Kedarnath Flash Floods: a Hydrological and Hydraulic Simulation Study

The recent floods in the Kedarnath area, Uttarakhand are a classic example of flash floods in the Mandakini River that devastated the country by killing thousands of people besides livestock. Though the duration of the event was small compared to other flood disasters in the country, it resulted in severe damage to property and life. Post-disaster satellite images depict that the river banks were eroded completely along the Kedarnath valley due to the flash floods and few new channels were visible. Extreme erosion took place in the upstream portion of Kedarnath, besides the breach of Chorabari Lake and deposition of debris/sediments in the valley. Hydrological and hydraulic simulation study was carried out in the Mandakini River using space-based inputs to quantify the causes of the flash floods and their impact. Chorabari Lake breach analysis was carried out using Froehlich theory. Flood inundation simulations were done using CARTO DEM of 10 m posting in which the combined effect of lake breach and high-intensity rainfall flood was examined. As the slopes are very steep in the upstream catchment area, lag-time of the peak flood was found to be less and washed-off the Kedarnath valley without any alert. The study reveals quantitative parameters of the disaster which was due to an integrated effect of high rainfall intensity, sudden breach of Chorabari Lake and very steep topography.