Discussion on Papers 3 and 4

Paper 3

Mr. M. W. Owen

Mr. M. G. Briggs

We stress the need for carrying out sensitivity testing during model studies for the design of breakwaters. These sensitivity tests would considerably enhance the confidence of the designer if they included for example the effects of different assumed design storm conditions, different water levels, different breakwater construction methods etc. In addition, it should be emphasized that a mound of randomly placed armour units subjected to random wave attack would necessarily produce random variations in damage. Several tests are therefore necessary to obtain a statistically meaningful result: to compare different designs on the basis of single tests on each, as is often demanded, could therefore be very misleading. Finally, we should like to point out that the published values for the Reynolds number needed to minimize errors in stability modelling are achieved at quite small wave heights. Typically significant wave heights required are about 80-130 mm, depending on the type of armour unit and the slope of the breakwater.