Mesoscale shoreline evolution on a carbonate sand island: Anegada, British Virgin Islands

Anna Lisa Cescon, Andrew Cooper, DWT Jackson, Antoine Collin, Shannon Gore

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Abstract

Anegada, the easternmost island of the Virgin Islands group (Caribbean Sea), is a low Pleistocene carbonate platform surrounded by Horseshoe Reef, the world’s third-largest fringing reef. The western part of the island consists of an extensive beachridge plain (>40 ridges). The sandy carbonate shoreline exists in three morphodynamic domains that exhibit distinctive behaviour over the 59-year study period (1953 to 2012). The northern shore is dominated by westerly longshore drift under fair-weather conditions and cross-shore sediment transport during high-energy events. Storm wave run-up and high nearshore sediment availability contribute to the construction of shore-parallel beachridges. The western end of the island is affected by refracted waves that drive strong erosion and sediment transport. This is reflected in a succession of alternating rapid shoreline recession and progradation phases over the study period. The south–central shoreline is exposed to low wave energy and is stable and colonised by mangroves. The fringing reef plays a dominant role in mesoscale shoreline morphodynamics, both as a sediment source and in wave energy dissipation. Quasi-stable points and embayments suggest a strong influence of the reef framework in controlling the shoreline’s morphology and position. Sediment transfer from the reef to the shoreline appears to take place via shore-oblique, linear sediment transport pathways that develop across the lagoon in response to the modification of incoming waves. Cannibalisation of the shoreline sediment over the past 50 years is leading to straightening of the shoreline planform. This is counter to the long-term (Holocene) development of beachridges and suggests a change from a strongly positive to negative sediment budget.
Original languageEnglish
Article number1725
Pages (from-to)1-26
Number of pages26
JournalJournal of Marine Science and Engineering
Volume11
Issue number9
DOIs
Publication statusPublished (in print/issue) - 1 Sept 2023

Bibliographical note

Funding Information:
The authors would like to acknowledge the following: Brian Atwater, Robert Halley, Michaela Spiske, and Jean Roger for fieldwork assistance and sharing their knowledge of tropical islands; the BVI Conservation and Fisheries Department for fieldwork authorisations; the BVI Survey Department for field assistance; the BVI Disaster Management Department; the inhabitants of Anegada; the Environmental Sciences Research Institute of Ulster University, for funding fieldwork and for the acquisition of the GeoEye satellite image; Carlos Loureiro for assistance with SWAN; Colin Anderson for assistance with the use of the high-performance cluster computer to run the models; Shane Murphy for assistance with MATLAB and the cluster computer.

Funding Information:
This research was undertaken with the support of a Vice Chancellor’s Research Studentship (VCRS) from Ulster University to A.L.C. Supervisors were J.A.G.C. and D.W.T.J.

Publisher Copyright:
© 2023 by the authors.

Keywords

  • Coral reef
  • extreme wave events
  • shoreline change analysis
  • beachridge
  • carbonate beach
  • coral reef

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