Analysis of flood extend and inundation of Upper Citarum based on hydrodynamic model and geographic information systems

Abstract

Flooding in the Upper Citarum river basin, especially in the Cekungan Bandung occur almost every year. In addition to its high rainfall, the floods also caused by excessive land conversion and deforestation. Flooding events in the Citarum basin not only hit the local settlements, but also damaging rice crops and other infrastructures located in the national rice production centers in the north coast of West Java. Therefore, these losses then affect the national rice production which destabilize food security. The purposes of this study are to analyzing the characteristics of river flow and flood discharge of Upper Citarum, preparing inundation maps of Upper Citarum in the scale of 1:100,000 with return flood period scenario of 2, 25 and 100 years, and analyzing the potential for rice crop losses caused by the flood and inundation in the upper Citarum river basin, West Java. Flood return period was calculated based on the Gumbel frequency. Flood and inundation was modeled using HECRAS which was developed by the U.S. Army Corp of Engineers (2002). While the rice crops losses by the flood and inundation was estimated using RENDAMAN.CSM model. Results of the analysis showed that the ratio of the maximum and minimum flow discharge was high and so the frequency and magnitude of extreme flood discharge. These suggest that the upstream watershed condition of Citarum river basin has suffered severe damage. These conditions result in the high flood demonstrated by the extent of the flood-prone areas resulted from flood simulation on a two-year return period. Potential loss of rice due to floods in the paddy fields on a two-year return period reached 8.4 billion rupiah, this amount will be tripled in the 25 years flood return period and becomes 6.4 times in the 100-year return period. Paddy spikes loss ratio of the period of 25 years to 100 years is higher than 2-year period to 25 years. This is because flood-prone areas in the 100-year return period not just located in the same area of 25-year flood return period but also includes the wetland area with water levels in between 55 to 110 cm. Losses in this area is higher compared to the losses of 25-years flood return periods.