Damietta Harbour is located on the northeastern coast of the Nile delta, Egypt. Two breakwaters were constructed in 1982 to prevent the prevailing NE and SW sediment transport from shoaling the navigation channel, which extends about 20km offshore. However, the harbour channel has experienced continued sedimentation, which has affected navigation. As a result, periodic annual dredging of the channel has being carried out since 1986, averaging of 1.18 × 10[sup 6] m³/yr. To provide a basis for evaluating this problem and to provide possible mitigation, an intensive 20-month measurement program was carried out including: intensive hydrographic surveying, waves, longshore currents, littoral drift, currents seaward of the breaker zone, offshore currents and water level variation. Results of this study have led to better understanding of the factors controlling the processes of sedimentation of the navigation channel. The sedimentation process is complex and is influenced by the temporal variability in the direction and intensity of the incoming waves, currents, orientation of coastline and seafloor morphology. Sediments are transported to the sink area including the navigation channel from adjacent coastal sources at Burullus and Ras El Bar as well as from the Damietta offshore shoals by several pathways comprising the opposing NE and SW littoral drift, north-northwest and north-northeast offshore currents as well as from onshore sediment movement. Sediments are dispersed primarily away from sediment sources toward the sink area by both contour-flowing bottom and cross-shelf (seaward-trending currents). The general characteristics and interpretation of depth of closure are applied to evaluate the behavior of the harbour breakwaters versus sediment bypassing and to propose measures to mitigate this problem. [ABSTRACT FROM AUTHOR]