DEBRIS FLOW HAZARD ANALYSIS TOWARD THE IMPLEMENTATION OF MITIGATION MEASURES

Abstract

A massive debris flow occurred on 28 April and 3 May 2016 in Beriti Hill, Bengkulu Province, Indonesia. The debris flow carried 4.3 million cubic meters of sediment materials containing 1-2 m diameter boulders that damaged roads, bridges, and geothermal facilities. This study assesses the debris flow hazard through comprehensive field investigation and laboratory testing and analyses the effectiveness of proposed mitigation measures against the destructive energy of the debris flow. A closed-type conduit Sabo dam is proposed as a countermeasure. The design of the Sabo dam considered the engineering geology, hydrologic and hydraulic, and geotechnical aspects. The hydrologic analysis used Synthetic Unit Hydrograph, which was continued by flood analysis using HEC-RAS. The geotechnical analysis was conducted to determine the Sabo dam stability utilizing the field and laboratory test data. The analysis shows that without a Sabo dam, the debris flows were distributed to a larger area downstream and destroyed the structure of the old bridge. The impacted area reduced significantly when the Sabo dam was implemented.