Influence of outer river flood level on drainage discharge in plain lake areas

The accurate simulation of the process of runoff yield and concentration in the drainage area is of important significance for the reasonable determination of the scale of drainage projects and their orderly operation.The Luoshan drainage area in Four-lake Watershed in Hubei Province was selected as the research area.The runoff yield and concentration model at a drainage area scale was developed by coupling SCS with MIKE11.The coupled model was calibrated with the measured water level of Luoshan pumping station in 1980 and 1983, and validated with the measured water level in 1991 and 1996.Results showed that the relative errors between simulated and measured water levels were -0.20% and -0.40% respectively, the correlation coefficients were 0.980 and 0.952, and the efficiency coefficients were 0.949 and 0.849 respectively during the calibration periods (1980 and 1983).The relative errors between simulated and measured water levels were -0.10% and 1.70% respectively, the correlation coefficients were 0.919 and 0.967, and the efficiency coefficients were 0.782 and 0.906 respectively during the validation periods (1991 and 1996).Good agreements between simulated and measured water levels indicated that the coupled model was appropriate to simulate the process of runoff yield and concentration in the drainage area.Then the coupled model was used to analyze the influence of flood levels of the outer river on drainage discharge with six scenarios, which were combinations of two design storms with three flood levels of the outer river.Two design storms, 175.57 mm and 212.07 mm, were corresponding to three-day storms with return periods of 5 years and 10 years respectively.And three flood levels of the outer river, 32.63 m, 33.45 m and 30.68 m, were corresponding to the maximum five-day mean water levels in flood season with return periods of 5 years and 10 years, and the design level of the outer river of the pumping station.The simulation results showed that for the same storm, the higher flood level of the outer river was, the larger the required pumping drainage discharge was, and vice versa.Furthermore, the adverse influence of the flood level of the outer river on drainage was greater with the rising of flood level of the outer river.If the drainage discharge was simulated according to the pump characteristic curve, the simulation accuracy of drainage discharge could be improved between 19.6% and 53.8%.The coupled model could be applied as a useful tool for the accurate determination of the capacity of drainage pumping stations in this drainage area which was affected by the flood level of the outer river.