The River’s Edge Levee Setback Project, part of the larger Dungeness River Floodplain Restoration Project, is the site of several upcoming volunteer planting and stewardship events with Clallam Conservation District, Jamestown S'Klallam Tribe and the North Olympic Salmon Coalition. Since we are helping project partners to revegetate the floodplain, we want to provide you with a little background on this large-scale salmon habitat restoration project that is being led by both the Jamestown S'Klallam Tribe and Clallam County.
A floodplain is the low lying area adjacent to a stream or river which can accept flood flows in high-water events. Water flowing along a floodplain surface moves more slowly than in the main river. Healthy floodplains have a mix of trees and shrubs, and often have complex side channels where water travels during flood events. They are built of sand and gravel deposited by the river or stream over millennia. Floodplains are complex, dynamic elements of healthy habitat.
The project's goal is to reconnect the river to 143 acres of its historic Dungeness River floodplain by removing an existing US Army Corps of Engineers levee and building 2,600 feet of new levee that is set back from the river's edge. Numerous studies have identified reconnection to the floodplain as an important strategy for the recovery of salmon in the Dungeness River.
When a river is confined to its channel, water moves faster and scours the channel bed causing erosion and downcutting. This happens because the energy of floodwaters are not reduced by spreading out onto a wide, flat floodplain. This causes several problems. High flows can destroy salmon redds (nests), sending eggs or aelvin's downstream never to mature. Additionally, since fine sediment can not be deposited on the floodplain during high flows the sediment is more likely to smother salmon redds when flows do allow sediment to settle out of the water column. Sediment laiden nests are deprived of oxygen, reducing the egg survival. Excess fine sediment moving downstream may exit the river and accumulate in Dungeness Bay, inundating shellfish beds and compromising their productivity.
Reconnecting the Dungeness River to its floodplain can help create more spawning habitat for salmon species. Water flowing onto the floodplain will allow side channels to develop. These side channels are critical areas for juvenile salmon to seek refuge from high velocity flows in the main channel during flooding. As trees and shrubs in the floodplain mature, more large woody debris will also naturally accumulate in the main channel and side channels, creating habitat complexity and places for salmon to hide from predators. The reconnection to the floodplain will benefit Chinook, summer chum, winter steelhead, and bull trout, all listed under the Endangered Species Act. The restoration of this area also creates vital habitat for migratory birds along the Pacific Flyway, as well as year-round residents, like bald eagles, harlequin ducks, and olive-sided flycatchers.
