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Pontoon moorage in Grays Harbor

We built a moorage location to store newly built pontoons before towing them to Lake Washington. 

Map of pontoon moorage location

What is moorage? Why did WSDOT store the pontoons in water?

Pontoon moorage was a method of anchoring the pontoons for storage in Grays Harbor until they were needed for the bridge replacement. Because the largest pontoons are a football field in length and weigh 11,000 tons each, they had to be stored and transported in water.

Where in Grays Harbor were the pontoons moored and how did they get there?

The pontoon moorage area was located on the south side of the Grays Harbor navigation channel. This location is approximately 1.5 nautical miles from the Grays Harbor shoreline near the Johns River. The moorage area is about 1 mile long, 700 feet wide, and set back 200 feet from the navigation channel. When each batch of pontoons was complete, the casting basin was flooded and the pontoons were floated out of the basin using tug boats. The pontoons then were inspected before being taken to the moorage location, where they were secured and stored.

Why was this moorage location selected?

We worked with regulatory agencies, tribes and the local marine community to identify the pontoon moorage location. The location was selected because it met key requirements, including:

  • Adequate water depth
  • Adequate protection from wind and waves
  • Clearance of charted navigation channels

What measures did WSDOT take to ensure that the pontoons were moored safely?

Crews conduct safety inspection
Maintenance crews conduct routine inspections to ensure safety.
  • WSDOT outfitted the pontoons with navigation lighting in compliance with U.S. Coast Guard requirements.
  • During moorage, we conducted routine inspections of the chains and lines to help ensure that the pontoons were moored safely. The anchoring system was designed to keep the pontoons secured and limit drifting.
  • We monitored the pontoons and anchors regularly to ensure they remained securely in place.
  • Pontoons always floated at least 7 feet above the harbor bottom, even during the lowest tides.

Where did the pontoons go next?

A tugboat tows a pontoon
A tugboat tows a pontoon to the moorage location.

Pontoons were moored until needed for the construction of the new SR 520 floating bridge. The pontoons then were towed from the moorage site to Lake Washington, where they are being assembled to form the floating foundation of the new bridge.