J.A. Zwamborn, G. Grieve


Modern bulk carriers require deeper and wider harbour entrances. As a result long approach channels have to be dredged outside the breakwaters. These large channels cause considerable changes in the waves due to refraction and diffraction which effect the wave conditions in the harbour entrance. As part of the Richards Bay harbour entrance studies, two phenomena were found to considerably effect the design of the entrance layout, namely: (i) wave attenuation for waves travelling near parallel to the channel axis, caused by refraction of wave energy away from the channel, and (ii) wave concentration on the channel side slopes, also mainly due to refraction, reaching a maximum for a critical approach direction of about 25 relative to the channel axis. As a result of the wave attenuation, waves travelling within an angle of 20 either side of the channel axis were found to cause no problems whatsoever with regard to wave penetration into the harbour. Unacceptable wave penetration was, however, experienced for wave directions close to the critical direction. A great number of variations to the entrance layout were tested to minimise this problem. The results showed the superiority of a flat channel slope of 1 in 100 above steeper side slopes and the beneficial effect of a Vee-shaped channel bottom. Also test results with irregular waves with regard to height, period and directions were found to be significantly different from those with uniform waves which considerably exaggerate the wave concentration phenomenon.


wave attenuation; wave concentration; harbor channel; approach channel

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DOI: http://dx.doi.org/10.9753/icce.v14.%25p