Flood risk scenario calculations as a decision support and evaluation tool in water management plans
Vanneuville, W.; Deckers, P.; Van Eerdenbrugh, K.; Mostaert, F. (2008). Flood risk scenario calculations as a decision support and evaluation tool in water management plans, in: International Conference Studying, Modeling and Sense Making of Planet Earth, 1-6 June 2008, Mytilene, Lesvos, Greece: proceedings. pp. 1-5
Whatever the measures taken there will always be a probability for flooding along rivers and in the coastal zone. In a densely populated area like Flanders most of the floods cause damage. But there are large differences in the amount of damage depending on land use. A flood risk methodology is developed for Flanders and implemented in the raster GIS software shell LATIS. The probability and consequences of floods can be evaluated under current conditions and for several types of alternatives. Socio-economic, climate and/or hydraulic changes can be simulated.
In a risk methodology the effects of measures must be evaluated for extreme hydrologic and hydraulic conditions but also for more regular events. All of the resulting damages are weighted with their probability of occurrence. These combinations lead to a more accurate appraisal of the expected annual damage: the risk.
Damage, victims and risk calculations need interpretation of the system’s operator. The robustness and sensitivity of planned actions cannot be expressed by one or some statistical values. LATIS produces risk maps. In addition to the overall gain of measures and evaluation of the spatial variations of risk can be made. Because measures can have different effect on damage and victims both are evaluated separately. The LATIS tool is not deciding but supporting the decision. In the decision process, the pronouncement of the risk model has to be refined by adding non tangible effects (ecological and historical values, well-being of inhabitants …). Also the existing and/or expected regulations on different policy levels that act as constraints have to be taken into account. This can be done is a social cost benefit analysis.
Until now the Flemish risk methodology is used to make a flood risk map for Flanders, to evaluate several smaller measures and for four regional water management plans. The most important ones are the Sigma plan for the river Scheldt and the Integrated Safety Plan for the Coastal zone.