This project involved the removal of three undersized culverts associated with upstream flooding within Mill Creek Regional Park and replacement with an arch structure to accommodate sediment and woody debris migrating downstream during the annual freshet.

Challenges on this site included multiple utilities including a water main, natural gas line, storm sewer and resident services as well as the requirement to provide 24/7 access for local residents. Traffic control for the one-lane, 100′ bypass bridge was automated and a pedestrian trail was constructed along the temporary gas line route. The temporary water-main was supported by the bypass bridge and tested prior to use.

Material was excavated and transported to a nearby laydown and stockpile area for future use. A sheet pile coffer dam prevented water from entering the site and a dewatering system was established to pump the stream flow around the construction site.

The streambed was reconstructed using a boulder base, infilled with materials previously trapped upstream by the undersized culverts. Boulders and riprap were installed to slow the flow beneath the arch. The arch was pre-assembled in the lawdown area and transported in sections for attachment to unbalanced channel on the compacted footing area. Boulder material was positioned within the arch using small equipment. Geosynthetic reinforced soil (GRS) headwalls were faced with Miramesh fabric to encourage vegetative growth and resist UV deterioration. The arch was anchored to the GRS backfill at designated intervals as the backfill was imported and compacted. Arch shape monitoring was conducted during backfill constructure to document forces applied during construction.

Once the tempoary bridge was removed, traffic was diverted from side to side as the utilities were re-established and the road grade returned to the preconstruction elevation. This projected was completed over a 40 day period in March/April.

Another successful project in collaboration with Terratech Consulting Ltd.