Hydrological Regime Changes Considering Mega Reservoirs In Upper Yangtze River Basin

A large number of water conservancy and hydropower projects with large capacity and considerable regulation ability have been planned and constructed in the Yangtze River basin,which can not only improve the spatio and temporal distribution of water resources,play a major role in flood control and reservoir profiting,but also change the hydrological regime in the downstream inevitably.It is fundamental for the exploitation,utilization,planning,design,construction,operation and management of water resources to master the evolution law of hydrological regime.Meanwhile,it is the basis for flood control,scheduling and management of water resources,which relates to people's lives and property directly.Therefore,this thesis aims to reveale the changes of hydrological regime under the impact of mega reservoirs in the upper Yangtze River basin.The main contens includes four aspects,i.e.,spatiotemporal law of water resources evolution in the upper reaches of Yangtze River,the spatiotemporal variation characteristics of hydrological regime of the main stream of the middle-lower reaches of Yangtze River,the impact of the operation of cascade reservoirs on the hydrological regime in' the upper reaches of Yangtze River and the impact of the Three Gorges project on the hydrological regime in the middle and lower reaches of Yangtze RiverThe thesis is mainly composed of four parts:(1)The spatiotemporal evolution of water resources is analyzed in the upper reaches of Yangtze River and its divisions according to the observed hydrology data.Based on the analysis of regional composition,inter-annual variation,annual distribution.The trend is explored by using the M-K test,Kendall test,Spearman test and LRT test,while the period is examed by using the periodogram,wavelet analysis and moving average.The results show that the annual runoff(1951-2013)presented a decreasing trend in the upper reaches of Yangtze River.Specificly,the decreasing trend was significant in both Mingjiang and Tuojiang River,relatively significant in Jialing River and the upstream of Yangtze River.The annual runoff exhibits periodical variation characteristics with 9 years period(primary period)and 17 years period.(2)Based on the observed runoff at the main hydrological stations,the spatiotemporal variation characteristics of hydrological regime in the middle and lower reaches of Yangtze River are analyzed.The year of 2003 is employed as the demarcation point considering the operation of Three Gorges Project.The spatiotemporal variation characteristics of runoff in different periods are identified and the tendency and mutability of runoff in mainstream is clarified on multi time and space(Yichang,Zhicheng,Shashi,Luoshan,Hankou and Datong stations)scale.Due to the impact of operation of the Three Gorges Project and the decreasing water from upstream,the average annual runoff of the downstream decreased since the operation of Three Gorges Project in 2003,especilly during the storage period(from September to November)of Three Gorges Project.Meanwhile,the monthly runoff decreased in the flood season while increasing in the dry season.The annual and monthly runoff in the mainstream downstream significantly changed,especially in the storage period of Three Gorges Project and the driest months in 2003 for the regulation of Three Gorges Project.(3)The changes of hydrological regime in downstream are analyzed by establishing the joint operation model of mega reservoirs in the upper reaches of Yangtse River.Three typical years,namely the year of 2010,2015 and future,are set up according to the construction of large reservoirs in the upper reaches of the Yangtze River.IHA and RVA methods are employed to quantify the variation of runoff at each hydrological station after the regulation of upstream reservoirs in different typical years.The results show that the impact of mega reservoir operation on the runoff from Sepetember to November in the upper reaches of the Yangtze River are increasing with the increasing number of reservoirs putting into operation.The average runoff at Yichang Station from September to November reduced 1.8%,8.6%,16%in three typical years than that in nature situation.The change degree at Yichang station in the three typical years(without considering the operation of the Three Gorges Project)was 68.4%,72.5%and 74.3%,respectively.(4)The river flow routing model from Yichang to Datong Station is established by using a large amount of hydrological and topography data(including runoff,water level at main stations along the mainstream)and the platform of Mike 11,The impacts of operation of the Three Gorges Project are quantified via the proposed model.The results showed that the Three Gorges Project has reduced the maximum peak flow at each main hydrological stations downstream.The peak flow from Yichang to Datong Station reduced 0.94?30.1%due to the operation of the Three Gorges Project,and the peak flow reduction in upstream was more significant than downstream.The average 10-day runoff at each hydrological station in the downstream was modest reduced during the storage period of Three Gorges Project and the variation range of runoff at each hydrological station in September and October was larger than that in November.The runoff increased during the supply period after the regulation of Three Gorges project.The average supply volume was about 25.5 billion 11m3,providing a strong guarantee for usage of domestic water,industry and ecology during dry season in the middle and lower reaches of the Yangtze River.