Analysis of flood characteristics in Loushui basin of Zhangjiajie region

Loushui basin of Zhangjiajie region was selected as study area.Based on available hydrology data(since 1966)of 25years,changes of flood characteristics were analyzed,including the changes of flood frequency,flood scale,flood transportability and relationship between water and suspended sediment concentration.By the application of sequential cluster,the time series of flood water and sediment characteristics can be generally divided into three periods,i.e.1966— 1969,1970—1985and 2007—2011.The results showed that 56% floods happened in summer. Most maximum flood discharges were in the range of 500~1 000m3/s during the study period. When the maximum flood discharge is larger than 1 000m3/s,the distributions of floods were different in three stages,and the maximum flood discharge can reach 7 000 m3/s.The contribution of flood to the total annual sediment load in Loushui basin was much higher than the contribution of flood to runoff.The transportation of suspended sediment was controlled by the maximum flood event,with the maximum contribution reaching approximately at 73%in 1966. Power function can be used to describe the relationship between flood discharge and suspended sediment concentration.The changes of the parameters of power functions indicated the insufficient sediment availability of floods in Loushui basin.There was an increase in floodsediment transport energy during the period of 1966—1985,with a sharp decrease after 2007.To some extent,the changes of hysteresis loops for flood discharge and suspended sediment concentration indicated the changing of sediment sources from sediment in channel bed/bank to materials on slopes or upper reaches in Loushui basin.