Survey of1 April Flood in Kashkan Catchment in Lorestan Province and Presenting Solutions

Water floods and floods in residential areas have always been one of the most common natural disasters in Iran after the earthquake that endanger human life. Between 2000 and 2008, approximately 99 million people are affected by floods worldwide each year. Kashkan River Basin with 8 sub-basins with an area of 9275.66 square kilometers, constitutes 22.4 percent of total Karkheh basin, with 290km length and 26 percent slope of the steepest and most flooded Karkheh basin. The results of statistical analysis on the instantaneous discharge data of Kashkan basin showed that from 1963 to 2019, 58 floods with average discharge moment of 1062.78 cubic meters occurred. In terms of time distribution, 65 percent of the floods in March, April and May and in terms of discharge rate 36 percent of the floods are more than 1000 cubic meters. The highest frequency of floods was observed in 1990-90 with 19 percent of floods and 14 percent of floods were severe, 22 percent moderate and 64 percent small flood. According to the Gamble distribution, a 200-year flood with a probability of 0.995 percent flood occurring at an instantaneous discharge of 4489.77 cubic meters with a tolerance of 535.06 cubic meters in the Kashkan Basin. As a result of the floods on 1 April, 14 people were killed and the damage was estimated to be 103.014 billion USD. The main causes of floods with an instantaneous discharge of 6,000 cubic meters per second in the Kashkan Basin can be attributed to precipitation with an average rainfall of 112.3 mm on 1 April and 321.5 mm for 9 days from 24 Mars to 1 April, respectively. Kashkan Basin, The occurrence of a flood with an instantaneous discharge of 3350 cubic meters on 5 March 2019, the absence of a significant reservoir dam for flood control, Impact of Babazid Bridge as a dam and runoff behind the bridge up to a radius of 5 kilometers and reaching the bridge ramp to the breaking point, thereby increasing the amount and velocity of the flood discharge to Poldokhtar, Decrease in river bed between 1 and 13 m in coastal wall reconstruction after flood on 4 February 2005 as a result of reduced capacity of Kashkan River in Poldokhtar during floods.