Flood risk zone mapping of the Subansiri sub-basin in Assam, India

Flood plain zoning of a river basin is an essential management strategy to regulate land use in order to restrict the damages in frequently flooded areas. The river Subansiri is one of the largest north bank tributaries of the Brahmaputra which creates flood havoc almost every year bringing untold miseries for the people living in the lower part of the basin, i.e. the part which falls in the Dhemaji and Lakhimpur districts of Assam. Flood plain zonation of this area is done in this study on the basis of the flood inundation map of 2004 collected from the Dartmouth Flood Observatory website and the flood inundated areas during the flood of 2008 where water remained stagnant even in the post flood period.These areas are delineated from post flood season imagery of October 2008. The final flood zonation map includes three zones viz. the chronically inundated, occasionally inundated and rarely inundated zones. A large part of the agricultural lands and villages of Dhemaji and Dhakuakhana lying on the left bank of the river Subansiri were submerged by flood compared to the right bank. This may be because of the low-lying nature of the basin in Assam where these parts are always vulnerable not only to the floods of the Subansiri and its tributaries, but also to breaching of the embankments of the river Brahmaputra.