Fuzzy rule-based approach to describe solute transport in the unsaturated zone

A fuzzy rule-based model is developed for simulation of solute transport processes in the vadose zone. Underlying physical processes of solute transport described by appropriate differential equations are captured in fuzzy rules. These rules are derived from a training set obtained from different test runs of the SWMS_2D model which simulates water flow and solute transport in two-dimensional variably saturated media. Fuzzy rules operate between two adjacent cells at each time step. Solute concentration of the upper cell, and solute concentration difference between two adjacent cells are used as premises. For a given time step, the solute flux between the two cells is taken as the response, which is combined with the conservation of mass to update the new solute concentration for the new time step. The methodology is applied to solve the breakthrough curve of bromide movement in a soil column. It is also generalized to the same problem under different soil and boundary conditions. In both cases, the fuzzy solution appears to be similar to the measured bromide concentration as well as the SWMS_2D model results. The methodology provides a more efficient alternative to existing modeling methods. (C) 1999 Elsevier Science B.V. All rights reserved.