Modeling the effects of deep chiseling with DRAINMOD for alluvial soils

DRAINMOD is a drainage model that has been widely used in the shallow water table regions of the U.S., including the southeastern U.S. Therefore, it is important that DRAINMOD realistically simulate the water balance components for alluvial soils that are prone to surface seal formation, which are the predominant soils in much of the southeastern U.S. In this study, DRAINMOD 5.1 was modified to address the problems associated with the assumption of constant vertical saturated hydraulic conductivity (Ks) and constant maximum surface depressional storage (STMAX) for these alluvial soils. The first objective was to modify DRAINMOD 5.1 to incorporate the effects of deep chiseling (Ks and STMAX vary) in order to improve its prediction of infiltration and surface runoff. The second objective was to evaluate the modified DRAINMOD models with dynamic Ks and STMAX subroutines (DRAINMOD-Ks, DRAINMOD-STMAX, and the combined DRAINMOD-Ks-STMAX), using two years (Sept. 1995 to Nov. 1996 and Nov. 1996 to Nov. 1997 when deep chiseling was carried out) of measured surface runoff data from the USDA-ARS Ben Hur research site. Simulations by DRAINMOD 5.1 were compared with those by DRAINMOD-Ks, DRAINMOD-STMAX, and DRAINMOD-Ks-STMAX to further determine the effect of the modifications on surface runoff and infiltration predictions. In general, DRAINMOD-STMAX, DRAINMOD-Ks, and DRAINMOD-Ks-STMAX improved surface runoff prediction by 57%, 73%, and 82%, respectively, in the 1995-1996 season and by 27%, 45%, and 62%, respectively, in the 1996-1997 season.