Effects of a cascade reservoir system on runoff and sediment yields in a River Basin of southwestern China

In the upper reach of the Yangtze River Basin in China, changes of the runoff and sediment yield in the middle reach of the Jinsha River Basin have been given close attentions because of their declination trends over recent years. Then, the impact factors for the variations of runoff and sediment yield were urgent need to be investigated through a distributed hydrological modelling under multi spatiotemporal scales. The results showed that climate change had a significant impact on runoff and sediment yield of the basin before the operation of cascade reservoirs. The contribution rate of the reservoirs operation to the reduction of the annual runoff and sediment yield in the watershed was 48.90% and 28.75% respectively. The Ludila reservoir played an important role in reducing annual runoff and sediment yield of the basin. The location of reservoirs with the sequence of Ludila, Longkaikou, Jin'anqiao, and Ahai from upstream to downstream had the greatest effect on the annual sediment yield of the basin. The function of multiple reservoirs on the monthly runoff and sediment yield of the basin was not the superposition of a single one. Under the simultaneous change of temperature and precipitation, the precipitation had a greater impact on runoff and sediment yield of the basin than temperature. Spatially, the annual runoff and sediment yield in the middle and upper reaches of the basin were sensitive to changes of temperature and precipitation. This research provides scientific support for management of water and sediment resources in watersheds with cascade reservoirs.