Barrier Islands

Protect
Written By Frank Hangler

Located offshore, barrier islands are dynamic landforms that are formed from offshore bars and, spits. Barrier islands undergo continuous migration through a process of erosion and accretion.[^1] [^2] Given the migratory process through which they derive their structure, hard approaches to coastal protection tend to disrupt the formation of barrier islands. Barrier islands have been protected for decades in some areas, e.g., Miami. However, impending SLR could lead to the abandonment of barrier islands as a retreat strategy.[^2] Barrier islands can be both inhabited or uninhabited. They evolve over time with coastal processes, to form several unique ecosystems, including subaerial beaches, dune fields, interior wetlands, and back-barrier bays or wetlands. These ecosystems provide habitat for a wide range of plants and marine species.

Types of barrier island

  • Detached breakwater systems are constructed without any direct connection to the shore. These systems are designed to promote sediment deposition on their leeside. They are appropriate in coastlines that are prone to significant sediment transport.
  • Headland breakwater systems are constructed as a series of breakwater structures that are attached to the shoreline. Each structure is set at an angle. This helps to break up predominant wave patterns. Behind these structures, the shoreline evolves as a log spiral embayment.
  • Nearshore breakwaters are detached systems that are parallel to the shoreline. They are designed to slow down littoral drift but they produce sediment deposition and shoreline bulge.
  • Rubble mound breakwaters are constructed using an armor layer, filter layer, and a core. They are built from quarry run rock that is overlaid by large boulders. Wave action is reduced by constructing crown walls at the top of the structure.[^14]

✓ Benefits

  • Provides storm surge protection from coastal erosion by reducing wave action
  • Protects coastal infrastructure, e.g., harbors and marinas
  • Reduces longshore sediment transport behind the breakwater [^14]
  • Create and support biogenic habitats that support marine life. Biogenic habitats are developed from the activities of one or more organisms. Coldwater corals are widely recognized as a biogenic organism.

✗ Challenges

  • Increases erosion on the lee side (north side) of the breakwater which counters the positive effect of accretion behind the breakwater.
  • Offshore breakwaters may hinder onshore sediment transport and thereby prevent the rehabilitation of an eroded beach [^14]
  • Depending on the type of system and design requirements, the cost of construction and maintenance may be high [^15]
  • May lead to habitat fragmentation thereby interrupting the migration of marine species

Example projects

Citations

<! data-preserve-html-node="true"-- Regular citations --> [^1]: “Barrier Island.” Wikipedia, Wikimedia Foundation, 2 July 2019, https://en.wikipedia.org/wiki/Barrier_island. [^2]: https://www.weforum.org/agenda/2018/09/barrier-islands-protect-coastlines-but-they-are-also-vulnerable/ [^3]: “Blue Dunes– The Future of Coastal Protection.” Rebuild by Design, http://www.rebuildbydesign.org/our-work/all-proposals/finalist/blue-dunes--the-future-of-coastal-protection. [^4]: Ibid. [^5]: Ibid. [^6]: Schupp, Courtney A., et al. Coastal Adaptation Strategies: Case Studies 2015. pp. 35. https://home.nps.gov/subjects/climatechange/upload/2015-11-25-FINAL-CAS-Case-Studies-LoRes.pdf.https://www.nps.gov/subjects/climatechange/upload/2015-11-25-FINAL-CAS-Case-Studies-LoRes.pdf [^7]: Ibid, 35. [^8]: Ibid, 35. [^9]: Ibid, 35. [^10]: US Fish and Wildlife Service. (2018). What are Coastal Barrier Landforms? https://www.fws.gov/cbra/Coastal-Barriers.html [^11]: USGS. Science for a changing world. Coastal and Marine Geology program. Louisiana Barrier Islands: A Vanishing Resource, https://pubs.usgs.gov/fs/barrier-islands/ [^12]: Knotts, C. P., Grandy, G. M., & Khalil, S. M. (2007). RESTORATION OF LOUISIANA'S BARRIER ISLANDS–EVALUATION AND ANALYSIS. In Coastal Engineering 2006: (In 5 Volumes) (pp. 1977-1988). 1

<! data-preserve-html-node="true"-- Images --> [^i1]: GEOLOGY AND GEOGRAPHY OF THE NEW YORK BIGHT geo.hunter.cuny.edu [^i2]: WYX/West 8. Blue Dunes Rendering. http://www.rebuildbydesign.org/data/images/724/ap-10-6-13-1-.png. [^i3]: NPS. Barrier Islands Provide Protection for Wildlife, Plants, and Humans. https://www.nps.gov/guis/learn/nature/images/WildernessLandingPage.jpg?maxwidth=1200&autorotate=false. [^i4]: Figure 1. Baurick, T. (2020). Building barriers: Inside the race to save Louisiana's first line of storm defense. https://www.nola.com/news/environment/article_df61c669-14cc-5ba7-821d-2ee7c57becd9.html

Frank Hangler
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