| In order to explore the influence mechanism and scope of total dissolved solids(TDS)on capillary water rising height of different particle sizes and different soil types,the variation characteristics of capillary water rising rate were analyzed,and the influence of TDS on ecological water level was analyzed.It provides theoretical support for scientifically determining groundwater ecological water level and effectively controlling soil salinization.In this paper,an indoor test device was designed for soil column test,and the influence threshold of TDS was studied by combining with numerical simulation,and the practical application related to ecological water level was carried out in Basraq,Xinjiang.Firstly,by constructing the physical test model of capillary water rise,the capillary water rise tests under different TDS and different soil types were carried out.The difference of capillary water rising height between particle size and TDS was quantitatively characterized,and the rising rate characteristics of capillary water were analyzed.The relationship between TDS and capillary water rising height was fitted.The experimental results show that TDS restricts the rising height of capillary water by changing the gravity potential and matrix potential of soil water;The change of capillary water rise rate is characterized by the increase of TDS,the increase of initial rise rate and the faster attenuation.Fluctuation of capillary water rate in silt and sandy loam due to small particle size and complex soil structure.The rise height(h)and time(t)of capillary water in the whole test period can be described by three-parameter logarithmic function.Secondly,aiming at the problem of TDS threshold that has not been solved in the laboratory test,this paper uses HYDRUS-1D software to simulate and verify the variation characteristics of soil water content and Cl~-concentration with height.Based on the method of“indoor test+numerical simulation”,considering the variation of soil moisture with time and burial depth,the TDS thresholds of medium sand,fine sand and silt were determined as 5～75 g/L,3～35 g/L and 1～35 g/L respectively,and the rationality of the thresholds was analyzed and discussed.Finally,the TDS threshold determined in this paper is applied to the determination of ecological water level in Bashrak region of Xinjiang.The influence of TDS threshold on ecological water level is mainly reflected in the upper limit of water level,because the upper limit of water level includes the rise height of capillary water.The TDS threshold affects the upper limit of ecological water level by affecting the rise height of capillary water.The analysis shows that the upper limit of ecological water level based on the influence of TDS threshold is 3.735m,which is 0.735m lower than the upper limit of 3 m water level under freshwater condition.The decrease reflects the influence of TDS threshold on the rise height of capillary water. |
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