The objective of work package C is to contribute to the development of an integrated and transparent framework for multi risk-based decision-support on the control and mitigation of flood risks in the coastal zone and along estuaries and rivers in the Netherlands.

The framework will enable broad evaluations of alternative measures and policies, taking the full chain of events and activities leading to undesired consequences of floods into account: not only measures regarding prevention of floods, but also early warning, preventive measures (such as evacuation) and recovery. For that purpose, among other things, knowledge and insight have to be gained in the following subjects:

1. the consequences of floods, so measures which might make areas less vulnerable to floods can be judged on their economic effectiveness;
2. the system behaviour of dike rings, i.e. the response of a complete system of dike rings to an imminent flood (taking mutual dependence between the protection levels of dike rings into account). This also plays an important role in the possible allocation of emergency storage area, which is seriously considered by the government at the moment;
3. the social basis (the perception of society regarding the technical risks), in order to be able to relate the mere technical risks to the opinion of society and to investigate how these subjective acceptance criteria should be incorporated in the final decision framework;
4. the functional specifications and general outline of the decision framework.

In the following these issues will shortly be elaborated. For a more extensively treatment the reader is referred to the work package proposal.

(1) Consequences
When a dike breach occurs, huge amounts of water will flow into a dike ring causing substantial damage in most cases. These damages are multi-dimensional and relate to the vulnerability of human, economic, environmental and landscape as well as cultural values. In the first stage of the Delft Cluster research (1999-2003) this topic was already given quite some attention. The research proposed for this second stage is partly a continuation and/or rounding off of that first phase research. Some topics need understanding in more detail, in other cases there is a need for validation, in particular based on data of flood damage in other countries. In particular there will be a focus on the modelling of evacuation, damage to lifelines (energy, telecommunication etc.), indirect economic damage and interactions between various types of damage. Damage models will also be checked for their usefulness to deal with various types of damage reducing measures like compartmentalization of dike rings and pro-active measures that will be brought into action when a flood is imminent

(2) System behaviour
After the occurrence of the first dike breach and the subsequent flooding of the concerned dike ring, several things may happen. The flood might be confined to the one flooded dike ring, but might also hit other lower-lying adjacent dike rings. The flood will also cause a fall in water level on the river. This could prevent other downstream situated dike rings from failure, which otherwise might have failed.

The determination of flood risks in the Netherlands has until now been limited to the level of a single dike ring (like in for instance the project “Veiligheid Nederland in Kaart”). However, in reality the effects of a flood might not be confined to a single dike ring alone. Interaction between dike rings occurs (as described above), which can have both risk reducing as well as risk increasing effects. This so called ‘system behaviour’ does not only effect the determination of the flood risks of the different dike rings in the current situation, but also the effectiveness of possible risk reducing measures in the future. An example of the latter is the possible allocation of emergency storage areas, which is seriously being considered by the Dutch government at the moment. An emergency storage area (or any other risk-reducing measure like dike improvement etc.) cannot be assessed correctly without incorporating system behaviour in the calculations. In order to determine flood risks correctly, the analysis of a single dike ring does not suffice; an integrated analysis of a complete river system will probably be necessary.

Pilot versions of tools that take system behaviour in highly simplified river systems into account have been developed in the first stage of Delft Cluster. These concepts and methodologies, however, need testing, extension and improvement of efficiency.

(3) Social basis
Once the flood risk of the total system has been determined, it is important to relate the risk to the perception of society. The risk-perception of people does not only depend on the mere technical risk, but is also influenced by (among others) the degree of voluntarism of the activity and the degree of personal influence on the success of the activity etc. The point of investigation is how to assess these subjective acceptation criteria and how to incorporate them, together with the technical risks, into an integral decision-supporting framework. A realistic case study will be used for developing and testing of the results.

(4) Specifications and outline decision framework
The topics (1), (2) and (3) are of course highly interrelated. For example changes in the system behaviour (resulting from measures in the system) can change the consequences of a flood and may result in a modification of the social perception of flood risks. These interrelations need consideration in the decision framework to be used by governmental bodies and other relevant authorities. This research will not provide a ready to use decision tool, but some kind of blueprint may be provided. Having such a document may give some guidance to the other fields of research.

Het voorstel voor Work Package C is als zogenaamd brugproject zowel voorgelegd aan Delft Cluster als aan het programma “Leven met Water”. Het zwaartepunt van de werkzaamheden voor Delft Cluster betreffen enerzijds schade aan bebouwing en infrastructuur en anderzijds systeemwerking. Voor “Leven met Water” ligt het zwaartepunt van de werkzaamheden rond de aspecten evacuatie, social basis en het decision framework.

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