Hydrodynamics And Waste Water Transportation Of Yangtze River Estuary Affected By Three Gorges Project

Some complicated physical processes exist in the estuary and coastal areas, where the inland runoff and the sea tides meet with each other. The strength compare of those two flows determines the characteristics of current distribution nearby estuary. When the tides from open sea are stronger, current moves in circles; while the inland runoff predominate, the current just flow mainly towards the open sea. The runoff flows into Yangtze River Estuary (YRE), which is the biggest estuary in China, is totally different in every season. After Three Gorges Project (TGP) has been completed and put into service in 2009, the water volume downstream to YRE varied apparently to the times before because of the water regulation of TGP. So the hydro-dynamic characteristics of YRE changed significantly, which, therefore, would have negative impacts on dilution and transportation of waste water discharged into YRE. To analyze and evaluate the aquatic environment and then making effective manage plans is important for social and natural environment harmonically develop. Analyzing hydrodynamic properties of water body by employing hydrodynamic models is an essential fundamental for water resource analysis, evaluation and estimation.A 3D hydrodynamic mathematical model for YRE was established by using ECOMSED in this paper. The water level and flow rate compared to the observed data collected in No-vember 2005 show that the model is sound. Then, a simulation is conducted to flood season of July 2010 to study the effect of the flood storage of TGP on the hydrodynamic properties and the dilution and transportation of waste water discharged from Shanghai in YRE. Several rules and acknowledgements were obtained as follows:(1) According to the comparison of tidal level and current velocity and direction between simulated and observed data, this mathematical model is not only displaying tidal characteris-tics in YRE, but also showing up the availability of this model working on the simulation of flow field there. It successfully demonstrated the hydrodynamic characteristics around YRE and Hangzhou Bay.(2) Three Gorges Project has a certain impact on the hydrodynamic of Yangtze River Estuary. Take the big flood that happened in July 2010 for example, the flood storage of TGP contributed extremely to decrease flow velocity in ebb tide, while increase in flood tide.(3) In fact, the floods (large volume of flow) do not have much influence on the hydro-dynamic properties of the north branch of YRE, which is because water in the north branch is running off and sludge is silting up badly. The north branch is affected mainly by open sea tidal wave, which brings out a serious problem of salinity intrusion.(4) The flood storage of Three Gorges Reservoir decreases the water volume from up-stream, accelerating the effects on YRE from outside tides, consequently, lifting the possibil-ity of salinity intrusion and giving rise to the period. All those are going to introduce impacts to life and productivity along the river.(5) On the whole, the flow velocity on the surface is high, while that in the deep down is low. Therefore, the effect from impoundment of TGP are mainly on the surface layer rather than on the under layer. Going along with the Yangtze River from upstream to estuary, the influence of the flood storage to the hydrodynamic characteristics keep dropping down from surface layer, to middle layer, and to bottom layer. In addition, the difference between layers is decreasing going along to the estuary.(6) The flood storage of TGP reduces water volume from upstream, slows down the speed of dilution of the waste water discharged near to Shanghai. At the same time, it dimi-nishes the transport possibility to outside sea, which makes it worse for coastal and Hangzhou Bay areas because the waste water just stay around without getting diluted or spread. Hence, we can figure it out how much the upstream water volume impacts on the effluent dilution.(7) The flood storage of TGP changes the current velocity near YRE, which would make effects on the sediment transportation and water environment.As a typical estuary in China, even in the world, YRE plays a non-substituted role in re-searches of hydrodynamic impacts on people living in coastal areas. The influencing elements are complex, even some of which are still in studying. So it needs much more efforts and will be a long and tough work to keep it going.