利用溶质锋信息估计溶质迁移参数方法分析

ESTIMATION OF SOLUTE TRANSPORT PARAMETERS USING INFORMATION OF SOLUTE FRONT

摘要:

获取土壤溶质迁移参数是利用数学模型预测土壤溶质迁移过程的前提。本文根据对流弥散方程(Convective-dispersive equation,CDE)的一级近似解,建立了土壤溶质迁移过程中溶质锋随时间变化的函数关系,并以时域反射仪(Time domain reflectometry,TDR)为手段、Cl^-为对象,通过与土壤溶质穿透曲线(Break-through curve,BTC)拟合法相比较,研究了利用该函数关系确定溶质迁移参数的可行性。研究结果表明,两种方法估计的R比较接近,而溶质锋信息法估计的水动力弥散系数D小于穿透曲线拟合法。TDR探测的溶质锋滞后于理论溶质锋,是导致利用溶质锋信息估计水动力弥散系数D偏小的原因之一。将溶质锋信息法估计的迁移参数代入CDE计算的土壤溶质穿透曲线与实测土壤溶质穿透曲线比较发现,风沙土中计算的穿透曲线整体滞后于实测穿透曲线,但两者的穿透过程基本一致,土中计算的初始、完全穿透时间与试验穿透曲线一致,但穿透过程有所差异,说明溶质锋信息法估计的迁移参数具有一定的可应用性,在估计水动力弥散系数的精度方面有待提高。

Abstract:

Acquisition of soil solute transport parameters is a precondition for predicting solute transport using the numerical model in practice. A new and simple method is recommended here for estimating transport parameters of D and R using changes in depth of the solute front with time by means of one order approximate solution of CDE (Convective dispersive equa tion, CDE). Time domain reflectometry (TDR) was used to determine the time when the solute front arrived at different fixed points in the soil column and at the same time effluent from the column was collected for parameters estimation with the BTC (Breakthrough curve, BTC) fitting method using the CXTFIT program at the bottom of the soil column. By comparison the retar dation factors, R, derived with the two methods are more or less the same, however the convective dispersive coefficient D esti mated with the solute front information method is generally smaller than the one with the BTC fitting method. One of the factors resulting in the smaller D is the lag of the measured solute front behind the theoretic one, which is testified by comparing the for mer with the latter calculated using the parameters figured out with the BTC fitting method. Comparison between the measured BTC and the calculated BTC shows that the two have the same dispersive process in sand soil and the same times soil solute made the initial breakthrough and complete breakthrough, which demonstrates that the parameters estimated based on solute front information is somewhat applicable, but the precision of this method need further improvement.