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The buried coast: developing novel geophysical techniques to reconstruct coastal landscapes

Dr Natasha Barlow (SEE), Dr Adam Booth (SEE), Dr Jared West (SEE), Dr George Tuckwell (RSK Geophysics Group) and Tim Grossey (RSK Geophysics Group)

Project partner(s): RSK (CASE)

Contact email: n.l.m.barlow@leeds.ac.uk

Coasts are important ecological systems.  They provide natural barriers from coastal flooding, habitats for diverse fauna and flora and are the location of much infrastructure and industry.  Understanding coastal system response to sea-level change is important to be able to predict future system response and developing novel research approaches is vital to better respond to the threats to our coastlines.

Former coastal sequences provides archives of system response over time to changes in relative sea level.  Some of the best-preserved palaeo coastal sediments are those from areas which have experienced periods of relative sea-level fall (often due to land uplift) burying them under modern terrestrial sediments.  To identify and reconstruct such environments, current research methods typically use a limited number of borehole records from which the sedimentological information is then extrapolated into 2-dimensions (e.g. Barlow et al., 2014).  Although this provides detailed point-samples of the paleo-landscape, it can be difficult to ensure accurate extrapolation between control points, particularly if a borehole samples an anomalous structure.  Geophysical survey represents a non-invasive means of expanding borehole control across a spatially extensive area, potentially offering 3-D insight into the large-scale morphology of the buried coastal system.  Of particular promise in this application is ground penetrating radar (GPR).

GPR methods are widely established in near-surface surveying, and offer rapid and high-resolution appraisal of subsurface structure.  Typical GPR surveys may only ‘see’ the subsurface to a depth of < 5 m, but resolve the detail of that subsurface on a sub-decimetre scale.  Dense grids of GPR acquisitions allow the subsurface to be viewed as a series of cross-sections, from which features of the paleo-landscape can be inferred (Figure 1).  Additionally, GPR is well-developed for civil engineering applications, and is useful for assessing the vulnerability of coastal infrastructure to sea-level rise.

With appropriate calibration, GPR data can also be used to quantify physical properties of the subsurface (e.g., West and Truss, 2006; Booth et al., 2011).  Laboratory techniques such as time domain reflectometry (TDR) provide a bridge between core samples of the subsurface and the GPR response.  In this way, a remote means of establishing (e.g.) subsurface porosity can be obtained.

This project will aim to develop a novel approach, using both GPR and borehole data, to reconstruct palaeo-coastal environments on a scale much greater than done previously.  This will allow us to understand on a much large spatial scale how a coastal system response to sea-level change, rather just at a single borehole location.  It also offers the potential by which to identify unconsolidated buried coastal sediments that may be susceptible to erosion under models of rising sea level.  Fieldwork will focus on areas in the UK, such as North Wales and Scotland with coastal sediments buried under the modern land surface, above the elevation of the current high tides. 

The University of Leeds owns two Sensors&Software PulseEKKO PRO GPR systems, and a range of antennas to ‘tune’ the acquisition to the specific field site under investigation.

Figure 1.  Upper: Paleo-surfaces and channel features images in a 3-D grid of GPR data.  Lower: A modern coastal environment, North Wales, showing similar channel geometries to those imaged in the GPR data.

Objectives

 In this project, you will work with leading scientists in the School of Earth and Environment at the University of Leeds to investigate the applicability of GPR methods in coastal processes and landscape evolution with the aim of providing a detail, large-scale reconstruction of palaeo coastal system response to sea-level change.  Field campaigns of geophysical survey and borehole sampling will be conducted at a number of sites, including North Wales, southern England and Scotland, to investigate the range of paleo-coastal geomorphology that can be successfully characterised.  Specific objectives include, but are not limited to:

  1. A reconstruction of paleo-coastal geomorphology at target sites.

  2. Development of methods for optimising techniques of GPR acquisition, processing and interpretation in coastal environments.

  3. An assessment of the vulnerability of coastal infrastructure to future sea-level rise.

  4. Laboratory analysis of core samples and comparison with GPR-derived quantities.

Potential for high impact outcomes

The development and application of this technique in coastal settings has such wide-ranging applications from being able to reconstruct paleo-coastal landscapes, developing models of coastal response to sea-level change, identifying areas of former coastal sediments and buried infrastructure at risk of future erosion.  The project will demonstrate the value of near-surface geophysics in studies of sea-level rise, of clear interest to international bodies focussing on coastal risk.  Advances in GPR methods will be applicable in diverse near-surface geophysics settings.

The studentship will be a springboard for further funding applications; its research themes are well-aligned to key areas identified by (e.g.) NERC, including focuses in Palaeoenvironments and Land-Ocean Interactions.

CASE partner

The proposal has been agreed as a CASE partnership with RSK, a leading environmental consultancy providing services to the environmental and engineering sectors.  RSK’s dedicated Geophysics Group plays an active role in research innovation, passing on developments in survey technology and software potential to clients.  Over the course of this project, RSK will support the development of new approaches to GPR processing, including approaches to efficient data characterisation and visualisation. 

RSK offer a financial contribution of £1000/year to the project, and travel and subsistence support during a distributed three month placement with the Geophysics Group; this placement can involve field deployments during which the successful candidate will become experienced with modern approaches to near-surface geophysics analysis.  Additionally, RSK provide access to a large archive of geophysical data for methods development, including in the coastal environments that are central to this project.

Training

The student will work under the supervision of Dr Natasha Barlow, Dr Adam Booth and Dr Jared West, with industrial guidance from CASE partners Dr George Tuckwell and Tim Grossey at RSK.  The project provides high-level specific training in:

  • appreciation of the significant research themes in the discipline of Quaternary environmental change

  • acquisition and processing of geophysical data, including ground penetrating radar

  • reconstruction of paleo-coastal landscapes and field methods in core collection,

  • laboratory analysis of palaeo-sediment samples.

Co-supervision will involve regular meetings between all partners.  The successful candidate will have access to a broad spectrum of training workshops facilitated by the DTP, and can access MSc-level modules in both Earth and Environment and Geography to hone skills in geophysical or geographical analysis.  Additionally, there is some scope to collaborate with colleagues in Leeds’ School of Computing to develop novel GPR interpretation techniques.  There will be opportunities to present at national and international conferences and join part of a growing coastal-research community in Yorkshire.  A total of three months can be spent working directly with RSK, in which the candidate will gain a unique insight into current practices in near-surface geophysical consultancy.

Student Profile

Candidates should have a background in geophysics, preferably with experience of GPR methods and/or acquisition and processing techniques in near-surface geophysics.  A keen interest in environmental processes is desirable, in particular with a on the coastal landscape.  Willingness to undertake fieldwork, including geophysical surveys and core sampling, is essential. 

References

Barlow NLM and 5 others (2014); Salt marsh reconstructions of relative sea level in the North Atlantic during the last 2000 years.  Quaternary Science Reviews, 99, 1-16.

Booth AD and 2 others (2011); Influences on the resolution of GPR velocity analysis and a Monte Carlo simulation for establishing velocity precision.  Near Surface Geophysics, 9, 399-411.

West LJ and Truss SW (2006); Borehole time domain reflectometry in layered sandstone: Impact of measurement technique on vadose zone process identification. Journal of Hydrology, 319(1-4), 143-162.

Related undergraduate subjects:

  • Environmental science
  • Geography
  • Geology
  • Geophysics