Comparison of Annual Rates of Beach Changes Determined from Land Survey and Remote Sensing Techniques along the Coastline of the Nile Delta, Egypt

Abstract

Analyses have been undertaken to examine shoreline changes established from remote sensing data and ground survey at a total of 48 positions and beach profiles along the coastline of the Nile delta during 16-year period from 1984 to 2000. Multidate satellite dataset from Landsat TM and ETM sensors covering the Nile delta and refer to summer 1984 and winter 2000, respectively, have been utilized for mapping shoreline and calculating the average rate of beach changes between the two dates. Rates estimated from the two methods at corresponding positions show high correlation coefficient of 0.99 (significant at 99% level). The erosion and accretion patterns have been identified both on large- scale along the entire delta and locally at coastal sectors which are being experienced significant beach changes. The results reveal longshore patterns wherein erosion along a coastal stretch gives way to accretion in an adjacent stretch, refining the sub-cells previously identified within the littoral system of the delta. Maximum shoreline retreat occurs along the delta promontories, Rosetta [-96 m/yr (land survey); 102 m/yr (remote sensing)] and Damietta [-13 m/yr (land survey); -14.5 m/yr (remote sensing)]. Significant erosion has also occurred along the central bulge of the delta at Burullus headland, but at a lesser rate [-5.5 m/yr (land survey); -5.4 m/yr (remote sensing)]. Areas of shoreline advance exist within saddles or embayments between the promontories [maximum of 16.8 (land survey); 18.38 (remote sensing) at Abu Khashaba saddle] and also at updrift jetties [5.6m/yr (land survey) 5.3 m/yr (remote sensing) updrift of Burullus lake inlet-jetty]. On a coast-wide scale, the longshore transport rates of changes are affected locally by shoreline orientation versus incident waves and by the construction of protective structures built to combat areas of rapid erosion. The identified patterns of erosion versus accretion along the delta coastline have been ascribed to effect of the wave-induced longshore currents and sediment transport. These processes fluctuate in intensity and direction due to the degree of shoreline orientation and the existence of coastal protective structures.