THE EFFECTS OF BALTIM DETACHED BREAKWATERS ON THE GRAIN SIZE VARIATIONS AND LITTORAL SAND DRIFTS, EGYPT

THE EFFECTS OF BALTIM DETACHED BREAKWATERS ON THE

GRAIN SIZE VARIATIONS AND LITTORAL SAND DRIFTS, EGYPT

BY

ABD EL MONEIM A. BADR*AND MOHAMED M SHATA

• Coastal Research Institute. 15 El Pharaana St., Elshalalat, 21514 Alexandn’a, Egypt.
…National Institute ofOceanography and FLsheries andfISheries
Key words: Grain size, hydrodynamic forces, sediment transport
ABSTRACT
Baltim sea resort is located on a very active dynamically convex
shoreline some 120 km to the east ofAlexandria. The beach resort area of
Baltim is located on a very active shoreline which has experienced a net
long-term shoreline retreat of about 4-5 m/year. An intensive protective
structures consisting oj a series of emerged detached breakwaters were
built to reducecoastal erosion at this resort beach . The present
investigation attempts to study the afficts ofBaltim detached breakwaters
on the variation of grain size and littoral sand drifts. Coarser peak of
mean grain size is observed at the 300 m distance ofprOfile no.2 for the
period 1992-1997. This peak could be related to Baltim detached
breakwaters which were built between 1991 and 1998. Also, median
diameter ofsand behind the detached breakwater has decreased steadily
with time and with secrward advance ofthe sand wedge into increasingly
protected zones. The eastern down-coast ofBaltim detached breakwater
(no. 4) suffiredfrom severe erosion. The total annual erosion drift rate at
the down drift Side of these beaywaters was estimated to be 2.68 x 106
mJ/year. This erosion normally resulted from the tombolo sandformations
trapped behind the detached breakwaters, which have totally interrupted
the longshore sand movement trending east. On the other hand, the annual
accretion drift rates at upcoast of the detached break- water were found
1.92 x 106 & 1.96 X 106 m3
/year, respeotively.