Gerald MÜLLER - Lecturer, Civil Engineering Dept. Queen’s University Belfast Belfast BT۷ ۵AD, UK
Guido WOLTERS - Postgraduate student, Civil Eng. Dept., Queen’s University Belfast

Breaking waves, when hitting a coastal structure, create high impact pressures and – probably more spectacular - throw a mass of water high up into the air, indicating the energy contained in the wave.The impact pressures are known to propagate away from the sea wall, generating pressures and pressure gradients on the sea bed and possibly damaging toe protection elements or eroding the bed.So far, these pressures were attributed to the wave impact itself; the effect of the down falling water mass on the area in front of the structure has not yet been investigated. A series of model tests was conducted at Queen’s University in order to investigate downfall generated pressures in front of a model sea wall. It was found that comparatively large, impact-type pressures and pressure oscillations occur during the initial stage of the downfall with magnitudes up to 8% of the highest horizontal pressures. The experiments showed that water-water impacts can generate substantial pressures which then travel through the water masses. Downfall generated pressures may be more significant for the stability of toe protection elements than impact-induced pressures since the downfall generated pressures are immediately followed by a large water mass flowing towards the sea.

wave impact, impact pressure, pressure propagation, seabed pressures, sea wall, wave downfall