Patterns of erosion/sedimentation, heavy mineral concentration and grain size to interpret boundaries of littoral sub-cells of the Nile Delta, Egypt

Abstract

Analyses have been undertaken of 68 beach-nearshore profiles spanning the years 1971–1995 to interpret sub-littoral cells of the Nile Delta that developed during cross-shore and alongshore sediment transport. Bottom sediments of these profiles taken along the 240-km length of the delta coastline have been analyzed to determine seabed level changes, textural and heavy mineral concentration distributions. The spatial distribution of seabed depth changes linked with the heavy mineral concentration allows identification of three zones of erosion (source areas) associated with accretion (sink areas). Erosion zones occur off the Nile promontories at Rosetta (−20 to −50 cm/yr), Burullus and Damietta (0 to −20 cm/yr). Accretion ranging from 0 to 40 cm/yr occurs between erosion zones at Abu Quir Bay, the Rosetta saddle, Gamasa embayments and along the western side of the jetty at the Suez Canal entrance, Port Said. This pattern was generally induced from the temporal variability in the direction and intensity of the incoming waves, currents, orientation of coastline, seafloor morphology and local protective structures. The correspondence among patterns of seabed depth change, heavy mineral concentration, and to some extent the texture of seabed sediments refine boundaries of littoral sub-cells of the Nile including sediment paths, sources, sinks, nodal points and zones of sediment transport convergence and divergence. This correspondence is not strongly correlated, as might be expected in this deltaic system where sediment has been recycled between recent and relict seabed settings moving in the alongshore and cross-shore directions. Nevertheless, the present investigation shows that the relationship between seabed level changes, heavy mineral concentration and to some extent mean grain size of the littoral zone can be practically applied in other deltaic settings to interpret sediment transport pathways particularly where there are less relict sediments.