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.
Examples
Best Practices Resources
Dam Safety Warning Signs Best Practices (FEMA P-2188), FEMA
Trainings
On-Demand Webinar: Identifying Hazards and Improving Public Safety at Low Head Dams
Citations:
Revision ID: 7331
Revision Date: 07/19/2023