CORVALLIS, Ore. – The Pacific Northwest coast has experienced increasingly intense winter storms and higher wave heights over the last 25 years, both of which may be leading to earlier and more severe winter erosion, scientists at Oregon State University say.
Entire beaches have been scoured away this fall and cliffside houses at Gleneden Beach and elsewhere are in jeopardy, says Paul Komar, professor emeritus in the College of Oceanic and Atmospheric Sciences at Oregon State University.
“We’ve seen some pretty intense winter erosion in Oregon,” Komar said, “but I don’t ever remember seeing the extent of the problem this early. Usually, the erosion doesn’t take effect until January, February or March. If the beach is gone in November, what will happen 2-3 months from now when additional storms hit and that buffer is gone?”
Komar said there is no consensus on why storms have been getting stronger. Some scientists believe global warming may play a role, while others say similar conditions occurred in the late 19th century, suggesting periodicity, if not some kind of cycle.
One thing is certain: Wave heights are increasing.
Komar and colleague Jonathan Allan, a courtesy professor at OSU who works for the Department of Geology and Mineral Industries, have been monitoring buoy data since 1975. They found that during the early years of measurements, wave heights – measured several miles off the coast – averaged about three meters. In recent years, that average has grown to four meters, a substantial increase. At the same time, the wave heights during major storms have increased from being on the order of 11 meters in 1975 to 15 meters now.
The researchers have published their findings in the Journal of Coastal Research.
“After looking at about 25 years of data, in 1997 we applied a model to estimate what we thought would be the 100-year storm extreme to help coastal hazard management plans,” Komar said. “Then in 1997-98, we had two 100-year storms, and the following year we had three more. Although we had correctly applied the model, it was kind of embarrassing.
“We went back and scrutinized the data and found that the wave heights actually have been progressively increasing,” he added. “And that certainly would signal more threat from erosion.”
During typical Oregon winters – which are not affected by El Nino and La Nina events – storms most frequently arrive from the southwest and hit the beaches at a steep angle, pushing sand northward. In “cells,” or beaches situated between two headlands, the sand will pile up at the north end and become barren to the south.
Summer waves, gentler and from the northwest, typically push the sand back into place and return the beaches to “normal.”
But the Pacific Northwest coast is dynamic and when a strong El Nino strikes – as happened in 1982-83 and 1997-98 – conditions change. The water rises, flooding over most of the beaches and allowing the waves to cause greater erosion.
Komar says that the Pacific Ocean off the Northwest coast has risen about 15 to 20 centimeters during the last 100 years. But during a strong El Nino event, the water rises 50 to 60 centimeters in a couple of months because locally it is warmer and expands, and regionally the ocean currents push waters northward from the equator and it piles up on the Pacific Northwest coast.
“A one meter rise in the ocean can push water approximately 50 meters inland,” Komar said. “So any rise in sea level is much more significant than it may initially sound.”
Erosion caused by these El Nino events is usually significant and in 1997-98, the El Nino was followed by a series of exceptionally large storms, the researchers say. One of those occurred as the Coast Guard was towing the New Carissa, a beached ship, out to sea near Coos Bay. Deep-water wave heights, measured by instruments on buoys, averaged 15 meters, or about 50 feet, while the maximum heights of individual waves reached 25 meters, or some 85 to 90 feet.
An earlier major El Nino, in 1982-83, eroded much of the Alsea River spit in Waldport, threatening dozens of homes. Revetments were built and gradually the sand returned.
“Ironically,” Komar said, “the sand covered up the revetments and new homes were actually built to the west of those barriers. When the next El Nino hit, a new protective wall had to be constructed to protect those homes. It’s one of the certainties of life – as the coast continues to develop, we’ll put more things in the path of the ocean.”
Ocean hazards on the United States’ Pacific shoreline differ from those of the hurricane-ravaged Atlantic Ocean, Caribbean and Gulf of Mexico, the researchers pointed out.
“The scouring effect is huge on the West Coast,” Komar said. “Hurricane Katrina had tidal surges and flooding. Our problems tend to be erosion that undercuts cliffs and undermines homes built in dunes or on sand spits. FEMA is now adopting some of our techniques and models for analyzing the erosion processes, employing them to establish West Coast hazard extremes.”
Those dangers, Komar says, typically result from high storms, high tides, large wave run-ups and rip currents that lower beaches. And all of those conditions have been worsening over the last 25 years.
“Having this much erosion by November is kind of scary,” Komar said. “We could be highly susceptible to severe damage this winter.”
Komar is the author of “The Pacific Northwest Coast: Living with the Shores of Oregon and Washington,” published by the Duke University Press.