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Preventing Rodent Damage to Flood Control Facilities

Abstract

In California, flood control facilities protect millions of people and critical infrastructure from flood events by containing water and debris behind engineered structures. Rodent burrow damage to flood control dams and levees results in failure to meet federal and state structural certification criteria. Non-certified structures pose substantial damage risks during flood events and are ineligible for federal flood insurance and reimbursement programs. Most dams and levees are compacted earth, faced with rock, and topped with gravel access roads. These facilities provide excellent habitat for ground squirrels; the rocks provide cover and the creeks, neighborhoods and nearby agricultural fields provide abundant food. Ground squirrels form the base of the food chain for raptors, coyotes, bobcats, and mountain lions, which routinely foraging along facilities. The Ventura County Watershed Protection District developed an Integrated Pest Management Program (IPMP) to prevent rodent damage to flood control facilities. We found that small amounts of anticoagulant (diphacinone) in bait stations along flood control facilities target ground squirrels with low risk to other fauna. The California Department of Fish and Wildlife, other conservation agencies, and members of the public have requested anticoagulant use be terminated to avoid secondary poisonings. Alternative controls do not provide the level of protection necessary to meet structural criteria. The current registered diphacinone label requires verification of pest infestations before application. However, infestation must be prevented at flood control facilities. Treating the few dispersing squirrels avoids treating an entire colony with anticoagulants, and therefore much less bait enters the food chain. Ventura County lobbied to change the label to allow some bait to be left in the bait stations to control dispersing squirrels. Discontinuing diphacinone is not yet an option, but we plan to conduct studies to further improve bait station design and bait application protocols, coordinate with neighboring landowners, and revise the IPMP to reduce bait use.

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