The changes caused by the deployed reefs also facilitated seaward expansion of the salt marsh. On the lee side of the reefs, there was accretion of 29 cm clayey sediments with erosion reduction of 54% as compared to control sites. Waves were totally blocked by the vertical relief of the reefs at water levels <0.5 m. The reefs were able to dissipate wave energy and act as breakwaters for tidal water levels between 0.5–1.0 m. The observed wave heights in the study area ranged 0.1–0.5 m. This was done over four seasons, including the rainy monsoon period. Data were collected on wave dissipation by the reef structures, changes in shoreline profile, erosion-accretion patterns, and lateral saltmarsh movement and related growth. Three breakwater reefs with recruited oysters were deployed on an eroding intertidal mudflat at Kutubdia Island, the southeast Bangladesh coast. A field experiment was undertaken to assess the benefit of oyster breakwater reefs to mitigate shoreline erosion in a monsoon-dominated subtropical system. Breakwaters may be either fixed or floating: the choice depends on normal water depth and tidal range.Oyster reefs have the potential as eco-engineers to improve coastal protection. The amount of deposition depends on the site characteristics and the design of the breakwater. However, the beach behind the breakwater often grows at the expense of the shoreline that is not protected by the structure. The dissipation of wave energy allows material carried by longshore currents to be deposited behind the breakwater. They act as a barrier to waves, preventing erosion and allowing the beach to grow. Sand starvation and retreat of the shoreline on the downdrift side are possible.īreakwaters are barriers built offshore to protect part of the shoreline. Jetties also prevent littoral drift and storm waves from entering protected channels. Sand that builds up against the jetty can be redistributed along the beach. Erosion prevention is another benefit of jetties. There are often two jetties used, one for each side of the channel. Their main function is to keep sand from flowing into a ship channel, which would make the channel increasingly shallow over time (shallow waters cause for ships to run aground). They are constructed of timber, stone, concrete, or steel. Jetties are long structures built perpendicular to the shoreline and extending out into the ocean. Once one groin is put into place, another is needed at the beach next door. This process often leads to a domino effect. Wherever sand on one beach is increased, other beaches down the coast lose a lot of sand. Although this method of ceasing beach erosion can be very effective, its drawbacks are obvious. However, as the current passes the groin it picks up additional sediment on the downcurrent side of the structure. A longshore current will lose velocity as it meets the groin, causing the current to dump part of its sediment load on the upcurrent side of the groin. Their purpose is to act as barriers to longshore currents in order to control or modify sand movement. Groins are constructed of stone rip rap, steel sheet pilings, or timber pilings. Groins are long, wall-like structures built along beaches that extend out into the ocean. Examples include groins, jetties, and breakwaters. Humans have devised many different ways of doing this. Protecting human-built structures from coastline erosion has been going on for centuries. They include lighthouses, commercial shipping ports, hotels, recreational marinas, and houses. There are many kinds of human-built structures that can be found on coastlines. The desire to build structures on coastlines has often interfered with the natural erosion processes.
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