Density‐driven water circulation in a typical tributary of the Three Gorges Reservoir, China

Abstract

A 2-D hydrodynamic model was developed for modelling water circulation from 2008 to 2011 in a typical tributary of the Three Gorges Reservoir. The model is capable of describing flow behaviour and mixing mechanisms for different density current patterns and performs well in computing the velocity, the intrusion layer at the plunge point, and the travel distance of the density current. The effects of 10 flow patterns on thermal stratification, hydrodynamics, and algal bloom risk are discussed and classified in terms of algal growth. Patterns (6) and (10) can effectively prevent algal blooms; Patterns (7) and (8) are good for algal blooms. More frequent transformations of flow-driven patterns, as observed in 2010-2011, could create more eddies and mixing and thus reduce bloom risk. Further studies are necessary and recommended for more accurate predictions, assessing the impact of water level fluctuations on transform flow patterns and water quality.

Biogeochemical Processes of Dissolved Nitrogen in the Backwater Zone of a Tributary in Three Gorges Reservoir, China: Implications from the Hydrologic Processes and Isotopic Tracing

“…As shown in Figure , the river water of surface and middle layers S4 and S5 was well replenished by the TGR mainstream, while the upstream of XBZ dominated the bottom water. These results were similar with the mixing pattern of mainstream-tributary reported in most studies, in which the mainstream mainly intruded into the tributaries from the surface and middle water of the rivers. , The average mixing ratio of the TGR mainstream to the XBZ was 98%, higher than that of the Zhuyi River (87%), Xiangxi Bay (76%) and Daning River (73%) . The discharge of TGR mainstream may affect the mixing process of mainstream-tributary, since the mixing ratios of the TGR mainstream to the Daning River and the Xiangxi Bay during the high-flow period were 6–26% higher than that during the low-flow period. , Thus, the higher mixing ratio of TGR mainstream to XBZ may be associated with the increased discharge brought by extreme rainfall events.…”

“…These results were similar with the mixing pattern of mainstream-tributary reported in most studies, in which the mainstream mainly intruded into the tributaries from the surface and middle water of the rivers. 69,70 The average mixing ratio of the TGR mainstream to the XBZ was 98%, higher than that of the Zhuyi River (87%), 71 Xiangxi Bay (76%) and Daning River (73%). 72 The discharge of TGR mainstream may affect the mixing process of mainstream-tributary, since the mixing ratios of the TGR mainstream to the Daning River and the Xiangxi Bay during the high-flow period were 6−26% higher than that during the low-flow period.…”

Hydrodynamic and environmental characteristics of a tributary bay influenced by backwater jacking and intrusions from a main reservoir

“…These dams block fish migration routes between upstream and downstream regions (Oldani and Claudio, 2002;Ziv et al, 2012) and change the fish communities (Gao et al, 2010). In the flood season, flood discharge produces water that is supersaturated in dissolved gas in the downstream river channel (Feng et al, 2014;Lu et al, 2011;Wang et al, 2011;McGrath et al, 2006). In the reservoir area, the elevated water level produces a much slower water velocity, which results in sediment deposition, eutrophication, and stratification in terms of water temperature and water quality (Zhu, 2017;Wu, 2013;Zheng et al, 2011).…”

“…A rise in the water level may lead to a rise or decline in the chlorophyll content, depending on the water cycle mode in the tributary (Ji et al, 2017). Previous studies have paid consid-erable attention to changes in hydrodynamic characteristics and the deterioration of the water environment in the tributaries but have not considered the influence of the main reservoir (Zhao, 2017;Long et al, 2019). There are few systematic studies on the variation in the hydrodynamic and water environment characteristics of tributary bays influenced by backwater jacking and intrusions from the main reservoir.…”

“…Based on the collection and analysis of basic data, we simulated the flow field, water temperature, and water quality of Tangxi River using the hydrodynamic and water quality model CE-QUAL-W2 (Thomas and Scott, 2008). This model performs well in computing the velocity, the intrusion layer at the plunge point, and the travel distance of the density-driven current (Long et al, 2019), and many scholars have obtained good results using this model to simulate the hydrodynamics, water temperature, and water quality of reservoirs and lakes (Bowen and Hieronymus, 2003;Lung and Nice, 2007;Berger and Wells, 2008;Debele et al, 2008;Noori et al, 2015;Long et al, 2018). We also evaluated the eutrophication status of the tributary bay and systematically identified the influence of backwater jacking and intrusions from the main reservoir on the tributary bay.…”