Topic 19Shoreline Engineering

GEOL 2503

Introduction to Oceanography

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Responses to an Eroding Shoreline

• Hard Stabilization– Seawalls, groins, breakwaters, etc.

• Soft Stabilization– Beach replenishment, dune building

• Relocation or retreat– Move back from eroding shoreline

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Engineering Structures

• Shore Perpendicular– Groins used to prevent erosion of sand by longshore

transport– Jetties and breakwaters to prevent longshore transport

of sand into ports and harbors• Shore Parallel

– Sea walls and bulkheads to prevent wave erosion when real estate is threatened

• All these measures upset shoreline equilibrium and damage the natural system

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Seawalls lead to loss of the recreational beach, and require continued maintenance

5If an eroding beach meets a seawall, the recreational beach narrows

6A tropical paradise no more

7NewJerseyization—the complete loss of the recreational beach

8Sinking islands in the Gulf of Mexico leads to generations of seawalls

9Houses become seawalls along this Puerto Rico beach

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Groins and groin fields

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Jetties

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Breakwaters

Fig. 10.24

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Shore Protection Projects- Breakwaters

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Waterway NavigationWaterway Navigation

Jetties

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Soft Stabilization (Beach Nourishment)

• Advantages– Widens the beach– Protects buildings while beach is in place

• Disadvantages– Temporary– Costly– Unknown environmental effects

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Beach NourishmentBeach Nourishment

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Relocation or Retreat

• Advantages– Responds to sea-level rise– Preserves the beach– Saves shoreline stabilization costs– Preserves buildings

• Disadvantages– Politically difficult– Potentially costly– Loss of land

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Moving the Cape Hatteras Lighthouse

Built 1600 feet back from shore in 1870. Threatened by erosion.

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Moved inland until again 1600 feet from shore

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Light and auxiliary buildings moved and new site designed to look like original

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“The Beaches are Moving” Video

• Hosted by Dr. Orrin Pilkey, one of the world's leading authorities on barrier islands, this video discusses coastal processes and the impacts of human development and engineering. The video deals mostly with North Carolina's islands, but is applicable to all barrier coasts.

• As you watch the video, think about Georgia's islands and how the topics discussed might apply to our islands.

• The video can be accessed online at: http://video.unctv.org/video/2365007946/

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Questions

• The following slides list several terms, names, and concepts with which you should be familiar after seeing the video. Think about these things as you watch the video. You should be able to answer each of these questions.

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1. What is a beach?

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2. How does sand move on beaches: onshore, offshore, alongshore, including beach recovery after a storm?

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3. What are tidal inlets and their associated flood tidal deltas and ebb tidal deltas? Address inlet movement: breathing, migrating, jumping.

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4. Discuss original formation of barrier islands beginning 15,000 years ago and subsequent barrier island migration, including evidence of barrier island migration.

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5. What does Dr. Pilkey mean when he says "Shoreline erosion is not island destruction, but island retreat?"

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6. What should we have learned by the original patterns of island development as practiced by the American Indians and by the earliest settlers? How does this relate to Dr. Pilkey's statement that we should learn to "live with an island, not just on and island?"

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7. Discuss the impact of development on natural barrier island environments.

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8. Know what seawalls, jetties, and groins are. Discuss the impact of hard shoreline stabilization on natural barrier island environments.

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9. What is beach replenishment? Discuss when this option would be appropriate.

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10. What is relocation? Discuss when this option would be appropriate.