upper carlson floodplain restoration project · 2015-06-11 · b e c k l e r r i v e r m i l l r i...
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SNOHOMISH COUNTY
KING COUNTY
DUVALL
SAMMAMISH
SNOQUALMIE
SKYKOMISH
CARNATION
NORTHBEND
FallCity
Preston
During the summer of 2014, the King County Water and Land Resources Division removed a 1600’ levee and revetment and constructed a new 1200’ revetment along Neal Road. These actions have begun to restore natural river processes along this reach and reconnect the river with 50 acres of forested floodplain.
The set-back revetment includes four log structures intended to protect the road and private property from the river as it migrates across the floodplain, while also providing good fish habitat. The log structures are backed by a new 850-foot long rock revetment at the lower end of the site to provide additional protection where the river is most likely to migrate.
About 300 trees were felled to remove the levee. With their rootballs and much of their length left intact, they were placed in the floodplain, where they will be recruited to the river as it migrates. As placed and standing trees fall into the river, log jams should form, providing high quality edge habitat for salmon.
Removing the levee and rock bank has allowed the channel to widen and begin to migrate, restoring the river’s connection to its floodplain. Initially the river channel may widen rapidly, followed by slower migration as wood falls into the river. These processes will form gravel bars and log jams that provide salmon spawning and rearing habitat that has been missing from the area for many years.
Sixteen acres of invasive knotweed were also treated across the floodplain, and the site is being planted with about 11,000 native trees and shrubs. Soil excavated from the project area was provided to nearby farmers to build farm pads that help protect farm animals and equipment during flooding while reducing disposal costs.
King County will continue to assess the project’s impacts on both flooding and salmon habitat. The ten-year monitoring plan includes mapping habitat features, documenting channel changes, tracking fish use, and monitoring water levels and vegetation.
PURPOSE/NEED:The Upper Carlson levee removal project
was undertaken to restore critical habitat for threatened Chinook salmon and steelhead on the
Snoqualmie River. The current channel was excavated in the 1930’s to straighten the river and the levee was built
to stabilize it, but doing so removed fish habitat.This project replaces needed flood and erosion protection
in a way that allows high quality habitat to be restored in the river and floodplain.
Upper Carlson Floodplain Restoration Project
1505_4579_WRIA7_FactSht_UPPER_CARLSON.indd skrau
Looking upriver, this aerial view shows the completed project in October 2014.
PROJECT SITE AT FALL CITY NATURAL AREA
★
PHOTO BY NED AHRENS
Department of Natural Resources and ParksWater and Land Resources Division
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Upper Carlson Floodplain Restoration Project
FUNDING FOR ACQUISITION, DESIGN AND CONSTRUCTION FOR THIS PROJECT WAS PROVIDED BY:
n Washington State Salmon Recovery Funding Board (SRFB);n Puget Sound Partnership’s Puget Sound Acquisition and
Restoration (PSAR); n National Oceanic and Atmospheric Administration (NOAA)
from the Nature Conservancy;n Department of Ecology’s Floodplains by Design grant with
support from The Nature Conservancy;n U.S. Environmental Protection Agency from the Snoqualmie
Tribe;n King County Flood Control District’s Cooperative Watershed
Management Grant; n King County Conservation Futures Levy; andn King County Department of Natural Resources and Parks
COST: $3.5 million
FOR MORE INFORMATION: www.kingcounty.gov/environment/animalsAndPlants/restoration-projects/upper-carlson-floodplain-restoration.aspx
The white lines show how the right bank of the river is expected to move into the forested floodplain over the years.
Pile-supported structures constructed at the site will provide flood protection as the river migrates into its newly-accessible floodplain.
During flooding in January 2015, the riverbank moved right significantly; the river is about 40’ wider than before construction.
Engineered LogjamsNew Rock RevetmentPredicted 10yr MigrationPredicted 20yr MigrationPredicted 50yr Migration
0 500 1,000Feet
E