R655.  Natural Resources, Water Rights.

R655-11.  Requirements for the Design, Construction and Abandonment of Dams.

R655-11-7C.  Outlet Details.

     A.  All outlets shall have a trash rack to prevent clogging.

     B.  All outlets connected directly to a downstream pipeline shall have an emergency bypass valve.

     C.  All outlets shall have a suitable energy dissipator at the discharge end to prevent erosion of the downstream channel.

     D.  All outlets will be placed on a concrete cradle or encased in concrete unless specifically exempted by the State Engineer in writing.

     E.  All outlets, with the exception of ungated outlets, shall have an operating gate or a guard gate on the upstream end.

     F.  All outlets shall have seepage control measures to reduce the potential for piping along the conduit.  Common methods may include locating the outlet conduit in bedrock and installing a conduit filter drain to intercept seepage.

     G.  Outlets encased in concrete should have battered sides to facilitate compaction against the encasement.

     H.  Every attempt should be made to locate the outlet on bedrock or consolidated materials.  In the event this is not possible, consideration should be given to articulating the outlet to allow for settlement.

     I.  Outlet gates and valves can be either mechanically or hydraulically operated.  In either case the hydraulic lines or mechanical stems must be adequately protected from debris, wave action, settlement, and ice damage.  Buried stems should be encased in an oil-filled pipe supported on pedestals.  No catwalks or similar access structures will be allowed on reservoirs where freezing occurs or significant floating debris is present.  All outlets which are operated with electrical equipment must have back-up generating capability or a manual bypass system capable of being operated in a reasonable amount of time.

     J.  All outlets shall be properly vented to avoid cavitation, surging, and reservoir vortexes.  On low head dams adequate ventilation may naturally occur through the conduit if a free water surface is maintained.  In most cases a vent pipe and air manifold around the perimeter of the conduit immediately downstream of the gate will be required.  The air supply lines should be conservatively sized for the anticipated flows and protected in the same manner as the outlet control lines or stems.

     K.  All operators and supporting equipment for outlet controls should be properly protected and secured.  Particular attention needs to be given to protection from vandals and unauthorized operation.  All outlet controls should be clearly marked as to which way the gates and valves operate so that overloading of a closed gate or valve should not occur.

     L.  Outlet controls should be accessible when the spillways are in use.


KEY:  dams, earthquakes, floods, reservoirs

November 29, 2001

Notice of Continuation July 12, 2001


Effective Date: 12/10/2003