An Analysis of the Current Situation of Ecological Flow Release from Large- and Medium-Sized Reservoirs in the Southeastern River Basins of China

Ecological flow is a crucial determinant of river ecosystem well-being and aquatic ecosystem stability. Large- and medium-sized reservoirs, with flood prevention, irrigation, and power generation functions, necessitate a scientifically devised ecological flow release plan for river ecosystem conservation and water quality amelioration. This study centered on three reservoirs in the Jiaojiang River Basin of Zhejiang Province, China. Using measured outflow data, the hydrological approach was initially adopted to calculate individual reservoir ecological flows. Subsequently, the entropy weight method was employed to ascertain the most suitable ecological flow. Ecological flow grade thresholds were then established to formulate the optimal release scheme. The outcomes demonstrated that the average ecological flows of Xia’an, Lishimen, and Longxi reservoirs were 1.90 m3/s, 1.95 m3/s, and 0.42 m3/s, respectively. The multi-year average ecological flow assurance rates were 62.53%, 77.72%, and 56.94%, successively. The entropy weighted downstream optimal ecological flows were 2.10 m3/s, 2.28 m3/s, and 0.44 m3/s. During periods when the monthly ecological flow assurance rate was below 60%, the three reservoirs implemented schemes of installing ecological siphons, renovating water diversion systems, and using post-dam ecological units, respectively.