Study on River Regime Control and Siltiation in Deepwater Channel

The deep waterway regulation project in the Yangtze Estuary provides bases to verify and deepen the theories and methods for regulation of tidal and estuarial channels.In macroscopic view,the river regime requires the North Passage(NP)to keep the status that the sediment transport should be dominated during ebb.The analysis shows that the rate of freshwater through the NP decreases after the project,which is close to the critical value of the transformation of the river regime.The shape of transect changes after the I,II phase of the regulating project,from broad-shallow to narrow-deep,forming continuous thalweg covering the navigation channel,which provides the important guarantee to maintain the channel.The opposite change occurs in transects(below-8 m)after the third phase of the siltation-reduction project and the velocity of flow in the middle of North Passage becomes extremely high.The sediment concentration and sediment transport in this zone are both very high and the direction of the net sediment transport may point to the main channel,which would enlarge the back-siltation amount.The field data reveal the mechanism of the formation of the high sediment concentration and fluid mud near bottom.To make further efforts to reduce siltation,it is important to recovery the reasonable widening rate of regulation line so that the sediment transport rate will be uniform along the waterway.