Mann Rd at Haystack Creek

October 2021 Update

Construction of a new concrete box culvert under Mann Rd at Haystack Creek was completed in September 2021. The larger concrete structure replaced two deteriorating metal culverts that contributed to road flooding during storm events. By providing a significantly larger and more natural channel for water to flow under the road, the new culvert will help reduce road flooding and better accommodate fish passage. Planting is planned for the end of October.


Haystack Creek flows from the hills south of Mann Road and crosses the roadway in three locations. The easternmost crossing consists of two corrugated metal culverts that are undersized causing debris blockages. Although Snohomish County Road Maintenance removes the debris on a routine basis, the blockages tends to cause road flooding during storm events several times a year. These culverts are also partially crushed and deteriorating. Haystack Creek is a fish bearing stream that drains to a slough of the Skykomish River.

To limit ongoing maintenance, reduce road flooding, and prevent road damage and possible traffic impacts due to culvert failure, the culverts must be replaced.

Project Plans

The project will replace the twin culverts with one 20-foot span by 6-foot rise, concrete box culvert. To accommodate the new culvert and improve sight distance, the road elevation will be raised for approximately 1,400 lineal feet. Ditches and driveway culverts will be installed on the south side of the roadway. Guardrail will be installed adjacent to the stream culvert. The new culvert will be designed to accommodate fish passage.


Construction to begin on June 21, 2021 and is expected to be completed by mid-August. Crews will be working approximately Monday - Friday 7 a.m. to 5 p.m. There may be some weekend work required.

Traffic Impact

During construction, traffic will be moved to a bypass road on Mann Rd between milepost 1.7 and milepost 2.0. A temporary traffic signal will be in place on the single-lane bypass road, alternating traffic 24/7. At times there may be up to a 10-minute wait.


Construction is estimated at $1.2 million and will be paid for by SWM Utility Fees.

Public Meeting & Documents

Other Projects in the Area