Orkney experiences one of the highest wave energy environments in the world. The west coast is exposed to the full force of the Atlantic waves, with hundreds of kilometres of fetch, hurricane-force wind speeds and deep water close inshore allowing huge waves to arrive at the cliffs unbroken. The outer parts of the east coast must also experience some very large waves, as oil rigs in the northern North Sea has recorded some monsters over the two decades.
Large parts of the Atlantic seabed around Orkney lie at depths of greater than 100m. To the west the significant wave height exceeded for 10% of the year is about 4m, reducing to about 3m to the east of Shetland (JNCC, 1997). Variations can be extreme and in 1996, 26% of all waves exceeded 4m, whilst in February 1997 89% of all waves exceeded 4m. During storms much higher waves are common. To the east of Shetland waves reached 18.5m in 1969 at 560N, 40W (Burridge, 1973). To the west of Shetland storm waves reached 15.13m at 600N, 40W in January 1974 (Marex, 1975), 24.4m at 590N, 190W (Draper and Squire, 1967) and 15m in 1997 (Met Office, 1997). Extreme waves are usually associated with intense winter storms. The highest waves approach` from between northwest and west.
There is an increasing amount of evidence to suggest an increase over recent decades of wave heights in the North Atlantic. The Waves and Storms in the North Atlantic (WASA) project used a combination of modelling and observational data to report increases in wave height of 2.5-7.5mma-1 over the period 1955-94 (Gunther et al, 1998). This is supported by the observational data of Gulev and Hasse (1999), who indicate a 1-3mma-1 increase in North Atlantic wave height in the last 30 years, possibly linked to intensification of the North Atlantic Oscillation (NOA). If this is the case then there appears to be little reason to suggest that the maximum heights achieved by extreme waves should not also be subject to a similar increase over time.