Thornton Creek Bridge




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The Thornton Creek Watershed is an important water system for the City of Seattle. A large portion of the Northgate area drains into Thornton Creek, which subsequently has been the target of recent stream and habitat restoration projects. This project specifically isolated a pair of 36 inch concrete culverts that did not meet the stream demands during a large flood event.

It was decided to replace the existing 36 inch culverts with a custom precast concrete four sided box culvert system to dramatically increase the hydraulic opening. The unique custom clam shell design allowed the contractor to set the bottom units and then fill them with the required stream material before setting the top units. This would not be possible with a standard 3 sided box design. This flexibility allowed for the entire culvert system to be installed in just 5 days with minimal impact to the adjacent neighbors.