Water and sediment trends and their causes in the Hongze Lake from 1975 to 2015

The flood disasters are frequent in the Huaihe River Basin,and Hongze Lake plays a key role in flood control.It is ofgreat practical significance for water resources management,streamflow and sediment regulation to detect the trend and changing points of streamflow and sediment in the Hongze Lake.The temporal characteristics of streamflow and sediment in the Hongze Lake were investigated with observed annual streamflow and sediment discharge data at representative hydrological stations from 1975 to 2015.The Mann Kendall trend test and the Pettit change point detection method were used to explore temporal trend and changing points of streamflow and sediment.The main influencing factors of streamflow and sediment changes in the Hongze Lake were identified from the aspects of river water resources development and utilization,basin rainfall and sediment retaining of reservoir.The research showed that the annual variations of inflows and outflows of the Hongze Lake was consistent,and there was not statistically significant trend or changing point.There was a slight and insignificant decreasing trend for the amount of sediment inflows at 0.05 significance level,but a statistically significant decreasing trend for the sediment outflows.Sediment inflows and outflows both had a changing point in 1991.Rainfall was the most important factor affecting the variation of streamflow.The streamflow showed a decreasing trend from 1993 to 2015,which was related to the increasing development and utilization of water resources in the basin.Decrease in sediment was mainly from the upstream reservoir constructions.The main reasons for the changing points were the engineering projects of the Huaihe River started in 1991,which included the reconstruction of reservoirs and conservation countermeasures of water and soil.

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