Groundwater Management Model Of Wuwei Basin In Shiyang River Catchment

Wuwei Basin, located in the northern foot of the QilianMountains, the eastern part of the Hexi Gallery, and the western marginof Tenggeli Desert, is a historical agricultural irrigation basin. Inthe area, some ecological environmental problems have caused byunresonable pumping of groundwater. This paper attempts to apply9roundwater management model to determine the optimal groundwaterwithdrawal program so that pumping of groundwater will reach themaximum economical benefit in the meanwhile to maintain the ecologicaland social environment tobe in good condition. The main points andresults are as follows.1, From the view point of system enginering, the research contentsand methods of groundwater management model are summarized, which shouldinclude groundwater system objective analysis, environmental analysis,structure analysis, modeling, optimization, and evaluation.2, The hydrogeological meaning of response matrix are discussedtheoretically and the two methods of generating response matrix withnumerical model are introduced. The methods of treating inhomogeneousboundary condition, inhnmogeneous initial condition, and naturaluncontrolled recharge end discharge are mainly discussed, which comeinto a conclusion that the contribution of inhomogeneous boundary andinitial conditions and natural recharge and discharge to the drawdownmust be explicitely modeled by an "additional drawdown" , and thedrandown caused by artificial pumping is expressed as "convolutionintegral" of pampage with response matrix under homogeneous boundaryand initial conditions. Therefore, the total dradown is thesuperposition of the drawdowns calculated above.3, The program package of groundwater system management modelisdesigned, which consists of seven main programs linked into anintegrative system by data files. This package makes it possible tosolve larger groundwater management problems on small computer. 4, The results and data of previous hydrogeological investigationin the Wuwei Basin are analyzed and summarized into a conceptual model.Much improvement of the numerical model, which are established by FanXipen (1984), has been made in fitting error by adjustinghydrogeological parameters and boundary conditions. All these provide abasis of hydrogeological model and a tool of numerical simulation forthe establishment of the management model.5, The response matrix of groundwater system of Wuwei Basin isgenerated which can be used not only to couple management model withnnmerical model but also to predict the change of groundwater levelunder the operation of the planned groundwater withdrawal project.6, Under the condition of conjuctive use of surface-ground waterof Wuwei Basin, which is designed on the basis of comprehensiveanalysis of component feature of water resources system, interchangerelationship of surface-ground water, pumping condition of groundwaterin the region, and the present state of water resources development inthe basin, the objective and physical, technical and economical, andsocial environmental constraints of groundwater management aredetermined. The groundwater management model of the Wuwei Basin isformulated using response matrix technique.7, By solving management model, the optimal groundwater withdrawalprograms of the Wuwei Basin in two irrigation periods are obtained,which shows that the pumping condition of groundwater in the region canbe divided into six sub-regions, the pumping sub-region with maximumpumpage is located in the river courses; the sub-region with minimumpumpage in the spring overflow zone; and non-pumping sub-region in theriver irrigated districts and desert area, and that the unique way toincrese groundwater pumpage is to pirate evapotranspiration in thegroundwater evaporation zone.8, The reasonable development and utilization projects of waterresources are proposed according to the optimal withdrawal program. Theprojects of water resources allocation and groundwater withdrawal areas follows.(1), The distribution of pumping well and pumpage must be adjustedin terms of the optimal withdrawal program. The evapotranspiration inthe groundwater evaporation zone must be pirated and the pumpage ofHuanhe irrigation district should be increased. Huanhe irrigationdistrict should be constructed into purely groundwater irrigateddistrict and from there, 60 million cubic meter per yeay of groundwateris transported to Minqin irrigation district. The maximum pumpage in the basin should be controlled in 495 million cubic meter per year whengroundwater is pumped according to the optimal withdrawal program.(2),The total amount of water resources which is transported toMinqin district must reach to 335 million cubic meter per year inaverage water year; 290 million cubic meter per year in dry water year;and 375 million cubic meter per year in wet water year.