Friday, October 22, 2010

Get Your Swim Trunks and Flip-Flops - OCC Goes Tropical

In the Fall of 2008, OCC was asked to perform a site visit and offer preliminary engineering services for a small, privately owned island in the British Virgin Islands called Eustatia Island.  Eustatia, which is Greek for "good place to stay," was voted in 2004 by Islands Magazine as one of the 20 most beautiful islands in the world.  When OCC first visited the island, there was extensive, chronic erosion occurring along the southeast portion of the island, adjacent to the beachfront villas, threatening both the beach as well as infrastructure.  OCC was asked to design a shoreline protection and restoration project to help rebuild the beach and protect existing structures.

Filling sand-filled geotextile bags
Designing a shoreline restoration project on a small island presents a unique set of design challenges compared to a longer, more lineal shoreline.  For example, existing reefs and nearshore features play a large role in sediment transport and changing prevailing wind and wave conditions result in varying littoral drift directions from one season to another.  In addition to the normal conditions, designs must also account for tropical storms and hurricanes common in the Caribbean.

OCC's solution to the beach loss at Eustatia was to build 9 shore perpendicular, sand filled geotextile groins in the area of beach with the highest erosion.  Each groin consisted of 4-foot wide by 15-foot long by 18-inch high geobags, filled with sand, laid end to end and stacked like a pyramid with two bags on the bottom and one on the top.  The groin field was tapered with the lengths ranging from 45 feet to 120 feet, with the longest groins located in the center of the field.  The design also included a shore parallel revetment also consisting of  sand filled geotextile bags.

Construction occurred in early summer 2010 by a local contractor.  Before the last groins were even completed, the design began to work and started accumulating sand where structures were already in place.  Today, after completion of construction, the groins continue to function properly to hold the beach in front of the villas. 

In September 2010, the system endured its first real test when Hurricane Earl passed directly north of the project site.  Despite 12 hours of 100+ mph winds, storm waves pounding the beach and surge levels covering the lower parts of the island in water, the geotextile groins maintained their positions and received no structural damage.  OCC and the client were impressed with the result since the same storm managed to rip palm trees out of the beach, tear the roof off a house on a neighboring island and sink several boats. 

With the success of this project, OCC continues to develop relationships within this region and offer coastal protection solutions to other islands and beaches experiencing similar erosion problems.  However, the solution for one location will never be the same for another since there are so many variables that play a role.  It is OCC's unique experience and expertise with this type of coastal dynamic, as well as shoreline protection methods that allows us to design and implement a successful project.

For more information, contact Ed Gorleski at
Before and after shot at section of beach where erosion was so bad, roots of the palm trees were in danger.  Note the beach in front of the palm tree in the after shot.

Before and after near area of endangered seawall.

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