Squeezing the middle ground: nature-based solutions and the hydrology of marginal lands

The climate and biodiversity crises are driving increasing global investment in nature-based solutions such as tree planting for carbon sequestration, natural flood management, biodiversity offsetting, and re-wilding. This is changing the value we place on landscapes that have traditionally been undervalued; the ‘squeezed middle’ of intermediate quality farmland (Slee et al. 2014), which is extensive across many upland areas in the UK and worldwide. Research on nature-based solutions often focusses on optimised scenarios of land use change, such as the conversion from improved grassland to forest cover, whereas many of the changes are likely to be more opportunistic and targeted at these more marginal areas. It is therefore essential to understand more about the function and value of marginal lands and how land use change on such areas impacts on the environmental services they provide.

The hydrological impacts of changes in land use in these areas is one area in which relatively little is known. This makes it difficult to evaluate how realistic land use change scenarios will alter flood peak magnitudes at a range of downstream catchment scales and our understanding of the effectiveness of nature-based solutions. This project will aim to investigate the hydrological impacts of realistic land use change scenarios in the UK uplands. It will involve primary hydrological data collection and analysis through field and laboratory work, analysis of land use change using GIS and remote sensing data, analysis of hydrometric data, and hydrological modelling. Fieldwork and catchment scale analysis will focus on the Eddleston Water Natural Flood Management pilot project in the Scottish Borders managed by the CASE partner, the Tweed Forum on behalf of the Scottish Government. As one of the UK’s largest and longest running NFM pilot projects, this site provides an exceptional basis for research in this area and impact on policy.

Key questions:
1. Where is land use change happening and how does this alter key hydrological parameters?
2. What are the potential hydrological impacts on flood risk at catchment scale?
3. What are the implications for realistic policy scenarios of NFM implementation?

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Image Captions

Overview of the Eddleston catchment showing diversity of land use., High flows in the catchment with upland stream gauging station and water chemistry sampling., Example of ERT survey work being conducted to understand subsurface water movement., Student installing groundwater monitoring wells using a hand-held rock drill.


The bulk of the research will focus on the Eddleston Water, 30 km south of Edinburgh in the Southern Uplands, which provides an excellent opportunity for undertaking detailed research as it hosts an intensive hydrometric monitoring network established in 2011 combined with significant natural flood management interventions (e.g. reforestation, remeandering, natural flood storage ponds). The existing infrastructure, detailed knowledge of the catchment (e.g. Archer et al., 2013; Black et al., 2021; Peskett et al., 2020), and existing hydrological models make it ideal for the project.

The project will use a variety of methods at different scales, building field-based plot scale experiments into a wider experimental design. Field methods will include deploying and developing methods to measure key hydrological parameters and fluxes such as: surface runoff and roughness through runoff traps (e.g. Monger et al. 2022); compaction and infiltration; and installation of soil moisture probes, piezometers and potentially geophysical methods (e.g. electro-resistivity tomography (ERT) surveys – see e.g. Peskett et al. 2020) to understand subsurface water dynamics. Catchment scale questions will be addressed through analysis of extensive existing hydrometric data (rainfall, stream flow and groundwater data), and the compilation and analysis of land use change, GIS, and remote sensing data. Land use change scenarios will be developed with partners based on scenario planning methodologies, with the impacts explored through the incorporation of field data into numerical hydrological models. Both HEC-RAS and Dynamic Topmodels have been developed for the catchment and provide a good basis for further modelling using new field data. Depending on student interests and time, there is scope to scale up the analysis to quantify the impacts of land use change on runoff at larger scales using national datasets and realistic policy scenarios for nature-based solutions in Scotland and the UK.

The project will involve collaboration with advisors and end-users outside of IAPETUS2 including the University of Dundee, which oversees hydrological monitoring in the catchment and the Tweed Forum, an influential regional NGO implementing many nationally important nature-based solutions projects across the wider river catchment. The research will also feed into national policy development by providing evidence to the project Steering Committee comprising representatives from Scottish Government and the Scottish Environment Protection Agency (SEPA).

Candidates should hold an excellent first degree in Environmental Science, Geography, Geoscience, Earth Science, Environmental Engineering or related discipline. Candidates with a non-geoscience background might also be suitable with a MSc in an environmental science-related subject. Candidates should have strong quantitative skills, enjoy fieldwork and hold a driving licence.

Project Timeline

Year 1

Year 1 will focus on familiarisation with the literature and the catchment, the existing research and monitoring network, initial hydrological and land use change analysis, and setting up experimental methodologies for subsequent years.

Year 2

Year 2 will involve extensive fieldwork in the catchment to collect primary data on key hydrological parameters in marginal areas to quantify surface runoff, infiltration and sub-surface water dynamics at the plot scale.

Year 3

Year 3 will use conceptual and numerical hydrological modelling (e.g. HEC-RAS and Dynamic Topmodel) to look at scale effects and quantify the impacts of different land use change scenarios in the catchment. Write-up thesis, write-up publications, dissemination of results.

Year 3.5

Year 3.5 (6 months) will focus on writing up the analysis, drafting the thesis and finalising journal publications.

& Skills

A comprehensive training programme will be provided comprising both specialist scientific training and generic transferable and professional skills. The project provides high level training in: (i) surface and subsurface hydrometric techniques; (ii) analysis and interpretation of surface-subsurface interactions; (iii) assessment of land use and management on hydrological processes; (iv) appropriate numerical modelling and analysis of catchments.

References & further reading

Archer, N.A.L., Bonell, M., Coles, N., MacDonald, A.M., Auton, C.A., Stevenson, R., 2013. Soil characteristics and landcover relationships on soil hydraulic conductivity at a hillslope scale: A view towards local flood management. Journal of Hydrology 497, 208–222. https://doi.org/10.1016/j.jhydrol.2013.05.043

Black, A., Peskett, L., MacDonald, A., Young, A., Spray, C., Ball, T., Thomas, H., Werritty, A., 2021. Natural flood management, lag time and catchment scale: Results from an empirical nested catchment study. J. Flood Risk Manag. e12717. https://doi.org/10.1111/jfr3.12717

Brown, I., 2020. Challenges in delivering climate change policy through land use targets for afforestation and peatland restoration. Environmental Science & Policy 107, 36–45. https://doi.org/10.1016/j.envsci.2020.02.013

Monger, F., Bond, S., Spracklen, D.V., Kirkby, M.J., 2022. Overland flow velocity and soil properties in established semi-natural woodland and wood pasture in an upland catchment. Hydrological Processes 36, e14567. https://doi.org/10.1002/hyp.14567

Peskett, L., MacDonald, A., Heal, K., McDonnell, J., Chambers, J., Uhlemann, S., Upton, K., Black, A., 2020. The impact of across-slope forest strips on hillslope subsurface hydrological dynamics. Journal of Hydrology 581, 124427. https://doi.org/10.1016/j.jhydrol.2019.124427

Rogger, M. et al. 2017. Land use change impacts on floods at the catchment scale: Challenges and opportunities for future research. Water Resources Research 53, 5209–5219. https://doi.org/10.1002/2017WR020723

Slee, B., Brown, I., Donnelly, D., Gordon, I.J., Matthews, K., Towers, W., 2014. The ‘squeezed middle’: Identifying and addressing conflicting demands on intermediate quality farmland in Scotland. Land Use Policy 41, 206–216. https://doi.org/10.1016/j.landusepol.2014.06.002

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