Photo courtesy of WHPacific The Monte Cristo Bridge has timber decking to allow rain to fall through, avoiding the need for stormwater pipes and catch basins.

WHPacific designed a low-cost bridge structure and recommended the project sequencing that allowed Snohomish County to reestablish access across the south fork of the Stillaguamish River. Heavy flows there caused a large section of the riverbank supporting the Monte Cristo Grade Road to wash away in 2003.

The project site lies near the border of the Mount Baker-Snoqualmie National Forest, a delicate natural environment that required special attention to potential environmental impacts. Other challenges included budget limits, aesthetics, pedestrian safety, future maintenance needs and a schedule imposed by the Federal Emergency Management Agency.

Several techniques helped resolve the complex set of challenges:

• Constructing the bridge solely from one side of the river and using the existing south abutment was possible due to the use of lightweight trusses.

• Using timber planks for bridge decking to allow rain to fall through, eliminating the need to construct stormwater pipes and catch basins.

• Designing for future migration of the river channel, leading to the strategic placement and design of the center pier and north abutment.

• Selecting materials such as weathering steel trusses to complement the setting and keep future maintenance costs low.

• Integrating a pedestrian refuge into the design, allowing pedestrians and vehicles to use the single-lane crossing simultaneously.