Discussion on Papers 7–9

P. ACKERS and J. D. PITT (Introduction to Paper 7) The usual methods of designing wave protection involve determining the wave climate for a selected return period of storm, selecting armour size in accordance with a formula relating size to wave height; knowing the size, the layer thickness is assessed and then various $ ancillary calculations are made for the grading and thickness of underlayers, upper limit to accommodate run up etc.

Most design relationships show armour size (linear dimension) to be proportional to wave height, and layer thickness to be a multiple of armour size. So tolerances on the design calculations give rise to at least an equal tolerance on costs. A 50% overestimate of armour size leads to at least a 50% overspend; but by the same token a 20% saving on costs by overoptimistic design would be exceedingly dangerous.