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Past, Present Infrastructure Cross Paths in Oregon

The concrete diversion dam in the Willamette River is one of the most prominent remaining elements of the Eugene Millrace
The concrete diversion dam in the Willamette River is one of the most prominent remaining elements of the Eugene Millrace. Courtesy of the Oregon Department of Transportation

When the ODOT constructed replacement bridges on Interstate 5 across the Willamette River, it took great care to preserve elements of the Eugene Millrace.

July 29, 2014—The past and the present of Eugene, Oregon—expressed as concrete infrastructure—intersect at the point at which Interstate 5 crosses the Willamette River. The remnants of the Eugene Millrace and its diversion dam are visible there, framed by the sleek lines of the new deck arch bridge recently completed by the Oregon Department of Transportation (ODOT).

That these two infrastructure elements would share a future together was not a foregone conclusion when the ODOT inspectors first discovered sheer cracks on the bridge’s predecessor, a span completed in 1961. The defects were deemed so significant that a parallel temporary span was built in 2004 and the design work began on a permanent replacement. (See “Oregon Program Bridges the State’s Transportation Gaps,” Civil Engineering, July 2010, pages 32-35.)

One hundred and fifty-three years earlier, Hillyard Shaw, an early settler, worked at the same site, building the first iteration of the Eugene Millrace in 1851. That was just five years after Eugene Franklin Skinner built the first structure in what would become Eugene City and later Eugene. The millrace fueled the growth of Eugene from a log cabin outpost into an important industrial center in the state, powering a collection of mills and early industrial facilities.

“This is the classic entrepreneurial story in America,” says Chris Bell, the cultural resources program coordinator with the ODOT. “The river ran wild for a long time here in Eugene. They built this fabulous structure and then the river would flood and wipe it all away. Then they would have to rebuild.”

When steam and electricity began to replace water-driven wheels as the power of choice for industry, the millrace enjoyed a second life as a recreational center. Portions of the millrace pass the campus of the University of Oregon, where students prized it for winter ice skating and summer water sports. The university staged a popular annual parade of decorated canoes and elaborate floats on the millrace, drawing national attention in the years leading up to World War II.

Although it would be difficult to overstate the importance of this infrastructure to Eugene’s development as a city, by the time the bridge replacement design began in earnest the millrace was essentially a historical relic—the most prominent element being a diversion dam and various head gate and containment features at the start of the millrace. The question ODOT faced was if and how the existing millrace elements would be preserved.

“It took some convincing to make the case that this was something worth making some really significant design shifts to avoid,” Bell says. “But I think once we did our homework on the resource, and once we understood the significance, it really informed the challenges. I think what was really cool was there was an early recognition by the design team that this wasn’t just a random artifact.”

Bell says the team approached the project with a goal of no adverse impacts on the millrace infrastructure and developed a detailed plan to achieve that goal. This was complicated by the design of the new bridge span, which essentially has a lone footing in the river and two piers near the approach spans. 

Image of the new bridge over the Willamette River, that crosses over portions of the Eugene Millrace

The graceful arches of the new bridge over the Willamette River
cross over portions of the Eugene Millrace. Some concrete
remnants of channel improvements are visible in the foreground.
Courtesy of the Oregon Department of Transportation

“You have to rethink your footing, and a footing placement can obviously make a big difference when you are thinking about a massive bridge like that,” Bell says. “With basically one of three landings in this location, it was a big deal.”

A team that included Hamilton Construction Company, of Springfield, Oregon, and OBEC Consulting Engineers, of Eugene, devised a plan to cover the millrace elements with a geotextile sheet and 10-plus ft of compacted soil. Upon this was built a bridge and scaffolding that serviced the heavy equipment and workers needed to remove the original bridge, build the replacement bridge, and then remove the temporary span.

Avoiding elements of the millrace turned out to be an even greater challenge than originally expected. Despite the best efforts of the team to map the historical elements of the millrace, during construction workers uncovered long-buried elements that weren’t on the maps.

“A couple of times when we were digging for these piers, we would drill into the millrace without knowing it was there,” Bell says. “A couple times we were able to shift the location of the footing a little bit. In other cases there was really no adjustment at that point.”

In those cases, the team made as clean a cut as possible and took an archeological approach. These incursions became learning opportunities that revealed a great deal about the millrace and 19th-century infrastructure construction methods in general.

The team found that the millrace was constructed and reconstructed over the years with a constant eye to minimizing the amount of materials used. Where a soil bank or stacked stones was deemed sufficient, they were used. In many places, the infrastructure is no more than a dug channel. Bell says they saw three distinct phases. The period of 1851 to roughly 1890 was marked by stones. Concrete was added to cover and reinforce the stones beginning in approximately 1890. And at the turn of the 20th century, workers started reinforcing the concrete with discarded or surplus trolley-line rails.

“We saw this continuum of improvements,” Bell explained. “The quality of the concrete that was used and the quality of the slag, all the different components, varied [by] how far down you went. I think that was the most edifying thing. There really weren’t many artifacts, per se. It was mostly the construction and what you could learn from it.”

When the bridge replacement was complete, the construction team removed the compacted soil and finally the geotextile layer. Bells says he felt “elation” and a “bit of surprise” when they realized the millrace had survived the project unscathed.

“They really came up with a clever way to essentially bury it until we were done and then uncover it. Honestly, it [is] a pretty stout resource. But we were building a bridge over it with substantial weight and ‘demoing’ a bridge that dropped a ton of weight. I wasn’t sure what might have gotten damaged. I was pleasantly surprised to see that we basically pulled the geotextile off and found more or less what we left years earlier.”

The $204-million project is essentially complete. The new bridges are open, orkers on-site making improvements to a nearby park. The project includes a bike trail and small bridge that employs the box beams from the temporary bridge. Interpretive signs will identify elements of the millrace and diversion dam to bicyclists and pedestrians.

What will become of the millrace remains an open question. A small amount of water naturally diverts from the river into the millrace, but it is a fraction of what once was there. Because some elements were prone to erosion, the millrace was dogged by questions of who was responsible for maintenance. But there are those in the community who would like to see the structure included on the National Register of Historic Places or restored as a working stream for recreation.

“Through this project we are going to have interpretation around the millrace,” Bell says. “We’re going to have people understanding it better. I think it’s the classic scenario where it’s forgotten and ... raising awareness never hurts.”



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