Probable Flood Inundation Depth and Extent in the Chao Phraya River Basin for Different Return Periods

抄録

Understanding the potential flood inundation depth and extent over river basins can provide a reference for understanding and mitigating the flood risk. However, the development of design hyetographs for the evaluation of flood inundation under extreme rainfall is challenging. We evaluated the flood inundation depth and extent in the Chao Phraya River Basin, one of the largest river basins in Asia, which is often vulnerable to water-related disasters. Rainfall data from 119 stations within the basin were collected for a frequency analysis. After processing the 36-year daily rainfall data, a frequency analysis of the maximum monthly rainfall was performed at each station using the Gumbel distribution. The maximum monthly rainfall for various return periods varied substantially among stations. For an inundation analysis over the entire river basin, we produced design hyetographs by integrating extreme rainfall values for each month according to the return period. These design hyetographs were included in a rainfall-runoff-inundation model to simulate the maximum inundation depth profile over the basin for different return periods. The Maximum inundation depths were 8.3, 9.0, 9.7, and 10.5 m for return periods of 50, 100, 200, and 500 years, respectively, over the Chao Phraya River Basin. Similarly, approximately 16.3%, 17.1%, 17.8%, and 18.6% of the basin area was inundated (depth > 0.5 m) over the return periods, respectively. The results of this study provide a good reference for risk analyses and evaluations of the Chao Phraya River Basin.