Quantifying the impacts of small dam construction on hydrological alterations in the Jiulong River basin of Southeast China

Abstract

The hydrological alterations induced by dam construction modify natural flora and fauna habitats and impair ecosystem stability. Although many studies have documented the impacts of large dams on streamflow, few have described the effects of small dam construction on hydrological conditions. The cumulative effects of intensive small dams may also cause severe ecological problems. To evaluate the impacts of dam construction on the indicators of hydrological alterations, a framework that combined a hydrological model and the post bias correction method was proposed. The hydrological alterations of two individual rivers in the Jiulong River basin that experienced impacts from intensifying small hydropower reservoirs, the North River and the West River, were analyzed using the proposed framework. The results show that the framework can successfully avoid misleading the impacts of dam construction on monthly runoff and multi-minimum values detected by the previously common method that did not separate the impacts of climate change and dam construction on flow regime. The small hydropower-dominated North River and the flood-control-dominated West River exhibited generally consistent change patterns of unchanging monthly river discharge, reduced high pulse count, reduced rise and fall rates, and increased number of reversals. Conversely, the changes to several Indicators of Hydrologic Alterations (IHA) differed between the two rivers. The flood-control-dominated West River exhibited 1) increased indicators, such as the base flow index, multi-day minimum flow and high pulse duration and 2) decreased multi-day maximum flow and low pulse count. Unlike the West River, the hydropower-dominated North River experienced 1) increased low pulse count and 2) decreased indicators such as multi-day minimum flow and low pulse duration. Our results implied that the ecological impacts of the small hydropower-dominated North River may exceed those of the flood-control-dominated West River. Therefore, the minimum ecological water demand should be considered not only in the large reservoirs operation, but also in the operation of small hydropower reservoirs.