Submitted to: Transactions of the ASAE
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/2/2003
Publication Date: 6/20/2003
Citation: Chinkuyu, A.J., Meixner, T., Gish, T.J., Daughtry, C.S. 2003. The importance of seepage zones in redicting soil moisture content and surface runoff from watersheds with Gleams and RZWQM. Transactions of the American Society of Agricultural Engineers. 47:427-438. Interpretive Summary: Developing models that can accurately predict surface runoff from agricultural land is critical to the development of farming practices that protect the environment while maintaining crop productivity. Although a number of management models are available, good surface runoff and soil water dynamics data to test and calibrate these models are rare. In this study, two of the most frequently used water quality models (GLEAMS Groundwater Loading Effects of Agriculture Management Systems, and RZWQM Root Zone Water Quality Model) are compared on intensive data sets from two neighboring watersheds located in Beltsville, Maryland. Results show that when model parameters were used from similar but different watershed their ability to predict surface runoff was poor. Only when the models were calibrated on-site does their ability to predict surface runoff become reasonable. Unfortunately, even site-calibrated models do a poor job of predicting soil moisture dynamics. Since neither model effectively simulated soil water dynamics their ability to simulate subsurface leaching processes will be compromised and further model development is justified.
Technical Abstract: The Groundwater Loading Effects of Agricultural Management Systems (GLEAMS) and the Root Zone Water Quality Model (RZWQM) were used to predict surface runoff and soil moisture content in two watersheds: one with and one without seepage zones. Daily simulated surface runoff and soil moisture content from both calibrated and non-calibrated GLEAMS and RZWQM were compared with one-year (2000) measured surface runoff and soil moisture content in the two watersheds. The results of the study show that GLEAMS and RZWQM using default model parameters were not capable of predicting surface runoff and soil moisture content in either watershed. Site-calibrated GLEAMS and RZWQM performed fairly well in simulating surface runoff trends from the watershed with and without seepage zones, but poorly predicted soil moisture content. Several statistical tools were used that showed that although both site-calibrated GLEAMS and RZWQM performed reasonably well, the RZWQM performed better than GLEAMS and is better suited in assessing the effects of seepage zones on soil moisture content and surface runoff from agricultural watersheds. Additionally, since neither model effectively simulated soil water dynamics their ability to simulate subsurface leaching processes will be compromised and further model development is justified.