Nature-based Solutions for cost-effective flood risk management in rural communities
middle bund.jpg
In rural areas, rising seasonal rainfall can cause flooding that threatens communities, tourism, and local businesses. Hard engineering methods like dams, reservoirs, channels, and embankments are costly and harm habitats, biodiversity, water quality, and soil fertility, while also reducing landscape value. In contrast, Natural Flood Management offers a cost-effective, nature-based alternative that reduces flood risk while benefiting ecosystems and local communities.
Context:
The Natural Flood Management solutions described in this Good Practice are suitable for forested landscapes and (semi-)protected areas within National Parks, where ecosystems quality and resilience need to be preserved and enhanced, and local communities rely on their natural capital for amenity and spiritual purposes as much as for the economic opportunities provided by features in the landscape (e.g., sustainable forest and nature-based tourism). NFM solutions are much less costly than hard engineering approaches and are particularly suited in complex catchments where implementation in multiple sub catchments might be required to yield good results while preserving the landscape and the natural capital for the benefit of local communities and the broader region. The objective of the NFM intervention is not to retain water for extended periods but to help mitigate flood peaks. The addition of native species in the newly created floodplains – especially when replacing existing conifer trees that were planted immediately next to the riverbanks – delivers a quadruple objective of further slowing the flow of water, increasing plant biodiversity, supporting animal (including fish) biodiversity, and reducing soil and water acidification.
Problem Description:
This Practice was developed in response to the highly damaging impact of flooding in a village located in the Queen Elizabeth Forest Park SUPERB Demo site in Scotland. The village of Aberfoyle is home to a vibrant community and strategically located to welcome the large influx of tourism in QEFP across the spring, summer, and autumn months. Several local businesses rely on the economic advantages provided by tourism, and travel across the village is essential for commuters from the local communities and further afield, as the links between QEFP and the busy cities of Glasgow, Edinburgh and Stirling preferentially transit through Aberfoyle. The River Forth flows through Aberfoyle after incorporating several tributaries from the numerous sub catchments upstream from the village. The intense winter precipitation in the catchment results in the Forth flooding Aberfoyle every year, often multiple times a year with severe consequences on transport and local businesses which on several occasions were not able to cope with the repair costs incurred from the flooding events.
Implementation Steps:
· Step 1 (recommended): Install water flow sensors in the target water course requiring NFM implementation. Gathering 1+ years of pre-NFM baseline data is recommended to allow impact assessment of the restoration activities. Depending on the frequency of flood events, it is recommended that 5+ years of data are gathered before implementation of NFM solutions;
· Step 2: Gather catchment data (i.e. depth of riverbed at multiple locations, topography of catchment) to inform placement of NFM structures and to allow interpretation of results and upscaling of findings;
· Step 3 (if required): After completion of Step 1, if existing conifer stands are present in the immediate proximity to the water course (especially if extending all the way to the riverbank), remove existing vegetation;
· Step 4: source appropriate planting materials for the floodplain area(s). Depending on the national and local policy context and landscape/environmental conditions, native species might be preferable. Choose tree species that are suited to physicochemical floodplain conditions, and are well adapted to present and future climates (Available tools for species selection include : Seed4Forest (https://app.seed4forest.org/) and in the UK the Ecological Site Classification (ESC, https://www.forestresearch.gov.uk/tools-and-resources/fthr/ecological-site-classification/) decision support tools);
· Step 5: Based on an analysis of the water course and surrounding landscape, identify suitable sites for installing NFM structures such as “leaky” dams and timber bunds.
· Step 6: Source materials and skilled workforce for the construction of leaky dams and timber buds. Where possible, consider using local timber and skilled workers.
· Step 7: Build the NFM structures and install them at selected locations along the watercourse.
· Step 8: Monitor water flow data from sensors. Make sure sensors are maintained in good working order and repair/replace as needed.
