Numerical Simulation Of Water Cycle Response Of The Sugan Lake Basin Under The Influence Of Inter-Basin Water Transfer Project

Dunhuang,located in the Danghe Valley of Gansu Province,is a famous historical and cultural city in China.In recent years,with the rapid development of the local economy and society,the contradiction between the supply and demand of Dunhuang water resources has become increasingly prominent.Wetlands in the West Lake National Nature Reserve at the end of the basin have gradually shrunk and the Dunhuang Oasis is being seriously threatened by deserts.According to the current economic development status and water resources conditions in the Danghe River Basin,the ecological environment problem in Dunhuang cannot be completely solved by water conservation and tapping potential water resources.The "Yin-Ha-Ji-Dang" water transfer project is a key project for realizing the optimal allocation of water resources in Dunhuang.It is of great significance for the restoration of the ecological environment and the protection of historical and cultural relics in Dunhuang.However,water diversion region of "Yin-Ha-Ji-Dang" water transfer project(Sugan Lake Basin)is an ecological sensitive area.If excessive water transfer from this area may strongly alter the water cycle process in the Sugan Lake Basin,the water table in the basin will decline and the lake area will shrink.Due to there are would be serious impact on the ecology of the Sugan Lake Basin,it is necessary to study the possible effects of future water transfer plans on the water diversion region.Because the hydrological,meteorological,and groundwater monitoring facilities in the Sugan Lake Basin are still incomplete,there is a lack of measured data and it is difficult to provide support for the assessment of the ecological environment impact assessment and water transfer scale demonstration in the reclaimed area.Because the hydrological,meteorological,and groundwater monitoring facilities in the Sugan Lake basin are still incomplete and there is a lack of measured data,it is difficult to provide support for the assessment of the ecological environment impact and water transfer scale demonstration in the water diversion region.Therefore,it is of great significance to build a groundwater model that is applicable to the Sugan Lake basin and can simulate the changes of the water circulation flux in the water diversion region under different water transfer scales.Based on the analysis of natural geography,hydro-meteorology,hydrogeology,and the characteristics of water cycle transformation of the Sugan Lake Basin,this paper combines the results of predecessors' research to evaluate the current groundwater resources in the Sugan Lake Basin.Based on the COMUS model,a groundwater steady flow modle suitable for the study area was constructed,and the rationality of the model was analyzed.Finally,a transient flow model was constructed based on the steady flow model,and the fluctuation of the water circulation fluxes in the water diversion region were analyzed under different water transfer scales.The main innovations and major achievements have been summarized as follows:(1)This paper proposes a new approach for simulating lake-groundwater interactions,which can be applied to the numerical modelling of groundwater flow based on a block-centered finite difference method.The lakebed is generalized by a slope across each lake grid cell,and the lake grid cells are classified as fully submerged,partially submerged,and unsubmerged to simulate the interactions between the lake and the aquifer according to the relative elevations of the lake surface and lake bed.Transitions between different states ensure the continuity of the boundary conditions,improving the convergence of the calculation process.The proposed method accounts for all source and sink terms for the lake,establishing a governing equation for lake water balance.The lake stage can then be obtained by solving this equation.Compared with the existing similar methods,the proposed method has significant advantages in its ease of use and calculation stability.(2)Based on a detailed analysis of the physical geography,climatic hydrology,stratigraphic lithology,hydrogeology,the characteristics of hydrological cycle,and groundwater resources of the Sugan Lake Basin,a groundwater numerical simulation model suitable for the study area was constructed based on the COMUS model.Using the measured data,the rationality of the model was verified,the rationality of the model was verified.Through the improvement of the model,the model not only can simulate the process of overflow and re-infiltration of spring water in the study area,but also can simulate the interaction between groundwater,spring water,and lake surface water,which cannot be achieved by existing models.(3)On the basis of constructing the model of groundwater steady flow,the transient flow simulation of groundwater in the study area was carried out.The output of the model was used to analyze the water cycle response of different water transfer scales in the Sugan Lake Basin.The predictions of groundwater level,spring overflow,phreatic water evaporation and the fluctuation in the area of Sugan Lake under different water transfer scales were carried out.Provide scientific support for the assessment of ecological environment impacts and water transfer scale demonstration in the water diversion region of the transfer project.