STUDY OF CRITERIA AND MODELS ESTABLISHING OPTIMUM LEVEL OF HYDROGEOLOGIC INFORMATION FOR GROUNDWATER BASIN MANAGEMENT.

It is shown that information is a structural part of the decision making process. The role of the information gathering process can best be described as Hayes' process to improve preposterior distributions in probability assignments that will serve as basis for decision making processes. Hydrogeologic information is characterized by a low degree of predictability and high variability. The general cost structure of the hydrologic information gathering process is represented in information cost curves which are combined with production cost or opportunity loss curves to give total cost curves. These may display a minimum which is the point of diminishing returns at which exploration activities should be ceased. One of the main unsolved problems is the proper definition of a universally applicable unit of information content. Optimum levels of information can only be established when utility functions can be expressed in monetary terms and give rise to clear objective functions. Three case histories were used to develop guidelines for the design and operation of monitoring systems for special wastes, minimum hydrogeologic information needed in watershed district management, and the need and role of information in the choice and construction of a proposed simulation model for a regional system under complex decision rules.