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COASTAL
SUSTAINABILITY IN THE FLORIDA KEYS Jennifer Hesson & Matt Williams December 22, 2007 University of Wisconsin - Madison CEE 514: Coastal Engineering |
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Protection Devices |
Proposal |
In the next section, we will examine more natural methods of protecting the coastlines, with natural barrier reefs, and engineered reefs produced using reef balls.
Groins
A groin is an engineered structure that extends from the shoreline. This structure traps sand flowing in the longshore currents, and does not significantly protect a given area from waves. Groins are generally used in series, and trap sediment on one side, while removing sediment from the other. This process is attractive to those that will benefit from the creation of a beach, however, recession of the opposite beach will be greatly increased.
Groins can be constructed using concrete, riprap, wood, or other materials. There are advantages to each material depending on local availability and available funds for construction. Riprap, or a pile of very large rocks, is one of the most effective materials to be used for groin construction. These rocks are solid enough to absorb the wave energy. Depending on the density of the rocks placed, some water can still flow through the structure. Wood is one of the least durable materials that could be used, but in some areas it is readily available and therefore cost effective to use.
Refer to the link below for a model produced by the University of Deleware. This model allows the user to input design parameters (groin length, wave breaking angle, and shoreline diffusivity) to see the effects of sediment build up on either side of the structure.
Groin Design Animation
See the photo below showing a series of groins located in Key Colony Beach Golf Course, FL.
Refer to the following links for more information on groins and groin design.
The Effect of Groynes on Rivers
A Guide to Managing Coastal Erosion
Jetties
A jetty is an engineered structure much like that of a groin, however, it is usually larger and not used in series. Jetties are used to prevent beach erosion, but they are mainly used to protect harbor entrances from harsh currents or waves. In addition to protecting against waves, jetties also reduce the amount of sediment that is brought into the harbor area. Since jetties are larger in size, the amount of sediment generally built up and transported from the area is phenomenal.
Like groins, jetties can be constructed with many different materials. Depending on availability and cost, concrete, wood, or rocks could be used in the design.
See the photo below showing a jetty located in Lower Matecumbe Key, FL where sediment has built up on one side, and much of the sediment on the opposite side has been transported down the coast.
Refer to the following links for more information on jetty design and case studies.
Design Codes for Jetties
Erosion Study of Jetties
Breakwaters
Unlike groins and jetties that extend from the coastline, breakwaters are built offshore and unattacted to the land. Breakwaters are built both parallel or at an angle to the beach; also, they can be designed to act as a single breakwater, or as a series of breakwaters. These will prevent the full force of waves from reaching a harbor. Breakwaters also produce unnatural build up and removal of sediment along the coast.
Breakwaters can be made out of any number of materials: wood, concrete, sand, rock, or a combination of these. Each material reacts to the wave action differently, and this should be taken into consideration when designing the structure.
See the photo below showing a breakwater located in Key West, FL. Notice the uneven build up of sediment in areas where the beach is protected by the breakwater.
Refer to the following links for more information on breakwater design.
Breakwater Overview
Breakwater Design Program by Delft Hydraulics
Breakwater Case Study at Palm Jumeirah, Dubai