Abstract

Java Island's geographical position and natural conditions imply proneness to flooding in many of its areas in terms of inundated land due to water overflows caused by heavy rainfall or runoff water from higher areas. Such flooding occurs in the Keduang Sub-watershed, a part of the Bengawan Solo Watershed. It is known as one of the big rivers significantly influencing human life in Java Island. The inundated area along the river is affected by many factors, one of which under human control is land use, which in this case is expressed by land cover. This research aims to develop a simulation model for predicting inundated areas affected by land cover change. Keduang Sub-watershed is selected as the case study. The model development contains two main stages: validating the computation (mathematical formula) of flood discharge and inundated area, and developing the program (simulation model). The design flood discharge is computed using the Nakayasu method and validated by comparing it with actual data. If suitable, it is used to spatially visualize the inundated area. The software applied to develop the program are HEC-RAS/GeoRAS and ArcGIS, combined with Visual Basic as the programming language. Visual Basic is used to develop a computation program for calculating design flood discharge and link it with HEC-RAS and ArcGIS. HEC-RAS is used to estimate the inundated area. Input of the simulation model is land cover, while its output is a map of the inundated area. By changing the land cover input, a new design flood discharge can be computed and a new map of inundated areas along the river can be drawn. The results have shown that the developed model is suitable and works well. In practice, it can help regional managers to refine land use policy related to flood risk in the watershed. Unfortunately, the link between the program of Nakayasu method and HEC-RAS has not been well developed due to some technical problems in programming language. It will therefore be developed in further research.