Design Floods Estimation Of Waizhou Hydrological Station In Nanchang City Under Cascade Reservoirs Operation

The characteristics and region composition of river flood have been changed when the cascade reservoirs have been built.The estimation of design floods at downstream section should consider the impact of the upstream reservoir storage and regulation.In this paper,the Ganjiang basin are chosen as the case study,design floods estimation of Waizhou hydrological station in Nanchang City was carried out under the Wanan-Xiajiang cascade reservoirs and the Guangang flood storage area operation.The main research results are as follows:(1)The useful data of hydrological stations are collected and checked.divide the research area into four sections,the natural design floods of each section of the hydrological station and the interval basin of Ganjiang river are derived respectively.(2)The joint probability distribution and conditional probability distribution for the maximum 7-day flood volume amount in the upstream section,and interval basin and the downstream section of each segment have been developed based on Copula function.The joint recurrence period and coincident recurrence period of maximum 7-day flood volume in the upstream and the interval of each section are deduced.At the same time,the upstream section is more likely to have the same flood frequency with the downstream section reservoir than the interval basin.And with the increase of the flood magnitude of the downstream section,the possibility of the upstream section and the interval with the same frequency decreases gradually.(3)Design flood region composition characteristics of each section of the research area is studied based on the observed data.The flood of the downstream section is mainly caused by the upstream section,and the proportion of the interval basin is relatively small.At the same time,the relation of each partition flood peak and flood volume is good and linear.In addition,the meet time of the flood peaks are relatively dispersed of interval basin and the upstream sections,and the possibility of flood peak encounter is relatively small.On this basis,four schemes are proposed to analyse the design flood region composition of each section.The results indicate that each scheme has a scientific,consistent,stability and reliability conclusion.(4)Several region composition methods are used to estimate design flood of the Nanchang Waizhou station by taking consideration of the impact of the Wanan-Xiajiang cascade reservoirs and the Quangang flood diversion and storage area.The design flood inferred by each program is smaller than the natural situation.The largest reduction range is schemes I of the same frequency region,and the smallest reduction range is schemes II of the same frequency region.The reduction effect of the typical year regional component program and the most likely regional component program is roughly between the two regional component programs of the same frequency region.The results are smaller than that of natural condition,which are accordince with the general laws and have high credibility.