Solving A Harbour Sedimentation Problem In Yemen

Abstract

The Ash Shihr, Yemen harbour on the Gulf of Aden was built in 1992193 by Nexen Inc. for the vessel fleet supporting the loading of oil into large tankers at the offshore Single Buoy Mooring (SBM). In designing the harbour, the greatest emphasis was placed on ensuring that the harbour provided effective shelter during the SW summer monsoon season, which can generate deep water waves of up to about 6.4 m significant wave height with a period of 14 seconds. This led to the harbour entrance being placed on the east side of the harbour to minimize wave agitation within the harbour. The dominant factor proved to be the littoral drift of sediment in a westerly direction. This led to the migration of large amounts of sediment into the harbour and the build up of sand on the beach well to the east of the harbour. As this situation developed it was effectively closing the harbour. A sedimentation study of the harbour was performed by Delft Hydraulics [l]. Various solutions were considered including by-pass maintenance dredging, a dredged sand trap, relocating the harbour entrance, and shielding the harbour with a sand trap breakwater. Westmar Consultants Inc. provided the detailed design for a 600 metre long sand trap breakwater which resulted in economically viable construction bids. The work was successfully completed by Yemen based contractors in May 2001. The quality of the work is excellent and the breakwater is performing as designed in trapping sand and preventing the longshore drift from accreting in the entrance. Transactions on the Built Environment vol 58 © 2001 WIT Press, www.witpress.com, ISSN 1743-3509