Developing novel geophysical tools to investigate urban plant-water processes

Overview

This PhD aims to improve our understanding of how vegetation influences soil-water dynamics in the built environment through the use of geophysical tomography.

Planted areas are a much loved part of the built environment; however, rightly or wrongly, great value is often attributed to their ability to manage urban surface water. However, how much can we rely on trees, shrubs and grassed surfaces; how effective are they at maintaining the function of urban soils beneath our pavements to support load, store and attenuate water (and pollutant) flow? It is vital that our cities are resilient to the increasing frequency of high intensity rainfall events that can cause devastation to homes, businesses and lives. The inclusion of Green Infrastructure (GI) is increasingly recognised as a sustainable approach to mitigate the risk of flooding, while vegetated solutions to ground stability problems (e.g. subsidence/heave, slope stability and pavement design) are also gaining increasing attention among the engineering community. Yet, the root-water uptake behaviour of vascular plants (e.g. street trees) and the implications on soil hydrology are poorly understood in extremely heterogenous urban soils and under ever more variable and extreme climatic conditions.

Based at the recently completed National Green Infrastructure Facility (NGIF), part of the UKCRIC network of BEIS funded national research infrastructure facilities, and building on Newcastle University’s strategic theme of Cities, this project will use innovative geophysical tools to improve our understanding of how urban subsurface moisture dynamics are influenced by GI and the changing climate.

Click on an image to expand

Image Captions

PRIME_Veg.png – “Fig.1 Resistivity image showing enhanced subsurface moisture abstraction (red zones) in heavily wooded areas of the sections (courtesy of BGS).”
Ensembles_labelled.png – “Fig.2 Photograph showing sub-sections of the vegetated ‘ensembles’ (plots) at the National Green Infrastructure Facility.”

Methodology

Based predominantly at the NGIF (Urban Sciences Building, Newcastle Helix), this project will use Electrical Resistivity Tomography (ERT) equipment developed by the British Geological Survey (BGS) and already procured at a cost of ~£100k by the UKCRIC infrastructure grant. Time-lapse ERT is a powerful tool for volumetrically and non-invasively imaging subsurface moisture dynamics, and is consequently very well-suited for the proposed research.

Previous studies have indicated that ERT is sensitive to plant-driven near surface moisture changes (fig.1), but to-date the technique is underdeveloped as a means of tracking these processes in the urban environment. The development of 4D ERT for this purpose will be validated against more traditional sensing methods from the fields of geotechnics, hydrology and agriculture/forestry.

The NGIF hosts a range of environmental engineering research activities, benefiting from state-of-the-art soil-plant-atmosphere monitoring capability and associated multi-disciplinary expertise. The external facility itself comprises an extensively instrumented street complete with purpose built, vegetated plots ranging from isolated and combined grass, shrub and tree planted plots (fig.2).

The work will combine laboratory characterisation techniques in the NGIF Sustainable Drainage Systems Laboratory and a fieldwork campaign utilising the mobile, full-scale ERT array on the experimental plots. By combining ERT with in situ point measurements, the influence of vegetation on soil moisture movement through the soil column will be visualised, under natural and artificial rainfall events imposed using the on-site rainwater harvesting system.

The project includes 6 month-worth of placement commitment at the BGS in Keyworth, Nottinghamshire. There, the student will have access to Geotechnical and Geophysical laboratories to undertake specialist soil electrical property classification work and have the opportunity to gain a deeper understanding of the theory that underpins ERT by working alongside specialists in the field. This is a unique opportunity that has proven highly beneficial to the success of previous collaborations between the University and BGS. In practical terms, the 6 month period is to be split according to the below timeline in order to provide an early grounding, assist in establishing the data flow and analysis training, followed by a later placement to support visualisation and interpretation of the project data.

Project Timeline

Year 1

Literature review; introduction to geophysical methods; planning and training in experimental design and instrumentation (NGIF); characterisation of soils (SuDS Lab); and initial stakeholder/research community engagement.

Year 2

Ground model development; experiment setup and commissioning; design simulated rainfall extremes and trials; initial 3-month placement with BGS; preliminary data analyses; and attend national dissemination events (academic and industry).

Year 3

Attend international dissemination event (e.g. academic conference); continue to undertake and develop field campaign (NGIF); expand application of ERT and approach to asset- and city-scale interventions; and final 3-month placement with BGS.

Year 3.5

Complete data analyses and interpretation; publish work in peer reviewed journal; and complete write-up and submission of thesis.

Training
& Skills

This project combines world-class facilities with the opportunity to conduct innovative, transdisciplinary research alongside leaders in the field of hydrogeophysics, geotechnics and Sustainable Drainage Systems. Together with the supervisory team, the student will develop a Personal Development Plan, identifying areas for development and training opportunities, focusing on research and employability. They will be encouraged to attend national/international summer schools, workshops and courses, and have the opportunity to participate in Masters-level training relevant to the project, for example CEG8201Geomechanics.

Uniquely, this project provides the opportunity to be trained by world-renowned experts in the development of electro-geophysical instrumentation and its application. The British Geological Survey’s Geophysical Tomography team have agreed to provide additional supervisory support both remotely and by hosting the student at their national headquarters in Keyworth (Nottinghamshire) for 6 months. This will provide an invaluable opportunity to progress the students training and ensure successful outcomes from this project.

Building on an existing and successful Newcastle-BGS collaboration, the applicant will be equipped with rounded expertise in instrumentation and monitoring, ERT processing and interpretation, and a comprehensive understanding of soil-water physics and ecological applications. This combination will position the candidate well to develop a stimulating and successful career in the use of these innovative techniques and design to meet the demand for cities to adapt to the growing pressures of climate and population change.

References & further reading

Pawlik and Kasprzak (2018) https://www.sciencedirect.com/science/article/pii/S0169555X17304178
Dick et al. (2018) https://www.sciencedirect.com/science/article/pii/S0022169418301446
Watlet et al. (Chambers) (2018) https://www.hydrol-earth-syst-sci.net/22/1563/2018/
Hen-Jones et al. (Stirling) (2017) https://link.springer.com/article/10.1007/s11440-017-0523-7
Urban Observatory: http://www.urbanobservatory.ac.uk/
UK Collaboratorium for Research on Infrastructure and Cities (UKCRIC): https://www.ukcric.com/

Further Information

Dr Ross Stirling: ross.stirling@ncl.ac.uk 0191 208 5268
Prof. Jon Chambers: jecha@bgs.ac.uk 0115 936 3428

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