Numerical Modeling of Flow to Wells

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Order No: BAS 11
Version: 2.0 (March 1994)
Price: Contact igwmc@mines.edu for more info
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RADFLOW is a menu-driven, user-interactive finite difference model for solving the horizontal radial time-varying flow equation in a confined, semi-confined or unconfined aquifer. The program calculates drawdowns resulting from a pumping well in the center of a circular homogeneous, isotropic aquifer subject to uniform areal recharge. The radial dimension is discretized using a logarithmic function starting at the outer edge of the well and increasing towards the outer boundary dividing each log-cycle in five sections. The grid is automatically generated based on the radius of the well and the distance to the outer boundary (100 nodes maximum) and the program adjusts the cell size at the inner (well) boundary and outer boundary in accordance with geometric requirements. The model includes a well of finite radius with allowance for the free water initially contained within the well, various conditions on the outer boundary, a change between the confined and unconfined states, allowance for leaky confined aquifer condition, and variations in saturated depth of an unconfined aquifer.

The program includes an automatic correction for well storage and well loss and has an option for taking delayed yield into consideration using Boulton's (1963) approach. If this option is used, the program works with an effective storage coefficient and effective recharge calculated using the reciprocal of Boulton's delay index.

The outer boundary may be: 1) impermeable (no flow boundary), i.e., assuming that all water pumped by the well comes from storage or areal recharge; or 2) at a constant value for head (recharge boundary), i.e., assuming zero drawdown during the simulation. Whether the confined or unconfined storage coefficient should be used depends on the drawdown relative to the top of the aquifer. The model allows for the groundwater potential to cross the top of the aquifer during the simulation. The storage coefficients for the cells in which this switch takes place are automatically adjusted. As transmissivity is a function of saturated depth times hydraulic conductivity, the model uses an iterative scheme to determine transmissivity for unconfined conditions (preset at ten iterations per time step). It should be noted that the program stops when the depth of water at the abstraction well is less than the original depth, displaying a warning.

RADFLOW is a DOS-based program with ASCII text output and simple on-screen graphics of the results. It is distributed complete with BASIC source code and a runtime version. The documentation contains installation instructions and background information.

**SYSTEM REQUIREMENTS
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Intel 80i86 based computer with math coprocessor, 640 Kb RAM, DOS 3.1 or higher, VGA graphics.

*Authors: Originally written by K.S. Rathod and K.R. Rushton (University of Birmingham). This version prepared by IGWMC.*