Capitol Lake’s concrete dam under inspection

A marine engineering firm is inspecting the concrete dam that divides Capitol Lake and Budd Inlet in downtown Olympia.

The Seattle office of Moffatt & Nichol was hired for the job, which began Thursday on the lake side of the dam along the Fifth Avenue Bridge. The engineers will check the Budd Inlet side Friday (July 29).

The goal is to ensure the dam is structurally sound and that no significant erosion has weakened the concrete. The last dam inspection took place in 2007. It also was commissioned by the state Department of Enterprise Services, which manages Capitol Lake as part of the Capitol Campus.

“This is just routine maintenance, just like any other asset on the Capitol Campus,” said Jim Erskine, Enterprise Services spokesman.

Byron Haley, a diver and civil engineer, plunged almost 21 feet into the murky Capitol Lake waters Thursday with a camera mounted on his helmet. He examined the effects of erosion from the sediment that comes from the Deschutes River.

The dam’s mechanical operations also will be reviewed, said Olympia Mayor Pro Tem Nathaniel Jones, who works as an Enterprise Services asset manager and is in charge of the project. The inspection will not affect the lake’s water level, according to Enterprise Services.

In 2007, the same engineering firm found minor cracking in the dam’s outer walls, but determined that the dam’s opening — also known as a spillway — was structurally sound. The report noted that the dam’s machinery was in “good condition for its age,” but will need replacement within 50 years.

“The Capitol Lake Dam should maintain its existing functionality over the next 50 years if an appropriate and aggressive program of inspection and repair is followed and natural disasters or other major events, such as earthquakes, do not occur,” according to the 2007 report.

The Fifth Avenue Dam was built between 1949 and 1951 to create the 260-acre Capitol Lake. The dam has an 82-foot opening that controls the lake’s water level.

The dam is at the center of a long-running debate about whether the lake should be allowed to revert to a saltwater estuary. This week’s inspections are unrelated to the lake-estuary debate, which is led by a committee of stakeholders.

Following this week’s inspections, the engineers will follow proper decontamination procedures to avoid the spread of New Zealand mud snails, an invasive species that was first discovered in Capitol Lake in 2009. The lake has been closed to boating and other recreational uses as a result of the mud snails, which are freshwater mollusks about as long as a grain of rice that wreak havoc on the local ecosystem’s food chain.

This story was originally published July 28, 2016 at 3:45 PM with the headline "Capitol Lake’s concrete dam under inspection."