Submitted to: ASABE Annual International Meeting
Publication Type: Abstract only
Publication Acceptance Date: 12/3/2007
Publication Date: N/A
Citation: Interpretive Summary: Abstract only.
Technical Abstract: Shallow water table depth (WTD) fluctuation over time is an important issue for planning drainage systems in some rural watersheds. The proximity of the WTD to the soil surface impacts soil properties, crop development, and agricultural chemical transport. DRAINMOD, a drainage model that has been widely used in shallow water table regions uses, the soil water characteristic curve, h('), to determine the water table depth–drainage volume (WTD-DV) relationship used to compute WTD. Determination of h(') 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(') data in the literature, which is rarely available for the soil profiles of interest. If data for the soil of interest is not available, h(') is often approximated for each soil layer by matching the textural and structural classes for soils whose data is available in literature. The goal of this study was to develop a simple algorithm (WTCHARTHETA) using new h(') equations developed by Saxton and Rawls (2006) and to modify the previous WTD-DV algorithm in DRAINMOD in order to increase the number of soil layers considered in the profile (WTDRAINVR). Saxton and Rawls’ (2006) moisture-tension relationships were rearranged and modified to determine the moisture content (') values corresponding to the fixed pressure head (h) values for each layer using readily available variables of soil texture and organic matter. The values generated by WTCHARTHETA are used as inputs by WTDRAINVR to determine the WTD-DV input. Sample outputs are presented in this study. These programs provide a potentially inexpensive method of obtaining sufficiently accurate input data used by DRAINMOD to compute WTD.