Storm processes and impacts in geologically controlled barrier islands: Outer Hebrides, Scotland

Overview

Barrier island systems occur along a wide range of coastal settings and their morphology is highly diverse, in response to the variation in wave climate, tidal regime and geological framework, while their dynamics and evolution are strongly linked to extreme storm events (Moore and Murray, 2018). The response of barrier islands to storms and the associated impacts are primarily controlled by storm magnitude and the morphological characteristics of the barrier, which can exhibit considerable spatial variability (Houser et al., 2008). Site-specific factors can also significantly moderate barrier storm response (Masselink and van Heteren, 2014), particularly along indented and sediment-limited coastlines (Cooper et al., 2004).

Along the coast of the Outer Hebrides in northwest Scotland, a unique barrier island system developed on a bedrock surface directly exposed to the extreme storm waves of the North Atlantic extratropical storm track (Cooper et al., 2012). This system differs from conventional barrier islands as it rests and migrates over an irregular bedrock surface that controls the morphology and compartmentalization of the barrier system, but also influences the morphodynamic behaviour and response to storms. Impacts of extreme storms in the Outer Hebrides barrier islands can be severe, ranging from widespread erosion to overwash, breaching and inundation, which result in significant damage to property and infrastructure (Dawson et al., 2007; Angus and Rennie, 2014). Such impacts are mainly perceived as negative, but in the wider context of coastal resilience in a changing climate (particularly under rising sea levels and changing storminess patterns), storm-induced morphological changes can also be viewed in terms of geomorphological reorganization and adaptation of barrier island systems in order maintain or regain its functions in response to extreme disturbance (Kombiadou et al., 2019). This requires a comprehensive understanding of coastal processes in relation to forcing conditions and, particularly for barrier islands on bedrock, a detailed consideration of process-morphology interactions between sediments and bedrock (Trenhaile, 2016) and geological controls on mesoscale coastal dynamics (Cooper et al., 2018).

This project aims to investigate the geomorphological response of geologically controlled barrier islands in order to advance the understanding of storm-induced processes and impacts in coastal areas where bedrock configuration is a primary control of contemporary and future coastal behaviour. To achieve this, the project’s specific objectives are to:

1) Characterize the oceanographic forcing and geomorphological change driven by extreme storm events that have impacted the Outer Hebrides barrier islands in the past two decades using a combination of field, remote sensing and modelling approaches;

2) Investigate the storm-induced morphodynamic response of these barrier islands and determine the relative contribution of different processes and their impacts;

3) Explore the role of extreme storms as mechanisms of coastal resilience in geologically controlled barrier islands in the context of rising sea levels and changing storminess.

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Image Captions

Aerial view of Outer Hebrides Barrier Islands

Copyright/licensing: Use of Google Earth imagery is permitted for non-commercial uses under the Terms of Service for web and applications as the images follow Google Earth and third-party data providers attribution rules (https://www.google.com/permissions/geoguidelines/)

Methodology

This project will use a combination of remote and field monitoring techniques, meteorological and oceanographic data, alongside numerical modelling, statistical and spatial analysis, in order to generate novel understanding of storm-induced coastal processes and impacts in mixed sedimentary and rocky coasts.

Identification and characterization of storms that have impacted the Outer Hebrides over the past decades will be achieved by statistical analysis of observed and hindcasted data from northwest Scotland. This will consist primarily of extreme value analysis of oceanographic and meteorological time series, in order to develop a database of extreme events and their forcing conditions. The storm database will guide the mining of medium (Landsat and Sentinel) and high-resolution (Planet, ESA Third Party Missions) satellite imagery to characterize significant morphological impacts of extreme storms in different sectors of the Outer Hebrides barrier island system. This will be achieved through a combination of image processing techniques and GIS-based mapping to determine changes in specific geomorphological components of the barrier island system (e.g. beaches, dunes, machair). The satellite imagery-based analysis will be complemented by dedicated field surveys using a range of field instruments to collect morphological and sedimentary data of the barrier islands in hotspot locations and characterize the bedrock surfaces. Forcing and response data will be integrated with other geospatial datasets (e.g. LIDAR topography and multibeam bathymetry) for hotspot coastal areas, and explored using a combination of spatial analysis and numerical hydrodynamic and morphodynamic modelling (SWAN and XBeach) for simulating specific storm events. The insights from the integrated data-driven and exploratory modelling analysis of storm-induced change will inform the assessment of geomorphological resilience to extreme storms in the Outer Hebrides, which will be performed considering the dependencies and feedbacks between the distinct barrier islands components.

Project findings will not only enhance process-based understanding of storm impacts in geologically controlled barrier island systems, but will also contribute to the evidence base for managing coastal vulnerability in Scotland, in line with the priorities of the Scottish Government and the Dynamic Coast project. To achieve this the student will be supervised by a multi-institutional team composed of scientists in the Universities of Stirling (Loureiro, Bradwell), Glasgow (Naylor) and Ulster (Cooper) and Scottish Natural Heritage (Rennie).

Project Timeline

Year 1

Literature review; compilation and validation of meteorological and oceanographic datasets; time series analysis and development of storm catalogue; satellite image mining and geomorphological characterization of the barrier island system; field visit. Attendance of British Society for Geomorphology postgraduate workshop and annual conference.

Year 2

Image-based storm impact characterization; data integration and drafting of baseline results; identification of hotspots and fieldwork campaign. Attendance of European Geosciences Union annual conference (in Vienna).

Year 3

Integration of storm-induced processes and impacts with exploratory modelling of event-based hydro-morphodynamics in hotspot areas; drafting of results for publication; assessment of coastal geomorphological resilience. Attendance of Coastal Sediments 2023 international conference (in the US).

Year 3.5

Finalize the writing of manuscripts/chapters; submit thesis.

Training
& Skills

The student will receive extensive training-trough-research under the guidance of the supervisory team, which will be complemented by specific training activities to equip the student with the skills and expertise to become an independent researcher. Specific training in research methods, including programming with Matlab and Python for statistical analysis, image processing and data integration; GIS for spatial analysis; fieldwork design and instrumentation; numerical modelling with SWAN and XBeach. These will be complemented by training in core scientific skills (writing, presentation and science communication) and transferable skills (data management, task coordination and exploitation of results with end users).
The student will also participate in IAPETUS2 training and events, which will complement the personal training plan.

References & further reading

Angus S and Rennie A, 2014. Ocean and Coastal Management 94: 22-29.
Cooper JAG et al., 2004. Marine Geology 210: 261-280
Cooper JAG et al., 2012. Geology 40: 923-926
Cooper JAG et al., 2018. Global and Planetary Change 168: 15-34
Dawson AG, et al., 2007. Scottish Geographical Journal 132:135-149
Houser C et al., 2008. Geomorphology 100: 223-240
Kombiadou K et al., 2019. Earth-Science Reviews 198: 102934
Loureiro et al., 2012. Marine Geology 329-331: 1-15.
Masselink G and van Heteren S, 2014. Marine Geology 352: 321-347
Moore LJ and Murray AB (Eds.), 2018. Barrier dynamics and response to changing climate. Springer
Pile et al., 2019. Earth Surface Processes and Landforms 44, 1482-1493.
Trenhaile A, 2016. Earth-Science Reviews 159: 1-13

Further Information

For informal enquiries, or if you are interested in applying, contact Dr Carlos Loureiro (carlos.loureiro@stir.ac.uk)

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