Effects of Slope Magnitude and Length on SWAT Baseflow Estimation

Abstract

The aim of this study was to improve streamflow predictability using the soil and water assessment tool (SWAT) model for baseflow estimation in a steeply sloped watershed. The two objectives were (1) to appraise streamflow predictions using SWAT for different slope magnitude and slope lengths in hydrologic response units (HRUs); and (2) to analyze baseflow contribution to streamflow through a baseflow separation method. To achieve these objectives, the SWAT model and the web-based hydrograph analysis tool (WHAT) system were implemented for five scenarios, comprising various slope magnitudes and slope length calibrations in the geologically distinct Haean-myeon watershed in South Korea. The results showed that SWAT streamflow predictions differed significantly when SWAT’s default slope magnitude and slope length was used versus the observed slope magnitude and slope length for baseflow estimation. Moreover, better prediction occurred when a representative slope length based on the observation was used rather than SWAT’s default slope magnitude and slope length. In this context, the effect of slope magnitude and slope length on baseflow and streamflow using SWAT was illustrated. Therefore, proper slope magnitude and slope length characterization will significantly improve the prediction ability of the SWAT model.