30. Occurrence and Mitigation of Flash Floods

Flash floods of short duration in rivers/rivulets cause immense loss of life, property, agriculture land and also damages the infrastructure created over years with huge investment in few hours. Rivers having no control structures like dams are most prone to flash floods. Flash floods – a natural disaster is occurring repeatedly world wide and even the advanced countries like USA are no exception. The recent high magnitude flash floods of July-August 2000 and 2003 in river Sutlej and its tributaries in Himachal Pradesh causing unprecedented damages in some districts have been discussed in terms of its occurrence, damages and mitigation measures aiming at to protect life and property. Apart from the conventional methods of flood protection such as construction of dam, channelisation of river etc. various measures to mitigate the flood damages like creating better data base, effective monitoring, creation of storages upstream in flash flood prone areas, flood forecasting and flood warning systems have become imperative. The various common causes of flash floods such as glacial lake outburst flow, cloudburst and land slides are to be analysed. The mitigation measures with new techniques relating to flash flood forecasting and warning systems are brought out in the paper. There is need of integrated model to forecast the flash flood based on remotely sensed data as used by National Oceanic and Atmospheric Administration in flood prone areas of California and Pennsylvania in United States. Other popular models like Automated local Evaluation in real time can also be used for forecasting of flash floods after proper calibration of relevant parameters of a basin.