Barker Gravity Pipeline Evaluation

The 36-inch-diameter Barker Gravity Pipeline transports raw water 11.7 miles from the Middle Boulder Creek Watershed and Barker Reservoir to Kossler Reservoir. The City of Boulder depends heavily on this pipeline for municipal water supply, and purchased the pipeline from Public Service Company of Colorado in January 2001.

Before the City of Boulder’s purchase, minimal maintenance was performed. In its current condition, the 90-year-old reinforced concrete pipeline has a rated capacity of approximately 45 cubic feet per second, which is equivalent to 29 million gallons per day. Its original rated capacity was 50 cubic feet per second, or 32 million gallons per day. The reduced capacity is due to leakage and obstructions within the pipe.

The pipeline had also previously experienced two failures within a 3-year span that required major repair efforts. During both failures, the City of Boulder was required to place water use restrictions on its customers.

GEI conducted a detailed field investigation to identify causes of pipeline failure and recommend potential rehabilitation and maintenance alternatives. In addition, a hydraulic analysis was conducted by GEI to determine the extent and location of flow restrictions. The pipeline is both open channel and pressure flow. GEI worked closely with the client to define the maintenance requirements necessary to extend the service life of the pipeline by at least 50 years and return the pipeline to its original rated capacity.

GEI prepared design drawings and specifications for a longterm maintenance program, which has included the removal and replacement of the existing concrete pipe with steel pipe, installation of siphon drain valves and valve vaults, and the construction of new retaining walls to stabilize the pipe bench. GEI coordinated wetland investigations and provided resident engineering services to ensure these sensitive areas were not impacted.