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Scappoose dams in need of cleanup

City has to find new location to dump extracted winter debris and sediment


by: SPOTLIGHT PHOTO: ROBIN JOHNSON - Currently, the water level behind the dam is about one foot deep. When the sediment is cleared away, the depth will be more than four feet, said Steve Smith, Scappoose Water Plant Operator.The three dams responsible for supplying water to the city of Scappoose are due for a deep cleaning.

Over the winter, harsh weather caused sediment to build up behind the dams on Gourlay, Lacey and South Fork Scappoose creeks.

The three dams collect water from the hills outside Scappoose, which is then pumped via a system of underground pipes to the Keys Road Water Treatment Plant. In order to operate efficiently, sediment buildup behind the dams’ concrete walls needs to be cleaned every couple of years, said Jon Hanken, Scappoose city manager.

There are a couple limiting factors preventing the cleanup projects from taking place, however.

“It’s cost dependent,” said Terry Andrews, field services supervisor at Scappoose Public Works. “It used to cost between $25,000 and $50,000, but that was when we had a place to dump the sediment.”

The soupy mixture of silt, gravel, rocks and mud pulled out of the dammed creeks had been dumped into a natural depression on a timber company’s private land for the past 10-15 years, Andrews said.

Now, city officials have to find another area to dump the sediment due to the historical depression having reached full capacity. And, with the new location, the city will probably have to pay for it.

Andrews said he doesn’t know how much the project will cost at this time, or when the city will be able to undertake it.

There is only a short window wherein the creeks can be worked on due to natural forces. It’s call the “in-stream work period,” and it only lasts from July 15 to Sept. 1, Andrews said.

The reasoning behind the limited window is so that harm to endangered species, such as coho and steelhead salmon, is minimized by prohibiting workers from entering the creeks as fresh rains arrive in the fall.

The dam on South Fork Scappoose is in need of repair as well as sediment drainage. In order to remove the sediment from the creeks, running water is diverted upstream through a large pipe that directs the water below the dam. The pipe is currently defective.

Water becomes a bigger issue during the summer months as residents use more of it and resources decrease.

“During the summer we only pump 200 gallons per minute in order to keep the creek from drying up. That’s down from 450 [gallons per minute] the rest of the year,” said Steve Smith, Scappoose Water Plant operator.

The city uses well water during the summer to make up for lower creek levels, but the wells are more expensive to treat since they contain iron, Smith said.