Simulation Of Groundwater In The Source Area Of Changbaishan River Coupled With Freezing And Thawing Process

Under the background of climate change,groundwater simulation coupled with freezing and thawing process has been a hot and difficult point in the study of water cycle in cold regions.The solid medium composition of water transport in the freezing and thawing period is different from the transport in non-freezing and thawing period.In the non-freezing and thawing period,the solid medium of soil water transport is mainly composed of soil particles.But in the seasonal freezing and thawing period,the solid medium is composed of soil particles and ice.This phase change of water increases the difficulty of groundwater simulation in frozen soil.Therefore,how to simulate the groundwater considering seasonal freezing and thawing process is great significance to reveal the mechanism of water cycle in cold region.Erdaobai River was selected in the source area of Changbai Mountain as a typical study area.First,the temporal and spatial characteristics of freezing depth and its response to driving factors were analyzed;Second,the mechanism of frozen soil degradation on hydrothermal process was revealed;Finally,based on the HydroGeoSphere model,the groundwater simulation of coupled freezing and thawing process was simulated considering the seasonal freezing and thawing process.The main achievements of this study were as follows:(1)Temporal and spatial characteristics of freeezing depth and its response to driving factorsIn this study,IDW,M-K trend test,Pearson correlation coefficient and GAM were used to analyze the temporal and spatial distribution of frozen soil,interannual variation and the response of frozen soil to the climate with climate in the Erdaobai River Basin.The results showed that the spatial distribution of frozen soil in the basin has obvious latitude effect,and the larger freezing depth distributing in the North.The frozen soil showed degenerated trend.The maximum freezing depth(1.2cm/year)and the average freezing depth(0.45cm/year)decreased The freezing and thawing period of frozen soil showed a trend of shorten,the freezing onset time delayed and the melting time advanced.Snow and temperature are the main factors influencing the annual average freezing depth and the annual maximum freezing depth(p<0.05).In the beginning of freezing and melting,temperature is the main factor affecting the change of monthly average freezing depth(9%?45%).In the continuous freezing,snow is the main factor affecting the change of monthly average freezing depth(29%?43%).(2)Influence mechanism of frozen soil degradation on hydrothermal transport processIn order to show the impact of frozen soil degradation on soil temperature and humidity,three years with different freezing depth are selected to analyze the changes of soil temperature and humidity in each layer under the surface.The results showed that in the freeze-thaw cycle,the changes of soil temperature and humidity showed a "U"shape change trend and the change of soil humidity is more frequent.The change process of surface soil temperature and humidity is greater.In the freezing of frozen soil,the deep soil temperature was higher(0.8??14.08?)and the surface soil temperature was low(-2.15??13.7?).In the melting,the surface soil temperature was higher(9.05??19.69?)and the deep soil temperature was slower(3.95??14.99?).With the degradation of frozen soil,the soil temperature and humidity in each layer show an increasing trend.(3)Simulation of water infiltration process of snowmelt during freeze-thaw periodBy analyzing the boundary,geological structure,surface properties,surface water sources and groundwater sources of Erdaobai River Basin,the conceptual model was established.The numerical model was established by means of Richards equation,Saint Venant equation,water balance equation and nodes coupling.According to the numerical model,the HydroGeoSphere model was used to calculate the change trend of groundwater in Erdaobai River.The results showed that the groundwater depth in the basin showed a decreasing trend,The actual change trend is-1.47×10^-4m/day,and the simulation change trend is-5.66×10^-4m/day.There is a significant correlation between the measured and simulated changes(P<0.05).The establishment of the model provides an important reference significance for the study of snow melting infiltration process in seasonal frozen soil area.