The impact of construction of detached breakwaters on wave system and sea currents

Seven detached breakwaters were built at a depth of 3–4 m between 1998 and 2003 to provide a safe area for swimming and recreational activities in El Nakheel beach west of Alexandria on The Egyptian Northern Coast. The purpose of this research is to investigate the velocity, pattern, and direction of sea currents, and study the hazard rate (HR) of swimming at various water depths due to sea current velocity, in addition to verifying the relation between these currents and the number of sinking accidents in the vicinity of the study area. The generated currents by existing pattern of the seven detached breakwaters were simulated by the numerical model Delft-3D. Four scenarios of detached breakwaters were studied. These scenarios included changing in the structural design of the existing breakwaters, such as reducing some of gaps or adding new breakwaters or transferring them to different depths. The generated currents in scenario (1), which suggested using emerged breakwaters to fully close some gaps between detached breakwaters by 50%, had the lowest velocity (0.25 m/s) with minimum circulation and rip pattern and their direction was mostly parallel to the shoreline. The hazard rate (HR) of swimming at a depth of 1.50 m in this scenario was 1.125 m2/sec and it is a suitable rate for most swimming age groups.