Pattern of Beach Erosion and Scour Depth along the Rosetta Promontory and their Effect on the Existing Protection Works, Nile Delta, Egypt

• Published in: Journal of coastal research 2008-07, Vol.24 (4), p.857-866
• Main Authors: Frihy, Omran E., Shereet, Samy M., El Banna, Mahmoud M.
• Format: Article
• Language: English
• Subjects: 20th century; Accretion; Beach erosion; Beach profiles; Beaches; Coastal erosion; Coasts; Dams; depth scour; Estuaries; Grain size; littoral cells; Marine; Mediterranean; Nile Delta; nodal points; Ocean floor; Promontories; River deltas; Rosetta seawall; Sand; Sand & gravel; Scour; Sediment transport; Sediments; Shoreline protection; shoreline rate-of-change; Shorelines; Soil erosion; Wave refraction
• ISSN: 0749-0208; 1551-5036
• DOI: 10.2112/07-0855.1

Beach profiles surveyed over a period of 18 y (1982 to 2000) at 41 sites were analyzed to assess beach changes, seabed scour, and grain sorting pattern fronting the 5 km long seawall built in 1991 to protect the Rosetta promontory from beach erosion, which had been retreating at a rate of −106 m/y. Although the seawall has succeeded in halting the recession, the shoreline shows adverse erosion at the leeside of the seawall ends (−14.4 m/y) associated with depth scour at a maximum of −0.50 m/y. The erosion along the promontory tip progressively decreases with longshore distance both to the east and to the southwest along the promontory flanks, reverting to accretion on both sides within the promontory saddles and yielding two nodal areas that represents zones where the sediment regime changes from erosion to deposition. Moreover, the seawalls have slightly altered the mean grain sizes of the beach sediment and seabed slope of the surf zone. The overall pattern of beach erosion and seabed scour results from wave refraction–induced longshore sediment transport along the promontory tip. The geographic correspondence between patterns of shoreline and seabed depth changes serve to refine boundaries of littoral subcells of the Rosetta promontory, including sediment paths, sources, sinks, nodal points, and zones of sediment transport convergence and divergence. The morphologic changes along this promontory reflect a combination of factors, including sediment availability, transport pathways from source areas, as well as the impact of protective structures at the Rosetta estuary.