IMPROVING WATER QUALITY IN AGRICULTURAL WATERSHEDS UNDERLAIN BY CLAYPAN AND RESTRICTIVE LAYER SOILS
Location: Cropping Systems and Water Quality Research
Title: A process-based method for evaluating terrace runoff and sediment yield
Submitted to: ASABE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: June 22, 2012
Publication Date: July 29, 2012
Citation: Hui, S., Baffaut, C., Gao, J. 2012. A process-based method for evaluating terrace runoff and sediment yield. ASABE Annual International Meeting, Dallas, Texas, July 29-August 1, 2012. Paper No. 121341006.
Interpretive Summary: Terraces are an effective conservation practice for reducing soil loss. However, many computer models commonly used to facilitate conservation planning do not easily incorporate the effects of terracing. For example, in the Soil and Water Assessment Tool (SWAT), terrace effects are simulated by adjusting empirical input parameters. In this study, we developed a computer program that incorporated a process-based model of terrace behavior. The model simulated each segment of the terraced slope and estimated water storage on the terrace and sediment yield from the field. A dataset collected on a natural rainfall runoff plot in southwest China was used for verification. Preliminary results showed that the program simulated runoff and sediment with acceptable errors in the control and terraced plots. The program simulated the terrace effectiveness, i.e. the difference in runoff and sediment yield between the terraced and control plots, with less than 10 percent error. This new program can be incorporated into the SWAT model to improve its evaluation of terrace effects at field and watershed scales, benefitting scientists and conservation planners who use SWAT analyses in watersheds where terraces are used or considered.
Terraces have been proven to be an effective conservation practice for controlling high soil loss. In large hydrological programs such as the Soil and Water Assessment Tool (SWAT), terrace effects are simulated by adjusting the slope length and the USLE P-factor. In this study, a computer program based on the SCS curve number method, MUSLE and the Kodatie model, was developed to simulate each segment of the terraced slope and estimate water storage on the terrace. A previously published 4-month long dataset with 10 runoff events collected on a natural rainfall runoff plot in southwest China in 2008 was used for verification. Preliminary results showed that the program simulated terrace effects with average errors ranging from 8 to 37 percent for control and terraced plots runoff and sediment yield. The average errors in terrace runoff and sediment reduction effects were less than 10%. This program can be incorporated into the SWAT model for process-based evaluation of terrace effects at field and watershed scales. Its physical basis provides a useful alternative to the use of the P-factor to characterize the effectiveness of terraces.