الفهرس | Only 14 pages are availabe for public view |
Abstract • Beaches are in a delicate balance between sand supply and natmaI forces of erosion. Beaches can be divided into eroding, stable, or accreting depending on the rate of supply and loss of littoral sediments. Beach erosion is for the most part episodic, with major retreats in the shoreline occurring during usually intense storms (Komar, 1983). The shore is considered stable when the longshore rates of supply and loss are equal. Beach erosion induced from sea level rise, land subsidence, storm waves, reduction of sediment supply to the littoral zone, removal of loose material from the beach by wind action, longshore sediment transport, sorting of beach sediments and mans interventions (dams, protection works, removal of material from the beach). The principal source of sand transport to beaches include: rivers, sea- clift7dune erosion, and material. of biologic origin, such as shells, coral fragments, and skeletons of small marine organisms. Waves are responsible for driving the nearshore currents system which, in turn, is responsible for the important process of longshore sediment transport. When waves approach the coast at an angle, they cause sand to be transported along the shore i.e. longshore sediment transport (CERe, 1984). ThisIongshore current, under certain conditions, may turn and flow seaward in which is known as a rip current Qnman and Brush, 1973). Longshore transport results from the stirring up of sediment by the breaking wave and the movement of this sediment by the wave energy in an alongshore direction. At the breaker line, as the waves break, great disturbance takes place due to dissipation of the wave energy. Longshore transport is divided into two general classes: transport parallel to the shore Qongshore transport) and longshore perpendicular to the shore (cross-shore transport). The material that is transported is called littoral drift (CERe, 1984). The Rosetta promontory is one of the most important areas for trade, agriculture and fishing activities in the northwestern coast of the Nile Delta, The Rosetta cityused to have a great importance since the latest Pbaraonic periods. |