Impact Of Underlying Surface Change On The Use Of Flood Resources

The underlying surface conditions of Haihe River Basin are significantly changed,which leads to the inconsistency of the flood series.In order to make the best use of the flood resource without reducing flood control standard,it is necessary to adjust the reservoir flood limited level according to the new achievements of design flood.Some key problem focusing on analyzing the impact of the changing underlying surface condition on the reservoir flood limited adjustment,such as seasonal flood period partition,staged design flood computation,adjusting of staged limited water level and risk analysis & efficiency assessment of staged flood limited level adjusting are investigated.The major research aspects are listed as below:(1)The flood season of Wangkuai basin was divided into three stages using the Fisher optimal partition method.The pre-flood period is from June 1 to June 30,the main flood period is from July 1 to August 20,and the post-flood period is from August 21 to September 31.Based on the analysis of the rainstorm and flood seasonal change characteristics,it is indicated that the division result by Fisher partition method is reasonable and believable.(2)The relationship between precipitiation and runoff and the relationship between the flood peak and flood volume are used to revise the time series of flood peak and flood volume.The design flood of different period was computed according to frequency analysis of flood before and after revise.The result shows that for the reason of underlying surface changes,the flood peak and flood volume both showed a decreasing trend.(3)Based on those two kinds of design flood results of flood season staging,Flood regulating calculation is preceding and the reservoir limited water level is determined based on the result of flood regulating calculation.The result shows that the maximum water level and the maximum discharge during the flood rounting process after flood time series has been revised are both smaller than respective results before the flood time series is unrevised.According to the result of flood rounting process,the flood limit water level of pre-flood period is 200 meters,the flood limit water level of post-flood period is 199 meters.the flood limit water level of main flood period is 192 meters before the flood time series has been revised,whilethe flood limit water level of main flood period is 195 meters after the flood time series has been revised.(4)Acoording to the risk evaluation index system of reservoir flood control,the risk indexes of the reservoir raising the limit level during the main flood period were calculated.the water supply under the two kinds of flood limit levels were also calculated.The rationality of the two kinds of flood limit levels were studied,according to the result above.It is concluded that: for the reason of underlying surface changes,the flood control risk indexes of main flood period after the flood time series has been revised is smaller than the flood control risk indexes of main flood period before the flood time series has been revised;In order to ensure the safety of the reservoir,it is appropriate to increase its flood limit water level of main flood period to 193 m which increase the water supply of 240 million.So the change of underlying surface benefits the use of flood resources.