Parameters Research On Models Of Water And Salinity Transport Based On Indoor Soil Column Experiments

In Qidong, Jiangsu province, which of the Yangtze River estuary, it tends to be affected bythe saltwater intrusion, the tide invasion, and runoff changing after the Three Gorges projectoperation, making the local ecological environment fragile and sluggish development ofagricultural production. In view of these, parameters researches on models of soil water andsalinity transport were taken in this study. The water characteristic curves on desorption andabsorption processes of three different depths on the soil from the estuary of the Yangtze Riverwere determinated indoor by the method of tension meter weighing in this paper. The parametersfitting were obtained from the Van-Genuchten model combined with Matlab software. And soilwater movement equation parameters were obtained. Based on indoor soil column method, inertsolute B-rpenetration test was taken and the breakthrough curve fitting was carried out combinedwith the CXTFIT software, so as to get the salt movement equation parameters. Meanwhile, saltcontent conditions of different soil depths were observed to get the salt migration coefficient.Under the operation of the three gorges project, this research would lay a good foundation forestablishing the water and salt migration numerical model during the process of saline intrusion inthe typical seasonal on the Yangtze River estuary area. The main results were as follows:1)On the experimental study of soil water characteristic curves on different soil depths,analysis results show that:①Along with the deepening of soil depth, the water binding capacitywas better. Whether surface soil, middle or deeper soil, it was easily absorption and harderdesorption, existing hysteresis phenomenon. The water-retaining property of surface soil was best,presenting the most obvious. Within lower suction range, the water supplying capability of surfacesoil was better and poorer of the lower soil; during higher suction range, the water supplyingcapability of lower soil was better and poorer of the surface soil.②When the soil suctions ofsurface, middle and deeper soil were209cmH₂O,235cmH₂O,222cmH₂O, respectively, theabsolute difference of soil moisture content was the largest and the soil water capacity were thesame during the desorption and absorption processes. Below this suction, soil suction strength wasgreater, while opposite in higher than this suction and soil drainage strength was greater.③When lower moisture content, soil moisture within the smaller soil pores was discontinuous, with poorersoil permeability and lower hydraulic conductivity. While soil moisture of each layer closed tosaturation, the bigger pores were filling with water sharply, presenting well pore connectivity,strong transmission ability. With soil depth deepening, water liquidity and transmission ability inunsaturated soil was less and less. Change rules of soil moisture diffusivity and hydraulicconductivity were roughly the same in the different soil layer. While water content was in therange of0.3⁰.4cm³·cm^-3, water flow performance was good and moisture diffusivity was bigger.2)The results of analysis on B-rbreakthrough curve showed that:①When pore volume ratioless than0.55, relative concentration was tiny, due to the process of B-rin this phase infiltratedfrom top column into the soil, been detected from the bottom column of the diffusate was slow,taking long time. Then, B-rconcentration detection of the diffusate was bigger. When the porevolume ratio reached to1.7, bromine ion concentration of the flow liquid closed to the addsolution. The pore volume ratio rose to2, B-rfully penetrating in the soil column.②Initialelectric conductivity in soil column was below to the add solution, and the process of Br^-migration was slow and complicated, hence, at the early stage of the saturated infiltration, the soilprofile conductivities of different soil depth changed intensity but approximately, without obviousamplitude of fluctuation. Over time, B-rmigrated from the top to the end of the soil column,arriving at shallow depth soil first, making the conductivity decreased along with soil depthdeepening at the same point in time. After most of B-rpenetrating the soil column, conductivitieschanged slowly, until residing liquid in the soil column been replaced by Br^-, conductivity tendedto be stable.③Within50days after saturated soil infiltration, soil solution conductivity changedunstably. After then, it was greater than the initial value, the soil presenting on salt depositionphenomenon. Salt accumulated easily and exchange frequently in superficial layer soil, with thehighest salt deposition, reaching to45.19%.④Early stage of infiltration, the change rule of soilsalt migration velocity was unobvious. Thereafter, B-rvertical migration to the soil column endplayed a leading role on soil salinity changes, and salt migration velocity tended to be stable. Andthe amplitude of soil salt migration coefficient of bottom soil, the thinnest soil layer, with biggest saturated water content was great and the migration velocity of it was largest.