ASDSO Dam Safety Toolbox

Hydraulic Roller

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Image Source: USACE

The hydraulic roller is one of the most common and most lethal hazards of low-head dams. Under certain water conditions, a dangerous submerged hydraulic roller can form immediately downstream of a low-head dam. As the water flow crests and falls to the base of the dam, it creates a recirculating current that pushes anything caught in it to the bottom of the stream, dragging it along the stream bed, then releasing it up to the surface of the water, then sucking it back into the face of the dam. This circulation can keep people, boats, and other objects trapped for an extended amount of time, repeatedly slamming them against the dam wall. These forces are brutal and largely inescapable. The surface of the water can often appear to be calm, hiding the submerged dangers below.


Learn more about the dangers of hydraulic rollers as experienced at Dock Street Dam (

Best Practices Resources

Dam Safety Warning Signs Best Practices (FEMA P-2188), FEMA


On-Demand Webinar: Identifying Hazards and Improving Public Safety at Low Head Dams


Revision ID: 7331
Revision Date: 07/19/2023