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Pontoon moorage in Grays Harbor

We have built a moorage location for new pontoons to be stored before being towed to Lake Washington. 

Map of pontoon moorage location

What is moorage? Why is WSDOT storing the pontoons in water?

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

Where in Grays Harbor will the pontoons be moored and how will they get there?

The pontoon moorage area is 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 is complete, the casting basin will be flooded and the pontoons floated out of the basin using tug boats. The pontoons are then inspected before being taken to the moorage location where they will be 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. This 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 is WSDOT taking to ensure the pontoons are moored safely?

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

Where will the pontoons go next?

A tugboat tows a pontoon
The pontoons will be towed to their moorage location by a tug boat

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