Cumulative effects of cascade development project adjustment on water temperature

In order to mitigate the adverse impact of low-temperature discharge from reservoirs on aquaticecosystems,it is necessary to consider the optimization and regulation of cascade hydropower developmentprogram in river basin planning. Taking the hydropower planning of the midstream of the Kaidu River inthe Xinjiang Uygur Autonomous Region as an example, the thermal structure and outflow temperature issimulated by using reservoir water temperature model. The effects of adjustment of the reservoir scale andthe layout and development timing of cascade power station are studied. The changes of the cumulative ef-fects on water temperature betweenone-reservoir with three-stage development projectandone-reservoirwith four-stage development projectfor upside reach of the midstream in Kaidu River are discussed. Thequantitative results show that:(1) Increased storage capacity or normal water level of a reservoir,the larg-er scale of reservoir is,the more effects on water temperature are caused.(2) The most decline of low-temperature caused by four-stage or three-stage development project is 4.8 ℃ and 4.6 ℃ respectively,themore hydropower stations in cascade development project the more effects on water temperature are accumu-lated.(3) Being the leading reservoir,Arensahentuohai Reservoir with big scale and high regulation playsan important role in controlling the cumulative effects on water temperature in Kaidu River. Without theleading reservoir,all levels of the reservoir has a positive effect on cumulative effects;while with the lead-ing reservoir,the cumulative effect turn to the passive one,increasing the maximum temperature differencebetween the release temperature and the natural river water temperature from 2.3 ℃ to 4.5 ℃ at the mostdownstream Chahanwusu Reservoir. The research results indicate that hydropower cascade development in riv-er basin has obvious cumulative effects on water temperature,and the number of cascade hydropower sta-tions and the controlled reservoir play a decisive role for the cumulative effect on water temperature.