| Hydrology regime and river channel evolution become complex because of double influences of river flow and tide. There is little appropriate method so far. Therefore, when the impact us assessed of water project on flood control, the following aspects should be focused on, river evolution and stability of project-sections, design tidal level, flood-tide combination scheme, pre-project and post-project impacts on river channel, water level and flow condition. No.2 Water Plant in Taicang Jiangsu Province is taken as an example in this presentation.First, according to measured data and literature, the river channel evolution rule and its reasons in the southern branch of the Yangtze River are discussed from the perspectives of historic evolution, recent evolution and the tendency prediction of river channel evolution. Besides, The local reservoir has been studied from the changes in thalweg and section as well as the calculation of local erosion and deposit. Consequently, the stability and feasibility of reservoir construction in the river section are approved.Second, on the basis of supplementing basic data and investigating the historic tidal level, the design tidal level has been analyzed and calculated. As the result of the comparison between P-III type frequency Curve and Gumbel Curve, the P-III Curve is recommended.Last, two schemes have been put forwarded for the calculation of initial conditions in mathematic model. For the first scheme, the initial conditions are calculated through one-dimensional mathematic model by the frequency combination of rising and falling tides. For the second scheme, the initial conditions are obtained from measured data. According to the initial conditions, the river level and flow condition have been simulated by two-dimensional mathematic model on the basis of measured data. In addition, with analysis of river channel evolution, the evaluation of the impact on flood control is ultimately made for the reference of policy-making.
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