Guido Wolters, Marcel Van Gent


Stability formulae for armour layers of rubble mound breakwaters are usually being applied assuming perpendicular wave attack. Often it is assumed that for oblique wave attack the reduction in damage compared to perpendicular wave attack is small. This seems however a very conservative assumption. Wave basin tests at Deltares provide information to assess the effects of oblique waves on the stability of rock slopes and cube armoured rubble mound breakwaters. This includes cubes in a single layer and cubes in a double layer. The results show that the few available formulae that include wave obliquity underestimate the effects of oblique wave attack; the observed damage to breakwaters with armour layers of rock and cubes is lower and therefore new stability increase factors and mass reduction factors have been developed. The tests were performed for wave directions between perpendicular (0) and 70. The results show that large potential savings in diameter and mass can be obtained for large angles of wave obliquity.


rubble mound breakwaters; breakwater stability; armour layers; oblique waves; rock slopes; cubes

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CEM. 2005. Coastal Engineering Manual, Part VI, US Army Corps of Engineers, Washington, D.C.

Frens, A.B., M.R.A. van Gent and J. Olthof. 2008. Placement methods for antifer armour units, World Scientific, Proc. ICCE 2008, Vol.4, pp.3337-3345.

Galland, J.-C. 1994. Rubble mound breakwater stability under oblique waves: and experimental study, Proc. Coastal Engineering 1994, 1061-1074.

Hudson, R.Y. 1959. Laboratory investigations of rubble mound breakwaters, J. Waterways & Harbors Div, Am Soc Civ Engrs, vol 85, no WW3, Paper no 2171, 93-121.

Rock Manual. 2007. The Rock Manual. The use of rock in hydraulic engineering, CIRIA, CUR, CETMEF, 2nd edition, C683, CIRIA, London.

Van Gent, M.R.A. 2003. Recent developments in the conceptual design of rubble mound breakwaters, COPEDEC VI, Colombo, Sri Lanka.

Yu, Y.-X., S.-X. Liu, C.-H. Zhu. 2002. Stability of armour units on rubble mound breakwater under multi-directional waves, Coastal Engineering Journal, Vol. 44, No. 2, 179-201.http://dx.doi.org/10.1142/S0578563402000482

DOI: http://dx.doi.org/10.9753/icce.v32.structures.34