Pemetaan Daerah Rawan Bencana Longsor Sebagai Upaya Mitigasi di Kecamatan Berastagi Kabupaten Karo Provinsi Sumatera Utara

Abstract

The objective of this research is to map the distribution of landslide susceptibility in Berastagi sub-district and to analyze the slope stability located at the residential area in Tambak Lau Mulgap I Village, Berastagi Sub-district in the effort to perform appropriate mitigation. Quantitative descriptive method is employed using Shapefile 2019 data based on Soil and Agro-climate Research Center (puslitanak) 2014. Then the data is weighted, each parameter that is prone to landslide is overlaid using Arcgis 10.6 Software. The mapping results shows that over all each village in Berastagi sub-district has the areas that have the potential of landslide with high susceptibility classification and even very high. Villages in very high susceptibility are Doulu Village, Sempa Jaya Village, Raya Village, and Tambak Lau Mulgap II Village. The slope stability in this research is represented by Tambak Lan Mulgap I Village using slope geometry measurement data and laboratory analysis result in the form of physical and mechanical properties of soil, then calculate the value of slope Safety Factor (henceforth referred to as SF) with Bishop method using rocscience slide. The causing factor in the occurrence of landslide movement in Tambak Lau Mulgap I Village are the steep slope condition that range about 35% - 55%, Unstable lithology of slope material, some of which are breksi volcanic and tufa riodasit, and trigger factor like excessive water infiltration into the slope during high rainfall intensity. The slope in Tambak Lau Mugap I village is in the unsafe or the unstable condition because its Safety Factor value is less than I,25. Safety Factor values are different from each observation location. Safety Factor on slope one is 0,663, on slope two is 0,610, on slope three is 0,442. Therefore, landslide disaster mitigation is required in this area. Among of ways to mitigate it are by plant re-vegetation on dull slopes, change the slope geometry, build stone retaining walls and surface trenches on unstable slopes and protect the region hydrological system.