An important branch of the Manistee River watershed in Michigan, the Pine River’s health is largely subject to the condition of its contributing streams, creeks, and drains. One of these tributaries, Silver Creek in Lake County, provided a challenge to maintaining the health of the Pine River due to an aging culvert under State Road.
Considering that the Pine River is a Blue Ribbon Trout Stream and protected by a Federal Wild and Scenic River Designation, it is easy to understand the interest of several state, federal, and environmental advocacy agencies in improving the function of Silver Creek at this culvert. In addition, the culvert had been targeted for replacement by the Lake County Road Commission. Conservation Resource Alliance took the lead on the project as an opportunity to improve water quality, stabilize creek banks, and enable fish passage.
The Silver Creek culvert presented several concerns that required mitigation, primarily the complete blockage of fish migration upstream. The existing corrugated metal pipe culvert caused high-velocity flows to erode a three-foot perch directly downstream of the culvert. This contributed to sedimentation problems, threatened the stability of the downstream banks, and blocked fish passage.
The solution called for the full replacement of the existing pipe culvert with a new, open-bottom concrete culvert. Implementation of this design allowed the creek to exhibit a more natural channel within the culvert itself, made up of rock and boulder rip-rap to preserve the creek bottom and protect against erosion. Although replacement of the culvert required the contractor to temporarily work within the waterway, steps were taken to effectively work in a natural water channel without disrupting water flow. The creek was re-rerouted during construction with bypass pumps to ensure sediment or other contaminants were not introduced to the creek.
While working in the channel was a challenge in itself, the design team and contractor had to confront several other unique characteristics. The physical location of the culvert did not help matters, considering it was 18 feet below the surface of State Road. In addition to excavating below the road to reach the culvert, the contractor had to excavate an additional 10 feet below the creek bed to accommodate the new culvert foundations.