Erosion of the Bear Creek streambed beneath the Jackson Street bridge in downtown Medford is forcing the creek to flow underground, one of two potentially major new barriers to fall chinook salmon now migrating through Medford.
The creek now tumbles about three feet over an exposed city sewer line encased in concrete that previously had been all but buried in the streambed just beneath the bridge's south side.
The water then flows completely under a 15-foot-wide rock and concrete mass spanning the creek just beneath the bridge's north side, gurgling through an eroded tunnel before bubbling into a pool where at least one chinook was trapped Wednesday.
Both obstructions had water flowing over them in the past, but last winter's high water may have scoured the substrate, leaving them exposed when irrigation season dropped the creek's flow.
It is possible that chinook headed upstream toward Ashland could be swimming through the subterranean section, because two chinook were visible late Wednesday afternoon in the pool just downstream of the pipe. Those salmon tried in vain several times to leap over the encased pipe, which is about 5 feet wide.
"It sure doesn't look like it's fish-passable," said Oregon Department of Fish and Wildlife fish biologist Dan VanDyke as he surveyed the obstacles.
"The fish are going to have to wait for higher flows," VanDyke said. "We'll keep an eye on it and see if fish can get above here."
At least a half-dozen large chinook finned past the obstacles Sept. 21, when the creek peaked at about 100 cubic feet per second under the bridge, flow records show.
But flows Wednesday were at 15 cfs, and no rain was forecast until deep into next week.
VanDyke said he wants to meet quickly with city public works officials, state Department of Environmental Quality and others "to see if something can be done in the short term."
"But I don't know, in an emergency basis, whether something can be done," he said.
Possibilities include notching the pipe and chipping out the concrete, though the state's normal window for work in salmon streams ended Sept. 15, VanDyke said.
Cory Crebbin, the city's public works director, said the sewer line is owned by the city, and it was believed to be abandoned, but city staff were researching that Wednesday.
"We don't want to do anything to a sewer line that isn't abandoned," Crebbin said.
As for the rocks-and-mortar contraptions immediately downstream of it, "I don't know what that is or if we have anything to do with it," Crebbin said.
VanDyke hopes to amass volunteers to keep an eye on the pool beneath the obstacles to see whether salmon migration truly is impeded.
"Obviously, if you get 40, 50 or 100 chinook sitting there, we know they're not going through," VanDyke said.
In such a case, VanDyke hasn't ruled out netting the chinook out of the pool and transporting them upstream for release.
While a short-term bane, the erosion could be a long-term boon for migrating chinook that have struggled at times to cross what VanDyke calls the "concrete wall" that now is atop the creek.
More high water likely will break up the already cracked concrete, allowing it to flow unimpeded under the Jackson Street bridge.
"I have a feeling the creek will solve this by itself this winter," he said.
— Reach Mail Tribune reporter Mark Freeman at 541-776-4470 or firstname.lastname@example.org. Follow him on Twitter at www.twitter.com/MTwriterFreeman.