· Step 9 (if possible): In the case of complex catchments with multiple sub catchments, consider utilising a hydrology modelling software to (i) model the impact of the implementation of the NFM structures, and (ii) investigate the implications of extending these restoration activities to other sub catchments, to e.g. avoid synchronous delayed peak flows.
Stakeholder Engagement:
The primary stakeholder group in this case is obviously composed of the local community affected by the flood events. Other key stakeholders include the landowner and the forest manager. The latter might be able to provide the timber required for construction of the leaky dams and the timber bunds. These key stakeholder groups need to be included in early consultations to understand the needs of the affected parties and the opportunities and challenges of implementing the NFM solutions in the selected area(s). Nature conservation and environmental protection agencies should be consulted, following which they might provide additional support. Local tree nurseries for planting material, and local, skilled workforce should be consulted to learn about any barriers and to consider the costs of the restoration actions.
Knowledge Types:
These NFM restoration practices combine multiple types of knowledge to obtain the desired outcome of flood risk mitigation. Within this setting, local knowledge primarily consists of quantification of the impacts and information about their frequency, periodicity, and severity. Scientific knowledge is required in the form of peak flow monitoring, spatial mapping of the floodplain and the surrounding catchment, and forest hydrology analysis of the impact and risks associated with the NFM structures. Practical knowledge is essential firstly as the forest manager’s knowledge of the landscape and forestry policy and practices. Secondly, the skillset for the construction of the NFM structures is likely to have been developed through previous experiences.
Replicability:
NO, the practice has been tested only in the same context and scale, but it is currently being proven for replicability and adaptability to various contexts.Key Success Factors:
• Political Enabler: Given the impact of flood events on local communities and on the broader geographical area that extends to the most frequent users of the area (for tourism and recreation, travel and commuting), significant pressure can be put on elected representatives to promote the use of NFM solutions and create the conditions for upscaling at the regional and national levels. Engagement with the local, regional, and when applicable national political spheres is essential to facilitate this. Strategic use of powerful communication channels can further increase the chances of policy support for these restoration actions.
• Technical Enabler: Demonstrating the cost-effectiveness and the impact of NFM solutions relies on solid monitoring frameworks and on the best suited NFM option (timber bunds, leaky woody dams, heather bale dams, etc.). Low tech solutions created from locally sourced timber material and installed using skilled local workforce can be very appealing to a broad spectrum of stakeholders.
• Economic Enabler: Upscaling of NFM solutions is likely to require private investment. Supported by the political enabler, local and regional councils might be incentivised to support the implementation of NFM practices, but this is likely to happen at scale only after cost-effectiveness has been proven – following the successful completion of a demonstration site. In the UK, schemes such as the Woodland Carbon Code (https://www.woodlandcarboncode.org.uk/) – for the riparian woodland component of the restoration action, and the emerging Woodland Water Code (https://www.forestresearch.gov.uk/research/developing-a-woodland-water-code/) – for the hydrological ecosystem benefits, might become catalysts to unlock private funding for NFM restoration projects.
Common Constraints:
Economic Barriers
1) Inability of require that those affected by floods pay for nature-based solutions 2) Flood scheme funding appears to be diminishing or being reprioritised (in UK), penalising smaller rural communities who might not have the means to cover repair and insurance costs – as observed e.g. for some businesses in Aberfoyle, Scotland. A small proportion of the local councils’ flooding budget could deliver significant NFM implementation. 3) The focus of available grants remains on woodland creation. While riparian woodland restoration is an element of nature-based solutions for flood risk mitigation, the largest costs are those of the NFM solutions (leaky dams, timber bunds, etc). The unavailability of specific grants to cover these costs is a limiting factor. 4) Lack of established market instruments and payment for ecosystem services beyond timber and carbon (e.g., flood risk mitigation, biodiversity).
