Kajian Risiko Banjir di Daerah Aliran Sungai Asahan dalam Bentuk Peta Risiko Banjir dengan Menggunakan Sistem Informasi Geografis

Abstract

The Asahan Watershed is a massive hydrological site directly connected to Lake Toba, the largest lake in Southeast Asia. The Asahan watershed is fed by the Asahan River, which flows from Lake Toba through Porsea Subdistrict and empties into the Malacca Strait through Nibung Bay. The Asahan watershed is an area that is often hit by flood disasters caused by hydrological activities along the Asahan River as the main river. Responding to flood events in the Asahan watershed requires a medium to map the level of flood risk in the Asahan watershed so that flood anticipation can be more controlled and directed. Mapping the level of flood risk is obtained by multiplying the flood hazard value with the flood vulnerability value in the watershed area. The risk value is the value of rainfall for the return period of 10, 25, and 50 years, while the vulnerability value is grouped into two parts, namely social vulnerability which is the value of population density, and physical vulnerability which is the value of land use, slope, drainage density, and landform. This research is a quantitative study that uses scoring and overlay methods using GIS (Geographic Information System). Based on the results of scoring and spatial processing of the results obtained information on the high risk level increased from 869,129 km2 (23,708%) for the 10-year return period to 1745,892 km2 (47,624%) in the 25-year return period and decreased to 1627,777 km2 (44,402%) in the 50-year return period while the low risk level is widest at 707.995 km2 (19,312%) in the 10-year return period.