Search

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. SWAT2005 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 article 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 raindrops, adapted from the 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 in-stream sediment routing. The SWAT model with the modified sub-daily sediment algorithms was calibrated and validated each for a one-year period at 15 min intervals with measured data from the USDA-ARS Riesel watersheds in Texas. Results show that 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 process are so important to quantify. [ABSTRACT FROM AUTHOR]

Growing urbanization has led to increasing concern and emphasis on better construction site stormwater management. The objectives of this study were to determine the effectiveness of using compost rather than conventional hydroseeding or topsoil to reduce erosion from disturbed soils. The runoff rates, interrill erosion rates, and interrill erodibility factors from five compost and two control treatments (hydroseeding and topsoil) were compared. Compost treatments followed Texas Department of Transportation (TxDOT) specifications for compost applied as an erosion control at 1.3 and 5 cm depths. Rainfall simulation was used to apply a storm of 92 mm h-1. Surface runoff was collected after 5 min of rainfall (first-flush) and during the last 30 min of rainfall (steady-state). The first-flush mean runoff from the 5 cm depth general-use compost treatment was significantly higher than that of all other treatments. The other treatments (50% woodchips and 50% compost blend at 1.3 and 5 cm depths) and hydroseeding had significantly lower runoff and erosion rates compared to topsoil and compost manufactured topsoil at first-flush and steady-state. Furthermore, there were no performance differences between 1.3 and 5 cm compost applications at first-flush or steady-state. The TxDOT specification for erosion control compost depth might be able to be reduced from 5 to 1.3 cm. [ABSTRACT FROM AUTHOR]

Structural best management practices (BMPs) that reduce soil erosion and nutrient losses have been recommended and installed on agricultural land for years. A structural BMP is expected to be fully functional only for a limited period after installation, after which degradation of the BMP is likely to lead to a reduction in the water quality improvement provided by the BMP. Assessing the impact of BMPs on water quality is of widespread interest, but no standard methods exist to determine the water quality impact of structural BMPs, particularly as the impact changes through time. The objective of this study was to determine the long-term (∼20 year) impact of structural BMPs in two subwatersheds of Black Creek on sediment and phosphorus loads using the Soil and Water Assessment Tool (SWAT) model The BMPs were represented by modifying SWAT parameters to reflect the impact the practice has on the processes simulated within SWAT, both when practices are fully functional and as their condition deteriorates. The current condition of the BMPs was determined using field evaluation results from a previously developed BMP condition evaluation tool. Based on simulations in the two subwatersheds, BMPs in good condition reduced the average annual sediment yield by 16% to 32% and the average annual phosphorus yield by 10% to 24%. BMPs in their current condition reduced sediment yield by only 7% to 10% and phosphorus yield by 7% to 17%. [ABSTRACT FROM AUTHOR]