Lee side erosion/accretion in case of breakwaters of finite length Water depth / offshore distance at which the sill is placedĪccretion in the lee of a submerged breakwater as a result of oblique incident waves and significant longshore sediment tranport.The grain size of the fill material can be varied to change the profile shape behind the structure. Note that the mildly sloping natural/artificial fringing reefs work in a different way (via wave dissipation) than relatively steep and reflective submerged breakwaters.ĭimensions and position of the submerged breakwater are important design parameters, because they influence the reflection coefficient and the position of the coastal profile. Also friction damping over a wide coral reef can reduce the hydrodynamic energy arriving at the beach. Then wave breaking over the reef occurs, which limits the wave energy reaching the beach. Munoz-Perez et al (1999) found that for a natural reef-protected beach to exist, the reef width must exceed three wave lengths. Reflection coefficient as a function of the breakwater width B and wave length L, and the water depth over the breakwater d and the water depth at the toe of the breakwater h e.įringing reefs, which are coral reefs along and close to the coast, can protect the coast by dissipating wave energy, rather than reflecting it. Further derivation can be found in Gonzalez et al. Subsequently, the water depth at the landward side of the sill can be used to position the equilibrium profile and determine the shoreline advance or retreat, given the grain size of the sediment used for the nourishment. The value for R can be derived iteratively and is dependent on the breakwater dimensions (B,d), location of the breakwater (h e) and the wave length (L). R = the reflection coefficient, defined as H r/H e, the reflected wave height divided by the incoming wave height. H e = the water depth at the seaward side of the structure, The water depth directly at the landward side of the sill (h i) is a function of the ratio between incoming and reflected wave energy: Also friction-induced attenuation over the structure is negligible, so wave reflection is then the main process determining the amount of wave energy arriving at the beach. (1999) argued that submerged breakwaters or sills generally are too narrow to have significant wave energy dissipation by breaking. The design of the submerged structure determines the amount of wave energy that passes the structure and arrives at the beach. He also found that the parameter A depends on the fall velocity of the sediment and derived an empirical relation for the parameter A (see above). This revealed that at this coast the third mechanism is dominant, resulting in a value of 0.67 for the parameter m. For this purpose, Dean (1977) compared 502 beaches at the east coast of the United States. This is based on the assumption of spilling breakers: H = 0.8 * h.įield data were used to verify the analytical solution and to tune the parameters A and m.
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