Three Gorges Reservoir: Density Pump Amplification of Pollutant Transport into Tributaries

Abstract

The impoundment of the Three Gorges Reservoir (TGR) on the Yangtze River in China burdened its tributary backwaters with severe environmental problems. 1Confluence zones of reservoir tributaries with the Yangtze River main channel are main drivers of pollutant dynamics in the TGR 2 and are thus keys to develop mitigation measures. Here, we show a novel experimental approach of spatiotemporal water quality analysis to trace water mass movements and identify pollutant transport pathways in reservoir water bodies. Our results show the movements of density currents in a major tributary backwater of the TGR. A huge interflow density current from the Yangtze River main channel transported its heavy metal carriage to the upstream reaches of the tributary backwater. Water from the upstream backwater moved counterwise and carried less but pollutant-enriched suspended sediments. This scenario illustrates the importance of confluence zone hydrodynamics for fates and pathways of pollutants through the widely unknown hydrodynamics of new reservoirs.

Environmental water body characteristics in a major tributary backwater of the unique and strongly seasonal Three Gorges Reservoir, China

“…The presence of thermal density stratication in the TGR tributary backwaters was shown in several experimental eld studies 4,9,14 as well as predicted by various modelling approaches. 15,16 One numerical modelling study even predicts the temporal occurrence of thermal stratication within the Yangtze River main stream of the TGR.…”

“…These pose a serious threat to the utilization of the TGR as drinking water and shery resources and have already been directly addressed by numerous scientic studies. 4,8,9 Further, there are creeping environmental hazards with long-term effects caused by pollutant transport, accumulation, and/or mobilization in/ from reservoir sediments. These have been less frequently studied so far [9][10][11] and synoptic conclusions on a reservoir scale are still missing for the TGR.…”

“…4,8,9 Further, there are creeping environmental hazards with long-term effects caused by pollutant transport, accumulation, and/or mobilization in/ from reservoir sediments. These have been less frequently studied so far [9][10][11] and synoptic conclusions on a reservoir scale are still missing for the TGR. In the long-term, however, these can be equally serious as algal blooms as the massive capture of sediments in the Yangtze River reservoirs has already been proven.…”

Thematic issue: water environment of the Three Gorges Reservoir

“…However, studies indicated that the changes in hydrodynamics and meteorological conditions due to the TGR impoundment were the driven factors of algae bloom formation (Yang 2014). Sensitive areas especially are where tributaries meet the main stream of Yangtze due to specific flow patterns caused by the extreme high flow rate of the Yangtze river (> 10.000 m 3 ) and the relatively low ones of the tributaries (< 1000 m 3 ) (Holbach et al 2013(Holbach et al , 2014. Previous studies showed that the TGR impoundment deepened water level, slowed water velocity, prolonged water retention time and reduced water self-purification capacity in the TGR, particularly in the backwater area of the TGR tributaries (Xiao et al 2009).…”

“…Previous studies showed that the TGR impoundment deepened water level, slowed water velocity, prolonged water retention time and reduced water self-purification capacity in the TGR, particularly in the backwater area of the TGR tributaries (Xiao et al 2009). The changed hydrodynamics were easy to form thermal stratification in the TGR tributaries, which lead to the occurrences of algae blooms under appropriate meteorological conditions (Holbach et al 2013(Holbach et al , 2014Liu et al 2012;Yang 2014).…”