Dynamic Floodplain Visualization of Unsteady Flood Models using Geographic Information System (Case Study of Downstream Ciliwung, Jakarta, Indonesia)

Abstract

Jakarta (also Djakarta or DKI Jakarta) is the capital and the largest city of Indonesia, located on the northwest coast of the island of Java, at 6" 11' S and 106"SO'E. It has an area of 650 km2. Down stream Ciliwung, located in DKI Jakarta, was the focus of study based on the reason that flooding has always been a constant problem to both the immediate residents and the local government. The river reach length used for the hydraulic models, is approximately of 5.09 kilometers. Local planners and decision makers are in need accurate information on the spatial distribution, magnitude and depth of flooding, and on the landuse affected by it. The objectives of this research are: 1) to predict design flood for site along a river and 2) to create dynamic floodplain visualization of Downstream Ciliwung by integrating HEC-RAS hydraulic modeling and Arcview GIs. The results of this study provide information on the unsteady flow hydraulic model method as well as what advantages it has over steady flow hydraulic models. The HEC RAS model's stream geometry was extracted from the digital terrain model, which ensured that the flood plain's extent was fully accounted for. The results of the HEC RAS unsteady flow model were also compared to the HEC RAS steady flow model based on steady flow peak runoff discharge values. The unsteady flow hydraulic madel's maximum water surface elevation was less than the steady flow hydraulic model's water surface elevation because the steady flow hydraulic model assumes peak runoff occurs simultaneously in the individual drainage basins within the watershed, while the unsteady flow model more closely mimics the movement of the flood wave through the drainage area. Flood delineation in the HEC GeoRAS post-processor is simple, but Anhation processing is tedious. This procedure required numerous GIs export file development iterations from the HEC RAS interface. Once accomplishsd, each time step was copied with a screen captured image and pasted into an animation software tool to develop an animated GIF of the flood event. Overall, the results of the research indicate that GIs is an effective environment for floodplain mapping and analysis.