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The most extensive coverage of surficial sediment samples collected to date on Egypt's Nile Delta coast and shelf is needed to better define sediment dispersal patterns across this setting's rapidly eroding margin. Changes in time are now induced by River Nile sediment cutoff by dams, sea level rise, marked shelf subsidence, and regional climate changes, which have altered the amounts and components of sediments; these require replacement, along with the implementation of more effective coastal protection measures. Multiple computer-generated offshore maps depict the distributions and proportions of sand, silt, and mud; the mean grain size and standard deviation (sorting); heavy mineral concentrations; and carbonate content. Heavy mineral lobes at the coast and offshore identify former Nile branch sites. Channel lobes extending seaward resulted from their progradational phase and from the delta's altered sedimentation from the early to late Holocene. The progressive deposition and erosion of these fossil fluvial lobes, and of two active Nile channels, selectively removed their quartz and less dense minerals, thus concentrating heavy minerals on the coast and inner shelf. The prolonged dispersal of original sediment effluence from relict and recent Nile tributaries induced variable depositional patterns on the present shelf. These coastal depocenters, along with extensive sand, silt, and mud from shelf sediments, were reworked further seaward and dispersed by bottom currents, thus masking most previous onshore-to-offshore transport patterns. The major surficial features document long-term responses to the diverse dispersal that influenced the shoreline to the outer shelf deposits from the Pleistocene to the present. [ABSTRACT FROM AUTHOR]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jenvman.2006.11.018 Byline: Moheb M. Iskander (a), Omran E. Frihy (a), Ahmed E. El Ansary (b), Mohamed M. Abd El Mooty (b), Hossam M. Nagy (b) Keywords: Mediterranean Sea; Detached breakwaters; Submerged ridges; Beach management; Beach morphodynamics Abstract: Seven breakwaters were constructed behind offshore submerged ridges to create a safe area for swimming and recreational activities west of Alexandria on the Mediterranean coast of Egypt. Morphodynamic evaluation was based on the modified Perlin and Dean numerical model (ImSedTran-2D) combined with successive shoreline and beach profile surveys conducted periodically between April 2001 and May 2005. Results reveal insignificant morphologic changes behind the detached breakwaters with slight coastline changes at the down and up-drift beaches of the examined breakwaters ([+ or -]10m). These changes are associated with salient accretion (20-70m) in the low-energy leeside of such structures. Concurrent with this sand accretion is the accumulation of a large amount of benthic algae (Sargassum) in the coastal water of the shadow area of these structures, which in turn have adverse effects on swimmers. Practical measures proposed in this study have successfully helped in mitigating such accumulation of algae in the recreation leeside of the breakwaters. The accumulation of Sargassum, together with the virtual insignificant changes in the up-drift and down-drifts of these structures, is a direct response to both coastal processes and the submerged carbonate ridges. Coastal processes encompass reversal of the directions of long-shore sand transport versus shoreline orientation, the small littoral drift rate and sand deficiency of the littoral zone. The beach response to the breakwaters together with the submerged ridges has also been confirmed by applying the ImSedTran-2D model. Results indicate that submerged ridges play a principal role in the evolution of beach morphology along the west coast of Alexandria. Although the study area is exposed to more than 70% wave exposures, the morphodynamic behavior of the beaches indicates that the submerged ridges act in a similar way as an additional natural barrier together with the artificial detached structures. Author Affiliation: (a) Coastal Research Institute, 15 El Pharaana Street, El Shallalat 21514, Alexandria, Egypt (b) Faculty of Engineering, Alexandria University, Egypt Article History: Received 25 July 2005; Revised 3 November 2006; Accepted 18 November 2006

Damietta Harbour is located on the northeastern coast of the Nile delta, Egypt. Two breakwaters were constructed in 1982 to prevent the prevailing NE and SW sediment transport from shoaling the navigation channel, which extends about 20km offshore. However, the harbour channel has experienced continued sedimentation, which has affected navigation. As a result, periodic annual dredging of the channel has being carried out since 1986, averaging of 1.18 × 10[sup 6] m³/yr. To provide a basis for evaluating this problem and to provide possible mitigation, an intensive 20-month measurement program was carried out including: intensive hydrographic surveying, waves, longshore currents, littoral drift, currents seaward of the breaker zone, offshore currents and water level variation. Results of this study have led to better understanding of the factors controlling the processes of sedimentation of the navigation channel. The sedimentation process is complex and is influenced by the temporal variability in the direction and intensity of the incoming waves, currents, orientation of coastline and seafloor morphology. Sediments are transported to the sink area including the navigation channel from adjacent coastal sources at Burullus and Ras El Bar as well as from the Damietta offshore shoals by several pathways comprising the opposing NE and SW littoral drift, north-northwest and north-northeast offshore currents as well as from onshore sediment movement. Sediments are dispersed primarily away from sediment sources toward the sink area by both contour-flowing bottom and cross-shelf (seaward-trending currents). The general characteristics and interpretation of depth of closure are applied to evaluate the behavior of the harbour breakwaters versus sediment bypassing and to propose measures to mitigate this problem. [ABSTRACT FROM AUTHOR]

Beach profile data along the northeastern Nile delta, measured during the years 1971 to 1993, identify long-term seafloor and shoreline changes and sediment transport patterns. Two major zones of pronouncederosion occur in the vicinity of the Damietta Harbor and along the tip of the Damietta promontory. The erosion along the Damietta promontory is largely the result of cut off sediment supply to the coast. Inthe absence of sediment supply from the Nile river, waves and currents have strongly eroded the delta promontory close to the river mouth. Accretion continued further west in sediment sinks at the Gamasa emabyment, east of the river mouth, and locally along Manzala lagoon barrier. Based on results of profile analyses the inferred directions of transport indicate that there has been a crossshore component to the sediment movement, with erosion of the beach face and inner surf zone and the transport of the eroded sand toward the offshore as well as in the longshore direction. The spatial distributions of shoreline and bottom changes reflect the natural effect of interrupted sedimentsupply, sediment transport processes, shoreline configuration, seafloor gradient as well as impacts of the construction of protective structures. [ABSTRACT FROM AUTHOR]