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The hydrological function of organo-mineral soils in downstream flood risk

Prof Joseph Holden (SOG), Prof Mike Kirkby (SoG), Jean Johnston (Natural England), Alistair Crowle (Natural England)

Project partner(s): Natural England (CASE)

Contact email: j.holden@leeds.ac.uk

This is a fully funded project and is not part of the DTP competition, applications should be made directly to the hosting department, see http://www.geog.leeds.ac.uk/study/phd/how-to-apply/ for more information.

We seek to understand hydrological processes operating in upland organo-mineral soils and how their management and vegetation cover influences river flow peaks. This novel field, lab and modelling project will expand our knowledge on the function and hydrology of upland soils which are of high conservation value. The project will directly provide urgently needed management decision-making evidence on upland soil management for flood peak reduction. Organo-mineral soils cover around 20 % of the UK, and are particularly common in upland areas with the main types being stagnohumic gleys and acid brown earths. Unlike peatlands, the function and hydrology of organo-mineral soils is globally very poorly understood with major gaps in the literature. These soils typically underlie upland heathland and grasslands in areas with high conservation value. It is unclear whether these soils are dominated by throughflow (and what their typical permeability range is), infiltration-excess overland flow or saturation-excess overland flow in different topographic contexts and rainfall events. It is also unclear how management of organo-mineral soils impacts their role in runoff generation.

There is an urgent need for evidence on ‘nature-based’ flood management solutions, particularly in UK uplands - source areas for the UK’s major rivers. Recent modelling work on peatlands by researchers at the University of Leeds has shown that controlling overland flow velocities by changing the surface cover conditions in key spatially identifiable parts of the catchment can play an important role in reducing flood peaks (by up to 20 % for some rainfall events) (Gao et al., 2016). However, we do not have data from organo-mineral soils, which are likely to function quite differently to peat, to inform such modelling and so practitioners have limited basis for upland management decisions which may benefit those downstream at risk of flooding.

Objectives

The above issues will be tackled through a combined monitoring, experimental and modelling approach involving:

1) Measuring and determining the dominant hydrological pathways (e.g. overland flow, subsurface flow) through monitoring of flow volumes / rates though and over stagnohumic gleys and acid brown earths (controlling for slope position using the topographic index), moisture content & water-table depths;

2) Permeability tests to measure the hydraulic conductivity (Leeds have a novel permeameter system allowing 25 soil samples to be tested simultaneously, allowing high throughput)

3) Experimental overland flow velocity measurements by supplying water to plots and measuring the velocities for different slope angles, flow depths and vegetation conditions (Holden et al., 2008)

The above three approaches will be used on areas of hillslope in Cumbria to test for differences in hydrological function related to soil condition and surface cover. The design will incorporate soils that have been assessed by Natural England to be in different states of degradation including high quality Atlantic Heath (dense dwarf shrubs with an understory of mosses), poor Atlantic heath, good acid grassland and acid grassland that has heavy grazing.

The three field and laboratory steps above will then enable the student to:

4) Modify a new spatially-distributed version of TOPMODEL recently developed by the University of Leeds (Gao et al., 2015).

5) Use the model to test different spatial organo-mineral land-cover scenarios to test optimal solutions to reduce downstream flow peaks.

Potential for high impact outcome

Flooding in northern England derived from uplands in December 2015 alone caused >£2 billion in losses. By providing evidence to demonstrate how, where and by what scale, upland soil management can reduce flood peaks downstream the project will directly impact policy & land management practice (e.g. changed land management in locations identified by the modelling). There is a lack of information about organo-mineral soils and their functions and how they respond to different types of management. Thus the research will yield highly publishable material and leading output. The research will be highly publishable in the international litrature as so little is known about organo-mineral soils. The work will directly inform Natural England’s understanding of grazing management impacts and this will be of importance for policy development and potentially influence future agricultural payment schemes.

Influential organisations beyond the CASE partners will benefit immensely.  Natural England, SNH, Environment Agency, Natural Resources Wales and National Park Authorities must assess and protect upland landscapes dominated by organo-mineral soils. Other charitable bodies such as RSPB and Wildlife Trusts, plus water companies, who often own or have influence over upland catchments, and those at risk of flooding downstream are all potential beneficiaries so the research nmay have impacts on those organisations.

Training

The student will be part of the River Basins Processes and Management cluster in the School of Geography and water@leeds which is the world’s largest interdisciplinary university-based water research centre. water@leeds hosts 140 PhD students. These groups provide access to routine training through seminars, structured feedback on project ideas and technical training. The successful PhD student will have access to a broad spectrum of training workshops that range from technical through to generic skills building.

The supervisory team will provide training on soil hydrological processes and modelling. Natural England will host the student for 3 months to ensure that the student gains experience of practical and policy implications of their work and in the functioning and structure of a government agency. The student will be able to explore the vast archive of ecological and soils datasets on file and gain ground experience of habitat and landscape condition assessments and management decision-making, upland conservation decision-making and practical constraints. The student will be able to undertake placements at headquarters in Peterborough with supervisor Crowle and at the Kendal office with supervisor Johnston. The student will be exposed to two different multidisciplinary settings; a co-ordination/policy environment and a regional field assessment and management environment.

A programme of personal, professional and career training will undertaken via a university-wide programme supported by dedicated hubs offering discipline-specific programmes, delivered by academics and researcher development staff with subject specialisms in water (e.g. MSc module in hillslope hydrology delivered by Holden), soils & plant ecology. Peer-reviewed paper writing, international conference presentations and social media use will also be part of the student's training

Student profile

The student should have a strong interest in environmental problems, fieldwork, hydrology and soils, and should be motivated to undertake hydrological modelling experiments. It is expected that the student will have a relevant masters degree or equivalent experience. The student should have a valid driving licence for use in the UK.

CASE Partner

The proposal has been funded by NERC in open competition under their Industrial CASE PhD scheme with Natural England providing extra funding towards research costs and training from the partner in practical and policy matters.

References

Gao, J., Holden, J. Kirkby, MJ. (2016) The impact of land-cover change on flood peaks in peatland basins. Water Resources Research doi: 10.1002/2015WR017667

Gao, J., Holden, J. and Kirkby, M.J. (2015) A distributed TOPMODEL for modelling impacts of land-cover change on river flow in upland peatland catchments. Hydrological Processes, 29, 2867-2879. DOI: 10.1002/hyp.10408

Grayson, R., Holden, J. and Rose, R. (2010) Long-term change in storm hydrographs in response to peatland vegetation change. Journal of Hydrology, 389, 336-343.

Holden, J., Kirkby, M.J., Lane, S.N., Milledge, D.J., Brookes, C.J., Holden, V. and McDonald, A.T. (2008) Factors affecting overland flow velocity in peatlands. Water Resources Research, 44, W06415, doi: 10.1029/2007WR006052.

Related undergraduate subjects:

  • Engineering
  • Environmental science
  • Geography