THWELLS

THWELLS is an analytical solution that calculates the drawdown or buildup of piezometric head caused by multiple pumping and/or injection wells. The model can be used for a confined, leaky, or unconfined aquifer based on the assumptions that the aquifer is homogeneous, isotropic, uniformly thick, and of infinite extent. This program is ideal where the geology and hydrologic conditions are fairly simple and the required information (i.e. hydraulic conductivity, storage coefficient, and saturated thickness) of the aquifer is reliable. THWELLS is a user-interactive dos-based program. Data entry is facilitated through a sequence of screens. Results can be viewed in table format and graphically either on screen or in a file, and can be saved for post-processing. The graphic display includes both time-drawdown curves for selected locations and contour plots for a user-specified time.

A model can be constructed quickly and provides reliable results when applied to an appropriate setting. Computational accuracy has been verified by comparing results with other programs; IMAGEW-1, WALTON35, CAPZONE, and GWFLOW. Boundary effect can be considered using image wells.

A primary weakness is that the graphic result cannot be routed directly to a printer, rather a surfer compatible ASCII file, containing grid information and calculated draw downs, is generated for presentation of contours and other post-processing tasks.  Another shortcoming is that the result-screen view always uses a full screen and cannot return to a normal screen. Thus, it is cumbersome to use simultaneously with other programs. Significant improvement in the output graphics should be considered in a future release.

Considering cost and convenience, THWELLS is an inexpensive yet readily adaptable code for evaluation drawdown from single or multiple pumping wells in simple settings. The program can be purchased from International Ground Water Modeling Center (http://typhoon.mines.edu/software/igwmcsoft/) for $50.