Flood risk assessment framework for Himalayan river basin

Increasing rate of flash-floods in Himalayan river basin causes immediate damage to human lives, daily living and infrastructure. The present work proposed flood risk assessment framework by blending the hydrodynamic modelling outputs and risk evaluation concepts. The different notions of risk as in hazard, vulnerability and exposure were evaluated over flood-prone Beas river with focus at Bhuntar, Kullu and Manali. The hydrodynamic model (MIKE 11) was established for 56 km river stretch right from Manali to Bhuntar. The flood depth and flow velocity outputs from the calibrated and validated hydrodynamic model were used for the estimation of flood hazard rating. Vulnerability maps were generated using depth-damage curves prepared by Joint Research Centre, EU, for each exposure of agriculture, settlement and roads. The 100 year return period flood risk maps were prepared and analysed for all the three towns. Key interviews and community focus group discussions were held further to strengthen, compare and verify the achieved outcomes. For a 100 year return period flood risk assessment, a total of 0.054 km², 0.226 km² and 0.334 km² area was flooded and extreme flood risk zones were identified with 4.7%, 6.8%, and 10.9% area of the total inundated area at the settlement regions of towns of Manali, Kullu and Bhuntar, respectively. The area on right bank of the river was inundated severely and got classified into extreme flood risk zones. The major settlements at all the towns under consideration are at the right bank due to relatively flat, low lying terrain leading to the dire risk. The outcome of the work can assist disaster managers and local administrations for flood disaster planning in advance, thus reducing human and economic loss.  Further, flood risk map could serve as catastrophic product to define flood insurance rate for various exposures in floodplain.

Keywords: Flood Risk Assessment, MIKE11, Hazard, Vulnerability, Hydrodynamic Modelling