Active erosion hotspots at the leeward sides of hard-engineered structures installed along the coastline of Egypt’s Nile Delta

An analysis of measured historical shoreline changes identifies five active erosional hotspots (EHSs) at the downdrift sides of the hard engineered structures constructed along Nile delta coastline, ~ 220 km long. The annual beach change rates at these hotspots, estimated by the Digital Shoreline Analysis System (DSAS), involve shoreline positions surveyed prior to and post-date of these structures (groins, jetties, and shore-parallel detached breakwaters). The observed elevated erosion rates in these cases range from 14.5 to 40.7 m/yr and extend alongshore for distances of 0.7 to 3.7 km. Morphodynamic processes leading to the erosion at these hotpots are interpreted on the basis of the integrated angle of wave breaking (α _b ), the slope of the seabed, wave-induced longshore current, and the and the sizes of beach grain sediment. On a regional scale, the numerous hard structures installed for various purposes have significantly disrupted the original shoreline configuration and depositional patterns along the entire length of the delta shores, as well as the sediment transport regime of the associated littoral subcells. This disruption is due to the various alternating patterns of local upcoast accretion and down-drift erosion occurring at the hard structures. A suitable environmentally friendly alternative to hard protection measures is proposed to tackle beach erosion at the identified hotspots.