Task Force recommends bridge types to study
Out of five options, the French Prairie Bridge Task Force recommended that Wilsonville City Council direct staff to study suspension and cable-stayed bridges before it ultimately selects which type of bridge would run across the Willamette River along Boones Ferry Road in Wilsonville.
The City will choose whether to accept the Task Force recommendation for the French Prairie Bridge or steer staff in a different direction at the Jan. 7 Wilsonville City Council work session.
According to City of Wilsonville Capital Projects Engineering Manager Zachary Weigel, the Task Force chose the suspension and cable-stayed bridges because they weren't the most expensive option, are aesthetically pleasing and would have less environmental impact than other options, which included tied-arch, steel truss and steel girder. Weigel also said people who attended the open house and participated in the online survey related to the bridge options generally favored the suspension and cable-stayed options. The St. John's Bridge in Portland is a suspension bridge while the Tilikum Crossing in Portland is a cable-stayed bridge.
"They (Task Force members) felt those two bridges would be the best for tourism interest," Weigel said. "They are more aesthetically pleasing bridges than say the steel girder or steel truss."
However, Weigel said that a minority of Task Force members preferred the steel girder bridge because it was less expensive and they believed the City could make it more appealing.
"(Some said) They could add railing or artwork to make it more aesthetically pleasing," Weigel said. "The steel girder bridge is pretty plain. It's
kind of like the I-5 Boone Bridge."
Unlike the other three options, the suspension and cable-stayed bridges would not require piers to be placed in the Willamette River or within the Boones Ferry Marina parking lot. The steel girder option, meanwhile, would require three piers to be placed in the Willamette River. Piers in the water would require the city to remove river bank material, which impacts vegetation, and closes access to the Willamette River during construction. The tied-arch bridge was the most expensive option.
Weigel said the suspension and cable-stayed options are similar in terms of environmental impact and cost but have one key difference.
"The key difference is the towers for the cable stayed bridge are 160 feet tall and for the suspension bridge the towers are half that height," he said. "The big difference is the visual impact. The renderings we're going to do will help people visualize what those two bridges will look like and how different they'll be in that setting."
After the two bridge types are decided upon, Weigel said the study will include more detailed cost estimates, renderings of the bridges from different viewpoints and more detail on impacts to the Willamette River, Boones Ferry Park and the Boones Ferry Marina.