As a densely populated country in a delta the Netherlands have to be very considered about flooding risks. Up to 65% of its surface is threatened by either sea or rivers. The Dutch government has started a research project 'Floris' (Flood Risk and Safety in the Netherlands) to calculate the risks of about half of the 53 dike-ring areas of The Netherlands. This project has four tracks: (1) determining the probability of flooding risks of dike-rings areas; (2) the reliability of hydraulic structures; (3) the consequences of flooding and (4) coping with uncertainties.As part of the third track, the consequences of flooding, the Ministry of Transport, Public Works and Water Management has asked the University of Twente to develop a Decision Support System for analyzing the process of preventive evacuation of people and cattle from a dike-ring area.This Support System, named Evacuation Calculator (EC), determines the results of several kinds of traffic management in terms of evacuation progress in time and traffic load. The EC makes a distinction between four types of traffic management scenarios: (1) reference; (2) nearest exit; (3) traffic management; (4) out-flow areas. The scenarios one and two represent a situation where no traffic management or limited traffic management is present. Scenario three (traffic management) calculates an optimal traffic management (given the model assumptions). Within the fourth scenario the user has the freedom to adjust the scenarios by (re)defining out-flow areas. In this way the user has the possibility to 230 Kasper van Zuilekom, Martin van Maarseveen and Marcel van der Doef adapt to local possibilities and restraints. The limited data need and efficient algorithms in the EC make it possible to model large-scale problems.Targets in the EC development were twofold: (1) a safe estimate of the evacuation time and (2) to support the development of an evacuation planning. These targets are met by the development of scenarios with specific and well defined objectives. Optimization methods were developed to solve the problems and meet the objectives.The classical framework of transport planning is used as a basis, but with extensions:Trip generation: a broad range of traffic categories are defined. For each category has there own departure rate in time.Trip distribution: the core of the EC. The objectives of the scenarios are determining the distribution. The evacuation time is calculated. Traffic assignment: visualization of the traffic flows. The paper will describe the structure of the EC, its objective functions and problem solving techniques. Furthermore a case study of dike-ring Flevoland is presented.

Abstract.Knowledge on the different components of flood risk has much improved over the last decades, but research which fully takes into account not only the interactions between those components but also between different areas in a catchment or delta is still rare. Integrated analyses EDVHG RQ D FRPSOHWH V\VWHP ¶V DSSURDFK DW VXIILFLHQWO\ large scale will improve our understanding of how flood risk systems with flood protection infrastructure in place behave under extreme conditions, it may help to develop sensible long-term strategies, and allows us to better prepare for flood events of all magnitudes. To illustrate the relevance of a hydrodynamic system ¶s approach for flood risk management we analyse the effect of defence breaches on flood risks elsewhere along the lower Rhine River and discuss the use of this knowledge for flood risk management.

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