North American beavers (Castor canadensis) have been gradually re-establishing populations in Sonoma County after historic extirpation. Beavers have been recognized in recent decades as “ecosystem engineers” that increase biodiversity and riparian system function through their dam building and wetland creation. Although beavers and their dams benefit both natural and human communities, they can also pose a concern for protection of infrastructure where development occurs close to waterways.
Sonoma Water is responsible for the management of miles of waterways within Sonoma County, and beavers have begun moving into some of these streams. Sonoma Water engaged PCI to study the potential effects and considerations stemming from beaver activity in urban waterways, and to identify management approaches to address them. PCI, with collaboration from the Occidental Arts and Ecology Center and Swift Water Design, conducted an analysis of the flood risk posed by beaver activities in one urban stream. Next, the team developed a generalized guidance document for Sonoma Water to use for future work around beavers, with a summary of ecological considerations; steps to analyze flood risks; an array of strategies for managing infrastructure concerns; and measures to protect beavers during essential work in and around the channels.
Some useful tools for working around beavers include monitoring for early signs of beaver activity, installing protective fencing around sensitive trees or culverts, installing pond leveler devices to manage water levels, and monitoring channel conditions to ensure devices are working properly. Key measures for protecting beavers while working in or near the channel include retaining as much riparian vegetation as possible, avoiding work near lodges and during kit season, and working with hand tools where possible.