Restoring salmon runs requires floodplain restoration

Spring 2014

Floodplains play a quiet but important role in the health of the landscape. They store nutrients, filtering pollutants and providing nourishment for a vast array of terrestrial and aquatic life. They absorb millions of gallons of what would otherwise be destructive floodwater, recharging the groundwater system and then slowly releasing it to nearby streams. They provide refuge for young salmon to forage and rear free from the battering of swift-moving waters. And when adult salmon return to their natal waters, the processes that support functioning floodplains support the creation of spawning habitats to perpetuate the epic life cycle.

When rivers are connected to their floodplains, the channel is able to migrate naturally. This process creates side channels, back-water sloughs, and other off-channel habitats for salmon. During high flow events, water is distributed across floodplain habitats—dissipating hydraulic energy and increasing the exchange of nutrients between aquatic and riparian habitats.

But floodplains are in trouble. Development, in both rural and urban settings, is degrading these vital habitats. Large portions of floodplains no longer function naturally because they have been filled, paved and diked, and otherwise restructured to meet urban and agricultural needs. Development has disconnected rivers from their floodplains and destroyed upland and wetland vegetation. The ecological implications are visible on the landscape—increased frequency and ferocity of flooding, loss of biodiversity, and declines in the region’s once abundant salmon runs.

If we are to rebuild our region’s salmon populations, we must address floodplains: protecting what is still there, and restoring the high-value areas that have been lost. This won’t be easy, as it requires us to revisit the way development occurs. Together we must find solutions to ensure that floodplains function as nature intended, local communities and local agriculture continue to thrive, and salmon return to our waters for years to come.

Learn more about floodplain habitat and salmon...

Home page photo courtesy Bonneville Power Administration