Budgeting water resources

Abstract

In this thesis, the concept of water budgeting is discussed. This concept is based on a comparison between water resources and financial resources. It aims to approach water resources management problems more like a treasurer would. Water resources can be distributed in such a way as to optimise the chance of achieving a desired goal. Depending on what the most important goal of the water manager is, different ‘water budgets’ are possible. The concept of water budgeting is: to distribute the available water resources in such a way as to optimally achieve a certain objective. Model Predictive Control is considered a potential tool for water budgeting. This tool can translate the desired objectives into operational water management. The objective for the water system, in the form of penalties and constraints, are used as input for the Model Predictive Controller. The controller then determines the operational water management, which is most successful at achieving the desired goals. The concept of water budgeting is applied to the South-Western Delta in order to test its usefulness. Different goals are set for the area, and these different goals result in different operational water management strategies. During the application of the water budgeting concept several shortcomings became apparent. These shortcomings follow from the fact that: the comparison between water resources and financial resources is complicated by the physical properties of water. Two very important properties of water in this respect are: water is bulky and water is fugitive. These properties result in: water being difficult to store and transport, in comparison to financial resources. Because water is difficult to handle, it is not straightforward to budget water. The water budgets become very variable in time and space. Due to this variability in time and space the sum of the water distribution does not tell the whole story. The moment at which the water resources are used is equally, or might be even more, important. The application of Model Predictive Control, as a tool for water budgeting, has also proven to be limited. The most important limitation of using Model Predictive Control is: the reduced transparency of the decision making process. It is difficult to trace back why the controller ‘chooses’ certain control actions. This reduces the predictability of the operational water management. Reduced predictability of the operational water management, results in a less predictable water system. This will make it harder for stakeholders to be dependant on the water system. The application of Model Predictive Control to a water system of this size and without a very clear (single) objective is relatively new. During the research it became clear that: it is very important to be able to control all the (large) in and outflow structures, and that it is important to included the parameter that needs to be controlled in the internal model. In the case used, it was not possible to control the Maeslantkering. This resulted in limited control over the water bodies connected to the Nieuwe Waterweg. In the internal model water salinity was not included. This made it very hard to control salinity. Penalties for the controller were developed that were assumed to influence salinity. These penalties were however not sufficient to prevent salinities to become too high in certain areas. This shows that the controller needs to be able to directly predict what the salinities will be.