SIMULATION OF WATER AND CHEMICALS IN MACROPORE SOILS .2. APPLICATION OF LINEAR FILTER THEORY

Description of flow in soils with macropores is difficult, yet quite important in describing the dynamics of field soils. Recognizing the two Structural domains of the macropore and matrix, and possible water-flow situations, three flow regions have been suggested: matrix, macropore, and transaction. The matrix and the macropore are the two domains, and the transaction represents the exchange of water between the matrix and the macropore. As a beginning point for the description of such systems, linear filter theory is applied to the Richards equation to obtain a general set of analytical solutions for water and contaminant movement in unsaturated soil in which there are no macropores. To develop these solutions, a unique relationship between water flux (q) and water content (0) is demonstrated by executing a numerical simulation based on the Richards equation. By piece-wise curve fitting of q(0), it is possible to establish and obtain a set of equations which describe water flow and chemical movement in soil, and which take the form of linear filter systems, providing analytical solutions by convolution. A two-domain approach applies equations for homogeneous soil to describe the matrix domain, with the macropore domain described with coefficients obtained by applying the Poiseuille and Chezy equations. These equations are analytically solved in correspondence with the three flow situations, resulting in a model, LASOMS (linear analytical solutions of macropore soils). Simulations, data and model comparisons of LASOMS have shown the above solutions to be reasonable under several conditions.