Effects of Revised SCS Curve Number Method on Ecohydrological Indicators and BMP Decision-Making Using the Soil and Water Assessment Tool
Author | : Jamie Weikel |
Publisher | : |
Total Pages | : |
Release | : 2021 |
ISBN-10 | : OCLC:1258263011 |
ISBN-13 | : |
Rating | : 4/5 (11 Downloads) |
Book excerpt: The Soil Conservation Service (SCS) Curve Number (CN) method is a widely used model developed by the Natural Resources Conservation Service (NRCS) that estimates the surface runoff generated from a land area using factors such as land cover, soil type, and precipitation depth. However, this empirical model was developed over 60 years ago with limited data; thus, NRCS proposed revising the method with support of an ASCE-ASABE task group. The proposed revisions include updating the initial abstraction estimation in the CN equation and modifying the curve number for all land use and soil hydrologic group combinations. The proposed revisions are expected to improve the hydrologic response estimation, especially for smaller precipitation events. Since surface runoff is the driving force that transports sediment, nutrients, and other chemicals in natural systems, this study aims to understand how predicted ecohydrological indicators vary between the original and the proposed revised versions of the SCS Curve Number method using the Soil and Water Assessment Tool (SWAT). Additionally, a small case study site was selected to understand how the revisions alter design storm runoff analysis. The Spring Creek watershed, located in central Pennsylvania, was selected as the study watershed for the SWAT simulation since it contains a mixture of forested, agricultural, and urban land covers. Results from the simulation study indicate a 5-13% increase in annual runoff predictions with the revised equation compared to the original equation. Though most average monthly runoff depths increased by 8-25% using the revised equation, winter months generally simulated runoff depths that were 1-5% lower than the original equation. Average daily nutrient loadings in the streamflow at the watershed outlet increased by 9-16% and 3-10% for nitrate and mineral phosphorus loadings, respectively. When using the revised equation, the average daily erosion and sediment loading in the streamflow was consistently within 1% of the original equation. The SWAT simulation results suggest that current agricultural and urban best management practices (BMPs) will experience higher runoff volumes on a yearly time scale, while the small-scale case study results suggest that urban BMPs can be designed to be smaller in size if rural lands are urbanized. More detailed evaluations of the proposed SCS curve number method are required on water quality simulations, stormwater management, and BMP designs.