用Brooks-Corey模型确定两流区模型参数

DETERMINATION OF PARAMETERS OF TWO-FLOW DOMAIN MODEL WITH BROOKS-COREY MODEL

两流区模型为描述优先流情况下的溶质穿透曲线提供了新的方法。但两流区模型的所有参数目前仅能通过反推参数法获得,限制了其应用。近年来,毛管理论和土壤水力特性模型的发展使得有可能从更加微观的角度来揭示土壤水分和溶质运动的机理,同时也为对流弥散模型参数的确定提出了新的思路。本研究在Brooks-Corey模型的基础上,推求了土壤中的孔隙流速分布;以平均孔隙流速为两流区的临界流速,得到了两流区模型参数与Brooks-Corey水分特征曲线模型形状系数之间的简单关系;提出了由土壤水分特征曲线确定两流区模型参数的方法。用实测资料对考虑和不考虑不动水体情况下这种方法的可靠性进行了验证。结果表明,不考虑不动水体,上述方法可靠性较差;考虑不动水体,用上述方法预测两流区模型参数有一定精度,不会对模型的预测结果产生太大的误差。

The use of a two-flow domain model improves description of soil solute breakthrough curves, especially in preferential flows. But all parameters of the model currently can only be figured out by the inverse method, thus restricting its application. In recent years, development of the capillary theory and the model of soil hydraulic property make it possible to expose mechanisms of soil water and solute movement from a more microcosmic angle, and use a new method to determine parameters of the convection-dispersion model. Based on the Brooks-Corey model, pore velocity distribution is deduced from soil water suction curve in this paper, relationship between the geometrical coefficient of the Brooks-Corey model and the parameters of the two-flow domain model established with the average pore velocity set as the critical velocity between the two flow domains, and hence a method for determining parameters of the two-flow domain model proposed in this paper. Data measured in field observation are used to test the reliability of this method either considering immobile water in soil or not. The results indicate that the predicted breakthrough curves are far from the observed without taking into consideration immobile water; and quite close to the observed with immobile water taken into account. Errors would not be too great for loam soils and sand loam soils in the prediction based on the two-flow domain model, and the model parameters determined through the method proposed above.