Discussion. Extension of Torshavn Breakwaters.

Abstract

The HRS in Wallingford and the Danish Hydraulics Institute have enjoyed good relationships and excellent co-operation for many years. In coastal engineering, engineers learn by mistakes or failures caused by exceptional circumstances. In either case, a study of what happened is a very worthwhile exercise. On this account alone the Authors are to be congratulated on producing such an interesting paper.81. As Mr Ssrensen has said, wave disturbance studies and wave flume studies would nowadays be conducted using random seas, the advantage being that quantitative as well as qualitative assessments can be made. However, such facilities were not available at the time of these studies. At that time the size of armour units was chosen by subjecting model slopes to regular seas, with a design wave height of a value equal to the average of one-third of all the largest waves.82. That brings me to my first questions. In the case under discussion, why was the maximum wave height chosen rather than the significant wave height? Secondly, do the Authors think that random sea testing would have produced a larger stone size? In a random sea there would be higher waves than the ones used in the tests.83. One point to settle in tests of this nature is the damage criterion. Should this be no damage, 2%, or some other figure. I should like to ask what the damage criteria were in this case.84. Referring to wave measurements ($29) the Authors state 'It was felt that the chances of success of such measurements within the short time available would not warrant the expense involved'. I should like to ask whether, with hindsight, they would have made the same decision today.85. Even during the construction of a scheme such as this there is a case for wave recording, for instance to help settle contractor's claims or as an aid in checking the design. Perhaps the Authors would comment. M r J. Palrner, Consultant, Rendel, Palrner and Tritton I was delighted to learn that the design of this harbour was produced by the harbour authorities, as I am afraid that I shall have to be critical of one or two points in the design; and the Authors will appreciate that my criticisms are therefore not directed against them.87. Mr Langvad mentioned that the cost of the breakwater was approximately €1.6 million though the Paper itself does not deal much with costs nor the tonnages of trade passing in and out of the harbour, nor any discounted cash flow calculations. Nevertheless, there was one vital economic statement in $1: 'Ships could not stay safely in the old port during south-easterly gales'. There is the complete economic Paper published