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Not All Oregon Coast Beaches Recovered from Last Winter's Erosion

Published 10/28/21 at 6:26 AM PDT
By Oregon Coast Beach Connection staff

Not All Oregon Coast Beaches Recovered from Last Winter's Erosion

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(Oregon Coast) – Last year's gargantuan wave action during the 2020/21 winter season left its scars and marks in most portions of the state's beaches. Dunes were chomped on and chopped up. Cliffs were cut into. One oceanfront home was declared unsafe after the ground gave out, pipes were exposed not far away, and in Cannon Beach rarely-seen bedrock poked out from beneath the sands. King tides that occurred in November, December and January happened to coincide with raging storms, creating a “perfect storm” of erosional conditions. (Above: Devil's Kitchen area of Bandon in January 2021: wave action ate away large chunks of cliffs. Courtesy tbowspencer / CoastWatch)

With this year's La Nina on track to create similar batterings of shoreline, this may be a tense situation in some areas.

Normally, sand levels bounce back during the summer, which creates conditions favorable to depositing sand rather than take it away. Dunes get puffed up again, more dunes are created where low-sloped beaches were in winter, and cliffs shrink in height as the sandy floor gets higher beneath them.

Not All Oregon Coast Beaches Recovered from Last Winter's Erosion

(Above: Devil's Kitchen area at Bandon this summer, still showing erosion signs. Courtesy CoastWatch's tbowspencer)

However, this past year saw some areas not getting buffeted up again as much as they normally do. Bandon's Seven Devil's area is one prime example, where CoastWatch volunteers filed reports back in January showing some eye-popping changes to the beach. In August, the volunteer that goes by the handle tbowspencer noted their mile had not built back up nearly as much as before.

In fact, erosion may have continued over the summer.

“Late August along Mile 99 shows noticeably lower sand dunes than in previous years,” they said. “Both Johnson and Crooked Creeks are at very low levels less than 2 inches deep as they enter the ocean. There is more erosion of the bluff along the east bank of Johnson Creek, with large gorse roots exposed.”

This may leave some beaches more vulnerable to this winter's harsh tidal conditions.

Jonathan Allan is a geologist with the Newport office of Oregon Department of Geology and Mineral Industries (DOGAMI).

“In general recovery has been slower this year with most beaches only now hovering around average conditions of recovery, while some areas e.g. Pacific City, Neahkahnie Beach, Rockaway Beach, Agate Beach (Newport) currently show less sand when compared with past years,” he told Oregon Coast Beach Connection.

Allan said that last season “produced the third largest excursion (movement) of the mean shoreline position since our records began,” which was around 1997.

Curiously, maximum winter storms last year along the Oregon coast were actually a little lower than previous seasons, clocking in at 26 feet, Allan said. Other recent years saw individual storms exceeding wave heights of 33 feet.

“However, on average the winter waves during the 2020/21 season were above average in height relative to past seasons,” he said.

Allan said recovery of the beaches over the year has varied greatly between areas, with some bouncing back well.

Why haven't the others bounced back? Is this a climate change effect?

Manzanita last year: sharp drops at the dunes (courtesy Barb Gould)

No, it is not, Allan said. It's a fairly normal, cyclical thing. Where climate would come into play is if these trends continued for many years or decades.

Why some areas are not recovering is “complicated,” as Allan put it, and there's a few reasons.

One: some areas are not getting the right wave conditions. “More swell-oriented waves that are transporting sand onto beaches from sand bars” are needed.

Two: Length of time for those conditions. “You have to have the right swell conditions occurring over a sufficient amount of time to loose sediment onto shore instead of taking it offshore.”

Three: there could simply be not enough sand just offshore of an area to replenish what was taken away. Maybe the sand eroded away into the deeper ocean, he said.

Four: sand moves in three dimensions, not two. It doesn't just move offshore and onshore. Oceans also move sand up and down along beaches, north and southward.

“It could take a few seasons or multiple seasons of quieter conditions to allow sand to move back onto that beach,” Allan said.

Manzanita is one spot that looks normal again – but isn't. Last year, those high dunes were starkly shaved off in many areas, creating sudden drops of three to ten feet, actually making for dangerous spots to run if you weren't paying attention.

This summer, the dunes seem to have recovered their shape at least. Those abrupt walls have crumbled and sloped, according to Seaside geologist Tom Horning.

However, Horning said that beach has been changed since last year, but you can't see it with the naked eye.

“The beach at Manzanita is narrower and steeper than before last winter's high tides,” he said.

Sands were mapped and measured here four years ago, finding some 250 feet of sand between the bluffs and to a certain point near the tideline.

“After January 10, 2021, we made our own topographic maps using drones, and found the beach had gone from 250 feet down to 110 feet,” he said. “So where did all that sand go? It got swept out to sea.”

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