Adaptation of flood management plans (2015)
Floods can be from many sources caused by multiple mechanisms including due to heavy rainfall or meltwater, when the infiltration capacity of the soil is exceeded and when discharges overpass the capacity of water courses and exit from usual riverbeds, spreading across the land. Climate change is expected to significantly impact on extreme precipitation events frequency and magnitude and on temperature (important for snowmelt). On the other hand, human modifications of the basin areas, jointly with land use change and anthropological pressure on the rivers, are consistently impacting on the retention and drainage capacity of the catchment areas. This could be translated in a substantial increase of surface runoff and, consequently, river peak discharge. In some parts of Europe an increase of peak discharges is expected. The so-called HQ100 value (the discharge of a 100 year event) is frequently taken as a basis for hazard maps. To ensure that appropriate flood defence systems are designed, an adjustment of the hazard maps to link the portability with a correct discharge is needed.
The Floods Directive (2007/60/EC) demands the production of hazard maps with different scenarios, including one of a probability lower than the HQ100 to take into account more severe impacts. According to the directive, the preliminary flood risk assessments will also updated every 6 years and in teir revision take the impacts of climate change on the occurrence of floods into account.
New guidance values for flood assessment are needed as they can no longer be based on measurements of past events only, assuming stationarity for what concerns land use and climate change. With regard to the Neckar River (in Germany) for instance, it has been determined that discharge for the HQ100could likely increase by 15 percent through by 2050 compared to the reference situation. Consequently, the value HQ100 has been recently adjusted taking into account a climate factor of 1.15. Installations will be rated for a 15 percent higher runoff rate or planned in such a manner so that they can be upgraded if necessary. Flood Risk Management Plans (FRMPs) should be adapted to new conditions due to climate changes, addressing both existing developments or infrastructure as well as new development projects to cope with the impact on human health, the environment, cultural heritage and economic activities. Both adapting constructions to mitigate the risk of flooding in flood-prone areas and the modification of behaviour to reduce risk of those living/working there are actions contributing to climate proofing. To implement the measures envisaged in FRMPs and mainstream them in existing policies practices, checklists have been developed. For example, the Greater London Authority (GLA) checklist aims to make sure that the effects of climate change are taken into account in the design and allocation of new developments and constructions. It provides guidelines to designers and planners, for example on the types of construction, suitable materials, and sustainable urban drainage systems that could be used.
In order to integrate the measures into new and existing developments in the flood prone areas, spatial planning approaches have been used, especially when a holistic, risk-based approach is taken. Spatial planning is not only useful in developing flood risk management plans, and searching for opportunities, synergies and trade-offs between domains, but also to facilitate communication between stakeholders, enhance participation and reduce conflicts. One of the key instruments which are often used in this process are (interactive) flood risk maps to identify and communicate the exposure and vulnerability of flood prone areas to stakeholders. The approaches to reduce flood risks and climate proof developments in flood prone areas differ between countries. In the UK, the national government has adopted the national ‘Planning Policy Statement 25: Development and Flood Risk‘ (CLG 2010) which should be taken into account by regional and local communities in any development activities in flood prone areas. The document provides an overview of the approach to assess the risks, the decision-making principles and how tasks and responsibilities are divided between the stakeholders. Local government can also select National Indicator 189 as self-assessment instruments for flood risks management (DEFRA). In addition, the UK government developed flood protection grant schemes to support local communities to prepare for the risks of flooding. Throughout the UK examples of self organisation, local initiatives, and voluntary agreements and partnerships between stakeholders to deal with flood risks can be observed. Flood risk management plans have to be ready by 22 December 2015 and updated every 6 years thereafter. Review and updating of the flood risk management plans drafts will be available for public consultation before this deadline.
- Stakeholder participation
- Success and Limiting Factors
- Costs and Benefits
- Legal Aspects
- Implementation Time
- Life Time
Stakeholder participation is one of the most important steps of the majority of the planning activities. Flood Risk Management Plans usually consider the implementation of a combination of structural and non-structural measures that could tangibly impact on the life of the local populations. The institutional involvement is the first step of the process. The introduction of Flood Risk Management Plans require the involvement of different levels (national and regional) of institutions and a large set of competencies. The economic structure of the basin under consideration need to be involved actively in the design and implementation phases. Very often private properties are affected, directly or indirectly, by the implementation of the strategies. As Member States shall encourage active involvement of interested parties in the production, review and updating of the flood risk management plans drafts will be available for public consultation before this deadline.
Success and Limiting Factors
Flood management planning is one of the most effective strategies to reduce the vulnerability and build the capacity for the system under consideration to cope with flood hazard. From the scientific point of view, the correct calculation of the dynamic components characterizing the hazard have to be taken into consideration minimizing the possible errors due to the high level of uncertainty linked with climate and socio-economic projections. Part of this uncertainty, for instance, is represented by the regionalization of the climate factor. The 6-year review cycle of the Flood Risk Management Plans allows to include changes in the expected impact of climate change.
Limiting factors for the successful implementation of Flood Management Plans are mainly represented by the technical challenges and by the substantial investments required for operating the set of actions designed. This is particularly true in case of Plans for the built environment in highly populated areas and/or where constructions have a lifetime of several decades
Costs and Benefits
The modification flood hazard and risk maps for different scenarios (including the HQ100) is seen as a proactive and effective approach to flood protection. The measure shows evident benefits in all areas that are threatened by flooding. It is typically a no-regret measure, especially with regard to the preparation of hazard maps for the general population and for public authorities.
The EU policy throughout which the measure could be promoted is the EU 2007/60/EC Directive on the Assessment and Management of Flood Risks (Floods Directive). The Floods Directive introduces a concept of integrated policy and territorial flood analysis that is compatible with, and aptly complements, the holistic approach to the integrated water resources management introduced in the Directive 2000/60/EC (the Water Framework Directive, WFD). For areas prone to significant flood risk the Member States are obliged to develop flood hazard maps and flood risk maps. Flood hazard maps have to cover the geographical areas which could be flooded according to the following scenarios:
- floods with a low probability, or extreme event scenarios;
- floods with a medium probability (likely return period ≥ 100 years);
- floods with a high probability, where appropriate.
For each of the above scenarios the assessment should provide insights into the spatial extent of the flood; water depths or water level; and flow velocity or the relevant water flow.
Plan: every 6 years. Measures: depending on the type (from months to decades).