Influence of shoreline erosion and accretion on texture and heavy mineral compositions of beach sands of the Burullus coast, north-central Nile delta, Egypt

Abstract

Shoreline changes result from shoreline orientation and jetty construction are investigated at the central sector of the Nile delta, on the basis of systematic beach profile surveys spanning the years 1971 to 1992. Maximum accretion (4.9 m/yr) occurs along the western barrier due to construction of the west jetty on the Burullus lagoon inlet, whereas, greatest erosion (−5.5 m/yr) about 3 km east of the Burullus inlet dominated along the unprotected sector of the eastern barrier. Beach-sand composition is, in part, relict, reflecting an alongshore mineral sorting of sediments of former Sebennitic branch. Two heavy-mineral groups “factors” were obtained by applying Q-mode factor analysis on the heavy-mineral data of the beach sand. One factor (group) is dominated by augite, hornblende and epidote, whereas, the second consists of opaques, garnet, zircon, rutile and monazite. These two factors are influenced by both the selective sorting of heavy minerals and point sources of relict sediment. Factor 1 is associated with the accreted coarse-grained sand west of the jetty derived from the Rosetta branch farther west, whereas, factor 2 tends to concentrate in fine-grained sands at eroded beach related in part to the former Sebennitic beach. The identified pattern of deposition on the updrift side near the west jetty and erosion near and at greater distance from the east is reflected in sand size and mineral composition of beach sand. These patterns reflect the natural processes of wave-induced longshore current and sediment transport. There are correlation between the rates of shoreline change and the heavy mineral groups and mean grain sizes of the beach sediments.