Susceptibility assessment of shallow landslides on Oahu, Hawaii

Sanjit Kumar Deb, Assistant Researcher, Department of Natural Resources and Environmental Management, UH

Abstract

The island of Oahu combines several essential components for the development of rapid shallow landslides and debris flows: steep hillsides with colluvial or regolith cover, heavy rainfalls, and strong demand for residential development in upland areas. Information pertinent to Oahu landslides is still limited, despite the fact that landslides, especially rapid shallow landslides, pose severe threats to life, infrastructure, and property. Annual landslide inventories are rarely done and there is almost no information on susceptibility or terrain-stability assessment with respect to landslide occurrence. Geotechnical studies to assess landslide-susceptible areas and engineering construction to stabilize potentially landslide-prone areas can be both time consuming and very expensive. Therefore, simple-but-reliable mathematical prediction tools for landslide susceptibility assessment would provide a viable planning and/or development alternative. This presentation describes and discusses the application of a deterministic model "Stability INdex MAPping (SINMAP)" to assess the shallow landslide susceptibility of slopes in the watersheds of eastern to southern areas of Oahu under extreme-rainfall events. The results of this deterministic model, which integrates an infinite slope stability model and a hydrological model, were calibrated using an inventory of storm-induced shallow landslides that occurred from 1949 to 2006, and previous susceptibility appraisals. Predicted slope-stability data will aid in explaining causes of known landslides, making emergency decisions, and, ultimately, mitigating future landslide risks.