MANAGEMENT OF DIFFUSE POLLUTION IN GROUNDWATER UNDER IMPRECISE CONDITIONS USING FUZZY MODELS

This paper presents a framework for evaluation of nitrate control stra tegies that use spatially variable nitrogen input in the presence of i mprecise information. The research stems from the fact that diffuse po llution has caused water consumers to be concerned with reducing the r isk posed by contaminated water supplies. An important element in quan tifying risk reduction is the use of simulation modeling to predict th e transport and fate of contaminants under variable rate application a s employed in a wellhead protection area strategy. Specifically, a gro undwater model is linked with an unsaturated zone transport (and crop production) model which provides the nutrient and recharge loading rat es to the saturated zone. To consider uncertainty stemming from the un saturated zone model output, in addition to aquifer parameters, a new groundwater modeling technique is developed in which fuzzy set theory is combined with finite-difference modeling methods. The groundwater m odel incorporates imprecise parameters (i.e., transmissivity) into the modelling process through the use of fuzzy set theory. Imprecision ha s been encoded directly into the finite-difference equations using fuz zy numbers as input, and level-set operations combined with non-linear optimization are used to solve the system of equations. The resulting fuzzy output can be interpreted as the level of imprecision associate d with the model. A case study is presented to illustrate the methodol ogy. Copyright (C) 1996 IAWQ.