GEOL 2503 Introduction to Oceanography
Dr. David M. Bush
Department of Geosciences
University of West Georgia
Topic 19. Shoreline Engineering
POWERPOINT SLIDE SHOW NOTES
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Topic 19. Shoreline Engineering
The current time of rising sea level is causing erosion on most shorelines around the
world. There are three main ways that coastal communities can deal with erosion.
Engineering structures are built to combat erosion with brute force. Structures are built
either perpendicular or parallel to the shore depending on the needs.
A seawall attempts to create a shoreline that is fixed in place. However, shorelines are
mobile features, moving with waves, tides, sea-level changes, and storms. Over time, as
storms remove sand from in front of seawalls, larger and larger seawalls must be built.
A South Carolina where the condo is now a seawall. The recreational beach is the dry
portion of the beach. It is above high tide and the part of the beach we want to lay out
our beach towels and enjoy the sea, sand, and surf.
In Puerto Rico, the seabreeze often causes enough wave energy to submerge the
recreational beach.
NewJerseyization is the name given to the complete loss of the recreational beach by
continued engineering.
Sinking islands in the Gulf of Mexico are in caused mostly by natural compaction of the
sediment, but also by withdrawal of oil and natural gas.
Note how the recreational beach has disappeared in the foreground where these Puerto
Rico houses have essentially become seawalls. However, in the distance there are no
seawalls. This has allowed the natural beach to survive and a wide recreational beach
remains.
Groins are a type of shore-perpendicular engineering structure built to capture the
longshore sediment transport. The result is a buildup of sediment on the upstream side
of the groin, but erosion of sediment on the downstream side. Jetties are usually shorter
than 100 feet in length.
Jetties are large shore-perpendicular structures built to stabilize and inlet for navigation
purposes. Some may be more than a mile long.
Breakwaters are shore-parallel structures built to block waves and create quiet water
behind them. They often lead to unwanted deposits of sediment.
The bulge in the shoreline behind this breakwater is caused by the slowing of longshore
transport because of waves being blocked by the breakwater.
Inlets stabilized with jetties tend to infill with sediment, requiring constant dredging to
maintain the navigational channel.
Soft stabilization, or beach nourishment, are attempts to maintain a beach by bringing
sand in from other locations. In the long run it is more costly than hard stabilization.
A replenished beach often has an unnatural profile, indicative of waves eroding into the
replenished sand and eventually smoothing out the profile by carrying sand offshore.
Beach nourishment projects are major engineering undertakings.
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Sometimes soft stabilization can be as simple as adding sand fencing to trap wind-blown
sand as in this Tybee Island example. However, this is not where sand dunes would form
naturally, and the beach profile will be out of balance just as with replenishment.
Relocation, or coastal retreat, is the cheapest response to an eroding shoreline in the
long term, and the most environmentally sensitive. However, it is almost impossible
politically because people who own property right on the shoreline rarely want to move
inland. Plus, these homeowners are usually are very wealthy and politically connected.
Relocation is not new. This is a sketch of a large hotel on Coney Island, New York, being
relocated in 1888.
Moving a single family home after Hurricane Hugo (1989), Myrtle Beach, SC.
Moving the Cape Hatteras Lighthouse, one of the most famous lighthouses. See
http://www.nps.gov/caha/historyculture/movingthelighthouse.htm
The lighthouse was moved in 1999.
Moving the Cape Hatteras Lighthouse.
The Beaches are Moving video. Before you watch the video, review the questions on the
following slides. The video can be accessed online at:
http://video.unctv.org/video/2365007946/
If you have trouble viewing it, try a different web browser. That worked for me.
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.
1. What is a beach?
2. How does sand move on beaches: onshore, offshore, alongshore, including beach
recovery after a storm?
3. What are tidal inlets and their associated flood tidal deltas and ebb tidal deltas?
Address inlet movement: breathing, migrating, jumping.
4. Discuss original formation of barrier islands beginning 15,000 years ago and
subsequent barrier island migration, including evidence of barrier island migration.
5. What does Dr. Pilkey mean when he says "Shoreline erosion is not island destruction,
but island retreat?"
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 an island?"
7. Discuss the impact of development on natural barrier island environments.
8. Know what seawalls, jetties, and groins are. Discuss the impact of hard shoreline
stabilization on natural barrier island environments.
9. What is beach replenishment? Discuss when this option would be appropriate.
10. What is relocation? Discuss when this option would be appropriate.