Evolutionary mechanisms and shifting trends in water circulation patterns in a tributary of the Three Gorges Reservoir, China

Abstract

Abstract A 2-D CE-QUAL-W2 hydrodynamic model was established to simulate evolutionary mechanisms and shifting trends of flow patterns per annum and over seasons from 2008 to 2018 in a reflective tributary Xiangxi Bay (XXB) of the Three Gorges Reservoir, China. Reasons behind shifting trends of flow patterns were also investigated. Model performance was validated and simulated data was synchronous to observed data. In general, percentage of Pattern (6) was 14%, 20%, 17%, 12% and 11% per annum and in spring, summer, autumn and winter respectively by 2013. It was increased by 26%, 30%, 22%, 25% and 35% per annum and in spring, summer, autumn and winter respectively since 2014. Increased temperature and flow dynamics (such as 10,000 m3 s−1 in spring) in Three Gorges Resevoir (TGR) since 2014 were underlying shifting trends of density current patterns. Correlation among patterns prior to and after newly built upstream reservoirs was novel and innovative in finding hydrodynamic thresholds to increase effectivity. Particulars elaboated and associated with respective density current patterns indicate increased surface velocity and water exchange with increased overflows. This could help understanding hydrodynamics and ecological variations in TGR and XXB. Thermal establishment and flow dynamics in TGR triggering overflow intrusion in XXB are required to be achieved. A hydrodynamic and water quality model of XXB coupled with TGR mainstream is recommended to correlate additive impacts of advantageous and disadvantageous patterns and to evaluate hydrodynamical thresholds triggering advantageous patterns in XXB.