City officials keeping an eye on Renton's slopes after Oso slide

With this past weekend’s deadly Oso Mudslide on everyone’s mind, attention has turned to many of the slopes and hillsides that so many of us live near as we wonder if the same thing could happen here.

“We have areas in Renton that are sensitive areas,” Public Works Administrator Gregg Zimmerman said this week but added that he has seen no pending problems around the city’s many hills.

According to Zimmerman, his crews routinely keep an eye on several slopes in the city, based primarily on historical experience. City workers have even produced a map of potential slide areas within the city.

Among the slopes they watch are along Lake Washington Boulevard, the slope to the west of Rainier Avenue adjacent to the airport and a slope on the north side of the Maple Valley Highway, across from the old Stoneway Concrete batch plant.

Zimmerman said crews from the city’s streets and surface water divisions are out this week keeping their eye on potential landside areas for any signs of weakness that may have been caused by this months persistent and potentially record-setting rainfall. Zimmerman said the city’s stormwater system have handled the rain well because though there has been a lot of it, it has not been in the type of short, heavy bursts that can overload a sewer system.

However, while good for the sewers, the steady, consistent rain works the opposite on hillsides, allowing the water to seep in, weakening the soil and reducing the stability of the hill.

“These are the type of conditions where you can get saturation of steep banks,” he said. “We also know that events can happen several days after the rainfall has stopped.”

Zimmerman said his crews are making “daily reconnaissance” of danger areas for the “telltale signs” of problems, such as land creaking and settling or trees that have shifted or are leaning.

Should the signs be found, Zimmerman said a geotechnical engineer would be brought in to assess the problem.

So far, Renton hills show no signs of weakness, but the public works crews are staying vigilant.

“We’re keeping our eyes on it,” Zimmerman said.

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