Development of sub-daily erosion and sediment transport algorithms in SWAT

Authors: JEONG, JACHAK - Texas Agrilife Research; KANNAN, NARAYANAN - Texas Agrilife Research; Arnold, Jeffrey; GLICK, ROGER - City Of Austin; GOSSELINK, LEILA - City Of Austin; SRINIVASAN, RAGHAVAN - Texas Agrilife Research; Harmel, Daren

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2011
Publication Date: 10/1/2011
Citation: Jeong, J., Kannan, N., Arnold, J.G., Glick, R., Gosselink, L., Srinivasan, R., Harmel, R.D. 2011. Development of sub-daily erosion and sediment transport algorithms in SWAT. Transactions of the ASABE. 54(5):1685-1691.

Interpretive Summary: New methods are needed to better represent stormwater best management practices (BMPs) such as detention basins, wet ponds, sedimentation filtration ponds, and retention irrigation systems in simulation tools, such as Soil and Water Assessment Tool (SWAT), because these practices are very important in small watersheds and urban watersheds. Accurate prediction of stormwater BMP effectiveness often requires time steps as small as minutes, but SWAT currently uses a daily time step. This paper presents modified methods (for splash erosion, overland flow erosion, and instream sediment routing) that were incorporated into SWAT for sub-daily prediction. The modified SWAT predictions were compared with measured data from the USDA-ARS Riesel Watersheds in Texas. Results show that SWAT with the sub-daily erosion methods performed as well or better in terms of sediment yield prediction than SWAT with the current daily output. In addition, SWAT (sub-daily) was able to adequately represent the timing, peak, and duration of sediment transport events. Thus, this initial evaluation indicates that the new sub-daily structure in SWAT is a promising tool for water quality assessment studies in small watersheds or urban watersheds where sub-daily processes are so important to quantify.

Technical Abstract: New Soil and Water Assessment Tool (SWAT) algorithms for simulation of stormwater best management practices (BMPs) such as detention basins, wet ponds, sedimentation filtration ponds, and retention irrigation systems are under development for modeling small/urban watersheds. Modeling stormwater BMPs often requires time steps as small as minutes to realistically capture the instantaneous flow and sediment load coming from upland areas. SWAT 2005 uses the Modified Universal Soil Loss Equation (MUSLE) for modeling upland erosion and sediment load. The MUSLE model is an empirical soil loss equation, which was formulated based on field observations rather than theoretically derived relationships to predict long-term average soil loss. This paper presents modified physically-based erosion models in SWAT for seamless modeling of erosion processes with the recently developed sub-hourly flow models. In the new algorithms, splash erosion is calculated based on the kinetic energy delivered by rain drops adapted from European Soil Erosion Model, and overland flow erosion is estimated using a physically-based equation adapted from the Areal Nonpoint Source Watershed Environment Response Simulation (ANSWERS) model. The Yang model and the Brownlie model were also modified for instream sediment routing. The SWAT model with the modified sub-daily sediment algorithms was calibrated and validated each for a 1-year period at 15 minute intervals with measured data from the USDA-ARS Riesel Watersheds in Texas. Results show that the SWAT with the sub-daily algorithms performed as well or better in terms of sediment yield prediction than SWAT with the current daily output structure. In addition, SWAT (sub-daily) was able to adequately represent the timing, peak, and duration of sediment transport events. Thus, this initial evaluation indicates that the new sub-daily flow and sediment structure in SWAT is a promising tool for water quality assessment studies in small watersheds or urban watersheds where sub-daily processes are so important to quantify.