New Oaks Bottom culvert installed; remediation begins
What had seemed like a very difficult challenge was successfully completed in a remarkably short period of time, at the Oaks Bottom Wildlife Refuge Habitat Enhancement Project, in August.
This large-scale project – a cooperative effort among Bureau of Environmental Services (BES), Portland Parks & Recreation, and the U.S Army Corps of Engineers – makes improvements to habitat for protected wildlife species, and adds amenities along the Springwater Corridor Trail. It should also reduce mosquito problems in the summertime.
With the Springwater Trail and railroad berm excavated, contractors installed the open bottom section of the new culvert, including the culvert arch footings. A cofferdam held back Willamette River water from entering the lagoon, allowing for a dry work area.
"Because this is an open-bottom culvert, it's going to have a natural grade going through," explained LKE Corporation President and Lead to Ecologist L. Kim Erion on August 25, as the culvert arches were being placed.
"We've put in stream cobble and small riprap, and sand that will be graded in, and then smoothed out on both sides – so it will be more of a channel structure, rather than just a flat bottom culvert," Erion explained.
Low summertime water levels and and low river tides created a challenge – the barge-mounted crane couldn't get close enough to the worksite to place the precast 20,000 pound arch sections in place.
"But we've solved this problem by using an ancient construction technique, just like the Egyptians," quipped Erion. "The crane is lowering each arch segment as far back as it can reach onto steel pin rollers in the keyway; then the excavator pulls it, on the 'rollers', into place."
With the arch segments now in place, contractors have been working around the clock to fill the cut in the berm, tamping down the material layer by layer, until it was back at grade with the Springwater Corridor Trail.
By Labor Day, the Oregon Pacific Railroad tracks were in back in place, and trains were running again. By the end of October the Springwater Trail will again be open through Oaks Bottom.
As THE BEE visited the site along with Portland BES Capitol Project Manager Sean Bistoff on September 5, we found looking up at the new culvert to be an awesome sight.
"The work that has been done so far is incredible," marveled Bistoff. However, he added, this project is far more that replacing a culvert.
"By removing the old culvert and the small dam – and adding roughly 2,000 linear feet of channel through Oaks Bottom, from the new culvert to the edge of the lagoon – this project is converting the area from being a reservoir into being a well-functioning wetland, which now will fluctuate naturally with the Willamette River water elevation."
The project's focus has been on providing juvenile salmon a refuge from the open river, in the lagoon, during their migration to the sea, Bistoff pointed out. "But it's also a project that benefits all native species that use this wetlands – including beaver, otter, mink, deer, and the many songbirds that make this home; improvements will benefit many species."
Before the project ends, workers will fine-tune the depth of the slough channel, continue installing channel-side amenities, and create a new "bump-out" viewing area along the Springwater Trail over the culvert.
The Springwater Corridor Trail should be open again by, if not before, Hallowe'en.