Quantifying the impact of release operations and weather conditions on the flow and temperature dynamics in the cascade-reservoir system

¹ College of Hydrology and Water Resources, Hohai University, Nanjing 210098, China
² Hydrology Bureau of Haihe River Water Conservancy Commission, Ministry of Water Resources, Tianjin, 300170, China
³ Department of Civil Engineering, Auburn University, Auburn, AL 36849, USA

^a Corresponding author: gangchen@hhu.edu.cn

Abstract

The objective of this study was to investigate the flow dynamics and temperature characteristics under different reservoir operation scenarios and weather conditions in the river-reservoir system, which can be used to set scientific guidelines for river management and conservation planning strategies. The calibrated three-dimensional model provided simulated unsteady water surface elevation, temperature, velocity and discharge at different layers (depths) in different locations. A series of operation scenarios were modeled to understand and quantify formation, propagation, and disappearance of density currents that are resulted from combinations of daily repeated large release (DRLR) of different durations and solar heating. DRLRs (140 m³/s) with longer durations pushed the bottom cold water further downstream and maintained the bottom water temperature cooler. Variations of weather conditions (e.g., drops of air temperature and solar radiation) directly controled variations of bottom-layer water temperature. The daily drop rate of bottom temperature was related to the rate and duration of air temperature drop. Under the practice for the water turbines running at downstream, it clearly showed the shocking withdrawal and stopping effect from the downstream operation. The velocity for the whole cross-section were almost increased with same magnitude of about 0.1 m/s at GOUS and JML.