Floodplain Mapping Using HEC-RAS and GIS in Nam Phong River Basin, Thailand

Abstract

Floodplain management and mapping is a new and applied method for the river engineering and is essential for prediction of flood hazards. The lower Phong Basin area regularly goes more or less under flooding every year in the monsoon season due to lack of flood protection and limited resources. Most of the flood protection works are carried out at the local level without preplanning and considering the problems at the river basin scale. Traditionally, individuals or communities have been trying to develop their own strategies for minimizing the effects of floods. However, due to limitation of resources and knowledge, many householders are unable to protect their properties or possessions from floods. A methodology was applied to integrate hydraulic simulation model, HEC-RAS and GIS analysis for delineation of flood extents and depths within a Nam Phong River in northeast of Thailand. It is necessary to simulate complicated hydraulic behaviour of the river in a more simple way for the purpose of managing and performing all river training works[F1]. In this research, the steady flow was used to simulate flood along 148 km end of Nam Phong River starting at upstream from Ubolratana Dam to Chi River in Northeast of Thailand. Floodplain mappings were derived using integrating of HEC-RAS and GIS analysis. Delineation of flood extents and depths within the floodplain were conducted in different return periods. Critical flooding area along the river was distinguished based on the grid layer of flood depths. The results indicated that hydraulic simulation by integrating with GIS analysis could be effective for various kinds of floodplain management and mapping and give as different scenarios for river training works[F2] and flood mitigation planning.