Pump... or Siphon?

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Message: Siphons Can Help Supply Water Needs in Lieu of Pumps

During an effort to construct an upstream pad for a drill rig to perform investigation drilling along the outlet works of the dam, work crews ‐ inadvertently (and unknowingly) placed material over the outlet works. The blocked outlet works were not discovered until the reservoir was at full pool. It was impossible to make irrigation deliveries into the downstream canal. It was the beginning of the irrigation season and irrigators were not able to receive water. The irrigation project needed a solution that would deliver water during the entire irrigation season and not involve the high maintenance costs of renting pumps for a long duration. Calculations were performed and it was determined that a siphon was possible.
Take-aways from the project:

1. The dam crest was notched to reduce the lift height of the siphon.
2. The bending radius of the HDPE pipe was used to elimiate bend fittings.
3. Three 18-inch siphons were installed.
4. Construction time was 5 days.
5. Steel bands were placed around the inlet side of the pipe to counter buoyancy of the pipe.
6. The maximum flow rate was 60 cfs.
7. Vortices formed when the siphon lift was approximately 16 feet. Valves were throttled back and the vortices subsided.

From Guidelines for Use of Pumps and Siphons for Emergency Reservoir Drawdown, Morrison Maierle, Inc. 2012

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  Dam Crest Elevation = 2,864 feet

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  Upstream Face of Dam.

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  Fusion of HDPE Pipe

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  Placement of Siphon Pipe.

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  HDPE Pipe Before it was placed.

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  Backfill being installed over outlet pipe.

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  Aerial view of siphons over dam crest.

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  Dam after repair of outlet works.

Note: The content on this page was originally created as part of DamOutletWorks.org (DOWL, 2018). It has subsequently been updated and reformatted as part of the Dam Safety Toolbox.
Revision ID: 4746
Revision Date: 12/02/2022