Characteristics of reservoir water temperatures in high and cold areas of the Upper Yellow River

Several reservoirs have been built in the high and cold areas of the Yellow River. This study analyzed the annual and seasonal distributions and variation characteristics of the water temperatures of reservoirs in different reaches based on water temperature observations. The results show that (1) the temperature of the water released from the reservoirs is less than 2 °C and is 2–4 °C lower than the natural temperature in the research area in the spring. Reservoirs in this area freeze in the winter, the water temperature structures of the reservoirs exhibit thermal stratification with inversion profiles, and the inversion profiles are greater than 50 m thick. The reservoir water is mixed to 4 °C and then becomes stratified in mid-April. Similarly, the stratified conditions turn to mixed conditions in November. (2) The operating conditions of the reservoirs influence the water temperature distributions in the reservoirs and the water temperatures of the downstream river channels. (3) The temperature of the water released from the reservoirs is significantly lower than the natural water temperature in the spring, which affects the spawning of downstream fish. (4) A three-dimensional water temperature simulation model was created, and the simulation results show that stratified intake can reduce the impacts of low water temperatures.