Flow regime of the three outlets on the south bank of Jingjiang River, China: an impact assessment of the Three Gorges Reservoir for 2003–2010

Abstract

Since the Three Gorges Reservoir (TGR) was constructed and taken into operation, a series of hydrological consequences between the Yangtze River and Dongting Lake (river–lake) have emerged and received worldwide attention, particularly the changes in flow regime, which are essential for proper understanding this large river–lake system. To assess the impacts of TGR on flow variation, the three outlets on the south bank of Jingjiang River, i.e., Songci, Taiping, and Ouchi, have been selected as case studies, the whole study period was divided into two sub-periods according to the year when the TGR started to store water, i.e., the pre- and post-TGR storage stages. Based on the water level-, flow volume-, and sediment data obtained from the major hydrological stations in the reach, the alterations in flow regime were investigated and the main influence factor were explored for the different periods through comparative analysis of the three major driving forces, i.e., the decline in inflows to the TGR (DWF), the operation function of TGR (TGRO) and the TGR-induced variation in the river–lake relationship (RRL). As a result, we found the river flow of the three outlets has reduced gradually after the impoundment of TGR and quantified that: the DWF accounts for 68.9 % of total decline in mean annual runoff, the TGRO and RRL account for only 13.9 % and 17.2 %, respectively. Evidence suggests that the riverflow reduction at the three outlets in the post-TGR period was mainly governed by the DWF closely related to precipitation changes and large reservoirs in the upper basin, while the impacts of TGR (i.e., TGRO and RRL) indeed made a contribution to aggravation of this river flow variations. These results can provide a reference for future studies on changes in the complicated RRL, and for the management of river networks on the south bank of Jingjiang River.