PORT ANGELES — Widening holes in the mudflats off Hollywood Beach are a growing mystery.
On Sunday morning, a low tide of -2.59 feet allowed a city engineer and crew to uncover a 20-inch aluminum pipe buried in the sand thought to be responsible for three large holes that have developed in the beach in the last few weeks.
“It’s just a piece of pipe that led us on a wild goose chase,” said Mike Szatlocky, an engineer with the city of Port Angeles.
However, the discovery only deepened the mystery, as the holes are not behaving normally for the conditions, he said.
“If you dig holes in the beach, they’re gone the next day,” he said, noting that normal tidal action refills sandy depressions with more sand.
Instead, these holes are growing.
On Thursday, city crews measured the first hole, about 50 feet below usual tide line, at 8 feet wide by 10 feet long and 2 feet deep.
By Sunday, it reached 10 feet by 12 feet and was 3 feet deep, Szatlocky said.
That added up to nearly four tons of sand displaced from the spot, he said.
Two other holes about 100 feet below the tide line were about 8 feet wide with one measuring 18 inches deep and the other more than 2 feet deep.
The holes can be dangerous for children and other waders at the beach, as they can suddenly find themselves in much deeper water than they expect, Szatlocky said.
The city placed tall signs in the sand Thursday, warning waders and swimmers about the holes and closing the area immediately around them.
Bob Campbell, facility coordinator for the Feiro Marine Life Center, reported the holes to the city last week.
Campbell frequently wades into the harbor’s waters to seine for small sea animals that live in the flats in order to show them to students at the center.
Pipe fish, small crab and other small creatures caught in the net are identified then released to the water.
The first of the holes — the closest to shore and largest — first appeared three or four weeks ago, Campbell said.
When he and other Feiro staff found two more about a week ago, Campbell called the city.
On Sunday, Campbell, Szatlocky and Ian Miller, a coastal hazards specialist with Washington Sea Grant who studies the mouth of the Elwha River and was on a family outing to Hollywood Beach, discussed the mystery.
Miller said he has a time-lapse video of the beach for a study of seaweed and would review the video for any clues.
He speculated that perhaps someone tested large, powerful boat engines in the shallows and inadvertently displaced the sand.
However, that doesn’t explain the holes’ growth, which he said defies expectations.
“This really is intriguing,” Miller said.
Szatlocky had crews take samples of the water in the holes to measure the salinity of the water inside them compared to the water in the harbor nearby.
If the water in the holes is of lower salinity, it would indicate that a fresh water source — either a natural spring or drainage from an unknown source — is finding an outlet at the beach and displacing the sand, he said.
The beach area was once open harbor, and was filled in with soil, rocks, and glacial sand from the 1920s through the 1960s.
Szatlocky said that the city did not keep good records of what was put in the ground at that time.
The water in the holes was crystal clear and not disturbed, he said.
He said murky water would indicate flow from underneath that could account for the growing holes.
The city may have to contact the Army Corps of Engineers to determine if the city can fill in the holes with gravel or take other action, Szatlocky said.
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Reporter Arwyn Rice can be reached at 360-452-2345, ext. 5070, or at arwyn.rice@peninsuladailynews.com.
