Dam Safety

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Obstructions in the Principal or Auxiliary Spillway

Probable Causes and Possible Consequences

Recommended Actions

  • Branches, logs, crop residue, sediment, and rocks can accumulate in spillway outlets.
  • Reduced discharge capacity will cause the reservoir to rise and possibly overtop the dam. Prolonged overtopping can cause dam failure.
  • Trees, hay bales, fences, and farm equipment are all common obstructions to flow in auxiliary spillways.
  • Fence lines in auxiliary spillways can catch debris and become a major obstruction to flow.
  • Obstructions reduce auxiliary spillway capacity and cause scouring and erosion to develop.
  • Inspect spillways after large flood events.
  • Remove debris in or around spillway outlets.
  • Use extreme caution when attempting to remove accumulated debris during periods of high flow.
  • Keep your distance when removing debris so that you don’t become trapped in flowing water when the flow increases after you remove the debris.
  • Do not allow trees to grow in the auxiliary spillway. Remove trees and other brush annually. Treat the stumps of deciduous trees with herbicide to prevent regrowth.
  • Do not store equipment or materials in the auxiliary spillway.
  • Relocate fence lines so they do not pass through the auxiliary spillway.


Spillway inlet completely plugged with debris.

Spillway inlet completely plugged with debris.

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