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(Created page with "Many older dams were not constructed with a means of draining the reservoir. Lowering the reservoir may be needed for temporary construction, for emergency response, or when regular releases aren't needed. Siphons can be a low-cost means of providing a reservoir outlet if one does not exist. The key operational parameters are: (1) the required hydraulic lift cannot exceed the effective local atmospheric pressure adjusted for vapor pressure and frictional losses; (2) the...")
 
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Many older dams were not constructed with a means of draining the reservoir. Lowering the reservoir may be needed for temporary construction, for emergency response, or when regular releases aren't needed. Siphons can be a low-cost means of providing a reservoir outlet if one does not exist. The key operational parameters are: (1) the required hydraulic lift cannot exceed the effective local atmospheric pressure adjusted for vapor pressure and frictional losses; (2) the discharge point of the siphon must be lower in elevation than the body of water to be siphoned; (3) the pipe or hose used for the siphon must be designed to operate at less than atmospheric pressures; (4) siphon outlets should only be used when there are no other feasible options; and (5) siphon outlets are difficult to prime.
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"Many older dams were not constructed with a means of draining the reservoir. Lowering the reservoir may be needed for temporary [[construction]], for [[Emergency Response|emergency response]], or when regular releases aren't needed. Siphons can be a low-cost means of providing a reservoir outlet if one does not exist. The key operational parameters are: (1) the required hydraulic lift cannot exceed the effective local atmospheric pressure adjusted for vapor pressure and frictional losses; (2) the discharge point of the siphon must be lower in elevation than the body of water to be siphoned; and (3) the pipe or hose used for the siphon must be designed to operate at less than atmospheric pressures. Note that siphon outlets can be difficult to prime."<ref name="DS-14">[[Design Standards No. 14: Appurtenant Structures for Dams (Ch. 4: General Outlet Works Design Considerations) | Design Standards No. 14: Appurtenant Structures for Dams (Ch. 4: General Outlet Works Design Considerations), Bureau of Reclamation, 2022]]</ref>


==Siphon Stories==
== Best Practice Resources ==
*[[Siphons when regular releases aren't needed]]
{{Document Icon}} [[Design Standards No. 14: Appurtenant Structures for Dams (Ch. 4: General Outlet Works Design Considerations) | Design Standards No. 14: Appurtenant Structures for Dams (Ch. 4: General Outlet Works Design Considerations)]]
*[[Siphoning May Not Always Be Possible]]
*[[Low Pressure During Siphoning Can Collapse Pipe]]
*[[Pump... or Siphon?]]
*[[Siphons can pose Reservoir Level Control Challenges.]]


==Siphon as an Outlet Replacement==
== Other Resources ==
4 Key Questions that must have a Yes answer:
{{Document Icon}} [[Simple Steps to Siphoning | Simple Steps to Siphoning, WDETN]]


#Is the dam small enough and at a low enough elevation so that the use of a siphon is physically possible?
==Examples==
#Will abandonment of the original outlet works not impact the reservoir's ability to pass the required inflow design storm (dictated by regulatory agencies)?
{{Website Icon}} [[Common Questions about Siphons | Get answers to some of the common questions about siphons]]
#Is there an alternate means to passively control reservoir level to prevent overfilling?
#Can the siphon reasonably be used for emergency drawdown if needed (in combination with pumps in some cases)?


References
==Trainings==
*[[File:Simple Steps to Siphoning.pdf]]
{{Video Icon}} [[On-Demand Webinar: Design of Siphon Systems]]
*[[File:Guidelines for Use of Pumps and Siphons for Emergency Reservoir Drawdown.pdf]]
 
*[[File:Drawdown System Selection Flow Chart.pdf]]
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Latest revision as of 23:42, 26 January 2026

"Many older dams were not constructed with a means of draining the reservoir. Lowering the reservoir may be needed for temporary construction, for emergency response, or when regular releases aren't needed. Siphons can be a low-cost means of providing a reservoir outlet if one does not exist. The key operational parameters are: (1) the required hydraulic lift cannot exceed the effective local atmospheric pressure adjusted for vapor pressure and frictional losses; (2) the discharge point of the siphon must be lower in elevation than the body of water to be siphoned; and (3) the pipe or hose used for the siphon must be designed to operate at less than atmospheric pressures. Note that siphon outlets can be difficult to prime."[1]

Best Practice Resources

Design Standards No. 14: Appurtenant Structures for Dams (Ch. 4: General Outlet Works Design Considerations)

Other Resources

Simple Steps to Siphoning, WDETN

Examples

Get answers to some of the common questions about siphons

Trainings

On-Demand Webinar: Design of Siphon Systems


Citations:

  1. ↑ Design Standards No. 14: Appurtenant Structures for Dams (Ch. 4: General Outlet Works Design Considerations), Bureau of Reclamation, 2022


Revision ID: 8304
Revision Date: 01/26/2026

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