Estimation of erosion using Soil and Water Assessment Tool (SWAT) model in Samin Sub-watershed, Karanganyar and Sukoharjo Districts, Jawa Tengah

Over the past 10 years (2005-2015) there has been an increase in settlement land use in the Samin Sub-watershed, with an average of 26.8 ha/year 1. Land in the study area is also widely used as plantations and agriculture without regard to soil conditions that are easily eroded and prone to landslides. Inappropriate land use has caused river siltation problems downstream and flooding. The purpose of this study is to determine the erosion rate of the Samin Sub-watershed predicted using the Soil and Water Assessment Tool (SWAT) model, test the suitability of the model in predicting erosion, and create scenarios for the application of Soil and Water Conservation in the form of terraces to reduce erosion level. The results indicated that the average erosion rate in the Samin Sub-watershed is 57.4 tons/ha/year. The highest erosion value is in dry land use. The three criteria for the Erosion Hazard Level (TBE) that predominate are the medium, light, and very light classes. Model suitability testing is carried out in 2 stages, namely calibration and validation. The calibration process obtained the value of R2 0.77 and NSE 0.23. The validation process resulted the value of R2 20.57 and NSE 0.40. The scenario of the application of Soil and Water Conservation technique in the form of a terrace will reduce erosion in the Samin Sub-watershed up to very light erosion hazard grade reaching 53%.