Simulation Of Poyang Lake Hydraulic Project On Runoff Of Yangtze River Mainstream

Since 2003,water level of Poyang Lake has been declining continuously, and dry season has been prolonging,therefore the proposal for construction of Poyang Lake Hydraulic Project has became a hot topic and aroused a broad discussion.But objectively speaking, the project will inevitably bring some uncertain impacts to hydrological and hydrodynamic characteristics of middle and lower reaches of Yangtze River to some extent.Aimed at working out the impacts of Hydro Project on the Yangtze total runoff,a Poyang Lake 2-dimensional Hydrodynamic model is developed on the basis of EFDC model in this paper.And the paper also simulates the daily flow that the Poyang Lake discharges into the Yangtze River in rainy year,normal year and low flow year respectively.on this basis,according to Poyang Lake Hydro Project scheduling scheme released by Jiangxi province in September,2013,this paper will compare and analyze the influence of Poyang Lake Hydro Project on the runoff of middle and lower reaches of Yangtze.This can provide a theoretical basis for the further study of ecological effects which Poyang Lake Hydro Project brings to Poyang Lake and Yangtze River,and it also provides a theoretical reference for the project construction.Specific results are as follows:(1)From this perspective of the scheduling period,according to the difference of simulating runoff when Poyang Lake Hydro Project operates or not in 2002, 2006,2003,it should be found that during the first scheduling period(connecting period of river and lake),the relative change is-0.1%,0.07% and-0.31% under scheduling.And from the second scheduling period(during September 1 to next March 14),the relative changes of rainy year,normal year and low flow year respectively is-0.66%,-2.17%and-1.21%, accounting for-0.17%,-0.31% and-0.1% respectively of the total runoff of Yangtze River over the same period.It shows from the view of this two important periods that under the current scheduling program, the project makes little difference on the total runoff that Poyang Lake discharges into Yangtze River It just changes the distribution time of runoff, but the impact on overall flow of Yangtze River is minimal.(2)According to monthly total flow that Poyang Lake discharges into Yangtze River with project scheduling the relative changes of 2002, 2006, 2003 is-0.29%,-0.08% and 0.82% respectively. Therefore, in rainy, normal, or dry year, according tocomparison with the monthly total runoff flow in the same month of the year, it's found thatthe discharge runoff of Yangtze with project scheduling has basically maintained the same level as that without project scheduling, maintaining the water flow balanced.But it does change time of flow distribution discharged into the Yangtze river.(3)The distribution time of the outer flow of Poyang Lake is mainly reflected in 4periods: project storage water period, Three Gorges Reservoirs storage period,Compensation and regulation period of Yangtze, Lake dry season.Specifically,in2002,the project storage period and Three Gorges Reservoirs storage water period have no effect on Yangtze;during compensation period, the outer flow of Poyang Lake to mainstream of Yangtze decreases 2.09% compared with that without the project.Within the same period, the main stream of Yangtze decreases 0.55%; During the dry season, the total outer flow of Yangtze is 1.26%, which accounts for 0.33% of total runoff flow within the same period.In 2006, during the compensation period, the outer flow under the project decreased 0.54%, which shows that the project affects the total flow of Yangtze insignificantly.While from January 18 th, 2007 to March 14 th 2007,during dry season, the total runoff on the contrary had some increase, with the increment of 3.83%;within the same period, the increment of Yangtze runoff is 0.55%,which was slightly replenished by the outer flow of Poyang.In 2003, during the compensation period, the drainage of Poyang with or without project decreased9.68%,while within the same period, the change of Yangtze flow is-0.84%.During the dry season, the increment of Yangtze by Poyang is 15.58%, and the increment of Yangtze runoff is 1.69%.(4)during the period of Compensation from November 1st to next January 10 th,all the outer runoff discharged to Yangtze River come to decrease,among which the change of outer flow during the dry years is maximum, rainy year second and normal water years minimum;In the dry season,the overall runoff of Lake which flows into the Yangtze River has obviously increased,easing the water pressure in the middle and lower reaches of the Yangtze River,among which the dry year increases largest, the water level year second, and high flow year smallest,which reveals that the project has big impact on the runoff of Yangtze River in the dry water year.(5)For the year like 2002 whose water level is significantly higher than 15 m during wet season and and the year 2006 whose water level was obviously lower than15 m,the current scheduling scheme has its obvious shortcoming in terms of water level and date of water dispatch.Therefore,for those particular years,the scheduleshould be optimized, and the highest water level should be respectively controlled based on the water level in rainy,flat and dry water year.