Extreme rainfall and vulnerability assessment: case study of Uttarakhand rivers

Abstract

The torrential rains in June 2013 combined with melting of snow caused voluminous floods in the rivers of Uttarakhand and subsequently triggered widespread mud, landslides and debris deposition. The event caused instability of the channel by shifting the banks. Erosion rendered many locations along the banks vulnerable to economic and human loss. The shifts in reaches are calculated by digitizing the bank line using satellite imageries of year 2005, 2010 and 2015. The extent and magnitude of risks have been assessed based on information of past events, rapid field assessments, current mitigation measures and interactions with the locals. The findings from these interactions, and secondary data based on geospatial analysis of bank line changes have been used in the identification of vulnerable reaches along the major rivers. Criteria to identify the vulnerable reaches are based on risk, exposure and hazards in that area. The magnitude of risks due to flood hazards on various exposures along the riverbank is calculated based on qualitatively derived scores. River basins focusing on rainfall, topography, drainage pattern, soil, landslide and exiting infrastructure in relation to vulnerability of the region using GIS data are discussed in details. A fuller understanding will enable decision makers towards more efficient resources management for prevention and protection of river banks due to flood events. In addition to this, an official online decision support system ( www.urmis.dhi-india.com ) with collaborating partners and organizations for relevant data, information and document has been created.