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Techniques and Methods 6–A31

Groundwater Resources Program

SWB—A Modified Thornthwaite-Mather Soil-Water-Balance Code for Estimating Groundwater Recharge

Chapter 31 of
Section A, Groundwater, of
Book 6, Modeling Techniques

By S.M. Westenbroek, V.A. Kelson,1 W.R. Dripps,2 R.J. Hunt, and K.R. Bradbury3

1Wittman Hydro Planning Associates, Bloomington, Indiana
2Furman University, Greenville, South Carolina
3Wisconsin Geologic and Natural History Survey, Madison, Wisconsin


Thumbnail of and link to report PDF (11.4 MB)

A Soil-Water-Balance (SWB) computer code has been developed to calculate spatial and temporal variations in groundwater recharge. The SWB model calculates recharge by use of commonly available geographic information system (GIS) data layers in combination with tabular climatological data. The code is based on a modified Thornthwaite-Mather soil-water-balance approach, with components of the soil-water balance calculated at a daily timestep. Recharge calculations are made on a rectangular grid of computational elements that may be easily imported into a regional groundwater-flow model. Recharge estimates calculated by the code may be output as daily, monthly, or annual values.

Revised March 14, 2012

First posted July 2010

For additional information contact:
Director, Wisconsin Water Science Center
U.S. Geological Survey
8505 Research Way
Middleton, Wisconsin 53562
Phone: (608) 828-9901
Fax: (608) 821-3817

Part or all of this report is presented in Portable Document Format (PDF); the latest version of Adobe Reader or similar software is required to view it. Download the latest version of Adobe Reader, free of charge.


Suggested citation:

Westenbroek, S.M., Kelson, V.A., Dripps, W.R., Hunt, R.J., and Bradbury,K.R., 2010, SWB—A modified Thornthwaite-Mather Soil-Water-Balance code for estimating groundwater recharge: U.S. Geological Survey Techniques and Methods 6–A31, 60 p.


Model Description
Use of the SWB Model
Test Problems
Summary and Conclusions
References Cited
Appendix 1: SWB Module Description
Appendix 2: Preparation of Gridded Climatological Data for SWB

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