Tsunami Scour and Forces at Onshore Structures

Tsunami induced scour at onshore coastal structures can cause exposure of the foundations and lead to failure. This paper presents experimental observations of a 147 s crest-led wave inundation, causing scouring and loading on 0.2 m wide square and 0.4 m wide rectangular onshore structures. At 1:50 Froude scale these equate to a 17.3 min inundation at 10 and 20 m wide structures. Scour development is measured using GoPro cameras situated inside the Perspex structures. The hydrostatic load is calculated from the integration of pressure readings along the front face of the structures, and the hydrodynamic loading is estimated from the approach flow velocity, as measured by a Vectrino II profiler. The results show that the maximum scour depth occurs during the inundation before significant slumping decreases the end scour depth. Both the in-test and final scour depths for the 0.4 m structure are greater, due to the larger blockage causing greater acceleration of the flow around the structure. For both structures, the hydrostatic loading is dominant over hydrodynamic load.