Landslide Vulnerable Zones Based on Engineering Geological Assessment, Case Study: Wonotopo Area, Gebang District, Purworejo Regency, Central Java, Indonesia

Abstract

Landslide is one of the geological disasters that frequently occur on the natural slopes, often threatening community of the adjacent area. Therefore, it is necessary to hold engineering geological research and assessment in disaster-prone regions such as Gebang district of Purworejo Regency, Central Java Province, Indonesia. This research was conducted to determine and analyze the type of mass movements, factor of safety, potential landslide areas, vulnerable zonation, factors influencing the stability of the slope, and to propose the disaster mitigation recommendation. The methods applied in the research are surface geological mapping, physical soil-rock properties testing, engineering geological assessment and analysis, and Regulation of Minister of Public Works of Republic of Indonesia number 22/PRT/M/2007, on Guidelines to Spatial Planning for Landslide Disaster Areas. To create information on the threats of land movements, a map on landslide potential zonation is developed by considering seven important aspects including: slope inclination, soil conditions, slope constituents, rainfall, slope water condition, seismicity, and vegetation or land use. The results show that, the landslide prone zone of the study area can be divided into 2 types, namely type B and type C. Landslide potential zone of type B involves high level of vulnerability and moderate level of vulnerability. Meanwhile, the landslide potential zone of type C consists of high level of vulnerability and low level of vulnerability.