A comprehensive assessment of multilayered safety (meerlaagsveiligheid) in flood risk management

Abstract

Multilayered Safety (MLS) is seen as the next step in Dutch flood risk management. In the last decades the idea that only flood defenses can prevent floods gave way to the realization prevention can also be implemented along other lines, e.g. giving the rivers more space. The next thought was that next to preventing floods it should be possible to reduce the loss due to flooding. Therefore, MLS is meant to introduce comprehensive flood risk management by implementing three layers, or put differently safety nets: 1. Prevention (dikes, space for rivers, etc.), 2. Spatial Solutions (flood-proofing houses, elevating houses, re-locating etc.), 3. Crisis Management (evacuation, warning, etc.). Before this study, there was no academic interpretation of MLS and it had never been tested comprehensively. Consequently, a theoretical framework is being developed in this thesis to be able to model MLS. This is followed by a hypothetical case study and additional one for the City of Dordrecht to examine the actual effect of MLS on the flood risk and its cost-efficiency. It was found that theoretically MLS is indeed an alternative to only Prevention. Furthermore, it introduces the option to better customize flood risk management to local circumstances. By doing so, flood risk management becomes more cost-efficient. As the cost-efficiency is found to be dependent on the initial safety level, it is concluded that in the Netherlands MLS only has the potential to supplement the existing flood protection. In areas with a heavy implementation of flood defenses like in Dordrecht, MLS is fit to complement flood risk management rather than replacing the prevailing Prevention approach. However, to do so (local) authorities need to be able to base their flood management policies on flood risk, e.g. by benchmarking a certain Individual Risk.