Rehabilitation and restoration of rivers and floodplains

River and floodplain rehabilitation and restoration embraces a great variety of measures having in common the emphasis on natural functions of rivers, which may have been lost or degraded by human interventions (e.g. damming, construction of levees and embankments, sediment dredging, changing of natural forms of rivers, construction of infrastructure on the floodplain, etc.). Many European rivers have been significantly modified in the past decades to serve only one dominant function (e.g. navigation) or few more. However, one-sided use, disregarding of different functions, is no longer optimal and is being replaced by an integrated approach. River and floodplain restoration is done to mitigate the negative effects of human modifications, which does not only produce benefits for the ecological functioning of the river but also for the human society, as in the case of flood risk reduction, water quality improvement and groundwater recharge. Floodplains are natural system to preserve and restore. River and floodplain rehabilitation and restoration imply complex and long interventions; raising support and public awareness are essential as the technical and ecological components.

The rehabilitation and restoration of floodplains and river wetlands provides seasonal aquatic habitats, creates corridors of native riparian forests and creates shaded riverine and terrestrial habitats. Furthermore, it helps to retain and slowly release discharge from water bodies as well as to facilitates groundwater recharge and improves water quality. The infiltration capacity of many soils in Europe changed due to significant land use modifications; the rate at which precipitation is able to infiltrate and recharge groundwater bodies is therefore limited in many areas. Climate change related variability in precipitation and increase of extreme events can lead to longer periods of droughts and floods which further worsen the situation. River and floodplain restoration can contribute to improve the hydrological regime and cope with these climate change effects. Moreover, river wetlands can help maintaining the functioning of estuarine and delta ecosystems and creating natural land features that act as storm buffers, thus protecting people and property from flood damages, also related to sea level rise and storm surges.

Improving water storing capacity in the floodplain through Natural Water Retention Measures (NWRM) is part of river rehabilitation and restoration and can be rather useful to reduce flooding risk. The implementation of NWRM can also occur on farmland; in general the land remains property of farmers and is used for temporary water storage. Retention areas are meant to receive the peak discharge of rivers and therefore to prevent flooding elsewhere. Emergency retention areas can be located along the major rivers to receive large quantities of water in extreme conditions to prevent life-threatening situations and large damage elsewhere in e.g. urban or agricultural areas.

Relocation of water-vulnerable land use types and activities to areas with lower flood risk is another option, which may facilitate the re-establishment of more natural hydrological regimes (see the adaptation option “Retreat from high-risk areas”). The cost of these measures can be high in case of need for expropriation, demolition and re-building elsewhere of infrastructure and economic activities. Rivers and floodplains in relocated areas have a high potential for restoration, which offers not only improved habitats, but contributes to flood protection by creating new retention areas.

In some specific cases, measures may also deal with the adaptation of dredging practices to changes in water depth, navigability, erosion and siltation in rivers. If the decision to deepen navigation channels for shipping traffic is considered inevitable, dredging should be implemented with minimisation of impacts and/or by ensuring that adequate ecological conditions are maintained in adjacent areas, e.g. by the creation of buffer strips. Applying (and financing) rehabilitation of the river and its floodplains, also as a compensatory approach of the deepening of the navigation channel, can ensure that habitats and their services (such as flood protection) are maintained.

There has been increasing interest in Europe in rehabilitation of rivers and floodplains, as in the case of the spatial planning programme “Room for the River” in The Netherlands. This programme included a number of measures leading to the rehabilitation and restoration of river beds and floodplains, to create more room for the rivers and reduce water levels, such as: lowering of the floodplains, relocating dikes further inland, lowering levees along the rivers and deepening the summer beds. Other examples are the Anglian River Basin Management Plan in the United Kingdom, which includes various river restoration projects aiming to mitigate the impacts of hydro-morphological modifications. Other floodplain restoration interventions are driven by the Water Framework Directive (WFD), e.g. , those taking in place in the Rheinvorland-Süd on the Upper Rhine, the Bourret on the Garonne, and the Long Eau River in England. Many river restoration projects are co-funded by EU LIFE programme. These projects are often set up and implemented by encouraging cooperation between water engineering, flood protection, land management and nature conservation.