Case studies: Eddleston water project
The Scottish Catchment Laboratory
The Eddleston Water is a 70km2 sub-catchment of the River Tweed, typical of many rural river basins in Scotland. The river has been extensively altered in the last 200 years to enable the building initially of a road and then a railway, and to improve agricultural drainage and production. As a result, the river has been straightened and shortened, and is now cut off from its floodplain by embankments for much of its length. The Eddleston Water project, begun in 2009 with a Scoping Study, is now Scottish Government's main long-term study of the effectiveness of Natural Flood Management (NFM) on reducing flood risk to downstream communities (Building with Nature). A parallel aim of the study is to assess the impact of NFM measures to improve river habitats; both aims to be delivered at the same time as working with the community to maintain sustainable farming in the valley.
Tweed Forum liaised with local landowners to explore whether and where they might allow NFM measures to be installed on their land. Working with 19 farmers, 3kms of river have been re-meandered, 30 ponds created providing temporary flood storage, and 120 engineered log structures installed on upland watercourses to slow the flow. Introduction of these measures was accompanied by detailed monitoring of hydrology and ecology led by Dundee University and Scottish Environment Protection Agency.
Funding from the Building with Nature programme was used to enhance development of this long-term study of Natural Flood Management in Scotland. New areas include detailed monitoring of aquatic invertebrates and fish populations; fluvial audit of the whole catchment, and the monitoring of flows and water levels.
Emerging results show the effectiveness of installing engineered log structures in the upper catchment, both in terms of delay in time of flood peak downstream and reductions in flood levels.
Studies of re-meandering previously straightened channels show recovery of river habitats and associated ecology.
Effectiveness of wide-spread tree planting has been demonstrated through modelling catchment response, including assessment of net costs benefits.
We developed a linked hydrological-hydraulic model of the catchment; one that can be used to assess the impact of different NFM measures, readily transferable to other catchments.
Ongoing work on costs and benefits of taking a Building with Nature approach to reducing the risk and damages from flooding show early promise in terms of net benefits and multiple ecosystem services provided by taking this approach alongside that of traditional structural engineering.
Collection of baseline data before NFM interventions were made, and use of a Before:After and Control:Implementation (BACI) design greatly improved assurance of impact. Uncertainties remain in the accuracy of the flood model, but these have been well controlled.
The Eddleston Water is a typical Scottish catchment and the issue of the impact on catchment hydrology and ecology of historical modifications to the banks and channel of the watercourse is a common challenge across Scotland and many areas of the EU. The results, including recent modelling, will be applicable in many other catchments. The role of Tweed Forum, a participatory NGO as project manager and as a 'trusted intermediary' to engage with landowners and other stakeholders, is a particular strength. Similarly, the detail, scope and extent of the empirical monitoring of the NFM measures installed is unrivalled in Scotland.
Future research directions
Future directions of research could include:
- further monitoring to improve flood models
- development of rapid survey methodologies to record changes in channel structure and habitats using drones
- sediment origin and movement, and its impact on flood water conveyance and out-of-bank flooding
- creating a catchment water balance, linking to past climate and land use/land cover compared to future conditions under different climate change scenarios
- investigating linkages between surface water, soil and groundwater and their contributions to flooding under different scenarios
All documents of the BwN project can be found at publications, below you find the documents belonging to this specific case study:
All publicly available information on the Eddleston Water project is accessible on the website, including reports, presentations and publications from studies supported by the Building with Nature programme and others:https://tweedforum.org/our-work/projects/the-eddleston-water-project/