Making Room for the River

Expanding floodplains protects fish, wildlife, and people

Farmers frequently build berms along rivers to protect their crops from flooding. When we acquired Dos Rios Ranch, River Partners removed these berms and excavated swales in order to re-activate the San Joaquin and Tuolumne River floodplains. Floodwaters can now spread across the Ranch and nourish newly-planted native trees, shrubs and grasses, which provide homes for wildlife, sequester tons of carbon, and protect downstream communities and neighboring farms from flooding.

Throughout the Central Valley, levees prevent rivers from nourishing adjacent floodplains and the species they support. Most of these levees and the floodways between them are regulated by the state and federal government under a complex set of rules that make modifications to the levees and floodways expensive and time consuming.

Within these official levees, however, some farmers have built informal levees or berms to make it easier to farm in the regulatory floodway. These levees are generally smaller than the official levees, but they can greatly reduce the area of frequently inundated floodplain habitat needed to maintain habitat for fish and wildlife.

A Short Drone Flyover of Habitat Creation at Dos Rios Ranch Preserve.

Restoring the Floodplain: Dos Rios Ranch Preserve

Frequently inundated floodplains are great for fish and flood tolerant plant species, but they are a mixed-bag for the San Joaquin Riparian Brush Rabbit, California’s most threatened endangered mammal. These endangered bunnies were once abundant across the lowlands of the San Joaquin Valley but conversion of the riparian forests to agricultural fields eliminated their habitat. By the late nineties, they were reduced to one population at Caswell State Park, the largest remaining fragment of old growth forest in the San Joaquin Valley.

According to the 1998 recovery plan, only ten to twenty individual rabbits survived the flood of 1986. Under natural conditions, the riparian brush rabbit would move to high ground during floods, but by the late twentieth century most of the high ground was planted in agricultural crops that do not provide the cover they need to hide from predators.

In an ongoing success story, River Partners and the US Fish and Wildlife Service have successfully expanded habitat for the brush rabbit at the San Joaquin River National Wildlife Refuge and along the Stanislaus River near Caswell. To ensure that the bunnies could escape flood waters, we built raised mounds within the revegetated floodplains. These bunny mounds saved rabbits from death by drowning, particularly during short duration floods, but created a new problem. During prolonged floods, bunnies crowded onto the mounds and quickly devoured all of the vegetation exposing them to both predation and starvation.

River Partners learned some important lessons from this experience that we have incorporated into the design of the Dos Rios Ranch restoration project. Instead of building mounds, we have constructed bunny ramps that allow the rabbits to move to higher ground when the site floods. As floodwater rise, the bunnies can save themselves by simply moving up the ramp, which will be vegetated to provide food and cover.

One bunny ramp is visible in the video and was created with soil we excavated to create a floodplain swale for juvenile salmon. When floodwaters rise, salmon enter the excavated swale and bunnies exit via the ramp. And when floodwaters fall, juvenile salmon follow the swale back to the river.

Dos Rios bunny mounds are shown in the left third of the photo, above the road.

At Dos Rios, lowering small levees or berms has created large areas of pooled water teeming with nutrients. These areas provide the perfect opportunity for tiny salmon to rest, forage, and bulk up before continuing toward the Pacific. Without floodplain habitat, juvenile salmon have no place to rest and feed. Instead, they get flushed toward the ocean before they are big enough to survive the journey.

Moving the berms and activating the floodplain provides ideal refuge and rearing habitat for young endangered salmon in the San Joaquin Valley. The floodplain swales not only provide an exit route, they also extend the inundation period so that juvenile salmon have enough time to take advantage of the nutrient rich flood waters during shorter duration flood events.

We are planting a forest the size of 1,500 football fields and allowing it to flood to recover endangered species, protect neighboring communities, and more.

Dos Rios Ranch Preserve and other restored floodplains provide a model for recovery of endangered salmon habitat throughout the Central Valley, an approach championed by the Central Valley Salmonid Habitat Partnership. American Rivers’ Aysha Massell, the coordinator of the partnership, visited the project in late May after the site had flooded and was visibly moved by projects scale and success. “The Dos Rios project is truly inspiring and a great example of what the Salmon Partnership hopes to replicate across the Central Valley.”

The urgent need to respond to more frequent flooding with expanded floodplains is also a central part of the vision laid out in the Central Valley Flood Protection Plan and the Mid-San Joaquin River Regional Flood Management Plans.

Many dedicated partners have come forward to support this new model for ecosystem uplift. Federal agencies including Bureau of Reclamation, US Fish and Wildlife Service, and Natural Resources Conservation Service have been instrumental, along with California’s Department of Fish and Wildlife, Wildlife Conservation Board and Department of Water Resources.

State and Federal regulatory agencies and the Central Valley Flood Protection Board and US Army Corps of Engineers provided leadership with regulatory clearance for a first-ever project of this scale in the San Joaquin Valley.

Our concerted and ambitious work also relies on local communities to support these projects. Together with our partners, River Partners is working to expand the pace and scale of projects like Dos Rios that offer large-scale protection from flooding, and provide a host of other benefits including critical support for endangered species.

 

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Additional co-authors include:  Michael Rogner, Jason Faridi, John Cain, and Terrel Hutton

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