Impact of Three Gorges Dam operation on the spawning success of four major Chinese carps

Abstract The impact of the Three Gorges Dam on the downstream flow regime and carp communities is assessed through a systematic examination of various indicators of hydrology (IHs) recorded during the pre- and post-dam periods. Specifically, the Spearman correlation method is used to identify a number of key indicators better correlated with carp population changes. The range of variability approach (RVA) is then applied to these key IHs to calculate their degree of alteration after the dam impoundment. Also, a new composite index is proposed here to determine the most important IHs. This index quantifies the relative impact among the competing indicators by accounting for both their alteration and correlation levels. It is observed that the presence of Three Gorges Dam disrupts the natural flow patterns and limits the downstream areas to small-scale, short-lived flow events. These flow events are insufficient regarding both the magnitude and duration to satisfy the carps’ breeding needs. Among 32 IHs considered here, high-pulse duration and rise rate of discharge or water level are found to be the most important flow properties for the carps’ spawning success; at the same time, they are the worst affected by the dam presence. Other indicators, such as base flow discharge and fall rate of discharge, also play a role, as they are adversely affecting the carp fry biomass. The present results are very useful for designing water releases that will be effective in improving the breeding conditions and augmenting the overall carp population.