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John Muir Institute of the Environment

River Bank Erosion:
Can we live with it?
Many creatures can’t live without it.

America's most beautiful and productive scenic rivers were carved out by geomorphic (land-forming) processes such as bank erosion and channel incision. How would they look when all the erosion is eliminated? As an extreme case, picture the Los Angeles River along the section where they filmed the car racing scene for the musical Grease. This example illustrates the extensive infrastructure sometimes used along rivers for flood and erosion control.

In June 2008, a paper funded by the John Muir Institute of the Environment’s Policy Paper Grant Program and published in the journal Bioscience, challenges policymakers to look at river bank erosion in a new light, as a natural process that sustains ecosystems. "Bank habitat and function are to some degree inseparable from functions within the larger riparian zone…and are vital centers of biodiversity," states this paper by authors Joan L. Florsheim, research scientist, geology, and Jeffrey F. Mount, director, Center for Watershed Sciences, both at UC Davis; and Anne Chin, associate professor, geography, Texas A&M.

Bank erosion releases a variety of sizes of sediment (particles of rock and soil) into every river. Coarse sediment contributes to downstream sandbars that serve as resting habitat for migrating birds, and is important for the survival of mayflies, caddisflies, and stoneflies that feed fish. Gradually eroding undercut river banks that develop over many seasons protect California shrimp and juvenile fish from predators and harbor over-wintering fish during winter storms.

River banks also support riparian plant communities that are colonized by fast-growing, water-adapted sedges, rushes, grasses, herbs, and seedlings of shrubs and trees. Birds that depend on riparian zones include the bank swallow, willow flycatcher, Gila woodpecker, and western yellow-billed cuckoo. Riparian lizards and river otters find food and shelter along the slowly eroding banks.

The authors urge river managers to preserve and restore functionality to rivers by taking a long-range view of the resources required to sustain these ecosystems. In the past, structures were built by property owners and various government agencies that provided protection from erosion for short and vulnerable sections of the river. When the cumulative long-term effects are not taken into consideration, progressive construction of channel bank infrastructure that was originally intended to limit only local bank erosion, tends to lead to channelization of the entire length of the river system. The river then becomes little more than a storm drainage channel, offering few of the benefits for plants, fish and wildlife that are offered by dynamic natural river banks.

The authors suggest a balanced and sustainable approach to accommodate river erosion. This involves widening the spatial extent of the riparian zone within the watershed. They recommend dynamic, process-based conservation, with erosion easements and live vegetation to moderate processes without eliminating the benefits. Understanding cumulative effects of the channel bank infrastructure is an important first step toward restoration and correction of past watershed management failures.

John Muir Institute’s Director, Debbie Niemeier, described the paper as "an example of UC Davis environmental research with the power to transform what matters to communities into solutions, just as it transforms students into environmental leaders." As river managers and policymakers begin to understand what is lost when rivers are armored, the communities along these rivers will once again be able appreciate the biologically diverse resources and recreation that riparian ecosystems provide in urban and rural landscapes.

Reference: (2008) Florsheim, J.L. et al, BioScience: Vol. 58, No. 6, p.519-529.