Environmental Impact Assessments Of The Groundwater Of The New City In Golmud

With the proposal of the second Ten-Year Plan of the Development of the West Regions in China, and the general program of supporting the development of Tibetan Regions, as well as the establishment of the Cycling Economic Test Site of Qaidam, Golmud is holding the distinguished advantages of economic development as the vital composition of Lanzhou-Xining-Gelmud area. A new construction project was proposed by the city government for the sake of improving the district status and satisfying the desired area of industrial development.A number of negative factors lie in the arrangement of urban building, construction of underground area and the environment of ecology as the results of the depth of groundwater level is less than5m in the new city zone commonly, and the depth of groundwater level is less than lm in overflow zone. In this thesis, the impact factors of the groundwater of the new city were analyzed based on the current situation of the development and utilization of groundwater in Gelmud, and the existing engineering geological and ecological issues. Sveral conditions were taken into consideration in the analyzation of these issues, including the hydrogeological condition of the area, the distribution of groundwater and the condition of the recharge-runoff-discharge system. And the corresponding treatment measure of the groundwater were put forward for each factor. The Visual Modflow software was used in the simulation of the seepage field of different treatments. The appropriate groundwater level for engineering construction and ecological environment was achieved based on the adaptability of groundwater in different treatments. Ultimately the following conclusions have been drawn in this study:(1) The alluvial and diluvial fan of Gelmud are typical and classic so that the permeability deteriorates from the top of fan to the plain stratum, and the groundwater level shallows in the same orientation. The new city zone locates in the fine soil plain of the Gelmud alluvial and diluvial fan, in which the main source of groundwater recharge are precipitation and snowmelt. Because of the impediment of the poor permeably clay layer, a part of phreatic water escape to the surface and gather into a river then flow into East Dabsun Lake undergone evaporation when the groundwater flowing through the new city.(2) The major factors impacting the recharge-runoff-discharge system of the new city are reservoir, river and the artificial lake to be built. The reservoir takes the primary responsibility for the rising of the groundwater level in recent years. And the groundwater is recharged by the Gelmud River mostly. Additionally, the artificial lake to be built will cause serious influence on the seepage field of the groundwater in the new city zone.(3) The adaptability of the new city groundwater level upon the engineering construction and the ecological environment was simulated under several conditions including before and after the seepage-proofing of the riverway, and after the artificial lake is completed withouth any seepage-proofing measures. The simulation indicated that after the riverway seepage-proofing the area of poor adaptability (the buried depth of groundwater level<1m) of groundwater level against engineering construction decreased by7.52km2, the area of swampiness and salinization (the buried depth of groundwater level<3m) decreased by4.12km2, and the area of eco-suitable (the buried depth of groundwater level3-5m) increased by2.09km2. On the other hand, it was also indicated that the area of swampiness and salinization increased by6.67km2after the artificial lake had been completed.(4) Combined with appropriate depths of groundwater level of the infrastructure, the damage of freeze thawing and frost heaving, and the ecological environment, the optimal buried depth of groundwater of the new city in Gelmud is3-5m.