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

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.