OREGON STATE UNIVERSITY

Extreme Tides in November, December Provide Hazards – and a Challenge for Scientists

11/18/2007

NEWPORT, Ore. – A series of extremely high tides, directly followed by strong “minus” tides, may provide more than a curiosity of nature along the Oregon coast this November and December.

The resulting tidal surge – especially if accompanied by a strong storm – can create danger for boaters and beachcombers – and threaten oceanfront homes with erosion and high water, according to ocean experts at Oregon State University.

And strong tide changes create an interesting dynamic at river bars – the creation of unpredictable, sharp-breaking waves that have claimed the lives of numerous boaters in Oregon.

“The Oregon coast is a dynamic place and when you get a combination of storms, extreme tides and high waves mixed in with a strong river current, it can get pretty wild,” said Tuba Ozkan-Haller, an assistant professor in OSU’s College of Oceanic and Atmospheric Sciences and an expert on nearshore and beach processes.

“The Columbia River is a great example of that,” she added. “There’s a reason why the mouth has been called the ‘graveyard of the Pacific Ocean.’ But it isn’t alone. In conditions like these, most of the bars and mouths of rivers in Oregon can be a hazardous place to be.”

Tidal measurements vary along the coast, but high tides reaching 10.0 feet at OSU’s Hatfield Marine Science Center in Newport are considered quite strong. On Friday, Nov. 23, the predicted high tide is 10.3 feet at 10:04 a.m.; and on Saturday (10:48 a.m.) and Sunday (11:33 a.m.), the high tides are projected to reach a lofty 10.6 feet.

Ocean water surging inland can carry high onto beaches, especially if the tidal impact is exacerbated by a strong storm, which increases the chances of coastal erosion. But it is the outgoing tide that concerns Ozkan-Haller, who has been studying the effects of where tidal currents meet ocean waves.

“When ocean waves come into shore, they eventually reach shallower water and shoal up,” she said. “They get shorter and steeper, and they can break offshore – typically off the mouths of bars. When the outgoing tide is strong, the impact on the waves can be quite significant. It can create a real problem for boats – not just recreational fishermen, but large, ocean-going cargo ships as well.”

And that is the challenge nature is throwing in November. Those huge 10.6-foot high tides are followed on Saturday and Sunday by -2.1 and -2.2 (minus) tides. That is nearly a 13-foot difference between high and low tides, Ozkan-Haller pointed out.

In her studies, Ozkan-Haller has found that even a modest 4-meter wave rolling toward the Oregon coast will grow to five meters as it begins to shoal. When it comes up against an average outgoing tide, it will grow to six meters. The stronger the tides, she says, the greater the impact on wave heights. Throw a storm, or high swells into the mix, and modest waves can become intimidating.

What the researchers haven’t yet discovered is how and when those tide-induced waves will break, she said.

“We’ve been working with bar pilots on the Columbia, who are desperate for some kind of predictive capability for waves breaking at the mouth of the river,” Ozkan-Haller said. “Bar pilots have to make a decision about leaving Portland 6-8 hours before reaching the bar and once they go, they’re committed. Many of the larger ships are too big to turn around, and there may not be enough room downriver to anchor safely.

“Making those decisions is an art based on experience and the observation of other pilots,” she added. “We’re trying to help add some research-based science to their extraordinary art.”

Scientists have capably demonstrated an ability to create models that predict when there will be whitecaps off the coast and when waves will break because of shallow water. However, preliminary attempts to predict when current-induced waves will break haven’t been successful and Ozkan-Haller and colleagues are seeking funding to initiate a project focusing on the Columbia River.

It’s a complicated world off the Oregon coast. And when surging high tides are followed by extreme minus tides, the turbulent nearshore processes become even more pronounced.

“A major tidal exchange doesn’t always end in catastrophe,” Ozkan-Haller said. “The Oregon coast has seen a lot of extremes over the years. But these are very high tides, followed by very low tides – and if a storm should happen to hit, it could be interesting.”

And if nothing happens in November, stay tuned. The same scenario will repeat itself in December.

Date High Tide/Time Low Tide/Time

Friday, Nov. 23 10.3 feet (10:04 a.m.) -1.6 feet (5:09 p.m.)

Saturday, Nov. 24 10.6 feet (10:48 a.m.) -2.1 feet (5:57 p.m.)

Sunday, Nov. 25 10.6 feet (11.33 a.m.) -2.2 feet (6:45 p.m.)

Monday, Nov. 26 10.3 feet (12:21 p.m.) -2.0 feet (7:35 p.m.)

Saturday, Dec. 22 10.5 feet (9:30 a.m.) -1.7 feet (4:59 p.m.)

Sunday, Dec. 23 10.6 feet (10:30 a.m.) -2.0 feet (5:48 p.m.)

Monday, Dec. 24 10.6 feet (11:20 a.m.) -2.0 feet (6:35 p.m.)

Tides Based on NOAA Predictions

A chart of tide table predictions for 2007 and 2008 is available on the OSU Hatfield Marine Science Center website at: http://hmsc.oregonstate.edu/weather/tides/tides.html.