Application Of ERT And Dye Tracing Method In Monitoring Soil Water Infiltration

The precipitation infiltrates to the soil and turns into soil water,then soil water flows through the unsaturated zone(or vadose zone)to the surface of groundwater and recharges groundwater.Soil water and groundwater are the most important components of water resources in arid and semi-arid regions.In order to ensure the sustainable utilization of water resources,it is necessary to estimate the groundwater recharge rate.In recent years,with the development of economy and the improvement of people's living standard,the water resources in Qingdao are becoming increasingly scarce.The Dagu river is an important water source in Qingdao,but it faces many problems such as the decline of groundwater level,the seawater intrusion,and the pollution of groundwater though the basin area is vast.So exploring the soil water infiltration process is one of the key researches on these issues.In the past twenty years,the Electrical Resistivity Tomography method(ERT)as a new hydro geophysical technology has been widely used in the study,because of its non-destruction,temporal continuity and high resolution characteristics.Otherwise,the dye tracer test has been paid more and more attention because it can clearly and intuitively reflect the soil water flow path.To understand the process of water movement in soil,this paper conducted a total indoor soil water infiltration experiment and field soil water infiltration experiment,analyzed in different infiltration conditions,water movement process in homogeneous soil and heterogeneous soils.In the indoor soil column infiltration experiments,the soil moisture sensor installed on different depth of soil column to monitor profile variation of soil moisture in water infiltration process.And using different models simulated water movement.The field water infiltration experiment was carried out in the Luncun of Jimo city in Dagu River downstream.Setting 2~4 measuring line,two frames were arranged in the center of the measuring line.The inner frame infiltrated 3g/L brilliant blue solution,while the outer frame infiltrated water,and the height of water and brilliant blue solution must keep 3 cm.Using the DCX-1G multi function and high density electrical instrument--real-time imaging system(ERT)monitored variation of resistivity before infiltration and infiltration process and after the infiltration in situ.The 2-D resistivity information were collated and imported into the 3D Voxler software,realizing the conversion from two-dimensional to three-dimensional,it can observe the soil water infiltration process more clearly.And using Hydrus-1D software simulated soil water movement.At the end of the experiment,along the inner frame excavated section every 5~10 cm,and using the camera recorded the profile of dyes.The research of this paper draws the following conclusions:(1)Through the analysis of the indoor infiltration experiment,it was found that the infiltration rate of water was large at the beginning of infiltration,and the cumulative infiltration rate changed rapidly.With the passage of time,the infiltration rate decreased gradually and tended to be stable.The infiltration process can be simulated by Philip model and Kostiakov model,and the fitting degree of Kostiakov model was better;the process of infiltration and redistribution process can be simulated by Hydrus-1D,and the simulation results of the former was better,but the simulation results of the latter was slightly worse.(2)Through fitting the resistivity values calculated by ERT and measured the water content data used Archie formula,the quantitative relationship between them were determined,the fitting degree between them was 0.765,the correlation was good.So the fitting formula can accurately describe the quantitative relationship between resistivity and water content.(3)In the early infiltration,soil resistivity was decreased rapidly,with the passage of time,the variation of surface resistivity decreased.According to the comparison of resistivity between water infiltration profile and brilliant blue solution infiltration profile,it was found that water moved faster than brilliant blue.In the process of brilliant blue solution infiltration,the brilliant blue solution can be adsorpted by upper soil,so the main reason of resistivity changes in preferential flow area was water movement.And when the infiltration amount is large,the water will accumulate in the poor permeability region.(4)A series of 2D resistivity profile information loaded into the Voxler software and converted into a three-dimensional resistivity distribution model,which can be used to enrich the information of the geoelectric section.It was found that the 3D resistivity model can accurately reflect the process of soil water movement by comparing with the 2D resistivity profile.(5)The Photoshop image processing software was used to process the image of the soil profile to be a two value image.By statistical analysing soil profile changes in dyeing ratio in the vertical direction,it was found that with the infiltration volume increased,the maximum dyeing depth,uniform dyeing range,preferential flow uniformity increased.