A study has been conducted to develop a new design of Low Crested Structures (LCS) along the North-
West coast of Egypt to protect swimmers from high waves and the shoreline from erosion while
maintaining good circulation conditions. The wind/wave conditions and bathymetric survey along the
study area have been used and the coefficient of wave transmission has been computed using various
equations in literature as well as some numerical models, e.g., BEM-FEM, SMS. The latter models have
been adopted to simulate the dynamic interactions among waves and a submerged breakwater for various
wave conditions. The BEM-FEM and SMS models have compared with experimental results. The
breakwater is suggested at a water depth of 8.0m and a few hundred meters offshore. Various dimensions
and internal properties of the breakwater have been considered and the transmitted wave conditions have
been estimated. Comparisons have also been made among the transmitted wave coefficients computed by
various empirical formulae and the numerical models. It has been noticed that the wave transmission
coefficient computed by the numerical models are very similar to those computed by [1, 2, 3]. However,
the BEM-FEM model predicts slightly higher values for the coefficient of transmission than most
empirical formulae. It has also been found that a submerged breakwater with its crest height equals 63%
of the water depth and its crown width is about half the incident wave length, or alternatively the crest
height is 75% of the still water depth and its crown width is 25% of the incident wave length, would
produce a trasnmission coefficient of approximately 60% for an incident wave height of 2.5m along the
North-West coast of Egypt. On the other hand, the coefficient of transmission for the prevailing wave
conditions (H=1.0m for about 25% of the year) has been found to range from 75% to 90% as computed
by various empirical formulae in literature. The proposed design would allow wave heights (Ht) < 1.5m
for 97% of the year and Ht >0.5m for 61% of the year. Thus, wide-crown LCS can be an effective tool in
limiting the wave heights in the area between the submerged breakwater and the shoreline while
maintaining good circulation and limited shoreline changes. |
