Effects of the impounding process during the flood season on algal blooms in Xiangxi Bay in the Three Gorges Reservoir, China

Algal blooms have been a serious problem in the tributary bays of the Three Gorges Reservoir (TGR), and hydrodynamic changes have been widely accepted as targets to control these algal blooms. To study the influence of the impounding process during the flood season on algal blooms in Xiangxi Bay (XXB), monitoring of XXB was conducted from June 18, 2017 to July 18, 2017. Based on a laterally averaged two-dimensional hydrodynamic and water quality model (CE-QUAL-W2) of XXB, this study analyzed the temporal and spatial variations in flow, water temperature, chlorophyll-a (Chl-a) during the impounding process. The results showed that during the impounding process, the total Chl-a in the euphotic zone of XXB (SA) decreased obviously compared with that on July 1. The Chl-a concentration increased with the increase in water temperature stratification. The variation in the depth of the plunge point of the density current was consistent with the variation in the SA; the depth of the plunge point decreased gradually, and the water temperature stratification was consequently weakened. The CE-QUAL-W2 model is suitable for water quality forecasts in XXB and could play an important role in the ecological reservoir operation.