Risk assessment to quantify the interaction between land use and water management

Heavy rainfall in recent years has shown that occasional flooding in polders cannot always be prevented, and it is likely that frequency and potential damage of flood events will increase in the future due to climate change, subsidence, and ongoing urbanization. So, to control the risk of flooding, water boards have to anticipate on both climate change and spatial planning. The question addressed in this paper is: how do climate change, and spatial planning increase the risk of flooding and how should the water authorities react? To answer this question two case studies have been carried out for Haarlemmermeer polder (Amsterdam, Schiphol airport), and Goeree Overflakkee. For both area’s a detailed risk analysis has been carried out, using GIS, hydrological models and damage-depth functions to determine the effect of climate change, spatial planning, and technical measures. The rationale behind risk analyses is explained in our paper, and illustrated with both case studies. The surplus value of risk analysis is that it allows a good cooperation between spatial planners and water authorities and provides a basis for a cost benefit analyses for the measures by the water authorities.