Santa Cruz filling in squirrel holes on San Lorenzo River levee with concrete [Santa Cruz Sentinel, Calif.]

Jun. 22—SANTA CRUZ — Walkers, runners and cyclists on the San Lorenzo Riverwalk may have found themselves befuddled by the numerous blobs and smears of dried concrete covering the river levee, primarily between Water Street and Felker Street.

The concrete-infused soil is part of an effort that began in late May by the city of Santa Cruz Public Works Department to fill in the tunnel systems created by California ground squirrels on the San Lorenzo River levee in order to receive a certification from the Federal Emergency Management Agency, which will keep flood insurance rates down for residents of the area.

According to Santa Cruz Public Works Operation Manager Filipina Warren, who is overseeing the project, the mix of cement, bentonite and water being used to plug the ground squirrels' tunnel systems has no adverse effects on the soil or wildlife in the area that she is aware of at this time.

"Grouting is a United States Army Corps of Engineering recommended method for repairing damage to earthen embankment flood control structures caused by burrowing animals," Warren wrote in an email. "The city of Santa Cruz's levees have sustained damage from burrowing rodents. Grouting was selected because it is a cost-effective and a minimally-invasive method of repair for burrowing rodent damage."

According to press release from the city, "Burrowing rodents are a threat to levee stability. Mitigation, such as population control, is required to proceed with FEMA certification. All mitigation activities shall be conducted with the highest level of concern and best practices to promote and preserve habitat value and conserve the aesthetic and environmental benefits that the San Lorenzo River levee provides to the community. City requirements include a biological survey of the area and avoidance of identified bird nests."

Constructed in the 1950s as a flood mitigation project through a partnership between the city of Santa Cruz and the U.S. Army Corps of Engineers and spurred by the devastating flood of 1955, the San Lorenzo River levee was managed by the U.S. Army Corps of Engineers until the summer of 2020.

In July of that year, the city received notification from the U.S. Army Corps of Engineers that the San Lorenzo River flood control project construction was officially completed and operation and management of the levee would now be solely in the hands of city government.

As the manager of the levee, the city is required to receive a FEMA certification of the flood control project within three years of it changing hands, which is next month. If the city does not receive the FEMA certification, which needs to be renewed every 10 years, it would risk losing the 50% discount on flood insurance rates for all properties within the floodplain of the San Lorenzo River. This discount saves property owners in the area about $1.5 million annually in flood insurance rates, according to a Santa Cruz City Council agenda report from December of last year.

The city hired Sacramento-based MBK Engineers to ensure that the FEMA evaluation criteria are met, which include an updated base flood elevation, engineering evaluations and the identification of federal code deficiencies. The consultants identified two maintenance activities that needed to be conducted before the city could be certified: a vegetation management project and burrowing rodent mitigation project.

"The United States Army Corps of Engineers requires Levee Maintaining Agencies to both reduce burrowing animal activity on or in flood control structures and repair any damage caused by burrowing animals," wrote Warren. "Burrowing rodent mitigation strategies that solely focus on population reduction do not adequately address damage already sustained."

The vegetation management project, which cost around $300,000, was completed earlier this year and the fumigation of the soil, which began in late May, and the grouting phase of the rodent mitigation project, which is estimated to cost about $200,000 is still underway. According to Warren, the timeline for completion of both phases is expected by the middle of July.

Questions or concerns about the rodent mitigation efforts should be directed to Warren at 831-420-5559 or fwarren@santacruzca.gov.

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