Spatially Distributed Mapping of Soil Erosion in a Debris Catchment After the 2018 Palu Earthquake

Erosion of the unstable ground surface in the debris catchment is an interesting topic to study. Besides being caused by loose soil surface, this instability is also caused by external factors such as earthquake shaking and land cover conversion. This study aims to map the erosion rate in one of the debris catchments in Central Sulawesi Province, Indonesia, namely Sombe-Lewara. The study was initiated by collecting data, especially land cover in the study area before and after the 2018 Palu earthquake which illustrates changes in soil erodibility factors that have the potential to affect erosion intensity. The analysis was performed spatially using the Soil and Water Assessment Tool (SWAT) under the Quantum GIS (QGIS) platform based on the Modified Universal Soil Loss Equation (MUSLE). Erosion modeling was carried out in two conditions: before and after the 2018 Palu earthquake, taking into account changes in soil surface morphometry and land cover due to the earthquake shocks. The simulation results show that the erosion rate increased after the earthquake from 155.86 ton/ha/year to 182.12 ton/ha/year. This increase in erosion rate is equivalent to 16.85% due to landslides covering an area of 3.37 km2 hectares and exposed dry land agriculture covering an area of 55.12 km2.