Flood mitigation for local rainfall in Bangkok Noi and Bangkok Yai district using MIKE 11 model

Abstract

In the past decades, the influence of climate change and rapid growth rate of urbanization have caused changes in the amount of rainfall in many areas which may affect the flood assessment and mitigation. This research aims to investigate the change in the amount of rainfall which impacts on changes of the water levels in canals and evaluate the appropriate mitigation measures for floods in Bangkok Noi and Bangkok Yai districts of Bangkok. Ten-year moving average and Mann-Kendall test were applied to determine the trend of the annual rainfall and maximum 1-day rainfall during the period of 1982-2010. The maximum 1-day rainfall in two periods, the 1982-1996 and the 1997-2010, were compared under different return periods of 2-, 5-, 10-, 25-, 50- and 100-year. The MIKE 11 model was then applied to assess changes of the water levels in canals caused by changes of amounts of design rainfall events for various return periods. The flood mitigation was also proposed by applying various pumping capacities and initial water levels, incorporating with building dykes and a floodgate. This study has found that the annual rainfall has increased while the maximum 1-day rainfall has decreased which causes the maximum water level being lower, especially for 25-, 50- and 100-year rainfalls. The highest flood risk areas are along Chakphra and Bangkhunnon canals and the eastern part of Jakthong Canal while the lowest flood risk area is Bangkok Yai district. Flood caused from the 10-year rainfall can be mitigated by building dykes with the height of 0.75 m (MSL) and maintaining the initial water level of 0.70 m (MSL). Furthermore, it has also been found that flood caused from the 25-year rainfall can be mitigated by building the floodgate to prevent the flowing back water at Wat Yangsuttharam Canal.