|Courtesy graphic This graphic shows the area of the Big Wood River where the Wood River Land Trust and the city of Ketchum are proposing a joint recreation-conservation project to provide fishing and whitewater rafting while preserving the health of the river.
Though recreationists may rejoice at the thought of the whitewater park proposed for the Hulen Meadows area north of Ketchum, staff at the nonprofit Wood River Land Trust said they are excited about the conservation opportunities.
Land Trust Executive Director Scott Boettger said during an interview on Thursday morning that every year, homeowners north of Ketchum apply for emergency stream-alteration permits during high flows to harden the banks.
While bank hardening prevents the homeowners’ backyards from flooding, Boettger said that it causes a “ripple effect” in which the river is prevented from flooding or meandering as it naturally would to deal with increased velocity.
This, in turn, causes homeowners downstream to need to harden the banks there, he said. And once too much of the bank is hardened, the river has to go somewhere—so it incises, or digs down into the channel.
While that might not sound like a threat, Boettger said that a severely incised river will actually separate from its floodplain. That means that wetlands that used to house songbirds and other riparian life no longer exist, and the high velocity of the resulting stream makes the water less hospitable to aquatic life as well.
But keeping the stream from incising and finding other ways to reduce the river’s velocity can prevent all of that, Boettger said.
“You have to find spaces where you can let it spread again,” he said.
What the land trust proposes is building new drop structures, or angular configurations of rock that essentially “break” the water. The structures form a V that points upstream, and when the water hits those structures, it deposits sediment before plunging into a small pool just downstream.
Wood River Land Trust spokesman Trey Spaulding said in an email that these structures, similar to ones that have been constructed just below the Bullion Bridge in Hailey, create excellent trout habitat and fisheries. Boettger said that the structures mimic natural wood debris pile-ups found in unaltered streams.
But the structures also create the rapids that the city of Ketchum is hoping to capitalize on, forming a whitewater park north of town. The city of Ketchum, along with the land trust, applied for a Recreation and Public Purposes patent on two parcels of land near Hulen Meadows in 2008, which would grant deed-restricted ownership to the city.
The first parcel covers 210 acres from the Sun Peak Day Use Area to the Lake Creek trailhead, while the second covers about 105 acres at the confluence of the Big Wood River and Warm Springs Creek.
If the agreement is approved, the land trust would oversee riparian, vegetation and habitat restoration, while the Ketchum Parks and Recreation Department would oversee management and maintenance of recreation components—including whitewater rafting near the Sun Peak picnic area.
Boettger said that drop structures were originally constructed in this area in 1991, when the Idaho Transportation Department realigned Highway 75.
According to a letter from Bozeman, Mont.-based Geomax Engineers to the Blaine County Planning Department dated March 11, 1991, engineers at the time were concerned that the channel created by realignment would erode nearby banks, cut off meander loops which had decreased water velocity in the area and essentially “capture” the river, preventing it from being able to naturally absorb high flows.
Boettger said that the drop structures originally constructed have since eroded—except for one, which could be rendered useless by severe erosion due to a future flood. If this structure were to erode, he said, the stream could be severely threatened.
“Then you are going to have an incised, captured river,” he said.
He said he is optimistic that the patent would be granted within the next few months, so that construction could begin as soon as possible.
Kate Wutz: email@example.com