Study On Regulation Of Water Movement In The Vadose Zone In Dulan Basin

Dulan Basin is located in the middle of Qinghai province.The precipitation of Dulan Basin is scarce,the depth of the groundwater level is large and the thickness of the vadose zone is huge.Carring out the research of groundwater migration in the huge thick vadose zone,and clarifing the law of soil water evaporation and the recharge effect of large area irrigation on groundwater is of great significance to guide the groundwater resources evaluation and the ecological environment construction in this area.In this study,the data of surface soil pressure,water content and soil temperature were collected from 2015 to 2017 by setting up the test site.The water retention curve was obtained by indoor tests with original soil samples.The water transport numerical model of shallow vadose zone in the three year observation period was built by HYDRUS-1D software.The soil water balance was analyzed by using the model.In 2015,the amount of soil evaporation was 139.77 mm,the amount of infiltration was 324.73 mm,the amount of soil evaporation in 2016 was 137.04 mm,the amount of infiltration was 118.72 mm,the amount of soil evaporation in 2017 was 248.27 mm,and the amount of infiltration was 633.04 mm.In 2015 and 2017,the shallow zone is in a positive equilibrium,while the shallow envelope in 2016 is in a negative equilibrium state.The influence factors of water evaporation in the vadose zone are analyzed.The greater the soil temperature gradient,the greater the rainfall and irrigation infiltration.The stronger the atmospheric evaporation capacity,the greater the soil evaporation.When the meteorological evaporation increase by 50% and 100%,the actual evaporation of the soil increase by 12.13% and 22.18%.The amount of soil evaporation in different lithologies is in this turn: silty sandy loam > loamy sandy soil > gravel medium sand > sand gravel,that is,the higher the proportion of clay in the soil,the smaller the soil particles,the greater the actual evaporation.At the same time,the empirical formula of soil water evaporation is deduced.The ratio between soil evaporation and meteorological evaporation is 0.543.The law of water infiltration and recharge in the vadose zone is analyzed.The small scale of rainfall can only recharge the shallow soil.Only the continuous and large intensity of rainfall infiltration supply and large area irrigation supply can provide recharge to the deep zone and groundwater.Combined with the irrigation experiment and numerical model,the variation trend of water infiltration coefficient at different depths in the soil profile is obtained.The loss of the rainfall and irrigation water in the deep submersible layer above 4.5m is larger,and the loss is nearly none in the sand gravel layer from 4.5m to 70 m.According to the calculation,the vertical infiltration recharge coefficient is 0.27.