Application Of The Entropy Concept In Design Of Water Quality Monitoring Networks

Abstract

The design of water quality monitoring networks is still a controversial issue despite the variety of methodologies proposed. Existing networks are marked with unsolved problems, and the data collected are often of a “messy” character. The basic difficulty lies in the lack of a precise definition for “information” expected from and produced by a network so that it is fairly difficult to assess the efficiency of monitoring practices. The same problem prevails in the evaluation of cost- effectiveness of a network where costs are easy to estimate, but where benefits are often described indirectly in terms of other parameters. In essence, benefits of monitoring can only be measured by means of the information conveyed by collected data. Since no design methodology up-to-date has provided a quantitative measure of information, benefits-of monitoring networks still remain as unquantifiable parameters in the decision making process.

The presented study proposes an information-based perspective for the technical design of a network with two basic objectives: maximization of information produced by the network and minimization of accruing costs. Both are evaluated by the entropy principle which provides an information based statistical measure to evaluate the efficiency and cost-effectiveness of a monitoring network, considered here as an “information system”.

The entropy concept serves four main objectives of network design: temporal design, spatial design, combined temporal/spatial design, selection of variables and determination of sampling duration. The application of the method for the first three objectives is demonstrated in case of the suspended sediment data of Dicle river basin in Turkey. The strengths and shortcomings of the proposed methodology are evaluated, with recommendations presented for future research on the application of the entropy principle in network design.