Cumulative Impact Study Of Cascade Reservoir On River Ecological Factors

China has abundant hydropower resources,a large number of cascade reserviors have been built, and are building or planning. At the same time, the hydrology, water quality, sediment problems and other aspects of the impact on the river ecological environment caused by the cascade reservoir have also been concerned widely. Under the background of cascaded hydropower development, intensive layout of cascade reservoir and the projects will make the effect on river ecological factors caused by the accumulative reservoirs. The cumulative impact on the key groups of ecological flow including pulse, flood, low flow and the extreme low flow and water temperature caused by cascade reservoir are especially obvious, it's also the pivotal studying content of this paper.In this paper, the literature at home and abroad about the cumulative impact and the impact on the river habitat caused by cascade reservoirs are referred widely, the domestic and foreign research progress is grasped resumptively. Based on the controversy of cumulative impact's definition and the deficiency of the estimate method, the cumulative impact's definition is given firstly, then the method of studying cumulative impact is built as three application stages, including "recognition", "analysis" and "expression" method. A general method system could be used to study the whole cumulative impact process is constructed. The ecological flow is divided as four key groupss including pulse, flood, low flow and extreme low flow, and the process indexes are designed to describe the effect. The cumulative impact estimate indexes of ecological flow's key groupss are constructed. Based on the impact mechanism of water temperature affected by cascade reservoir,a vertical 2D k-εtwo-equation model is built for water temperature simulation in the cascade reservoir. The complex flow dynamic process is simplified to average velocity, then a mechanism estimate model considering water temperature changing both along the river and the branch river is built for dam downstream water temperature calculation; Xiluodu - Xiangjiaba cascade reservoir on the Jinsha River is chosen as application example, and nonlinear characteristics is revealed in the example..The cumulative impact is the impact for the disturbances to the nature operates collaboratively at the temporal and spatial layer caused by the human activities including resources exploitation, projects construction, material production, which pays more attention on actual impact compared with only considering the single project previously. In this paper, the ecological flow key groupss and water temperature's cumulative impact caused by cascade reservoir is studied by using the cumulative impact theory at both model and application aspects, some preliminary research results are achieved.