When flood risks are recognized, either by modelling or because of previous flood events, action can be taken to prepare for possible future floods. As written in Chapter 2, in the phase before a flood event it is possible to reduce flood risks by (1) keeping people away from flood prone areas; (2) decreasing exposure to floods through defence infrastructure; and (3) mitigating the risk by decreasing the magnitude of a flood using water storage or by flood proofing buildings and infrastructure.
There is a relation between the three strategies. In case of full prevention (not living in flood prone areas), there is no need to construct defences or mitigation measures. Yet, in most countries space is scarce and it is not desired to leave the fertile and attractive land close to water unused. On the contrary, there is a lot of social and economic pressure to live and work in flood prone areas. Furthermore, due to climate change new areas are facing flood risk. There is also a relation between flood defence and mitigation. Large past investments in flood defences make most mitigation measures unfeasible from a cost-benefit perspective. This is for instance the case in the Netherlands with its high dikes. If for example one lives in a deep polder and run the risk of flooding by 5 m of water, there is little one can do to flood proof his or her house. When the expected magnitude of a flood is lower (e.g. 0.5 m water in a house), it may be more efficient to take mitigation measures than to build a dike.
This chapter is organised around the following six common challenges and questions that we found in comparing the six countries analysed in STAR-FLOOD:
- How to defend yourself against flooding (§5.2);
- How to provide sufficient space for water (§5.3);
- How to include flood risk in spatial planning (§5.4);
- How to ensure sufficient money for physical measures (§5.5);
- How to prioritise measures (§5.6); and
- How to raise awareness and actions by citizens (§5.7).
We refer the reader to more common challenges and related good practices in Chapter 4 on integrated planning, collaboration and coordination, Chapter 6 (During a flood) and Chapter 7 (After a flood).