Many environmental and hydrological systems have been modified and are still being modified by human intervention. This intervention usually takes the form of constructions intended to change system behaviour to better serve the needs of society. Some of these interventions result in structures that have a purely passive role (dikes, coastal defences), others are have no moving parts, but use physical principles to regulate or divert flows, finally there are structures where the configuration can be changed. This last category can be under manual or automatic control and the role of forecasts in the control process is increasing.

This implies that these systems and their behaviour are being designed. They are no longer governed by natural processes alone. Therefore hydrologists will need a model of both the natural and the artificial part of the system in their study of the system. As the demands placed on water systems by society increase and are increasingly in conflict with each other, it will become harder to define goals for the modification of these systems and their behaviour. It will also become harder to design systems and operating rules to satisfy these goals.

As a result of these developments both hydrologists and water managers are more and more interested in topics that are traditionally the subject of operations research (the study of the optimization of design and operation of complex systems) and control theory (realization of desired system behaviour through automatic control). Hydrologists are already familiar with not only water systems but also with many concepts and techniques used in control theory and operations research such as robustness, adaptivity, feedback, optimization, statistics and modelling of complex interacting systems.

For control theory water systems pose some unique challenges because of the presence of large delays and very limited means of control. In fact for some systems the limits on the size of the change that can be effected in a given time period necessitate the use of forecasts to anticipate on system behaviour. For operations research the special challenge is the presence of incommensurable and conflicting optimization targets, the complex network of relations between stakeholders and the lack of one clear shared motivation amongst stakeholders. Moreover, a new awareness of more variability in the climate on longer time scales and rapid social changes both pose new challenges for the decision making process. This implies a need for more frequent reconsideration of decisions and a shorter time scale for the decision process. This process will therefore need faster models, for instance simplified dynamic models of hydrological systems, statistical process emulators, surrogate models (e.g. linear or nonlinear regression) based on data to feed faster optimization algorithms.

The aim of our session is to bring together experts in the fields of hydrology, water management, control theory and operations research to discuss novel methods or novel ways of using traditional methods to define and implement desired water resource system behaviour.