Beaver Damage Mitigation for Roadways

Kevin Swift, Swift Water Design
Topic Area
Sustainability and Resilience in Transportation Systems

Background
In 2017, nearly a thousand beavers were depredated in California alone, and many of these permits were issued for flooding roadways and blocking culverts. Meanwhile, climate change is predicted to worsen extreme weather events, suggesting that the majority of culverts (already undersized) are only going to become more problematic. Additionally, most roads were designed without taking beavers into consideration, and beaver damage mitigation strategies are not well-known. That's why maintenance departments nationwide are wasting valuable man-hours clearing culverts and tearing out beaver dams, only to have them rebuilt overnight. And all the while, roadways remain in danger of catastrophic damage. Obviously, it would much cheaper to prevent damage in the first place, but that's not easy to do.
Inventors, tinkerers and frustrated engineers have been working to defeat the wily beaver for over a century, with limited success. But in the last couple of decades, new designs for beaver damage mitigation structures have proven to be fast, inexpensive, and highly effective solutions for a broad range of beaver problems.

Flood prevention and culvert protection strategies
Beavers are very adaptable and persistent, but they're not deep thinkers. It's possible to exploit their instincts and defeat their dam-building attempts with a few simple structures and strategies.
- Flexible pond levelers are artificial spillways, added to beaver dams, that allow landowners to set and maintain the water level where they want it.
- Culvert protection fences discourage damming and act as super-sized trash racks, while allowing wildlife passage. And used together, they can permanently alleviate the most difficult beaver problems.
- Tree Protection-even if your road's dry there's no guarantee a beaver won't drop a tree across it. This section shows how to wrap and fence trees to exclude beavers, even in snowy areas. Fast, cheap, cheerful, and easy enough a middle-school class can do it.
These strategies have very high (>90%) success rates, can usually be installed by a single person in a day using simple hand tools, and require no equipment or vehicles in the wetted channel.

Case Studies
Here are how these strategies work, and what sort of results they produce:
- A flexible pond leveler, installed in one day at a restoration site, has protected a CalTrans roadbed for four years with zero maintenance.
- At a Sonoma ranch, a culvert protection fence has prevented beavers from damming a pond outflow since 2015.
- In partnership with Napa County Flood Control, a pond leveler was installed to de-water a construction site to allow for bank stabilization, while preserving the beaver pond and habitat.

Wrap up
- How much maintenance is required, and how it's done
- What a typical installation costs
- Quick permitting overview

Abstract Keywords
Beaver Damage Mitigation
Culvert Protection
Flexible Pond Levelers