Hikers strolling through the woods on the Old Salmon River Trail enjoy old growth trees, fresh mountain air and the beauty of the Salmon River. Unbeknownst to them, however, is that parts of the river aren’t necessarily pristine wilderness.

When the Army Corps of Engineers altered portions of the Salmon River in
1965, it was made to be straighter and with less impediments for the passage
of high water, drastically changing the appearance of the river from its historic
state.

“People are still having a hard time with what an actual beautiful river looks
like, it’s been changed for so long,” said Greg Wanner, Supervisory Fish
Biologist at the Zigzag Ranger District.

Wanner oversaw the restoration of four sites on the Salmon River this
summer, helping to reactivate historical side channels to mitigate flooding and
restore rearing habitat for fish, as part of a partnership between the USDA
Forest Service, The Freshwater Trust, RLK and Company (Timberline Lodge
and Ski Area), Bureau of Land Management, Sandy River Basin Watershed
Council, National Forest Foundation and Sandy River Basin Partners. At one
site on the river, just downstream of a confined canyon where the river opens
to a wide floodplain and near the Old Salmon River Trail, the evidence of
man’s influence – by the Army Corps and the restoration work – could be seen
last month.

The back story
A 1964 flood initiated the work performed by the Army Corps, and Wanner
noted that historical photographs indicate the Corps moved the river into a
historic side channel, the straighter and faster route, thereby turning a section
of the main river channel into a side channel. The Army Corps removed large
wood and likely used a bulldozer to scour the river bottom and create a
boulder field on one bank in order to straighten the river, all done to increase
water conveyance and mitigate flooding.

Wanner added that before the work, the immediate area featured wetlands
along side the trees in the area, creating a diverse ecosystem ideal for fish,
noting that the work effectively “disconnected” the river from the flood plain.
“We’ve learned since then, that’s not how you reduce floods,” Wanner said,
offering that the steps to mitigate flood damage instead increased the
intensity of a flood. “You want the floodplains because that’s how you reduce
flooding by attenuating that flood. We’re keeping the water up on the
mountain a little bit longer by having the water go out on the flood plain.”

Wanner also noted how large trees fell in the river for thousands of years,
creating a natural river habitat with approximately 150 to 250 pieces of large
wood per mile on the river. The Army Corps, however, removed all of that.

Restoring the river
When planning the restoration of the site, Wanner’s biggest challenge was
taking approximately 40 pieces of large wood (some up to 70 feet long and 36
inches in diameter) through a few hundred yards of forest between Salmon
River Road and the site on the Salmon River. Ideally, he would have used a
decking site near the trail, but because of the high usage of the trail and it’s
visibility, the option was not pursued.

Instead, Wanner’s crew used part of a user-created trail (one outside the
official trail network) to create a path, temporarily moving ferns off to the
side, setting down logs to protect the soil and even adding bark to some trees
in case more protection was needed. The path was big enough for a log
skidder to take each piece of wood down to the river for the restoration work,
but without damaging any of the trees on the way – a trip that Wanner
estimated took 10 to 15 minutes.

At the site, workers used laser levels to gauge the elevation of the river and
dug a trench eight feet deep, matching the maximum anticipated depth the
river will scour down to anchor an engineered log jam at the apex of an island
where the side channel splits from the main river channel. The wood pieces
were intertwined in the structure, giving it the stability to survive a high water
event and not be washed downstream.

“This thing ain’t going anywhere,” Wanner said. “We could have a 100-year
flood and this thing should stay and hopefully add up more and more wood.”
The bank with the boulder field created by the Army Corps has typically been
completely dry during the summer, with Wanner describing the net result as,
“essentially a dyke.”

To complete the project and reactivate the side channel, workers put a line of
sandbags in the river to divert the flow for one day and protect the river from
any added sediment while slightly lowering the riverbed in the area of the
boulder field to send the river’s energy into the wood structure. Wanner
estimated approximately 10 to 20 percent of the water flow will then be
diverted into the side channel, reconnecting the river back to the flood plain
and creating areas of low water flow where fish can thrive.

“What we’re doing right now is resetting the clock, putting the river back to
1964,” said Wanner, noting that perennial flow through the side channel was a
goal of the project.

With the work complete, the workers cleared out the sandbags and restored
the path they created to get the logs down to the river, including loosening of
any compacted soil and carefully replacing ferns and logs.

By next summer, Wanner expects the site to be completely vegetated and
back to normal.