الفهرس 
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Abstract
The development of a coastal mea is needed for tourism and eOlllll1crciul purposes. this development affects the equilibrium of the coast. Consequently, the coastal area undergoes accretion and erosion in sandy beaches, which can be a severe problem. An offshore breakwater can be used to create calm water for recreational usage and may cause this problem. The offshore detached breakwaters are parallel to the shore and located at a specific distance from the original shoreline. The response or the shoreline to these structures is governed by at least 14 geometric-, wave-, and sediment-related , variables. To understand the influence or detached break waters on the physical process as well as the morphological evolution, physical models or numerical models are developed. The numerical models do not s1:1ffer’ from the scale effect. In this study, a. numerical model of shoreline change is used The data for the model calibration are prepared by making a survey to the shoreline and analyzing the grain size distribution at Marabella Village. The model is used to predict the shoreline, based on statistical yearly wave climate of Egyptian Northern-Coast. It was found. from the prediction model that the erosion in down drift is still going on under many alternative conditions. Also it was found from the simulation of different alternatives (nourishment, mechanical bypassing, groin,), that the semi-lransl1arent offshore breakwaters are very suitable in such coasts. the study consists of the following:
• Problem formulation.
• Wave data collection, measuring shoreline position. and grain size analysis
• Model calibration to use it to predict the shoreline positions.
• Simulating the shoreline positions for different alternatives.
• Selecting the most suitable solution, that minimizes the shoreline changes, while keeping the wave heights within the allowable limits. Finding the relationships between the width of the gaps and breaking wave heights, and the relationships. between the transmission coefficient and the formation of shoreline behind the four detached breakwaters.