Long-term shoreline changes and the concentration of heavy minerals in beach sands of the Nile Delta, Egypt

Abstract

Analyses have been undertaken of shoreline positions established from beach profile surveys at 65 positions along the coastline of the Nile Delta spanning the years 1971 to 1990. The analyses identify long-term linear trends as well as any cycles in the horizontal movement of shoreline positions. The results reveal longshore patterns wherein erosion along a stretch of coast gives way to accretion in an adjacent stretch, defining a subcell within the overall littoral system of the delta. The rate of shoreline retreat has been greatest along the Rosetta promontory (− 106 m/yr) and Damietta promontory (− 10.4 m/yr). Significant erosion has also occurred along the central bulge of the delta coast, but at a lesser rate (− 6.5 m/yr). Areas of accretion exist within the saddles or embayments between the promontories, with the maximum shoreline advance averaging about 13 m/yr. The identified patterns of erosion versus accretion along the delta reflect the natural processes of wave-induced longshore currents and sediment transport. Associated with this longshore sediment movement is a selective transport of different minerals according to their densities and grain sizes, with the light minerals (quartz and feldspar) having the highest advection rates and the dense opaque minerals the lowest rates, tending to remain behind as a lag within the erosion areas. As a result of this longshore grain sorting paralleling the patterns of shoreline erosion versus accretion, there are correlations between the rates of shoreline change and the heavy-mineral contents and mean grain sizes of the beach sediments. These large scale delta-wide patterns are affected somewhat by local shoreline changes and mineral variations induced by the construction of jetties or shoreline protection structures.