Study On Regional Groundwater Circulation Under The Influence Of Typical Thermokarst Lake In Qinghai-Tibet Plateau

In the context of global warming,the distribution and development of permafrost have a very important impact on the regional environment and ecosystem.And the Qinghai-Tibet Plateau,known as the "roof ridge of the world ",as the " amplifier " and " driver " of the climate,which characteristics and evolution trend of permafrost on it are similar to that of other parts of the world.Therefore,the research significance and value of the Qinghai-Tibet Plateau as a typical representative of the study of permafrost can not be ignored.On the basis of the research method of permafrost proposed by scholars at home and abroad,this paper establishes a reasonable numerical model of permafrost water-ice-thermal coupling under the influence of sutra,and calculates and analyzes the variation of temperature,ice saturation,flow field,active layer thickness,permafrost distribution and so on under different permeability,atmospheric temperature and hydrodynamic condition.The interaction of groundwater flow,seasonal permafrost active layer and permafrost in the regional hydrological system of Qinghai-Tibet Plateau in which thermokarst lakes is involved is analyzed.And it further enriches the theoretical system of the groundwater circulation of Lake in the field of frozen soil research at home and abroad.The research results obtained in this paper are as follows:(1)In the absence of groundwater flow,the thickness distribution of permafrost is the most uniform,and the influence of thermokarst lakes on the surrounding permafrost is the least.The time required to forming penetrating melt zone at the bottom of the lake increases with the increase of permeability,but the melting rate of permafrost increases with the increase of permeability.The thickness of the active layer gradually thickened with the decrease of the distance from the active layer to the lake under different permeability conditions,and the surface runoff and the water on the frozen soil layer were discharged to thermokarst lakes.(2)The thickness of permafrost and the time required to form the lake bottom through the melting zone all decrease with the increase of atmospheric temperature as a whole.The thickness of the active layer at the same position at the same time is the thickest at high temperature,the second is the heating condition,and the thinnest is at normal temperature.(3)At the close of the lake,the degradation degree of permafrost from large to small is the discharge of the lake,the equilibrium condition(the water level at the bottom of the lake is equal to the water level outside the model at the same height)and the recharge of the lake,and when the lake is discharged,the isotherm of 0? near lake is the steepest.When the hydrodynamic conditions change,it mainly affects the permafrost near the lake,and has little effect on the frozen soil in other positions.No matter what kind of hydrodynamic conditions,groundwater circulation is dominated by superficial flow.(4)When formation permeability is high at high temperature,the rainfall infiltration may all enter the aquifer,the rainfall infiltration can not maintain the high water level of the formation and the depth of the water level increases,so surface vegetation can not get enough water from the aeration zone and gradually desertification,which poses a serious threat to production life and ecological environment.When the permeability of the local layer is small,part of the rainfall stays on the surface,and the depth of water level is shallow,there may be a tendency to swamp in flat terrain.And in higher places,Under high altitude evaporation conditions,the groundwater is mainly discharged by local evaporation,which may lead to soil salinization,affect vegetation growth,and make the ecological environment more fragile.