The Eddleston Water project was set up in 2009 to assess the effectiveness of natural flood management (NFM) measures. Reducing the maximum water volume of a flood, temporarily storing excess flood water, and delaying the arrival of the flood peak downstream are the main objectives for NFM projects. But NFM can also provide a wide range of other benefits for society, from creating habitats and reducing soil loss to improving water quality and providing woodland and green spaces for wildlife and people.
Up to now, methods to assess the additional ecosystem services NFM delivers and integrate their value into decision-making processes for appraisal of flood risk measures have been lacking. The Eddleston Water project is addressing this issue. Funded largely by the Scottish government, with support from the EUâ€™s Interreg initiative and the Scottish Environment Protection Agency among others, the project is led by Tweed Forum, the Rivers Trust for the Scottish Borders and north Northumberland. Tweed Forum appointed us to investigate how the multiple benefits from NFM can be effectively integrated into the process to assess and manage flood risk measures in Scotland.
The first step was to review existing environmental and social appraisal methodologies in the flood management sector to determine a single agreed approach for assessing additional ecosystem services. Information from the Ecosystems Knowledge Network Tool Assessor (ESKN) was supplemented by the expert knowledge of the project steering group and the results of a stakeholder engagement survey.
CIRIA B£ST â€“ a benefits estimation tool to assess and monetise many of the financial, social and environmental benefits of blue-green infrastructure â€“ was selected to help evaluate multiple benefits in flood risk management appraisals. We tested the tool on the Eddleston Water to evaluate its suitability, and our trial found that B£ST could reliably quantify all significant multiple benefits in the form of ecosystem services for the project.
When the methodology was applied to the Eddleston Water project, it was shown to provide ecosystem services benefits across amenity, biodiversity and ecology, carbon sequestration, education, flows in watercourse, water quality and pollution. Across a 100-year appraisal period, the value of the ecosystem services associated with the NFM measures already implemented at Eddleston Water â€“ including the planting of 207ha of riparian woodland, re-meandering of 2.2km of river, planting almost 300,000 trees, removing of 2.9km of flood embankments and creating 28 â€˜leaky pondsâ€™ â€“ were estimated at approximately £4.2M. A further £950,000 in flood damage was avoided. An additional hypothetical NFM business case building on the work of the Tweed Forum estimates the potential value from a higher density of NFM measures within the catchment would reach £17.7M overall and avoid flood damages of about £2.85M.
Including an assessment of the multiple value of NFM measures in flood risk management appraisal would enable decision-makers properly compare the costs and total benefits of all flood risk management measures â€“ both grey and green. By prompting the use of CIRIA B£ST (or other methods) across flood risk management appraisals in Scotland, the consistency of appraisals should improve, ultimately increasing the value of flood risk management investments.