Technical Barriers
At present, there is not enough evidence to confidently say whether NFM solutions are able mitigate extreme flood events. This lack of data might prevent wider implementation of these activities and reduce funding availability. At normal or slow flow speeds, siltation (the accumulation of sediments) might be an issue for both in-channel structures such as leaky dams, and in flood storage reservoirs. Siltation can reduce the effectiveness and storage capacity of NFM solutions, which would require periodic maintenance. In areas with existing beaver populations, or with plans for reintroducing beavers, careful consideration should be given to the location of NFM solutions relative to beaver population habitat, and frequent monitoring of the water course, flow meter data, and integrity of woody NFM features should be planned into the project activities.
Legal Barrier
If poorly implemented, NFM solutions installed on multiple sub catchment might incur the risk of producing synchronous events. In this scenario, peak flows in the main water course might be exacerbated by peak flows in the NFM-equipped tributaries in case the flows delayed by the NFM solutions were to happen in synchronicity. In these cases, affected parties might argue that the NFM solutions have worsened the flood, which would introduce matters of liability of damage for having installed the NFM solutions. It is therefore of key importance when implementing NFM solutions on multiple sub catchments that a hydrological modelling exercise is carried out to inform locations and extent of NFM installation. It is also recommended that for pilot projects a small sub-catchment be selected to ensure that any unintended consequences would not cause additional harm to downstream local communities.
Lessons Learnt:
· Stakeholders from local communities who actively use the forest area and/or extract direct benefits from the amenity and recreational values of the forest (e.g. because they rely on tourism for their income) were particularly appreciative of the low intrusiveness of the NFM solutions compared to hard engineering approaches.
· The low visual impact of NFM features, and the fact that they seem to integrate organically within the landscape, provided opportunities for creating a network of paths to allow the public to see these structures from a close distance, promoting knowledge sharing and educational opportunities.
· The low implementation costs of NFM structures make them particularly appealing to elected officials of local councils and central government.
Positive Impacts:
- Improved societal support
- Increased freshwater quality and supply, and/or stabilized water regime
- Increased landscape diversity
- Increased share of forests dominated by native species
- Reduced flood risk
Flow-meter sensors have been used in the location of the NFM structures for five [DF1] years before these were installed, thereby providing an excellent baseline dataset to compare the post-intervention flow data with. Preliminary results from the analysis indicate the effectiveness of the intervention on the localised sub catchment, but no data are available to assess the effectiveness of the intervention on the flood risk of downstream communities. It is likely that the project would need to be scaled up to include more sub catchments (after thorough considerations around the risk of synchronous, delayed peak flows), before a significant impact on flood risk to local communities could be observed. Buy-in from stakeholders including local communities was assessed via analysis of stakeholder contributions during three annual stakeholder engagement workshops. Workshop participants visited the NFM site and engaged in discussions over the many facets of NFM project implementation, including amenity values and other ecosystem services. Removal of pre-existing conifer plantations and their replacement with mixed conifer-broadleaf native species increased the structural and species complexity of the riparian forest in the sub catchment. Biodiversity benefits were not directly monitored and hence can only be inferred from the expected impact of higher species diversity and use of native species. Similarly, at present water quality improvements can only be estimated following the removal of the soil and water acidifying conifer plantation.
Negative Impacts:
- Reduced access to markets or income sources
- Reduced monetary value of the land/ forest stock
- Reduced timber quality or quantity
The main drawbacks of this practice are the loss of timber production potential of the previous conifer plantation following removal, and the current scarcity of alternative markets for the numerous other ecosystem services provided by NFM and riparian forest restoration, including flood risk mitigation, increased biodiversity, increased amenity, and freshwater quality.
Media
-
Timber bund during high flow condition
- Economic & Financial
- Monitoring & Projecting
- Social & Stakeholder
- Landowners & Practitioners
- Planners & Implementers
- Policy Actors
- Afforestation, reforestation
- Climate change mitigation
- Restoration after natural disturbances
- Risk mitigation and disturbance prevention
- Show 1 more
- Atlantic
- United Kingdom
- Social
- 125