Gibraltar Reservoir Flume

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  Gibraltar Reservoir Flume


City of Santa Barbara

Project Name
Gibraltar Reservoir Flume

Civil Engineering
Land Surveying

APWA Central Coast Chapter, Project of the Year Award
ASCE San Luis Obispo Chapter, Project of the Year Award


Surface water discharged from the Gibraltar Reservoir flows through a below-grade tunnel to an existing valve house, then by gravity through a below-grade pipeline to the Mission Tunnel, before reaching the City of Santa Barbara’s (City) Cater Water Treatment Plant. The flow rate out of Gibraltar Reservoir is currently measured using a broad crested weir, which is inaccurate due to its design and installed conditions. This project improved the accuracy of this flow monitoring facility.

Detailed design plans for a new flow monitoring facility were developed. The new facility is designed around a fiberglass H-flume, which was installed outside the existing valve house. New 30-inch steel piping and appurtenances convey water at up to 10 million gallons per day (MGD) from the existing weir, through the wall of the valve house, to the new flume. The new flume discharges to the existing gravity conveyance pipeline and is housed in a new concrete and masonry building. Due to the remote location of the project site, the design included provisions for cell phone use, high fire hazard areas, restroom availability, and temporary residence at the project site.

As a separate project, MNS completed a topographic survey of the project area and downstream pipeline alignment. A three-dimensional digital model of the valve house was generated. The survey provided the basis for detailed design of the new flume and associated improvements.

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