In Egypt, the construction of the Aswan High Dam and others on the Nile River has caused extreme erosion problems at the Nile Delta, where whole villages have disappeared as the shoreline has retreated at rates of 30 to 50 m/yr! Before construction of the dams for flood control, irrigation, and water supply, the Nile delivered about 20 million metric tons of sediment annually to the Mediterranean Sea. This sediment supply resulted in two large deltas (Damietta and Rosetta), which extend 50 km into the sea. As each of the dams on the Nile was completed, the reservoir behind the dam began to capture a significant portion of the annual riverine sediment load.

To combat the ensuing erosion, large coastal structures have been placed along the shoreline near the river mouths to limit further shoreline retreat. Nevertheless, erosion is continuing in water depths below the base of the structures, and storm waves are attacking the coast with increasing intensity.

Surprisingly, the length of shoreline affected by the erosion is relatively short. Further, field measurements conducted by the Alexandria Coastal Research Institute show that, farther from the river mouths, the shoreline continues to advance in response to the prior era of abundant sediment supply and delta building.

INTRODUCTION

The world's coastlines, dividing land from sea, are geological environments unique in their composition and the physical processes affecting them. Many of these coastlines have beaches composed of loose sediments such as gravel, sand, or mud that are constantly acted upon by waves, currents, and winds, reshaping them continuously.