Reservoir Drawdown

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“Where practicable, reservoir release facilities should be provided to lower the pool to a safe level adequate to correct conditions that might threaten the integrity of the dam”. The outlet works should be designed to draw down the reservoir within a reasonable period of time assuming normal inflows from the watershed. Several state dam safety agencies require that dams have the ability to draw down the reservoir pool by a specified depth of water within a certain timeframe. These requirements vary by jurisdiction.

“Low level outlets are provided to maintain downstream flows for all levels of the reservoirs operational pool. The outlets may also serve to empty the reservoir to permit inspection, to make needed repairs, or to maintain the upstream face of the dam or other structures normally inundated”.

See also: Hydraulics > Hydraulic Performance of Outlet Works

Examples

Learn about the important of having an operable reservoir drain at DamFailures.org

Best Practices Resources

Criteria and Guidelines for Evacuating Storage Reservoirs and Sizing Low-Level Outlet Works (ACER TM No. 3), USBR, 1990

Design Standards No. 14: Appurtenant Structures for Dams (Ch. 4: General Outlet Works Design Considerations), USBR, 2022

Selecting and Accommodating Inflow Design Floods for Dams (FEMA P-94), FEMA, 2013

Hydrologic Engineering Requirements for Reservoirs (EM 1110-2-1420), USACE, 1997

Citations:

Revision ID: 6679
Revision Date: 03/16/2023