Hydraulic Performance of Outlet Works

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“The hydraulic analysis of the flow through a flood control conduit or sluice usually involves consideration of two conditions of low. When the upper pool is at low stages, for example during diversion, open-channel flow may occur in the conduit. As the reservoir level is raised, the depth of flow in the conduit increases until the conduit flows full. In the design of outlet works, the number and size of the conduits and the elevations of their grade line are determined with consideration of overall costs. The conduits are usually designed to provide the required discharge capacity at a specified reservoir operating level, although adequate capacity during diversion may govern in some cases. Conduits should normally slope downstream to ensure drainage. The elevation of good foundation materials may govern the invert elevation of conduits for an embankment dam.”

See also: Hydrology > Normal Flow Conditions > Reservoir Drawdown

Best Practices Resources

Technical Manual: Outlet Works Energy Dissipators (FEMA P-679), FEMA

Technical Manual: Plastic Pipe Used in Embankment Dams (FEMA P-675), FEMA

Design of Small Dams, USBR

Hydraulic Design of Stilling Basins and Energy Dissipators (EM 25), USBR

Hydraulic Design of Reservoir Outlet Works (EM 1110-2-1602), USACE

Other Resources

Simple Steps to Siphoning, WDETN

Trainings

On-Demand Webinar: Inlet and Outlet Hydraulics for Spillways and Outlet Structures

On-Demand Webinar: Terminal Structures and Energy Dissipation at Outlet Works and Spillways

Citations:

Revision ID: 8296
Revision Date: 01/23/2026