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Big waves along Washington's coast
- High energy
The Pacific Northwest coast has one of the highest wave energy levels in the world. Wave heights on average are large.
- Big storm waves
Winter storms can generate waves more than 22.8 feet (7 meters) high. An intense winter storm during the 1997/98 El Niño produced waves 48 feet high.
- Getting bigger
Between 1975 and 1999, the largest storm waves off the coast of Washington increased in height from 26 feet (8 meters) to 39 feet (12 meters). What's causing the increase? El Niño may be a factor.
- The biggest
Extreme waves 50 to 90 feet in height have been recorded on and beyond the continental shelf.
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Surf's up!
Heavy surf on the Columbia River bar tests a Coast Guard vessel. At the mouth of the Columbia River, average deepwater significant wave heights range from 4.6 feet (1.4 meters) in July to 9.8 feet (3 meters) in December.
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Wind sends energy, waves deliver
- Wind speed: Big winds generally make big waves.
- Fetch: Fetch is the distance wind blows over water.
The Pacific Ocean provides an immense fetch. Storms from all over the Pacific send waves to Washington's coast. The largest waves often come from winter storms in the Gulf of Alaska and the North Pacific.
- Duration: The longer the wind blows, the bigger the waves grow. Duration is the length of time wind continues without changing direction or speed.
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Measuring waves
How long?
Wave length is the distance between two crests or troughs. Storm waves in the Pacific average 590 to 650 feet in length (180 to 200 meters). Swells, or waves from distant storms in the Pacific, are often more than 3,200 feet long (1000 meters).
How fast?
Wave period is the time it takes, in seconds, for a series of wave crests or troughs to pass a fixed position. Ocean wave periods can range from 1/10th of a second to over 24 hours. The average wave seen breaking on the beach has a wave period between five and twenty seconds. An earthquake can form a long period sea wave called a tsunami. The wave period of a tsunami can be 15 minutes or longer.
How steep?
Wave steepness is the ratio of wave height to wave length. Storms bring steep waves -- or short, high choppy waves. During strong El Niño years, waves along Washington's coast often increase in steepness, causing erosion and flooding.
How many?
Storms over the Pacific Ocean stir up waves of many different sizes and shapes. This mix of waves includes a lot of small waves and a few very large waves. The significant wave height is the average of the largest one-third of the waves. A 20 minute set of 10 foot waves, could include a wave 18 feet high.
How high?
Wave height is the distance from the top of the crest to the bottom of the trough. Summer waves off the Pacific Northwest coast average about 5 feet (1.5 meters) in significant wave height; winter waves average about 10 feet (3 meters). Strong El Niño years bring higher waves. During the 1997/98 El Niño, the average December significant wave height was about 12.5 feet (3.8 meters).
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Winter
During the winter, higher waves come from the southwest. Wave energy and water levels are higher. Winter wave periods range from 10 to 20 seconds. Sediment transport shifts north.
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Summer
During the summer, lower waves come from the northwest. Wave periods range from 5 to 10 seconds. Sediment transport moves south.
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