Sines Revisited

The reason for submitting one more scenario to this spectacular failure is that it may prevent a similar occurrence. It is suggested that failure was due to bed subsidence or liquefaction, so causing the supporting rubble material to slide, together with armour units, in a sudden downward movement. Breakage of dolosse at depth rather than in the upper region fits this explanation well, as does the bulging at the base being less than the cross‐sectional area removed at the top of the face. The progressive scouring from the northern end toward the southern head matches the prior subsidence and lack of damage at these extremities, respectively. The bed failure was caused by its erosion from reflection of waves arriving obliquely to the straight N‐S segment of the breakwater, which was damaged over almost its complete length simultaneously. Similar scour to that hindcast for Sines has been recorded or predicted for other large breakwaters. Perhaps frequent hydrographic surveys, with planned remedial measures implemented quickly, may prevent a future calamity, but the reasons for collapse must be understand for these to be effective.