EROSION AND ACCRETION REGIME AND THEIR ASSOCIATED SEDIMENT CHARACTERISTICS ALONG NORTHERN COAST OF MANZALA LAGOON, NE NILE DELTA, EGYPT

The Manzala lagoon is one of the main coastal lagoons of the Nile delta with extensive wetlands which form a highly productive buffer zone between the Mediterranean Sea and the uplands to the south. This is the largest coastal lagoon in Egypt significant for both tourism and gas exploration. Sediment samples collected from the 40 km long beach of the Manzala lagoon, NE Nile delta have been analyzed for sedimentological and mineralogical investigations to identify beach and back-shore sediment changes.

Several man-made breakwaters constructed at the breaker zone to protect the villages and to promote tourism affected the distribution of sediment types. Along the coast of Manzala lagoon, two sectors of accretion and one of erosion have been recognized. The first accretion sector is located west of the Manzala lagoon, which has been fed by sediments from the eastern part of Damietta promontory. The second accretion sector is located behind the system of detached breakwaters at the eastern part of the Manzala lagoon. The erosion sector is located in the northcentral region of the Manzala lagoon. Sediments from the accretionary areas are characterized by dominance of very well- to well-sorted very fine sands. Sediments of the eroded sector are characterized by moderately- to well-sorted medium to fine sands.

Abundance of heavy minerals in the sands of the study area ranges from 0.2% to 29.42%; the higher amounts are observed in the erosional sector. The wave induced hydrodynamic processes lead to the concentration of relatively coarse sands and abundance of heavy mineral concentrations in the eroded sector. The dominant constituents of heavy mineral species in beach sands are opaques (i.e., magnetite and illmenite), amphiboles (i.e, hornblende), pyroxenes (i.e., augite) and epidote with smaller amounts of rutile, tourmaline, zircon, garnet, staurolite and kyanite. The dominant constituents of heavy mineral species in beach sands of the Manzala lagoon show similarity with heavy minerals reported from the Nile sediments suggesting that the sediments on the beach of Manzala lagoon area represent the Holocene clastics delivered by the old Nile distributaries.