Green Infrastructure and Flood Management - Promoting cost-efficient flood risk reduction via green infrastructure solutions

Background and Goals

Europe's floodplains once covered wide stretches along European rivers and were valued for their high ecological importance. Over a number of years they have been cleared for agricultural purposes and changed through urban expansion and artificial flood control structures. Existing natural waterways do not always have the capacity to bear any excess water which can lead to the flooding of downstream areas. As a rough estimate, around 20 % of European cities are classified as being vulnerable to river floods. Therefore, increasing urbanisation and soil sealing, along with wetland conversion or degradation, have contributed to increased run-off and flood risk. Green infrastructure (GI) can provide essential benefits to flood management and co-benefits to society and the economy. Evidence shows that investment in green solutions, such as landscape conservation and restoring for upstream floodplains or wetlands, is more cost-efficient and provides improved infrastructure solutions. This comes at an opportune moment as decision-makers and investors from both the public and private sectors are seeking out new, innovative and more sustainable infrastructure-based solutions to mitigate flood management. Green solutions can also provide additional benefits such as increased biodiversity, recreational opportunities, and carbon sequestration, which makes for a compelling investment case. This European Environment Agency (EEA) report looks at a number of case studies that demonstrate the effectiveness of so-called 'GI solutions'. This EEA report presents various options for reducing the risks of flooding with GI solutions in European floodplains and presents improved evidence for the financial justification of green investments.

Steps in the process of adaptation to climate change

Step 1: Understand and describe climate change

Approach and results

Chapter 5 and Annex 6 of the Report the model approach for determining flood plain potentials in a 100-year flood event is displayed. With the help of regional circulation models of RACMO22E, RCA4, REMO2009 and CCLM4-8-17 it was possible to model projections with a current EEA flood plain layer and the Corine land use layer for the rivers Elbe, Rhine, Scheldt and Vistula.
Large areas suitable for potential flood plains are a result of the modelling.

Parameter (climate signals)

River flooding

Further times

Baseline: 1990-2013
Modelling for 2050

Step 4: Plan and implement measures

Measures and/or strategies

Chapter 3.5 of the report shows an overview of available green infrastructure measures for flood risk reduction. This study uses the Natural water retention measures (NWRM) catalogue of GI measures as a starting point for the analysis of available solutions for flood protection management. “NWRMs cover a wide range of actions and land use types.

Many different measures can act as NWRMs, by encouraging the retention of water within a catchment and, through that, enhancing the natural functioning of the catchment. NWRMs are measures that aim to safeguard and enhance the water storage potential of landscape, soil and aquifers, by restoring ecosystems, natural features and characteristics of water courses, and by using natural processes. They are adaptation measures that use nature to regulate the flow and transport of water so as to smooth peaks and moderate extreme events (floods, droughts, desertification, salination). They reduce vulnerability of water resources to climate change and other anthropogenic pressures and are relevant in both rural and urban areas.”

Box 6.1 in the report “summarises the average unit costs in the EU for implementing green and grey flood protection infrastructure solutions based on the average for the three categories of costs displayed in the matrix. The infrastructure measures have been rated on three typical biophysical characteristics that provide flood protection (their direct effects) as well as on their characteristics that provide additional indirect effects (ancillary benefits) in the form of the provision of different types of ecosystem services. In a cost-efficiency comparison of green and grey infrastructure measures it is crucial to include in the assessment both direct benefits (effects) as well as indirect benefits (effects) in order to take into account all the benefits that each type of infrastructure measure provides to society. This overview matrix shows how the NWRM project scored GI measures (NWRMs) in these different categories, where a '0' in the table represents 'no effect', '1 = low effect', '2 = medium effect' and '3 = high effect'.”

Annex 5 of the report provides a detailed description of the case studies in the four selected river basins: the Elbe (Germany), the Rhône (France), the Scheldt (Belgium) and the Vistula (Poland). Each case study identifies:

flood risk;
the vulnerability of the main city of concern;
the existence of Flood Risk Management Plans (FRMPs); and
their current status of implementation

Chapters in the main report refer to these in-depth case studies, highlighting additional insights into the cost-efficiency assessments of the chosen flood protection measures (Chapter 4) and the potential for additional floodplains (Chapter 5).

Costs of the measures

Annex 1 of the report provides available evidence on the different types of costs and benefits related to green, grey and hybrid solutions, to allow comparative analysis in general across Europe.

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