![]() ![]() Wave absorbers are sometimes constructed inside harbors to dissipate short-period wave energy. Dikes are usually constructed of stone, timber pile clusters, or piling with stone fill. A common application is the use of training dikes interior to a jettied inlet to confine currents to the navigation channel and help prevent channel shoaling and erosion of nearby banks and shores. Training dikes serve to direct current flow in a desired path. These structures are used in conjunction with breakwaters and/or jetties, depending on the conditions at and configuration of the harbor. Structures besides breakwaters and jetties can help reflect and dissipate wave energy at harbors and ports. Thus, sediment transport must be addressed in jetty construction, and mitigation measure may be implemented. By blocking longshore sediment transport, jetties can impound sediment into updrift fillets and starve downdrift beaches of sand, which leads to erosion. While jetties provide the important function of reducing sedimentation in navigation channels, they also can contribute to erosion downdrift of stabilized inlets. Jetties built parallel to each other will also confine flood and ebb flow, thereby raising flow velocities and providing adequate sediment flushing into the flood and ebb deltas. Jetties should be long enough to prevent littoral transport around the jetty ends and into the navigation channel. This single-jetty configuration, however, can allow a channel to migrate and is therefore not preferable in some situations. A single jetty may also be used, located on the updrift side of the entrance. Sometimes jetties are used in combination with a breakwater. Jetties are usually built in pairs, with one on either side of a channel entrance. ![]() When located at inlets through barrier beaches, jetties help to stabilize the inlet. Jetties at the entrance of a bay or river also serve to protect the entrance channel from storm waves and crosscurrents. All breakwaters must be high enough to prevent excessive wave overtopping and sufficiently impermeable to deter wave transmission through the structure.Ī jetty is a shore-connected structure, generally built perpendicular to the shore, extending into a body of water to direct and confine a stream or tidal flow to a selected channel and to prevent or reduce shoaling of that channel. Other structural types include concrete caisson, timber crib, sheet pile, composite, and floating. Most breakwaters built on the open coasts of the United States consist of rubble-mound construction. It is also important that breakwaters be constructed to limit wave reflection, which can cause hazardous navigation conditions. It is preferable for breakwaters to prevent wave energy from entering a harbor rather than try to dissipate excessive wave energy inside the harbor. Many systems utilize a combination of shore-connected and offshore breakwaters to protect anchorage or mooring areas. But this design may have an adverse impact on water quality or sediment transport, so detached offshore breakwaters are used in certain situations. These structures must be designed to effectively serve competing requirements for wave blockage and safe vessel passage from fully exposed waters through a constricted entrance into tranquil harbor waters.īreakwaters are often constructed as shore-connected structures, thereby allowing access from land for construction, operation, and maintenance. Breakwaters reflect or dissipate wave energy and thus prevent or reduce wave action in the protected area. Breakwaters are used to protect a harbor, anchorage, basin, or area of shoreline from waves. ![]()
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