FLOOD DISASTER RISK INDEX MAP STUDY DUE TO THE FAILURE OF WAY ELA DAM, AMBON ISLAND

• Main Author: PRAMONO YAKTI (NIM : 25015002), BAGUS
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/26017
• Institution: Institut Teknologi Bandung

Way Ela Dam was a dam located in Negeri Lima Village, Leihitu District, Ambon Island. This dam was formed naturally by landslide due to high rainfall on 13 July 2012. A year after it was formed, on 25 July 2013 flooding occurred due to an extreme rainfall that caused the failure of the natural dam. According to Badan Nasional Penanggulangan Bencana (BNPB), the generated flood depth was about 6-7 m and took the lives of 1 person while the number of refugees reached to 3,000 people. The flood caused by the failure of the natural dam at least destroyed more than 350 housing units and other public facilities. <br /> <br /> <br /> Directorate General of Water Resources Maluku River Basin Organization planning to build way ela dam. Based on Government Regulation Number 37 (2010) states that every dam must have an Emergency Action Plan Document. One important element in the Document is flood risk analysis in the event of a dam failure. This study focused on the flood disaster due to the failure of the planned dam to be built. This study aims to analyze the risk index of flood hazard and flood risk reduction in Negeri Lima Village. Dam failure analysis is done with the help of HEC-HMS 4.0.1. The inflow hydrograph used for HEC-HMS simulation is HSS Snyder – Alexeyev. The results of the simulation are hydrograph outflow due to the failure of the dam, where the largest peak discharge is 1434,21 m3/s caused by bottom piping failure. Modeling of 2-D flooding is done with a model of Unsteady Flow using HEC-RAS 5.0.3. <br /> <br /> <br /> The 2-D overland flow modeling was first performed on the old dam, which had failure in 2013. The modeling of the old dam was used as a comparison to calibrate the roughness value of manning to be used in modeling for the planned dam. Calibration is done by validating with the inundation area that ever happened. The calibrated manning value is for the populated area, where the manning value for the populated area that has been calibrated is 0,172. <br /> <br /> <br /> The results of the Flood hazard Hazard Index mapping in Desa Negeri Lima are 100 grids with moderate risk, and the other 48 grids have high risk index of 148 grid.. High risk indexes are in densely populated areas. Negeri Lima Village is indicated to have a high potential risk of hazard, it requires serious handling either from the government or community role in order to reduce the impact of flood hazard due to the dam failure. The flood risk reduction in this study was conducted by non-structural methods IE early warning system floods either formal warnings or natural phenomena. Based on the relation of distance and time of the villagers to the evacuation site, early warning should begin after 3 minutes of water break out from the spillway to Desa Negeri Lima. <br /> <br /> <br /> Flood risk reduction is done by several alternatives by increasing the capacity index in Negeri Lima village to medium index for alternative 1 and high index for alternative 2. Each alternative 1 and 2 can reduce the risk by 14,2% and 22,94%. Of the two alternatives that have been implemented, flood risk reduction is still not maximal where the risk index in the Negeri Lima Village is still in medium risk index. This is because the risk reduction based on the capacity index is not effective enough, where the influence of the hazard index is still high. Reduction of flood risk index needs to be done based on the targets to be achieved, such as high reduction and flood velocity (reduction of hazard index), reduction of vulnerability index or increase of capacity index. <br /> <br />