The Influence Of Water Movement In The Vadose Zone On The Groundwater Recharge And Evaporation In Zhongning Plain

Zhongning is located in the arid and semi-arid region of Northwest China, which is one of the most water scarcity areas in China with shal ow groundwater depth. Precipitation and artificial irrigation is the main source of groundwater recharge, and phreatic water evaporation is one of the main consumption items of groundwater. The vadose zone is a link among atmospheric water, surface water and groundwater., The deeply understanding of recharge and discharge of groundwater and the correct evaluation of infiltration recharge flux and evaporation flux with the study of vadose water transport rule have an important theoretic and practical meaning for the rational development and utilization of groundwater resources.Combining in-situ test and numerical simulation analysis of vadose zone with soil water as the research object in Zhongning test point, we analyze the mechanism and regulation of infiltration and evaporation. The results are as follows:Establishing vadose water transport model of bare land groups and vegetatio n groups of in-situ test location by Hydrus-1D, we analyze the variation of infiltra t io n flux and evaporation flux of vadose zone:(1) Under the same rainfall and irriga t io n conditions, infiltration flux and evaporation flux of vegetation groups is higher than that of bare land groups.(2) With the enhance of precipitation and irrigation, infiltra t io n flux and evaporation flux will increase.(3) Groundwater vertical infiltration recharge coefficient of bare land and vegetation land is about 0.3 and 0.4 respectively.Through analysis of the influence of irrigation, vegetation, groundwater depth and lithologic characteristic on groundwater recharge, we can conclude:(1) Irrigation can enhance groundwater infiltration flux. Under the natural rainfall condition, precipitation recharge coefficient of the test point is 0.14, and groundwater recharge of Zhongning is mainly from irrigation.(2) Under the same rainfall and irriga t io n conditions, vadose infiltration flux of vegetation land is only slightly greater than that of bare land, but groundwater infiltration flux of vegetation land is significantly higher than that of bare land.(3) When the simulation depth is less than 5 meters, with the increase of groundwater depth from 1m to 5m, groundwater infiltration recharge coefficient gradually decreases from 0.41 to 0.09.(4) The finer the vadose zone lithology particle, the more lag the groundwater infiltration process, then the more gentle the infiltration curve. In the same weather conditions, the thicker the vadose zone lithology particle, the larger the groundwater infiltration coefficient.Meanwhile, through analysis of the influence of vegetation, groundwater depth and lithologic characteristic on phreatic water evaporation, we can conclude:(1) With the increase of groundwater depth, phreatic water evaporation flux gradually reduces. The limit evaporation depth of the test point is 3m. The phreatic water evaporation formula of the in-situ site is established:(?).(2) When the groundwater depth is shal ow, phreatic water evaporation of vegetation land is significantly larger than that of bare land. When the groundwater depth is deep, there is no obviously difference between phreatic water evaporation of vegetation land and that of bare land.(3) The groundwater limit evaporation depth of different lithology of vadose zone is different, the general rule is that the larger the particle, the smal er the groundwater limit evaporation depth. The phreatic water evaporation formula of silty clay, clay loam, silty clay loam, clay loam and sandy loam is established.