THE IMPORTANCE OF SEEPAGE ZONES IN PREDICTING SOIL MOISTURE CONTENT AND SURFACE RUNOFF USING GLEAMS AND RZWQM

Abstract

Seepage zones have been shown to be of critical importance in controlling contaminant export from agriculturalcatchments. To date, no multi-purpose agricultural water quality model has incorporated seepage zones into its process-levelrepresentations. We chose to test two commonly used models of agricultural water quality, Groundwater Loading Effects of AgriculturalManagement Systems (GLEAMS) and the Root Zone Water Quality Model (RZWQM), by seeing how well each predictedsurface runoff and soil moisture content in two agricultural fields: one with and one without seepage zones. Dailysimulated surface runoff and soil moisture content from both calibrated and default (or non-calibrated) GLEAMS and RZWQMwere compared with three years of measured surface runoff and soil moisture content in the two fields. The results of the studyshow that GLEAMS and RZWQM, using default model parameters, were not capable of predicting surface runoff and soil moisturecontent in either field. Site-calibrated GLEAMS and RZWQM performed well in simulating surface runoff trends from thefield with and without seepage zones, but they predicted soil moisture content poorly. Several statistical tests were used thatshowed that although both site-calibrated GLEAMS and RZWQM performed well, RZWQM performed better than GLEAMSand is better suited in assessing the effects of seepage zones on soil moisture content and surface runoff from agricultural fields.