PROBABILISTIC FLOOD HAZARD MAPPING FOR EMBANKMENT BREACHING

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Abstract
The study proposes a methodology for producing probabilistic flood hazard maps based on an ensemble of 2-D hydrodynamic model and frequency analysis of discharge data. With available floodplain topography and limited river bathymetric data, a 2-D hydrodynamic model has been set-up to predict flood inundation area for recently breaching location of the embankment of the river Brahmaputra for a given flood hydrograph. Frequency analysis of the flood waves in nearby gauged records has been conducted and the flood inundation at the breaching location for flood waves of different return period and average monsoonal condition (dry, normal and wet) has been simulated. After that, spatial analysis of the simulated flood inundation depth and maximum velocity is conducted to categorize flood hazard zones. The methodology was applied over a 600 km2 of flood prone area, close to the northern bank of a 64 km reach of the river Brahmaputra (Assam, India). In this study, probabilistic flood hazard mapping approach for embankment breaching at Matamara, Lakhimpur district, Assam was evaluated with the flood inundation obtained from satellite imagery. The spatial variation of simulated flood inundation of 20 years return period closely matches with the observed inundation. The most vulnerable zone within the floodplain area is identified considering random breaching locations. This study demonstrates that probabilistic flood hazard maps in a river valley can be prepared by this approach with limited topographic dataset.