12.Towards sustainable flood risk management

12.1.     Introduction

Chapter to be improved

Millions of European citizens are threatened by flooding events from rivers, estuaries and the sea. Over the past ten years Europe has suffered more than 175 major floods, causing deaths, the displacement of people and significant economic losses. Although many flood defense measures were implemented in the European river basins and coastlines during the last century, the ongoing urban developments and changes in land use, as well as the social and economic development have increased the potential for flood damages. This significant increase of the flood risk is furthermore due to climate change and extreme weather events e.g. heavy rainfalls.

The EU Floods Directive (2007/60/EC) aims to reduce and manage the risks of floods to human health, the environment, cultural heritage and economic activity. The Directive requires Member States to assess what rivers and coast lines are at risk from flooding, to map the possible extent of flooding and the assets and humans atrisk in such areas, and to take adequate and coordinated measures to reduce the risks. All EU Member States have to develop such flood hazard and risk maps by 2013. Using hazard maps, this planning aims to limit increases in potential damage, to avoid aggravating it in risk areas, and even to reduce it in the longer term. European countries outside the EU generally have similar legislation.

The implementation of the Water Framework Directive means a chance for many European countries to combine those measures to reach a Good Ecological Status (GES) with rehabilitation measures.

Working with nature, not against it

For centuries, hard infrastructure, including bank enforcements and dykes, navigation including canals, locks, dredging and bank reinforcement, water storage reservoirs and dams, and drainage through straightening rivers and pumping canals, has been used for flood defences. All these activities are typically associated with a range of hydro-morphological alterations and adverse ecological effects. In many countries, activities in relation to the WFD and flood risk planning have been an impetus for changing the way we manage flooding to enhance the environment and protect people from the damage.

Flood defence works besides their positive effects on flood safety could cause possible ecological alterations and impacts associated with flood defence measures.  Figures 12.1 and 12.2 illustrate such alterations and impacts in case of river channelling and application of flood defence dykes.

Figure 12.1: Illustrative range of possible ecological alterations and impacts typically associated with flood defence works – river corridor channelling (straightening and deepening)

Figure 12.2: Illustrative range of possible ecological alterations and impacts typically associated with flood defence works - dykes

12.2.     RBMPs and flood defense activities

Member States input and case studies on pressures related to flood defense and RBMPs are very much appreciated.

Ireland – Flood protection and WFD

Source: Gilligan 2008

The Office of Public Works (OPW) is the lead authority for Flood Risk Management in Ireland. OPW maintains 11,500 km of watercourses for drainage & flood relief purposes and implements an ongoing programme of urban Flood Relief Schemes.

Ireland's Article 5 Initial Characterisation Report under the WFD establishes that Hydromorphology is the 2nd largest pressure behind Diffuse Pollution. Hydromorphology accounts for 40% of the river waterbodies being designated either “At Risk” or “Probably At Risk” of failing Good Ecological Status (GES). Channelisation and Flood Relief structures account for over half of these pressures.

For Drainage/Flood Relief pressures in Ireland, the Programme of Measures under the WFD will focus on enhancement of drained rivers and sustainable flood relief practices. In addition, Ireland is incorporating River Continuity into the hydromorphological criteria, which will set a new framework to manage fish passage obstructions. A recent example of river continuity improvements is where the OPW replaced a weir obstacle with a new Rock Ramp structure as part of an urban Flood Relief Scheme.

Germany  increased floods due to morphological changes and loss of flood plains

Source: UBA 2010

The man-made changes to many German rivers were designed to create land for industry and housing, make waters navigable, intensify agriculture, utilise hydropower, and protect against flooding. Owing to the straightening and shortening of river courses, flood waves now travel faster and transport larger volumes of water per unit of time. For example, since the first large-scale straightening of the Rhine in the mid-19th century by hydro-construction master Johann Gottfried Tulla, the number of riverine meadows on the Upper Rhine between Basle and Karlsruhe has diminished by 87 %.

