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River restoration

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Description

Rivers are dynamic by nature as they carve their own course, distribute sediments and spill onto flood plains during flood events. Classic flood management measures restrict river courses to protect property from flooding, often by the straightening them and establishing dykes. Though these actions protect against flooding, if there is severe water level rise, damages can be magnified if the flooding overruns the dykes, or if the retaining structures break under pressure. Ecological river restoration involves ecological, spatial and physical management practices to return a river back (or close) to its natural state. Common restoration techniques include reconnecting rivers with floodplains, reestablishment of the river’s meandering form with no barriers along its banks, and stabilizing surrounding soil to reduce sedimentation and erosion. Restored rivers have increased water retention capacity due to their ability to naturally expand their banks and flood onto floodplains, thus making them more effective for flood risk management. Additionally, they support biodiversity and healthy ecosystems, providing a host of ecosystem services, for example recreational activities.  This method of ‘working with nature’ is a key strategy for severe flood management and climate change adaptation. 

Implementation

River restoration activities begin with a catchment assessment, mapping the river’s original natural course and identifying restoration opportunities.  Stakeholder engagement (local authorities, NGO’s, land-owners, local citizens) is essential – particularly for affected land-use groups. In some cases this may include establishment of agreements over land rights, for example compensation to private landowners. Restoration measures on ground include activities such as digging meandering trenches for the river to follow. After initial construction and realignment, management and maintenance is usually required (e.g. ensuring bank stability and vegetation health). 

Environmental Benefits

- Supports healthy ecosystems and enhanced biodiversity, eventually producing more resilient ecosystems and communities.
- Helps to improve water quality and increase sediment deposition.
- Leads to seasonal flooding of floodplains, which can provide valuable habitats for various species, including fish and waterfowl.

Socioeconomic Benefits

- Decreases likelihood of destructive flooding events, and reduces damage should a flood occur.
- Reduces maintenance costs of structural barriers and other flood-proofing infrastructure. 
- Provides other ecosystem services such as recreation opportunities and food (fish) for local communities. 
- Improves soil stability and composition on or near floodplains, which can improve agricultural production.

Opportunities and Barriers

Opportunities:
-    Restored river systems can reduce flood likelihood and severity, building climate resilience 
-    Floodplains provide significant biodiversity and socioeconomic benefits
-    Benefits a wide variety of stakeholders 
-    Once the river is restored, there are relatively low operational costs and multiple benefits

Barriers:
-    Restoration measures may take away valuable land area, such as cropland from local communities. This can be a potential cause of conflict and will require additional governance arrangements.
-    Not all locations are suitable for restoration changes, for example reconnection of a river with flood plains may not be possible if the intended flood plain land is  being used and has high value, for example for houses, industrial activity or agriculture
-    Land ownership laws may complicate restoration work on privately owned land

Implementation considerations*

Technological maturity:          3-4
Initial investment:                   2-4 (depending on the level of restoration)
Operational costs:                  1-2
Implementation timeframe:     3-5

* This adaptation technology brief includes a general assessment of four dimensions relating to implementation of the technology. It represents an indicative assessment scale of 1-5 as follows:
Technological maturity: 1 - in early stages of research and development, to 5 – fully mature and widely used
Initial investment: 1 – very low cost, to 5 – very high cost investment needed to implement technology
Operational costs: 1 – very low/no cost, to 5 – very high costs of operation and maintenance
Implementation timeframe: 1 – very quick to implement and reach desired capacity, to 5 – significant time investments needed to establish and/or reach full capacity
This assessment is to be used as an indication only and is to be seen as relative to the other technologies included in this guide. More specific costs and timelines are to be identified as relevant for the specific technology and geography.


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