The Role of Uncertainty in the Use of Ground Water Models for Administration of Water Rights

Abstract

Competing demands for water resources are creating high profile disputes throughout the western United States. Models are increasingly being used to help sort out the disputes. Invariably, the models themselves end up being the object of court cases due to the inherent uncertainty of modeling natural systems (Cosens 2006). As the water use issues were brought to a head by persistent drought in the eastern Snake River Plain in southeastern Idaho, the Idaho Department of Water Resources (IDWR) embarked on developing a ground water model which would become the basis for conjunctively managing the surface and ground water resources. Recognizing that model uncertainty has been used in the past to undermine the use of scientific models in natural resource management, IDWR attempted to address model uncertainty through a consensus approach. With a priori knowledge of the major points of dispute, IDWR invited the primary water users to have their hydrologic consultants participate in the re-formulation of the ground water model of the eastern Snake River Plain aquifer. In some respects, this constituted using a social approach to address the issue of model uncertainty. A similar approach was successfully used in developing a surface water model in the Milk River Basin in Montana (Cosens 2006). The purpose of this paper is to draw on experiences gained in the eastern Snake River Plain in Idaho to propose some concepts of the use of models in supporting conjunctive administration decisions and the role of uncertainty in that process.