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For more information on Soil Bioengineering, contact:
Mark Maurer
maurerm@wsdot.wa.gov
Phone: 360 705-7242
Fax: 360 705-6815
or
Sandy Salisbury
salisbs@wsdot.wa.gov
Phone:360 705-7245
Fax: 360 705-6815
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Lower Bear Creek Enhancement Project
The SR 520 Lower Bear Creek Enhancement project was created through a
partnership between WSDOT, the City of Redmond, and King County. The project
successfully combines the following objectives:
- wetland creation and enhancement
- fish habitat enhancement
- wildlife enhancement
- flood conveyance
Project permitting and plan development took several years. The design
concept included Bear Creek floodplain excavation to increase diversity
in wetland hydrology, the creation of a new creek channel to diversify
fish habitat, introduction of large woody debris in the new and existing
portions of Bear Creek, and the addition of a diverse plant community.
Construction plans included project phasing to allow for creation of
the new channel early in the construction process. Phase One was constructed
in 1999, and Phase Two was completed in Fall 2000.
Excavation of the Lower Bear Creek floodplain and new channel were undertaken
in the first stages of Phase 1 construction. Sheetpile was used to separate
the existing and new channels during construction.
After new channel excavation, large woody debris and stream gravel were
installed in the new channel. Large woody debris provides shade and feeding
sites for fish. In addition, it causes scour in the stream bottom, providing
"holes" and deep pool habitat. Stream gravels provide fish spawning
habitat and critical erosion protection to prevent erosion of exposed
soils after new channel construction.
| Construction materials for portions of
the creek included wood, rock and living plants. These materials provide
the combined benefits of: |
- shading and feeding for fish habitat
- bank protection
- creation of pool and riffle habitat
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| Living plants were incorporated into the
banks of the stream by installing layers of soil and live branches
on top of the large woody debris. Live branches are cut from plants,
such as Willow, and are placed in between layers of soil that are
wrapped in a natural fabric. When the wrapped soil layers are watered,
the soil stays moist and the live branches root, providing thick streambank
vegetation. |
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| In conjunction with new channel construction,
a portion of the old channel was filled. Other portions of the old
channel remain open as stream remnants, and will create wetland habitats.
Wood was placed in and around these areas for habitat enhancement.
The new and old channels are separated by log jams to direct flow
into the new channel. |
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| Erosion control was a critical element
of the project, since sedimentation (suspended soil particles in water
as a result of loose soil and water movement) can destroy fish habitat.
This is extremely important since the Lower Bear Creek floodplain
endures heavy winter flooding each year. Immediately following earthwork,
soils were protected against erosion with a combination of mulch (wood
fiber) and seed. Seed species were selected for quick germination
and growth. |
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In some areas that would receive especially heavy flooding, a natural
erosion control fabric was installed to protect the soil. These
areas were also seeded.
Native trees and shrubs were planted in the fall after earthwork
completion, new channel construction and seeding.
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The Lower Bear Creek project is visited by many
people seeking information about natural resource projects. The
site has provided an outdoor classroom for high school and college
classes, as well as for professionals in environmental sciences.
The City of Redmond Bicycle Trail was constructed immediately to
the north of the project and adjacent to the newly constructed Redmond
Town Center. The Bear Creek enhancement provides a natural environment
for trail users.
One year after completion of Phase One construction, salmon are
spawning in the new channel gravels, redtail hawks, and great blue
herons sit on the snags and logs in the channel, and the plants
are healthy and vigorous.
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