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Identifying design solutions for stream and wetland mitigation in an urban setting
| Project Lincoln Creek Restoration Civil engineer David Evans and Associates, Inc. Project goals Improve Lincoln Creek’s stormwater capacity and water quality and create a connection from a new university transit center to adjoining neighborhoods, while incorporating sustainable design and student participation. |
The creek restoration was the first step in WWU’s plan to upgrade the transit center that currently provides frequent shuttle service to its campus and connects three major transit systems along Interstate 5 for Whatcom, Skagit, and Island Counties. The center is key to WWU’s efforts to transition students, faculty, and staff to sustainable modes of transportation and provides a valuable resource to the community.
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| Half of an acre of asphalt was reclaimed for the restoration of Lincoln Creek and its associated wetland and buffer complex. The project design included relocation of 530 linear feet of the creek to improve stream functions such as wildlife habitat, sediment removal, and flooding. |
The property for the transportation center has been leased for use as a park and ride since 2004, but in 2006, WWU purchased the former Samish Twin Drive-In Theater property. Before improvements could be made to the site layout and facilities, site stormwater and environmental considerations needed to be addressed to mitigate the impacts of the improvements.
Lincoln Creek had long ago been routed into a steep trapezoidal channel with little room for natural habitat. It frequently flooding into a parking lot. Half of an acre of asphalt was reclaimed for restoration of Lincoln Creek and its associated wetland and buffer complex. The project design included relocation of 530 linear feet of the creek to improve stream functions such as wildlife habitat, sediment removal, and flooding.
Creek relocation provided several challenges for the design team. The team needed to develop a design that could accommodate the flow of the creek, which would eventually be much larger, and conduct the stream restoration in an urban setting. The creek is expected to increase in capacity over time, so the team needed to design for its projected capacity. However, in the interim, the creek’s design needed to ensure that the current water flow would also reach the wetland areas.
The team’s solution was to create a wide section for the creek with a moderate slope. The creek bed was gradual enough that water could enter the wetland area in times of low water levels, yet it still had enough slope that it wouldn’t inundate the creek and increase the risk of flooding.
The creek was also restored to a more natural channel with scour pools and habitat features including log jams, root wads, and nest boxes. To curtail foot traffic from trampling vegetation and damaging the newly created habitat, a pedestrian bridge and crushed limestone trails were included in the design. Moreover, the bridge and trails provided an inviting entry for pedestrians entering from the nearby neighborhoods.
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| One major sustainable design element incorporated into the project was a pedestrian bridge made from an 89-foot recycled railcar. The bridge spans the floodplain and connects the community to the transit center. |
The university wanted to incorporate sustainable solutions wherever possible. One major sustainable design element was the pedestrian bridge, made from an 89-foot recycled railcar. The bridge spans the floodplain and connects the community to the transit facility.
The use of a pre-manufactured bridge was a new experience for the design team. The Railspan railcar was supplied by Skip Gibbs Company. Prior to delivery to the site, the bridge was cut to fit the designated area and a protective coating was applied. DEA designed the bridge abutments, and a thin concrete deck was poured on the top of the bridge to provide an appropriate walking surface.
Traditionally used in more rural areas, the railcar bridge was detailed to aesthetically fit within its urban context. Railspan bridges come from flatcar units that have been retired from railroad service because of changing demands on rail transportation or because the moving parts underneath the flatcar require a great deal of maintenance and upkeep.
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| Under David Evans and Associates’ guidance, Western Washington University students designed and created interpretative signs to explain wetland and stream hydrologic processes. |
WWU wanted its students to have an opportunity to be involved in the project. Students were able to get involved initially with pre-construction water quality testing. Later, under DEA’s guidance, they designed and created interpretative signs to explain wetland and stream hydrologic processes. Water-quality testing sites were constructed at each end of the creek for ongoing student involvement, adding the opportunity for new classes in stream ecology, stream restoration, habitat establishment, and plant biology.
Both DEA and WWU were pleased with the completed project. The restoration of Lincoln Creek was a success and several sustainable elements were used in the project—most notably the pedestrian bridge. Additionally, the project is now a source for future teaching opportunities for the university.
Earlier this year, the Washington chapter of ACEC recognized the Lincoln Creek Transportation Center Stream Restoration project with a 2008 Gold Award for Social, Economic, and Sustainable Design.
Danielle Johnston is a civil engineer with David Evans and Associates, Inc. She can be contacted at drjo@deainc.com.
