Hydrodynamic improvement of a goose-head pattern braided reach in lower Yangtze River

The Three Gorges Reservoir (TGR) began operation in 2003 with alterations in the natural hydrological regime and with severe environmental impacts. Baguazhou Reach, a goose-head pattern of braided channels in the lower Yangtze River has emerged due to a series of changes in the water and sediment conditions caused by the TGR. This paper makes simulations of the hydrodynamic characteristics under the condition of clear water releasing from the TGR and analyzes the features of deformation within the branches of the reach, as well as predicts the future development of the hydrodynamic improvement and the additional fluvial processes. The results show that the decline of the tributary is mainly due to the weakening of the inflow energy and the channel resistance. The particular protective measures can effectively improve the hydrodynamic performance and the present situation but, they all result in a deflection of the main water flow and increase the local velocity, and over the long term, leading to the deposition in the junction areas, where a special protection is required.