Restoring Floodplain Processes to Increase Salmonid Populations

by Eric Ginney, ESA PWA

Looking upstream at the Three Rivers Levee Improvement Authority’s (TRLIA) Feather River levee setback—which increased the Floodplain by nearly 1,200 acres.

Rivers and their floodplains are among the most productive and diverse ecosystems on Earth. In California, particularly its Central Valley, they are also one of the most-altered ecosystems. Water supply and flood management systems generally overlay the network of natural waterways that are host to habitats and species that have been dramatically affected by human change— in some cases pushed to near-extinction or beyond. There is increasing recognition of the importance of rivers and creeks being connected to their floodplains in supporting key ecosystem functions that can increase the number of successfully out-migrating smolts and sustain key in-channel habitats such as pools and riffles. While physical, institutional, and legal constraints on transportation, water supply, and flood management systems create enormous challenges in restoring river-floodplain connectivity, there are also new drivers at work: recognition of species dependence on functional floodplains; deficiencies in existing infrastructure systems to meet societies needs; and the need to rethink society’s infrastructure—particularly our flood management and water supply systems— in light of ongoing climate change.

In this workshop, we explore the functions of, and linkages between, the channel and its floodplain. We examine how fishes use floodplains, and how rivers and creeks interact with floodplains relative to the fluvial geomorphic process that create and maintain the habitat necessary for sustaining salmonid populations. We also explore strategies and design criteria for restoring floodplain habitat that benefits salmonids. Lastly, we touch on how these restoration techniques provide other benefits to society, chiefly increased options for safely managing floodwater, especially when changes in climate are considered.