Seepage and Strainers

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Some dams will develop seepages or flows of water into or through the dam via cracks or joints over time. These water flows can draw objects from the river, including people, trees and plant matter, and trash to the face of the dam. These objects can become pinned against the face of the dam by the force of suction created by the water flowing through the dam. Additionally, the structure of dams is such that they will often catch river debris such as large fallen trees, animal dens, or large mats of plant material against the dam face and spillway crest or between piers. The force of currents moving through the trapped debris can pin a swimmer or diver against the blockage, creating a strainer that allows water to flow through but does not allow larger objects, such as humans, animals, or boats to pass through, raising the possibility of significant injury or death.

Always be alert to the possibility of large clusters of debris and give a wide berth to both the dam structure itself as well as to any floating hazards from trees, plants, and trash.

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Revision ID: 4424
Revision Date: 11/18/2022