Flood Hazard Modeling in Thua Thien Hue Province, Vietnam

Nguyen Khac Tien Phuoc

Abstract

Thua Thien Hue is one of the costal provinces in the center part of Vietnam which has the tropical monsoon climate and it is often affected by tropical cyclones. High rainfall intensity in rainy season and steep gradient of terrain are the two main reasons that make floods a serious natural disaster in Thua Thien Hue. Flood hazard estimation and forecast are very necessary information for flood management and development planning for this province. The better flood hazard estimation we have the better the ability to mitigate flood hazard will be. Thus, this research aims to undertake a flood hazard study by applying the following tools: ArcGIS 9 software for terrain and catchment analysis; MIKE11 model (developed by DHI Water&Environment) to replicate rainfall-runoff and hydrodynamic processes; a GIS-based tool waterRIDE (developed by Patterson Britton and Partners from Australia) to produce inundation and flood hazard maps.

In this research, a raster-based DEM (Digital Elevation Model) data of Thua Thien Hue was utilised to identify river network and sub-catchment boundaries. The historical flood event from November 1999, estimated to be equivalent to 1 in 100 years average recurrence interval (ARI) flood event, was chosen for flood analysis in this research work. The rainfall-runoff results obtained by NAM model were used as upstream boundaries for the hydrodynamic model in MIKE11. A variable tide level was used as a downstream boundary of this model. The water level and velocity values at every cross section along the Huong and Bo river network were obtained by MIKE 11 model. This information was then processed by the waterRIDE software to interpolate the values between cross-sections and to produce a continuous water surface across the model domain. The water surface was then intersected with the terrain surface in order to produce relevant inundation maps. The water depth and velocity values were used in

calculation of flood hazards and such information was presented in a GIS-map. The maps produced show very useful information about flood hazards in this region which after some adjustment of parameters corrspond to the historical flood event from November 1999. As a potential remedial measure, the effect of reservoirs constructed at upstream end of the Huong and Bo river were modelled. The effectiveness of such remedial measure was evaluated in terms of reducing the extent of flood hazard at the downstream end of the two rivers.

The research work undertaken in this MSc gives an example of how the use of hydroinformatics technologies can be of invaluable benefits to the solution of real life problems such as the flooding in Thua Thien Hue province. In addition, it indicates that the information obtained from this study could be potentially used in a real time flood warning application of the flood mitigation programme for the province.