Experimental Study On Variation Characteristics Of Water Movement Parameters In The Vadose Zone Under Multiple Factors' Influences

The vadose zone plays an important role in the hydrological cycle,becoming the main channel of groundwater recharge and discharge.The influence of natural conditions,sedimentary environment and other factors causing a strong variability with medium property,structure and water movement parameters,including water characteristic parameters are particularly important.The variability of water movement parameters causing a great limit for the application of water movement model of the vadose zone in a larger scale.How to scientifically and reasonably determine the water movement parameters in larger scale of vadose zone becomes the difficulty of research for water movement in the vadose zone.Based on the surface project of the National Natural Science Foundation of China: study on coupling process of water movement parameters in the vadose zone and signal of ground penetrating radar on small watershed(41372260),this paper uses means of indoor test and fitting software to carry out experimental study on the variation characteristics of water movement parameters in the vadose zone under the influence of multiple factors,analyses the variation of water movement parameters in the vadose zone under the influence of the three factors of different grain compositions,different bulk densities and different sample sizes and tries to predict water movement parameters in larger scales of vadose zone through the construction of soil transfer function,providing scientific basis for the application of the water movement parameters in larger scales of vadose zone.Based on a large number of experiments and theoretical exploration,this paper has made the following main conclusions:1.Water characteristic curves.The changes of the shapes of the water characteristic curves of the media are the same,that is,the negative pressure decreasing with the increasing of water content,and vice versa.Nevertheless the shapes of the water characteristic curves of the media vary with the different media,bulk densities and sample sizes.With the negative pressure increasing,the effects of grain compositions,bulk densities and sample sizes on the shapes of the water characteristic curves of the media are gradually increased.The greater the content of fine particles in the media is,the stronger the water storage performance is and the more significant the effects of grain compositions on the water characteristic curves are.The effects of bulk densities on the water storage performance of the media are more complicated.Comparing with bulk densities,the effects of grain compositions on the shapes of the water characteristic curves of the media are more significant.The sample diameter is not sensitive to the water characteristic curve of pure sand.The larger the sample height is,the influence of the sample diameter on the water characteristic curve of pure sand is more significant.2.Water movement parameters.The more largely the sizes of the medium particles are different,the more strongly it influences the residual water content Cr and the saturation water content Cs and the more weakly it impacts the reciprocal of capillary rise height ?.The greater the content of fine particles is,the greater the values of the residual water content Cr and the saturation water content Cs are.The greater the content of fine particles is,the more strongly the medium bulk density influences the saturation water content Cs and the more weakly it impacts the residual water content Cr and ?.when the content of fine particles are more than the content of coarse particles in the medium,? and bulk density show the linear positive correlation.The saturated water content Cs and bulk density show the linear positive correlation.When the medium sand content is high,the residual water content Cr is linearly positively correlated with bulk density.The larger the sample height is,the more strongly the sample diameter influences the residual water content Cr and ? and the more weakly it impacts the saturation water content Cs in pure sand medium.The larger the value of sample diameter is,the larger the values of the residual water content Cr and ? in pure sand medium are.The effect of sample diameter on the saturated water content Cs in pure sand medium is not significant.Empirical fitting parameter n is not sensitive.3.Soil pedotransfer functions.Rosetta soil transfer function model based on neural network does not have universal applicability.