Mann Rd at Haystack Creek

October 2021 Update - Completed

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 consisted of two corrugated metal culverts that were undersized, causing debris blockages. Although Snohomish County Road Maintenance would remove the debris on a routine basis, the blockages tended to cause road flooding during storm events several times a year. These culverts were 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 were replaced.

Project Plans

The project replaced 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 was raised for approximately 1,400 lineal feet. Ditches and driveway culverts were installed on the south side of the roadway. Guardrail was installed adjacent to the stream culvert. The new culvert was designed to accommodate fish passage.


Construction was estimated at $1.2 million and was paid for by SWM Utility Fees.

Public Meeting & Documents

Other Projects in the Area