Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/29/2013
Publication Date: N/A
Citation: Interpretive Summary: Terraces are an effective conservation practice for reducing soil loss. However, many computer models commonly used to facilitate conservation planning do not fully simulate 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 process-based model of terrace behavior and incorporated it into SWAT. The model simulated each segment of the terraced slope and estimated water storage on the terrace and sediment yield from the field. Data sets collected on a terraced field in Franklin County, Kansas was used for testing and validation of the model. Results showed that the program simulated runoff and sediment with acceptable errors. This new program will benefit scientists and conservation planners who use SWAT in watersheds where terraces are used or considered. It allows for predictions of the multiple effects of terraces on runoff, sediment and nutrient transport, and groundwater recharge. In addition, different kinds of terraces can be considered, i.e., normal terraces as in the US and bench terraces as in China and Asia.
Technical Abstract: Terraces have been proven to be an effective conservation practice for controlling high soil loss. In large hydrological programs such as Soil and Water Assessment Tool (SWAT), terrace effects are simulated by adjusting the slope length and the USLE P-factor. In this study, a process-based terrace algorithm was developed and incorporated into SWAT (version 2009) to simulate the environmental effects of different kinds of terraces, i.e. normal and bench terraces. The terrace algorithm was activated at the Hydrological Response Unit (HRU) level. Terrace description, storage effects and the flow interaction between the terraces and the HRU were also introduced in the method. The modified SWAT model was evaluated using a 4-year long 6-plot event runoff and sediment data set with 5 years of crop yield data collected on a natural rainfall terraced field in southeast Franklin County, Kansas. Results indicated that the model did a satisfactory and consistent prediction in simulating single and average plot runoff as well as average plot sediment yields with Nash-Sutcliffe efficiencies always greater than 0.5 and often greater than 0.7. The model’s performance was less consistent in simulating sediment yields from the no-till plots. In general, the development and incorporation of the terraces algorithm provides a process-based alternative to the use of the P-factor in representing the effectiveness of terraces.