What is it about?
The comparison between the impact forces generated from a tsunami wave and those from a wind-driven wave are presented here. Wind-driven wave forces are derived from established maritime theory going back to the nineteenth century. The understanding of tsunami impact forces is derived from more recent research correlated further by some recent model testing. The maritime theory on wave impact force for breaking and non-breaking waves is very well developed from breakwater/seawall engineering. It commenced with Stephenson and Hiro’s nineteenth century rule of thumb equations, which was then followed in the twentieth century by Sainflou’s theory (1928) for standing waves in deep water. Minikin’s studies in the 1950s yielded results for breaking waves and noted high dynamic localised loads and these was followed in 1985 by Goda’s equations applicable for both breaking and non-breaking waves. At Alderney, typical impact pressures of 40 t/m2 (400 kN/m2) for 20 m/s waves were recorded, although a Ciria document published in 1992 notes that the average wave pressure on sea walls varies from 150 kN/m2 down to 50 kN/m2 pressure. Users are cautioned about the extremely high wave forces associated with the Minikin method. In 1984, Blackmore and Hewson developed a method to estimate an average wave pressure from broken wave loads.
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Why is it important?
The present analysis which was undertaken for the bathymetry and climatological data of the Mediterranean Sea then outlines the Malta scenario. It can act as a guide to structural engineers in selecting suitable values for the impact pressures that vertical walls may be subjected to for the cases of wind-driven or tsunami waves.
Perspectives
Civil engineers designing coastal defences and other structures around the Mediterranean still need to account for the very real risk of massive impacts from tsunami waves. The most recent Mediterranean tsunami was triggered by an earthquake off the coast of Algeria in 2003, which destroyed over 100 boats in Mallorca and flooded the Balearic capital Palma. And previously, following a 7.8 magnitude earthquake in the Aegean seabed in 1956, a wave over 20m high killed 53 people as it swamped the Greek island of Amorgos. On-shore velocities here can reach up to 13m/s, so Camilleri says civil engineers need dsign for horizontal loadings of up to 400kN/m2. The force of tsunamis can be enormous and Camilleri explains how, with a tsunami surge of only 10m deep, boulders of “around 200 tonnes can be displaced inland by hundreds of metres”
Mr Denis H Camilleri
Institute of Civil Engineers
Read the Original
This page is a summary of: Tsunami and wind-driven wave forces in the Mediterranean Sea, Proceedings of the Institution of Civil Engineers - Maritime Engineering, June 2012, ICE Publishing,
DOI: 10.1680/maen.201024.
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