Lones Levee Setback and Floodplain Restoration Project
Green River Watershed
Lones Levee is located on the north side of the Middle Green River about four miles upstream of the State Route–18 bridge which crosses the river just east of the City of Auburn. The King County Department of Natural Resources and Parks (DNRP) owns the property.
- Maintain or improve existing level of off-site flood and erosion protection for agricultural land, private farms and residences and Green Valley Road.
- Restore natural river processes (channel migration, wood recruitment, etc.).
- Increase quantity and diversity of salmon habitat.
Improved flooding and erosion protection
The removal of this aging flood facility and construction of a modern, setback flood facility will increase protection of existing property and farmland from channel migration and overbank flooding. The current levee has been damaged and will result in erosion and flooding of private property, structures and farmland if it fails. The construction of a new berm at the downstream end of the site will reduce current levels of flooding on the adjacent two properties during large flood events. Mainstem river floodwater surface elevations will also be lower upstream of the site as a result of the levee removal. This is expected to reduce the frequency of inundation of upstream farmland and potentially reduce flooding and sediment accumulation in Burns Creek.
The setback revetment will reduce river bank erosion for adjacent landowners and protect existing farmland, residences and infrastructure from channel migration.
Fish and wildlife habitat
The new setback revetment will reconnect off-channel habitat and increase channel migration, flow splitting , wood recruitment and other natural processes critical to the formation of high-quality, diverse salmon habitat. The result is expected to be increased productivity, abundance, diversity of Green River Chinook salmon and steelhead stocks.
As the reach responds to levee removal, we expect to recover:
- 10 acres of high quality, off-channel habitat immediately landward of the levee that will be connected nearly year-round to the mainstem river;
- 30-45 acres of connected, forested floodplain within, upstream and downstream of the project area;
- 20-25 acres of active river channel that will be: wider and shallower with finer substrate; potentially split into multiple threads with periodic mid-channel bars and islands; higher quality spawning habitat; and more frequently connected to adjacent floodplain areas at lower flows.
- Remove the 1,600 Lones Levee and construct a setback facility.
- Remove>25,000 cubic yards of rock and native substrate from 1,600 linear feet of levee; distribute the substrate.
- Remove 600-800 trees from the levee and oxbow area and distribute them throughout the adjacent river and floodplain areas to be recruited gradually to the river and promote natural river and floodplain processes.
- Constructing a 1,500 foot-long erosion protection facility that consists of:
- 400 linear feet of buried rock revetment, and
- up to 12 engineered log jams;
- Construct a 600 foot-long berm at to maintain or reduce flooding on private property;
- Construct two side channels through the levee to convey water into the old 1950’s river channel; and
- Construct a 1,900 foot-long (0.8 acres) gravel maintenance road.
The large rock that currently covers the river side of the levee will be removed and used to construct a new buried revetment. Removing the rock will expose the underlying native cobbles, gravels, sands and silts which make up the core of the levee. Some of this material will be pushed into the floodplain to form gravel bars that can be eroded by the river and provide spawning gravel for salmon, and some will be trucked to an adjacent King County property where it will be spread and planted with native trees and shrubs.
The new flood and erosion protection facility will include a buried rock revetment and engineered log jams, (large rock and interlocking logs). A gravel maintenance road will be placed on top of the revetment. A shallow berm will also be constructed to reduce overbank flooding across a farm field.
The project 81.4 acre site is owned by King County and mostly within a forested floodplain on the middle Green River just downstream of its confluence with Burns Creek.
The 1,600-foot long levee was built in 1960 with gravel from the river and imported, large rock (rip rap) to protect it from erosion. The levee forms a “T” shape with an access road to the levee that separates two riverine wetlands. The levee provides some minor flood protection to adjacent properties, but does not contain flood water during moderate to large events. Its primary purpose was for erosion control.
This construction of Lones Levee limited channel migration and other habitat-forming processes in the more than 60 acres of floodplain areas adjacent to and downstream of the levee for the past 50 years. It is also a fish-passage barrier, preventing salmon from accessing 4.6 acres of riverine wetland habitat located behind the levee.
Project construction will begin in the spring of 2020, 2021 or 2022 (funding dependent) and will be completed by the fall of the year of construction. Replanting the site with vegetation will occur in the winter following construction.
The mainstem Green River was historically very productive for Chinook and other salmon species. However, the habitat needed for salmonid spawning and rearing has been substantially reduced as a result of landscape and river changes, such as the construction of dams and levees to contain rivers. The 1999 listing of Chinook salmon as “threatened” under the federal Endangered Species Act triggered the need to develop a plan to increase productivity of the Green River Chinook population. The WRIA 9 Salmon Habitat Plan (2005) prioritized the need for juvenile salmon rearing in the mainstem of the Green River and identified specific projects to promote the creation of this habitat such as the Lones Levee Restoration Project. This project will restore critical rearing habitat and protect adjacent farmlands which are now vulnerable because Lones Levee, constructed over 50 years ago, is in disrepair.
Lones Levee 40 percent design drawings (30.5 MB)
The Determination of Non-Significance and SEPA Environmental Checklist posted below are open for public comment through August 30, 2019.
Determination of Non-Significance (638Kb PDF)
For more information about the the Lones Levee Floodplain Restoration Project, please contact Dan Eastman, Project Manager, King County Ecological Restoration and Engineering Services.