All in all, the flood plain of the Upper Rhine was reduced by 60 % or 130 km². River straightening measures lead to a shortening of the run – on the Upper Rhine by approximately 82 km, and on the Lower Rhine by approximately 23 km – which in turn led to an acceleration of runoff. For example, the flow rate of the flood wave in the Rhine on the section between Basle and Maxau has been reduced from 64 to 23 hours.

Restoring flood plains in the Rhine river basin

12.3.     WFD and flood risk management

In general, measures for managing flood risk and mitigating hydro-morphological pressures that work with nature rather than against it should be promoted, such as making more room for rivers.

Sustainable flood risk management is a shift away from our predominantly hard-engineering flood defences to a river basin approach, which uses natural processes and natural systems to slow and store water in addition to measures such as flood warning, spatial planning and emergency response. Natural floodplains are allowed to flood and wetlands to act as giant sponges to soak up excess water then release it slowly back into the river.

This is generally a cost-effective way of achieving many objectives, including the good status objective of the WFD and national water policies. For many European rivers, restoring former floodplains and wetlands would both reduce flood risk and improve the ecological and quantitative status of freshwater. Opportunities to enhance the natural environment and improve its capacity to perform ecosystem services should be identified.

There are many national activities in Europe aimed at more sustainable flood management and restoring rivers. Examples include the Dutch Room for the River (Ruimtevoorderivier, 2010), the UK programme for making space for the river (DEFRA, 2008), the Swiss guiding principles for sustainable water management (BAFU, 2010; the SOER 2010 country assessment on Switzerland (EEA, 2010g)), the Austrian Stream Care Scheme (Lebensministerium, 2010) and the Spanish National Strategy for Restoring Rivers (MARM, 2010).

>national examples may be further developed

Text box: Natural flood defenses

Source: Environment Agency

The development of riparian forests is valuable for retaining water in upstream areas of river catchments and therefore to lower the floodwater levels in the river. Another measure, which has an effect on the water level in the main river, is the construction of secondary gullies. But if those are planned very well, the positive effects are dominant.

If densely populated areas are at a risk, still heightening of dikes or the implementation of technical measures is a solution. Especially in urban areas space along the riverbanks is very much limited and therefore, barriers along the river promenade in combination with footpaths or other combination of functions can be a useful option. Cities along rivers should carefully look right now whether planning with the river or water in the city can prevent future problems. Maybe a new consciousness or attitude to floods of the people living in a catchment can contribute to this.

Text box: Germany – flood risk management

References

BAFU 2010: Flood protection and ecology of watercourses. http://www.bafu.admin.ch/wasser/01444/01993/index.html?lang=en  [accessed 13 September 2010].

DEFRA 2008: Making space for water. Available at http://www.defra.gov.uk/environment/flooding/policy/strategy/. [accessed 13 September 2010].

EEA/SOER 2010 country assessment on Switzerland

Environment Agency http://www.environment-agency.gov.uk/homeandleisure/floods/31738.aspx

Gilligan 2008: Hydromorphology and river enhancement for flood risk management in Ireland. In proceedings from 4^th ECRR Conference on River Restoration Italy, Venice S. Servolo Island 16-21 June 2008. Avaiable at http://www.ecrr.org/archive/conf08/pdf/proceed8.pdf

Lebensministerium. 2010: Wassernet: Running waters – Rivers and brooks. Vienna, Austria http://www.wassernet.at/article/articleview/67691/1/1460. [accessed 13 September 2010].

MARM 2010: Estrategia Nacional de Restauración de Ríos. http://www.mma.es/portal/secciones/acm/aguas_continent_zonas_asoc/dominio_hidraulico/conserv_restaur/index.htm [accessed 13 September 2010].

Ruimtevoorderivier 2010: Homepage for the Dutch project “Room for the River”.  http://www.ruimtevoorderivier.nl/meta-navigatie/english.aspx [accessed 15 September 2010].

SDF The former INTERREG IIIB project SDF - “Sustainable Development of Floodplains” http://www.ecrr.org/sdfproject/sdfproject.htm

UBA 2010: Water management part I p. 104-107