Study On Hydrological Calculation Methods For Flood Prevention Plan Of Cities In Plain Tidal River Network Area

Based on property of water system and hydrology, this paper mainly studies on the hydrological calculation methods for flood prevention plan of cities in plain tidal river network areas.According to the demand of flood prevention, the paper analyses the influence of urbanization on hydrology situations, the property of flood and water-logging, the mechanism of disaster generation, and traditional definition of "city" is expanded. Considering the difference of runoff characteristics on different underlying surface in the area of plain tidal river network, four kinds of surface is divided,namely, waters paddy field-, dry land and central urbanized area,and suitable method is adopted separately in each surface to simulate runoff process. Xinanjiang Model usually applicable for mountain areas is introduced to river network area, furthermore, the paper researches runoff calculation of central urbanized area, the underlying surface is divided into pervious and imperviousness areas.In perviousness areas, Hoton Infiltration formula and corresponding spatial infiltration rate curve are used to establish the relationship between infiltration rate and soil moisture in order to decide the infiltration. According to practical situation.Urban drainage network is consdidered in the confluence in urbanized areas. Saint_venant Equations discreted by 4-point Preissmann implicit scheme, is used to calculate river flood water level. To solving the node equations, Successive Over Relaxation Method which based on the Matrix Mark Method for solving large size sparsity linear equations is used. At last, river water level in different plan condition is calculated integrating the method of city runoff and river network hydraulics, to provide technical supports for flood-prevention projects.The achievements of this paper have provided guidance for the flood prevention plan of Zhangjiagang City, and the methods suggested here are applicable to other similar hydrological problems of cities in plain tidal river network area.