BY STEVEN H. MILLER
Construction on water is a significant challenge. Factor in a fast- moving river and a waterfall producing high-velocity currents on the downstream side and you’ve complicated the project tenfold. To repair the Willamette Falls Fishway, Advanced American Construction met those challenges with ingenuity and innovation and won the 2022 Construction Risk Partners Build America Award in the category of Environmental Enhancement.
Willamette Falls is situated in the midst of the Willamette River in Oregon, between Oregon City and West Linn, about 30 miles upstream from Portland. The falls— about 1,500 feet long with an elevation change of about 42 feet — formed an im- passable barrier for river navigation until the construction of the Willamette Falls Locks along the northwest bank (the West Linn side), which opened in 1873 and bore boats upstream and down until 2011.
The falls also presented a challenge to salmon migrating upstream to spawn. When the T.W. Sullivan hydroelectric plant was built at the bottom of the falls in the late 1800s, a fish ladder was carved out of the solid rock to give the salmon a path upstream. In the 1970s, that natural fish ladder was replaced by a man-made structure, a 900-ft-long serpentine concrete channel that winds around the falls, the hydroelectric plant and a paper mill that is no longer in service.
Over five decades, the river took its toll on the man-made fish ladder, creating issues with stability that prompted the restoration and repair project undertaken by AAC for the Oregon Department of Fish and Wildlife (ODFW). One of the concrete aprons at fishway leg 2 had become dislodged. A structural joint on the transport channel needed to be reworked to allow for movement. A tensioning sys-tem needed to be added at fishway leg 1 to hold it together. Unless they were repaired, scour would continue at fishway leg 2, and the separation of the structure at leg 1 could lead to failure of the fishway in the near future.
“A VERY CHALLENGING SITE…”
The site posed significant difficulties: It is right in the middle of the river. Much of the access was only by water, and a significant amount of the work had to be performed on or over the water, which affects both logistics and worker safety. Water level of the river is not constant, it depends on the weather in this, one of the rainiest parts of the West. Water levels at the bottom of the falls are also affected by the operation of the hydroelectric plant, where the strong current made access problematic. Moreover, the river’s water and its precious population of salmon had to be protected from pollution by construction activities.
Other complications included the COV- ID-19 pandemic and a brutal wildfire season in the Northwest. As COVID-19 rose, AAC turned to the Oregon-Columbia Chapter AGC and AGC of America for guidelines and best management practices, and were able to develop a pandemic preparedness plan clearly highlighting proactive solutions and responsible preventative measures that allowed the project to continue safely. The summer of 2020 also saw the most destructive wildfire season in Oregon’s history, with more than a million acres burned and 40,000 people needing to evacuate their homes. The smoke-filled air posed an extra burden for the project.
There were repairs on both the upstream and downstream sides of the falls. At the bottom of the falls, some of the work could be performed on land (rock) but getting there wasn’t easy.
“There was no land access at all,” explains AAC Operations Manager Evan Clemson. “All the material, personnel and equipment had to come from the marine approach.”
AAC used a ramp barge to move equipment, materials and a drilling subcontractor’s equipment to the site. Fast-flowing water discharged from the hydro-electric power station made it difficult for the barge to get close. AAC coordinated with the electric utility, Portland General Electric, to get a slowdown of the power plant that would tame the current and allow the barge to reach the site. The slowdown was limited by high power demand in the heat of the summer, but even so, the reduced flow lowered the water-level beneath the falls enough to create draft problems for the barge. “We had to dodge some rocks to get in there,” recalls Clemson.
A drilling subcontractor installed 7” diameter micropiles to secure the foundation of the existing fishway, and shotcreted another fishway foundation surrounded by gabion rock baskets. Then AAC set reinforcing forms and poured a concrete pile cap over the new micropiles. They also installed and torqued 40-ton tensioning rods to hold together fishway leg 1 and limit thermal expansion. In addition, they added a joint sealant system in the fishway, and made general concrete repairs.
INNOVATIVE CONCRETING
On the upstream side, the work was primarily concreting. A failed concrete apron of the dam surrounding the falls had to be partially removed and repaired. There was a narrow causeway that allowed personnel to walk out on the site, but all equipment and materials had to come by barge pushed by a tugboat. AAC assembled a crane barge and had to sneak a 100-ton crane underneath the power lines that crossed the river. The crane performed concrete demolition on the fishway apron, picked material and a mini excavator onto the site, and removed demoed concrete.
“Placement of concrete on the upstream side was the biggest mousetrap that we had to figure out,” states Clemson. “I got quotes to pump concrete up there, but it just wasn‘t feasible and reliable,” not to mention the potential risk of concrete spillage into the river.
“We really looked at opportunities to produce high-quality concrete right there on the upper part of the falls. Our scheme involved mixing trucks on the barges, where we actually produced the concrete and pumped it right in place.”
They purchased two barrel trucks and drove them onto the flexifloat modular barges at a local boat ramp. Tugboats pushed the barges into place above the falls. Instead of a batching plant to feed the trucks, they brought in supersacks of dry-mix concrete, and used the crane to load into the trucks.
“For something around 350 cubic yards of concrete,” says Clemson, “it was a unique way to do it, but it solved the problem for us.”
To protect the river from contamination by construction equipment and activities, AAC made sure all the equipment was in good order and free of oil leaks, and it all had secondary containments. They monitored the river daily for turbidity generation, and deployed straw waddles, silt fence and related environmental controls for the land work. They had sorbent materials at the ready, if needed, and provided concrete slurry containments.
SAFETY FIRST
While construction is an inherently dangerous occupation, working over water increases the safety concerns significantly. In addition to daily safety meetings on-site, and detailed planning of every operation, AAC coordinated with Clackamas County Fire & the Sheriff’s Office Marine Division, the local emergency responders, “about how they would approach, and what they might need from us as far as support,” Clemson recalls.
“We also talked through with our personnel how to self-evacuate if we did have an incident or an injury. A lot of the workers on this job are also divers,” although none of the work on this project was under water. “When they’re not diving, they work as pile- bucks (marine carpenter). The divers have a more-than-common level of training in first aid and safety preparedness, because often they are the individuals who have to treat their fellow divers” in an emergency. Despite the challenges, the project was completed in time for the annual fish migration, and before the unpredictable fall weather coul impact construction. Bring on the salmon!