A framework for incorporating stream use in the determination of priority watersheds

The identification of priority watersheds is an important component in planning activities associated with non-point source pollution abatement. The identification of priority watersheds is a complex issue at best, but it is made even more so in certain cases by the desire of water quality planners to take stream use into account when making decisions. Thus, for example, certain streams may be classified as potential sport fisheries, while others may be designated as suitable for tolerant forage fish. It may be the case that the impact of non-point source pollution upon one stream is less than that upon a second stream when viewed strictly in terms of the physical condition of the streams. Yet, when viewed from the standpoint of habitat suitability for different fish species, the priority judgement could be reversed. A methodological framework is presented which allows planners to take stream use into account in the determination of priority watersheds. The framework provides a formal structure for organizing non-point source data associated with specific watersheds and stream habitat data for various fish species in a manner suitable as inputs to two fuzzy set models. The fuzzy set models incorporate the imprecision and fuzziness characteristic of non-point source water pollution problems. In an illustrative application to the Kewaunee River Basin in Wisconsin, U.S.A., the methodology is used to identify priority watersheds when streams are categorized on the basis of potential fisheries.