Frog, fish populations under threat in the Upper Deschutes
Mar 30, 2020
Erratic flows from winter to summer have damaged river habitats, biologists sayBy Michael Kohn
Standing on a concrete bridge in this wooded protected area, a pair of Oregon fish biologists peered down at a stretch of the Upper Deschutes and lamented the condition of the river.
Below the bridge, the banks of the Deschutes River were visibly shorn off from summertime high water flows. The channel was wider than its historic width, they said. And unnatural, isolated winter ponds caused by seasonal low flows did not appear to provide suitable habitat for fish and other wildlife.
The picture of the river presented by the biologists — Amy Stuart and Brett Hodgson — was bleak. Both spoke of Oregon spotted frog populations “winking out” across the river ecosystem, and fish populations in an equal state of collapse. They say there is precious little time to reverse course and save fish and frog populations, but better management of the river could help the river heal.
“The Upper Deschutes from Wickiup to Bend (has been managed) as an irrigation ditch for 70 years,” said Hodgson, a Deschutes district fisheries biologist for the Oregon Department of Fish and Wildlife. “Not only does that result in lower flow and water quality, but it also has huge impacts on the stream channel itself.”
The erratic flows are the result of long-standing water management goals by irrigation districts in Central Oregon, which conserve water during winter in Wickiup Reservoir, close to the headwaters of the river, and then siphon it off downstream in summer to irrigate crops and fill ponds for livestock.
Natural flow, said Hodgson, was between 600 cubic feet per second in winter and 900 cfs in the summer, before the construction of Wickiup. A return to something close to those levels is needed to sustain fish and wildlife in the long term, he said.
The natural swing from 600 cfs to 900 cfs was gradual, occurring over a period of months during the spring and fall months. The river flows were moderated by a large amount of groundwater and springs that helped keep the flow consistent.
“The groundwater influence makes the Deschutes one of the most stable river systems in the entire world, because of how snow melts off the mountains,” said Hodgson.
After Wickiup was built in the 1940s, the river flow slowed to 20 cfs in winter, said Jeremy Giffin, the Deschutes Basin Watermaster. Flows in the summer were 50 times higher, even reaching 2,000 cfs in the 1960s.
“It’s totally different now,” said Stuart, who spent 31 years with ODFW before retiring in 2014. “You go from drought-like conditions to a flood event every year. In the past, those fluctuations only occurred once every 25 years.”
The result of the extreme fluctuations is a river that is 25% to 30% wider than it was historically, said Hodgson. The scouring of earth from the riverbank prevents riparian vegetation regrowth, which puts some fish and animal species in peril.
Another consequence of a wider channel, said Hodgson, is that the river spreads over a greater area, like a flood plain, creating shallow pools of water. Shallow pools are more likely to freeze solid, killing everything in the pool.
Redband trout eggs are less likely to survive in shallow pools, as they have less protection and are more susceptible to being “sluiced out” when river flows change in the spring, said Stuart. The swings in river flow also wash out woody debris and other riparian cover needed during the different stages of a redband trout’s life cycle.
“The status of the redband trout between Wickiup and Benham Falls is extremely dire,” said Hodgson. “There are very few redband in the river.”
Those life cycle needs include gravel for egg incubation, shallow margin pools for juvenile fish and larger pools for fish when they reach the adult stage, said Hodgson.
“They need different habitat types for different stages of their life history and all of those are compromised by low flow periods,” said Hodgson.
Oregon spotted frog
From the bridge over the Deschutes River, Hodgson and Stuart walk to another section of river, known as Dead Slough, to inspect a breeding habitat for the Oregon spotted frog, which is protected under the Endangered Species Act.
Like the redband trout, frog habitats are also very sensitive to the volatile flow of the Deschutes. In the slough, the biologists pointed out the low stream flows and the great distance from the water to the vegetation line.
Spotted frogs prefer to be near both vegetation and the waterline, but when the waterline shifts dramatically, their life needs are compromised.
Instead of breeding in the vegetation in spring, the frogs end up breeding in the mudflats, where the eggs are more easily washed away. When the river level drops in the fall, the frogs tend to move away from the water to stay closer to the vegetation, where they are vulnerable to extinction in that area.
“Until we get a more natural flow we will just have these little isolated pockets that are disconnected,” said Stuart. “You won’t have that contiguous population and that is how populations start winking out.”
Both Stuart and Hodgson said the risk of extinction will be reduced if the frog populations can stay connected up and down the river.
“With a better water management program, you are going to end up with far more frogs in this location and you are going to create better habitat in other reaches of the river,” said Hodgson.
Evening the flows
Today the irrigation districts and other authorities involved with the local water supply are working to even out the flows — to increase winter flows and lower summer flows — but they still have a ways to go.
“That has been the plan for over 25 years, and we are all striving towards it,” said Giffin.
Winter flow in the Deschutes is now 105 cfs. Flows in the summer reach around 1,500 cfs. A Habitat Conservation Plan devised by the districts seeks to push the winter flows north of 300 cfs in 11 years and 400 cfs within 21 years.
Reaching 300 cfs will be accomplished using a variety of tactics, according to Craig Horrell, the Central Oregon Irrigation District manager.
“Main canal piping, small lateral piping, past the point of delivery and on-farm improvements, as well as other creative water marketing options that we currently work on,” said Horrell. “This is a heavy lift, and it’s going to take everyone’s focus and participation.”
Hodgson and Stuart agree that increasing the flow of the Deschutes to 300 cfs in the winter would be a big benefit for fish and frogs, but say the timeline is too far out. The biologists would like to see the irrigation districts advance their time frames and put more water in the river sooner — and also lower the summer flows below 1,200 cfs.
“We think the flow restoration in the Upper Deschutes needs, and can occur in, a much shorter time frame than is being proposed,” said Hodgson. “As we look to the future — with climate change and the growth of Central Oregon — wise and conservative water use will be critical.”
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