Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
A METHOD OF CONVERTING NO-FLOW CELLS TO VARIABLE-HEAD CELLS FOR THE U.S. GEOLOGICAL SURVEY MODULAR FINITE-DIFFERENCE GROUND-WATER FLOW MODEL By Michael G. McDonald, Arlen W. Harbaugh, Brennon R. Orr, and Daniel J. Ackerman U.S. GEOLOGICAL SURVEY Open-File Report 91-536 DISCLAIMER This is a scanned reproduction of the original document for distribution purposes via electronic format. Effort has been made to provide an accurate and correct document. The document is supplied "as-is" without guarantee or warranty, expressed or implied. To reduce the file size of this document, listings of source code, which are available on some original open-file reports, are not included. Wen-Hsing Chiang Hamburg, April 1998. U.S. DEPARTMENT OF THE INTERIOR MANUEL LUJAN, JR., Secretary U.S. GEOLOGICAL SURVEY Dallas L. Peck, Director For additional information write to: Copies of this report can be purchased from: Chief, Office of Ground Water U.S. Geological Survey MS 411 National Center 12201 Sunrise Valley Drive Reston, Virginia 22092 U.S. Geological Survey Books and Open-File Reports Section MS 411 Federal Center Box 25425 Denver, Colorado 80225 A METHOD OF CONVERTING NO-FLOW CELLS TO VARIABLE-HEAD CELLS IN THE U.S. GEOLOGICAL SURVEY MODULAR FINITE-DIFFERENCE GROUND-WATER FLOW MODEL BY Michael G. McDonald, Arlen W. Harbaugh, Brennon R. Orr, and Daniel J. Ackerman ABSTRACT The U.S. Geological Survey Modular Ground-Water Flow Model, commonly referred to as MODFLOW, sfmulates ground-water flow through porous media using the finite-difference method. The region being modeled is divided into a grid of cells, and each cell is defined to be either no-flow, variable-head, or constant-head. The model calculates a value for head at all variable-head cells whereas head at constant-head cells is specified by the user. Cells are designated as no-flow cells if they contain impermeable material or are unsaturated, and accordingly the flow of water is not simulated in such cells. As originally published, MODFLOW could simulate the desaturation of variable-head model cells, which resulted in their conversion to no-flow cells, but could not simulate the resaturation of cells. cell could not be converted to variable head. desirable in many situations. That is, a no-flow However, such conversion is For example, one might wish to simulate pumping that desaturates some cells followed by the recovery of water levels after pumping is stopped. An option that allows cells to convert from no- flow to variable-head has been added to the model. In this option, a cell is converted to variable head based on the head at neighboring cells. The option is written in FORTRAN 77 and is fully compatible with the existing model. This report documents the new option, including a description of the concepts, detailed input instructions, and a listing of the code. Example problems illustrate the practical applications of the option. Although solution of the modified flow equations can be difficult for the model solvers, the example problems show that it is possible to solve a variety of complex problems.