Flood hazard and risk analysis using geomorphological approach and its application for land use planned evaluation on Sintang City area, West Borneo

Abstract

The Sintang City, located in West Borneo, is annually inundated by flood during rainy season. The city itself is growing in the Y-junction of two big river i.e. Kapuas and Melawi, or geomorphologically it is growing in the major floodplain of those rivers. In 1963, flood disaster has occurred during several days, inundating most of settlements and there were many of victims and damages. Although in the last recent years the floods are moderate, but such big event could be repeated in the future time. Study of flood and mitigation will be important for the study area for reducing disaster. The aims of this research are to (1) analyses and mapping of flood hazard and risk zones and (2) to analysis and evaluate the Sintang’s land use planned (RDTRK) based on flood hazard. Geomorphological approach is used for analyzing flood hazard based on morphogenesis and morphology parameters, and history of floods. The flood hazard map will be used together with actual land use map for analyzing flood risk. Scoring of geomorphological and land use parameters is applied and GIS spatial analyses (overlay) is used for assessing hazard, risk, and evaluation of RDTRK. The results indicating that 0,8% area of Sintang classified as very low of hazard, 57,2% low, 31,5% moderate, and 10,5% high. It represent that most of area of the city is really hazardous areas of flooding, it match to its morphogenetic landforms of study area dominated by fluvial landforms. According to risk analysis result, there are 0,9% of city’s area has very low risk of flooding, 70,1% low, 22,5% moderate, and 6,5% high. These two later classes wholly cover developed areas, such as residential, office, and commercial areas, signifying that all developed areas in the city will be threated moderately to highly by flood hazard. The risk analysis of RDTRK is divided in two, namely the RDTRK’s actual risk and the RDTRK’s potential risks successively represented the planned area that has been realized and those for not realized yet. The result shows that 352 Ha developed areas, 1.435 Ha vegetated areas, and 10 Ha developing agricultural area classified as moderate to high actual risk, while 1.467 Ha developed areas, 178 Ha vegetated areas, and 745 Ha developing agricultural area classified as moderate to high potential risk. These figures demonstrated that the greatest extend of potential risk possed by developed areas planned. Hence RDTRK should be re-evaluated together with mitigation planned in order to minimize the extend of risk. Flood mitigation program will be an urgently program, such as building of rivers dykes or drainage canals of study area, and reboisation of upland areas of Kapuas and Melawi watersheds.