Change detection of the northeastern Nile Delta of Egypt: Shoreline changes, Spit evolution, margin changes of Manzala lagoon and its islands

Abstract

Rapid changes, natural and anthropogenic, across the Damietta promontory of the Nile delta have been analyzed by undertaking comparisons of Landsat satellite image data, acquired in 1978, 1983, 1990, 1993 and 1995. These images were utilized together with a series of topographic maps dated 1909, 1922, 1944 and 1955 to cover a 86-year monitoring period. Changes documented in this study include: areas of shoreline erosion and accretion, evolution of Damietta coastal spit and changes in the lagoon margin and contiguous islands. The analysis describes areas of erosion along the promontory tip adjacent to the river mouth (-0.51 km2 yr-1) reverted to downcoast accretion along the promontory flank (0.30 km2 yr-1). Part of this sand is carried south-west along the shoreline as a seaward sand spit. This spit is actively migrating to the south-east (0.17 km yr-1) and is accompanied by changes in width (0.06km yr-1). Local areas of erosion and accretions are also detected along the Manzala lagoon sand barrier. The pattern of erosion versus accretion along the coast of the Damietta promontory is attributed to the construction of dams on the upper Nile River, first the Aswan Low Dam in 1909 and particularly the Aswan High Dam in 1964 that cut-off almost all water discharge from the river and the delivery of sediments to the coast. In the absence of a sediment supply, the continued transport of beach sand by waves and currents toward the east has resulted in beach erosion of the promontory close to the river mouth, while shoreline accretion has continued further to the east. An analysis of changes of the total area of Manzala lagoon has indicated that the lagoon has progressively shrunk in size with an average rate of 5.2km2 yr-1, while its embeded islands have accreted at 2.93km2 yr-1. The changes in the lagoon area and islands have resulted from extensive reclamation of the lagoon margin, weed growth and siltation processes.