Study on design rainstorm flood simulation method in small and medium watersheds of hilly area — Taking Yangzhuang Reservoir of Tianjin City as an example

Taking Yangzhuang Reservoir in Tianjin City as an example, the flood simulation calculation is carried out by using the China Flash Flood Hydrological Model(CNFF), and the flood peak flow frequency values of small watershed units and hierarchical nested watersheds in the basin are analyzed. The results show that the CNFF model is suitable for flood simulation in small and medium-sized watersheds in hilly areas. The average absolute value of relative error of peak volume of 14 floods is 12.0%, the average absolute value of relative error of flood peak flow is 9.0%, the average absolute value of relative error of flood peaking time is 1.1 h, and the average Nash coefficient is 0.82. The average peak flow of 5-year, 10-year, 20-year, 50-year, 100-year small watersheds are 27 m³/s, 53 m³/s, 85 m³/s, 132 m³/s, 172 m³/s, respectively. The average peak flow of each hierarchical nested watershed is 122 m³/s, 137 m³/s, 382 m³/s, 611 m³/s, 777 m³/s. The research results can provide a method and technical reference for the design storm flood simulation of small and medium-sized watersheds in hilly areas, and provide technical support for the flood forecasting of Yangzhuang Reservoir watershed.