Laboratory Studies Of Sand Column On The Dynamic Evaporation On A Shallow Water Table

Phreatic evaporation is the main depletion way of shallow groundwater, it is the main form for groundwater to turn into the soil water and atmospheric water and also an important part of transformation in four-water. The study of phreatic is of great importance for four- water transformation mechanism, irrigation, saline control and evaluation of water resources.Surpporting by the National Natural Science Foundation,this paper takes the method of theoretical analysis combining with laboratory to study the dynamic evaporation process of the water table, the research and preliminary results are as follows:(1) By referring internal and external literatures, the paper summarizes the advantages and disadvantages of the methods of determining the soil water characteristic curve. Based on some conventional experiments including density, particle-size distribution, saturated hydraulic conductivity coefficient, we develop a laboratory experiment of sand column to measure the soil water characteristic curve. It turns out that the curve presents"S"well. At the same time, we see that van Genuchten model is able to match the measured moisture-suction data of the sand material used in the experiments well. Furthermore, pressure-membrane apparatus is applied to determine the soil water characteristic curve,from which inherent advantages and deficiencies of the methods are analyzed. Based on the analysis and comparisons, the laboratory experiment of sand column provides great accuracy, low cost, simple operate in determining the soil water characteristic curve.(2) On the basis of analysis of Phreatic evaporation and the existing observation methods ,according to the principle of conservation of mass, By the experiment of initial saturated sand column to study the changes of Phreatic evaporation and the evaporation coefficient with depth in different evaporation duration, Phreatic evaporation in the experiment was mainly influenced by the depth and the aatmospheric evaporation, with the increase of depth,the influence of atmospheric evaporation increases too, Phreatic evaporation and the evaporation coefficient will both decrease. Index formula C = 23.331e-0.8464D can better fit the measured evaporation coefficient changing with depth.(3) To soil water dynamics theory, we established a mathematical model of Phreatic dynamic evaporation,using Hydrus-1D to simulate the dynamic evaporation of the sand column experiments. Except for some specific points, the Model calculation and the measured evaporation have less error,the macroscopic morphology was well fitted ,so the model can better simulate the overall change process of Phreatic dynamic evaporation, the trends of numerical simulation and measured are identical and the requirements of precision can be satisfied.(4) Due to objective conditions, there are still some shortcomings in the experiments needed to be improved, the paper has put forward some suggestions for further improvement.