Guideline for ex-post evaluation of measures and instruments in flood risk management

Abstract

Effective risk reduction requires the optimal understanding of the causes of risk, options of risks reduction and ways of their implementation. Especially with regard to risk reduction options much has changed in recent decades. Many measures and instruments, which are the actual tools of risk reduction, have developed to reduce risk in various settings. This includes the advancement of existing as well as the development of new options and approaches. While measures are direct physically tangible interventions (e.g. dikes), instruments mainly form the scope of action and often are prerequisite for the implementation measures (e.g. flood zones, flood warning). Often, several measures and/or instruments are applied in a portfolio. Many of these options are hardly being taken into consideration due to a lack of knowledge how they perform under conditions of flooding. Even with regard to traditional measures, the knowledge regarding their actual performance appears scarce. As a result, planning for flood risk reduction often takes recourse to an only limited record of past experience. On the one hand, this limitation applies to the variability of options. Mainly decentral measures are not sufficiently known and understood. Also many instruments are usually not taken into consideration as option. On the other hand, the limitation applies to the information regarded when deciding on the options. Often, mainly the expected effectiveness is considered. Aspects outside the range of primary intentions, sustainability or long term performance are often not sufficiently considered.