Probable Causes and Possible Consequences
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Recommended Actions
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- Areas of trees, brush, and open water provide ideal habitat for burrowing animals.
- An overabundance of rodents increases the chance of animal burrowing, which creates holes, tunnels, and caverns.
- Tunnels may reduce the required length of the seepage path, which could cause internal erosion of the dam.
- Tunnels can lead to the collapse of the dam crest and may cause dam failure.
- Rodent holes make earthen spillways more susceptible to erosion when flow passes through the spillway.
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- Remove trees and brush from the dam and surrounding areas to reduce attractive habitat.
- Start a rodent control program to reduce the population and prevent future damage to the dam.
- Backfill existing rodent holes with mud-pack. Mud-pack is made by adding water to a 90 percent earth and 10 percent cement mixture until a slurry of thin cement consistency is attained.
- Large holes may need to be excavated and backfilled with compacted soil.
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Upstream and downstream burrows can become dangerously close, causing internal erosion that may lead to dam failure.
(Diagram source: FEMA)
Looking inside a rodent hole in Lancaster County that extended from upstream to downstream, entirely through a dam (Note daylight in the center of the photo).
