Stephan Baart, Reinder Ebbens, Julia Nammuni-Krohn, Henk Jan Verhagen


Present design tools, as found in the Rock Manual or Coastal Engineering Manual, for the determination of toe rock size for rubble mound breakwaters are based on test data with a large spread: data is relatively dispersed around the centre and descriptive equations have limited applicability ranges. New research has been undertaken to contribute to a more accurate description of toe rock stability. Flume tests have lead to an empirical design criterion for toe bunds in very shallow water based on the Hudson-type stability number. Herein the foreshore slope turns out to have an important influence. An approach with theoretical background has been used for toe bunds in surging wave conditions. The resulting stability description, based on local flow velocities, has been verified with existing data sets. Additional flume tests were performed to measure flow velocities at the toe bund. Results are used to calibrate the velocity-approach, providing an improved design criterion.


rubble mound breakwater; toe structure; toe bund; rock stability; wave load; foreshore slope

Full Text:



Baart, S.A. 2008. Toe structures for rubble mound breakwaters: analysis of toe bund design tools and a method for toe rock stability description, MSc thesis, Delft University of Technology,

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

Docters Van Leeuwen, L. 1996. Toe stability of rubble-mound breakwaters, MSc thesis, Delft University of Technology,

Ebbens, R.E. 2009. Toe structures of rubble mound breakwaters: stability in depth limited conditions, MSc thesis, Delft University of Technology,

Gerding, E. 1993. Toe structure stability of rubble mound breakwaters, MSc thesis, Delft University of Technology,

Nammuni-Krohn, J. 2009. Flow velocity at rubble mound breakwater toes, MSc thesis, Delft University of Technology,

Rance, P.J. and Warren, N.F. (1968) Threshold of movement of coarse material in oscillatory flow, proceedings of 11th ICCE, London, p. 487-491

Van Der Meer, J.W. 1998. Geometrical design of coastal structures, in: Dikes and revetments: Design, maintenance and safety assessment, Pilarczyk, K.W. (ed.), Balkema, Rotterdam