Embankment dams and levees are vulnerable to damage from wildlife intrusions and animal impacts

Earth embankments sit where animals want to be: near water, in vegetation, away from people. Nutria, beaver, muskrat, and gophers burrow into them, and grazing animals strip the cover that protects them. A 2011 study put the cost of rodent damage to earthen structures in the United States at more than a billion dollars a year.

Burrows change how water moves through a dam. They raise the phreatic surface, shorten seepage paths, and alter pore pressures, which lowers the factor of safety against slope failure and opens the door to internal erosion. When burrows collapse under rain or equipment, sinkholes follow. Grazing leaves rills and gullies. The lesson draws on four failures: Santa Clara Dam in Utah in 2012, breached through rodent burrows at a cost of $7.5 million; the Iowa Beef Processors waste pond in Washington in 1993, which released 300 acre-feet and derailed five locomotives after inspectors had already recommended removing the animals and filling the burrows; Sid White Dam in Washington in 1971; and a Secchia River levee in Italy in 2014.

Best practices

• Inspect for burrows and animal sign on every visit, and after high water
• Fill and compact burrows; do not leave voids
• Keep livestock off embankments
• Manage vegetation so the surface can be seen and inspected
• Control animal populations where regulations allow

Read the lesson at damfailures.org