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The City of Prineville and Ochoco Irrigation District have completed an infrastructure project that combined a new arterial roadway with a major irrigation pipeline upgrade, delivering what officials described as the largest single transportation project in the city鈥檚 history.
The Combs Flat Road Extension Segment 1A and OID Ironhorse Piping Project extended Northeast Combs Flat Road approximately 5,900 linear feet, constructed a new roundabout at Northeast Hudspeth Road, and installed 7,200 feet of 78-inch high-density polyethylene irrigation pipeline 鈥� all within a shared corridor in northeast Prineville.
鈥淣orth Main Street has been the only practical way to connect northern neighborhoods to downtown,鈥� Casey Kaiser, public works director for the City of Prineville, said in the Top Projects nomination form. 鈥淭he Combs Flat Road extension provides a second route to relieve congestion on Third Street.鈥�
DOWL served as prime consultant and lead engineer, with Black Rock Consulting managing OID鈥檚 irrigation pipeline design. Taylor Northwest held the single construction contract covering both project components, completing work on schedule and within budget.
A key innovation was co-locating the 78-inch HDPE pipeline beneath the new roadway, reducing land disturbance, permitting complexity, and overall pipe quantities. The pipe was manufactured locally by Krah USA in Prineville, supporting local employment and reducing transportation-related emissions. Installation required electrofusion welding, precise backfill compaction, and weld inspection protocols to meet operating pressures of 30 to 60 psi.
The project navigated significant environmental constraints, including two wetland fingers crossing the alignment and saturated soils requiring borings to 41.5 feet. Engineers developed a low-profile roadway design using mechanically stabilized earth walls and wetland passage culverts to minimize fill width. Permanent wetland impacts were held to 0.67 acres, allowing the city to use legacy credits from the Crooked River Wetland Mitigation Bank rather than constructing a new mitigation site.
The project was completed with zero injuries. Construction adjacent to Barnes Butte Elementary School required coordination with school administration on traffic management and pedestrian safety protocols. The enclosed pipeline also eliminated a hazardous irrigation intake structure near the school.
Few infrastructure projects require two independent public agencies to collaborate and fully integrate their capital programs. The delivery structure pioneered by the city and OID 鈥� shared legal counsel, coordinated grant applications, a unified construction contract, and a single integrated engineering team 鈥� demonstrates that agencies, when aligned around shared outcomes, can achieve results neither could accomplish alone.