An Experimental Study On Solute Front Transport In Soil And Parameter Estimate

The emission of the industrial waste water, gas and residue, the running off of the excess agricultural fertilizer and pesticides, all of these result in serious pollution of groundwater, and also in transport and dynamic distribution in porous medium need to be studied, and the mathematical models should be developed to describe solute transport in different circumstances and determine the parameters in the models.Boundary layer method is based on CDE equation .When it is combined with the boundary layer conditions, the explicit analysis formula about the Time spatial of concentration can be deduced by describing and generalizing the solute front in the process of transporting in soils. Here, the boundary layer, referring to the distance between the solute front and the soil surface, is a function of time. The boundary layer transport is micro performance of solute transport in porous medium. It doesn't restrain the size and direction of solute transport. Different from the free boundary, it is observable, but not controllable. The explicit analytic formula of time and distance, deduced by using boundary layer method, can be used to estimate the parameters in solute transport models.To a certain degree, the parameters estimated by boundary layer method are different form those definite by fitting breaking-through curve. One of the possible reasons is that the boundary layer monitored by TDR lags behind the actual position for its limitation of sensitivity. In addition, the result shows that the boundary layer method of the small flux, compared with the transient boundary layer method, is more precise in estimating solute transport parameters. This means it is plausible to definite a small flux ε₀ in the boundary, which in turn can be seen as the observation error. Determination of solute front's position is a key to estimate transport parameters. The time domain reflectrometry(TDR),is a measurement devices for continuous and non-destructive determination of volumetric soil moisture. It is extensively used to research on soil moisture and solute transport in recent years. According to the theory, the value of TDR Level will change with the change of solute concentration.