Flood risk assessment in the eastern part of Dhaka City Bangladesh

Dhaka City is surrounded by a network of rivers which makes the city vulnerable to flooding. The present study provides an assessment of flood risk of eastern part of Dhaka City. In the risk assessment task, following flood frequency analysis, flood inundation map is produced using hydrodynamic model HEC-RAS and Hec-GeoRAS extension Arc GIS 9. Then secondary depth-duration-damage function of various land use classes is used to produce raster-based vulnerability map. Present monetary value of property of various land use classes is collected through survey. Then expected damage map is generated as a mathematical product of vulnerability, property value and area in GIS environment. Finally expected damage value is classified into several classes where each class represents risk of the study area. The study findings show the Log Pearson Type III distribution is the best distribution for flood frequency analysis in the study area. The uncertainty consideration and subsequent flood inundation mapping using finer resolution of TIN show that the depth and the extent of inundation obtained by present study for 1988 flood is smaller than that of obtained by Halcrow study. The study also finds that land use pattern is very sensitive to the vulnerability and the expected damage of the study area. In comparison to the classical inundation maps, produced expected damage map generates more information about the flooding event because they bring into account the effects of flooding. These maps can be useful to evaluate policy alternatives and the results of this study may be used for future flood damage mitigation plan in the study area.