-water model. [...