Combined Effect of Danjiangkou Reservoir and Cascade Reservoirs on Hydrologic Regime Downstream

The construction of dams has significant effects on hydrologic regimes downstream. The combined effect of the Danjiangkou Reservoir and the downstream cascade reservoirs on the changes in the hydrologic regime at Huangzhuang station were investigated using the indicators of hydrologic alteration (IHA) and the range of variability approach (RVA) in the middle-lower Hanjiang River. The single operation of the Danjiangkou Reservoir had effects with an overall alteration degree of 40.6%, in which the number of reversals, and flows in March and September were highly altered. The combined operation of Wangfuzhou Reservoir changed the flows in March and August and the extreme minima from high or moderate alteration to low alteration and increased the alteration of the extreme maxima, pulse behavior, and rise rate, with an overall alteration degree of 46.7%. Furthermore, with the combined operation of Cuijiaying Reservoir, the overall alteration degree increased to 63.5%, and 56.2% of the indicators were of high alteration. These changes are mainly caused by the reservoir regulations, which have profound effects on the river aquatic environment and biological habitats.