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United States Department of Agriculture

Agricultural Research Service

Research Project: HYDROLOGIC AND ENVIRONMENTAL IMPACTS OF CONSERVATION PRACTICES IN OKLAHOMA AGRICULTURAL WATERSHEDS

Location: Great Plains Agroclimate and Natural Resources Research Unit

Title: Evaluation of a computer program used to estimate water characteristic curve

Authors
item Moriasi, Daniel
item Schneider, Jeanne

Submitted to: ASABE Annual International Meeting
Publication Type: Abstract Only
Publication Acceptance Date: January 31, 2009
Publication Date: N/A

Interpretive Summary: Abstract Only.

Technical Abstract: The soil water characteristic curve, h(theta), can be used to estimate a variety of parameters in unsaturated soils. One practical application of h(theta) is its use by DRAINMOD, a drainage model that has been widely used in shallow water table regions, to determine the water table depth–drainage volume relationship used to compute water table depth (WTD). Determination of h(theta) for all soil profile layers by laboratory methods is difficult, costly, and often impractical for many hydrologic studies. The next best alternative is to use tabulated h(theta) data from the literature, which is rarely available for the soil profiles of interest. If data for the soil of interest is not available, h(theta) is often approximated for each soil layer by matching the textural and structural classes for soils whose data is available in literature. In a previous study, a simple computer program (WTCHARTHETA) that predicts soil volumetric moisture content (theta) values corresponding to given pressure head (h) values ranging from saturation to wilting point for each of up to six soil profile layers using readily available variables of soil texture and organic matter was developed. WTCHARTHETA was developed by rearranging and modifying single-layer moisture-tension relationships developed by other USDA-ARS scientists in order to determine theta values for given h values for each of the soil profile layers, using depth to the bottom of each layer and the corresponding soil texture and organic matter data. The goal of this study was to test how well WTCHARTHETA program predicted theta for the each of the soil profile layers corresponding to given h values. Measured soil texture and organic matter for two soils in Oklahoma were used to estimate theta at known h values and compared to measured theta corresponding to the same h values. Results and their discussion are presented in this study. This program could provide a potentially inexpensive method of obtaining sufficiently accurate input data used by DRAINMOD to compute WTD.

Last Modified: 7/31/2014
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