The Minto Island Bicycle and Pedestrian Bridge will traverse the Willamette River Slough to link Riverfront and Minto-Brown Island parks in downtown Salem, Oregon. GreenWorks in collaboration with OBEC Consulting Engineers
A new pedestrian and bicycle bridge will create an entirely off-street connection linking three parks in downtown Salem, Oregon.
July 9, 2013—A tied-arch bridge planned for downtown Salem, Oregon, whose main span will be free of intervening piers will complete a decades-long plan to connect the city’s three urban parks and more than 20 mi of trails. The project is expected to provide recreational opportunities, encourage the use of nonmotorized vehicles, and boost the city’s downtown economy.
In 1975 Salem officials conceived a plan to connect the city’s Riverfront, Minto-Brown Island, and Wallace Marine parks by way of two pedestrian bridges over the Willamette River. The first of those bridges was realized in 2009 with the renovation of the venerable Union Street Railroad Bridge, a truss bridge that served the Union Pacific Railroad for many years. Now OBEC Consulting Engineers, a firm based in Eugene, Oregon, is finalizing the design of the second bridge, which will be an entirely new structure with a new adjoining trail. “The community has been thinking and envisioning this for many years,” says Annie Gorski, the project manager in the City of Salem’s Urban Development Department. “The Union Street Railroad Bridge was restored for pedestrian access in 2009, and that really moved the momentum forward to getting this last connection.”
The Minto Island Bicycle and Pedestrian Bridge, as the new structure is being referred to, will traverse a slough of the Willamette to link Riverfront Park on the east with Minto-Brown Island Park on the west. From 2009 to 2010 the Salem City Council solicited the views of residents regarding bridge types for the site. In 2010, on the basis of that feedback, the council approved a tied-arch bridge whose main span would be free of intervening piers. That bridge type was selected because both the council and the community wanted a signature-style bridge that could be constructed without having to place piers in the river. “Having no piers in the water reduces the impact on the surrounding environment and allows for continued promotion of recreation in the waterway,” notes Gorski, who explains that “OBEC has taken that 2010 decision, refined the design, and really given it an identity.”
The roughly 500 ft long, 14 ft wide bridge will have five spans. In addition to its 300 ft long main span, it will feature four cast-in-place concrete side spans, each between 30 and 50 long. Two 30 in. diameter steel tube arches will support the main span. Each arch will be approximately 320 ft long and will attach to the superstructure via steel suspender rods spaced at 10 ft intervals. Six concrete piers founded on drilled shafts located on and to the outside of the riverbanks also will support the bridge. “One of the city’s objectives was to minimize any adverse environmental effects, so we’ve located the piers to be outside of the active channel of the slough,” says Bob Goodrich, P.E., the bridge structures division manager and project manager for OBEC.
The bridge will be a clear-span structure with no piers in the water
that might interfere with recreational traffic in the Willamette River
Slough. GreenWorks in collaboration with OBEC Consulting
While there will be no piers in the river channel, the designers also had to ensure that the soil near the bridge foundations on Minto Island and in Riverfront Park would not be unduly disturbed. Both areas, as well as much of the riverfront along the Willamette, were home to industry in the past. Although the Oregon Department of Environmental Quality (DEQ) has halted its regulatory oversight at the former industrial sites on Minto Island and in Riverfront Park in recent years, additional testing was conducted last year to confirm previous soil and groundwater characterization results. On the basis of those data, the DEQ confirmed that constructing the bridge and the adjoining trail would pose no risks to people or the environment.
The bridge’s drilled shaft foundations will require minimal excavation, simplifying the containment of any hazardous materials that may be unearthed during construction. “We will continue to coordinate with the DEQ as we move forward into construction,” Goodrich says. “If hazardous materials are identified during construction, that material will be characterized, sampled, tested, and disposed of properly during construction.” Crews will also be on the lookout for artifacts from the Kalapuyans, Native Americans who once inhabited the area. If any are found, a so-called inadvertent discovery plan will be activated in coordination with the Confederated Tribes of Grande Ronde, an organization of more than 25 Native American tribes with ties to present-day western Oregon. The Oregon State Historic Preservation Office will be kept informed of developments throughout the project.
OBEC is also designing 3,800 ft of new paved trails that will extend from the bridge and through a currently inaccessible part of Minto Island before connecting with existing trails in Minto-Brown Island Park. In addition to designing a new connection to the bridge at the south end of Riverfront Park, the engineers are redesigning an existing trail there so that it will pass beneath the bridge as it runs parallel to the river. “We have to lower that portion of the path three to four feet to provide adequate vertical clearance for bicyclists,” Goodrich explains. “We didn’t want to raise the whole bridge up to provide clearance because that would have cost more money, so we elected to lower the path and rebuild it.”
The entire project is expected to cost approximately $9 million and is being funded by state and federal grants, tax increment financing (which relies on increased property values resulting from the project’s completion), and private donations. If all of the funding is secured in 2013, construction is slated to begin in 2014, and completion is anticipated in 2015. Salem residents will then easily be able to travel from one city park to another and will be able to reach the downtown area by bicycle without having to travel along busy streets. “There are a lot of people who say they want to ride their bikes and recreate but aren’t comfortable in a bike lane or on a street with the kind of traffic volumes we have coming through downtown,” Gorski says. “This will create a pretty significant off-street network for bicycles, pedestrians, Rollerbladers, and other nonmotorized users between south Salem, downtown, and west Salem.” As an added benefit, city officials expect the new circuit to draw tourists to the area and to encourage downtown development. “There are a number of opportunities and benefits,” Gorski says.