DESIGN OF AN OVERTOPPING BREAKWATER

Abstract

The Maritime Services Board of New South Wales, Australia, is constructing a major new port facility on the northern foreshores of Botany Bay. A principal part of this project has been the construction of a large armoured revetment from the northern shores. The entrance to Botany Bay faces southeast and it is from this direction that a large proportion of offshore wave energy arrives. Some of the wave energy which is directed onto the Bumborah Point revetment is reflected towards Yarra Bay on the northern shores of Botany Bay. Yarra Bay is largely undeveloped, but a sailing club has stood for many years on the beach at the southern end. As a consequence of this reflected wave energy being directed towards Yarra Bay, its wave climate has been changed considerably so that during the storms of May-June, 1974, Foster (6), damage was suffered by the club-house. Additionally the more severe wave climate and consequent steeper beach have made it much more difficult to launch sailing boats. The Maritime Services Board is charged with the responsibility to carry out remedial works where damage is caused by the port development. Figure 1 shows the revetment and sailing club site. To assist in coastal engineering design aspects of the port development, a large fixed bed wave model of Botany Bay has been built to an undistorted scale of 1:120. This model, some aspects of which have been described by Lawson (4), has pneumatic wave generators which enable offshore wave directions between east-north-east and south to be generated with prototype periods in the range of 5 to 16 seconds. A pneumatic tide generator enables a sinusoidal tide to be generated.