Flash flood and its Preventive Measures in Hilly Areas

Flash floods generally occur suddenly caused by heavy rainfall due to cloudburst, damage to infrastructure (buildings, roads etc.) and life. In the India flash flood occurs only in monsoon season (i.e. June to Sept). Flooding contributes to more than 100 deaths each year across India with most deaths due to flash flooding. The main causes of flash flood in hilly areas are cloudburst or stationary rainfall, heavy rainfall and rapid snow melt in high mountain areas, glacial lake outburst, failure of dams built-up by landslide, rock falls or debris flows and overspill following the failure of water reservoir dams. Most flash floods occur due to intense rainfall caused by cloudburst, the magnitude of a flash flood is dramatically affected by pre-existing physical factors such as ground cover, topography and soil moisture. This study looks at flood prevention and mitigation in India and guiding principles with regard to flash flood are presented here and also looks at the relationship between the number of flash flood events and rainfall within that year in hilly areas such as Uttarakhand, Himachal Pradesh and Jammu& Kashmir. Results showed that with increasing the number of cloudburst and snow melting there is an increase in the average annual number of flash flood events. A composite factor was developed to account for both cloudburst and heavy rainfall together. This factor when compared to the average annual number of flash flood events indicates that densely populated areas within hilly to high terrain are the most susceptible to flash flooding. It is the hope that these results will highlight hydro logically vulnerable areas that are prone to flash flooding in the northeast India. With this improved understanding, Central Water Commission (CWC) forecaster situational awareness will increase, leading to more accurate and timely flash flood warning.