Assessing resilience of river systems

Abstract

Rivers provide many of our day-to-day needs. They allow, for instance, the production of drinking water and the movement of goods via inland waterways. However, river systems experience disturbances, such as droughts and pollution plumes. These disturbances can impair the functioning of river systems and their ability to provide the desired functions and services. Since some of these disturbances have very little impact while other cause many problems, it is important to determine how a river system handles different disturbances. Resilience is often used to indicate and assess the behaviour of systems with regard to disturbances. Using the concept of resilience with regard to river systems can help determine how well river systems handle disturbances. In order to determine how resilient a river system is, a method to assess the resilience of river systems is needed. Research into the resilience of river systems has only been done with regard to flood resilience. This resilience does not consider other disturbances, such as droughts, and therefore does not represent the full resilience of the system. Furthermore, this research often resulted in suggestions and pointers to create and improve resilience, but not in a clear method to help assess it. Hence, the objective of this study was to develop a method to assess the resilience of river systems. In order to create this method several questions need to answered. First, a clear definition of resilience of river systems is needed. For this it should first be determined what resilience is. This is done using a literature study. The first part of this literature study focussed on general and field-specific definitions of resilience. This resulted in the definition of resilience of river systems as used in this study: the resilience of a river system is the ability of the system to continue functioning during a disturbance. Where continuation of functioning is defined as the continued achievement of the goal of a certain function, such as the continued production of crops for the function of agriculture, even if this only occurs to a smaller extent, and the continued shipping of goods for the function of shipping. The disturbances considered are short-term disturbances, such as droughts and pollution plumes. After the determination of the definition of resilience of river systems several remaining questions need to be answered. The impact of disturbances on the different river system functions has to be determined and visualised. Next, the impact of these disturbances has to be classified. Finally, the resilience of river systems should be assessed using the classification for the impact of these disturbances. The second part of the literature study, focussing on the assessment of resilience, is used to help determine, visualise and classify the impact of disturbances. The development of the final method is an iterative process between application to a case study and the amendment of the method based on this application. Using the results of the literature study, a first design of the resilience assessment approach, the method for the assessment of resilience of river systems, was made. This approach consists of four steps with several sub steps. In the first step a system overview is created. This step is based on the ideas of flood resilience theory. It states how a system overview should be created, what external factors, characteristics and functions should be included and how to categorise them. The second step consists of the creation of disturbance-impact graphs for the different functions and disturbances. These graphs, based on the idea of stressor-response graphs of system robustness analyses, are used to visualise the impact of the disturbances. The third step gives an assessment of the resilience of a function based on the disturbance-impact graphs and a resilience classification with associated scoring system, which is based on the ideas of a current impact classification used for droughts. The fourth and final step consists of the assessment of the resilience of the entire river system based on the assessment of the individual functions. The approach was applied to a case study, the Meuse river system, to test it. This case study focussed on low discharges caused by droughts. The approach was applied to the whole system, thus to all its characteristics (water quality, water quantity, vegetation and fauna and sediment) and all its functions (shipping, electricity, industry, drinking water production, agriculture, flood protection and recreation), to create a system overview (the first step of the approach). The application focussed specifically on the functions shipping and drinking water production. This application was used to check the content and applicability of the sub steps of the first step of the approach, using the system overview, and to check the content, applicability and order of the sub steps of the second step of the approach, using the functions shipping and drinking water production. The application of the system overview led to a clear distinction between external factors, characteristics and functions, which has been adopted in step 1. Furthermore, the application to the specific functions resulted in a clearer definition of system boundaries and a clearer link between the external factors and the disturbance. Finally, the application led to an additional sub step. This sub step consists of a check to determine whether the chosen disturbance is actually relevant for that specific function. The application of the approach showed that both shipping and drinking water production of the Meuse river system appear to be very resilient with regard to low discharges due to droughts. This is likely due to fact that both functions have already been adapted to this disturbance. For shipping this is likely largely due to the fact that the water level in the Julianakanaal is managed to ensure continued shipping possibilities during discharge fluctuations. Pumping facilities have been constructed in order to maintain water levels even when very small discharges occur. The large resilience of the drinking water production by Waterleiding Maatschappij Limburg is likely largely due to the fact that the intake point is located in the Lateraalkanaal. The water level of this canal is managed using weir and sluices for shipping and drinking water production. Only the first two steps of the approach have been tested using the case study. The final version of these steps, as found in this report, can be used in practice. The tested steps have shown to be applicable to the tested functions and it assumed that these steps are also applicable to the other functions. The third and fourth step should be tested before they are used in practice. Especially step 3a (the assignment of the different levels of the resilience classification to the disturbance-impact graphs) might require additional adaptation.