Seasonal flows affect fish habitat, reshape the river
In focus: The Deschutes River
By Kate Ramsayer / The Bulletin
Published: December 02. 2008
During the late fall and winter, the Upper Deschutes drops to a fraction of its natural size. It’s a hard time of year for fish in the Upper Deschutes River. A chunk of their habitat disappears, and they have fewer hiding spots or escape routes as the amount of water flowing past Wickiup Dam drops to a fraction of the summertime flow.
Every fall, water managers start storing water in Wickiup Reservoir so farmers and ranchers can irrigate their crops the next year. But as water collects behind the dam, the effects can ripple through the river ecosystem — restricting fish habitat, reshaping the river and probably helping to clog Mirror Pond.
It’s an issue that Bend residents might not notice, said Ryan Houston, executive director of the Upper Deschutes Watershed Council, as the most significant problems happen in the 20-mile or so stretch of water between Wickiup Reservoir and Sunriver, where other rivers empty into the Deschutes.
“The problem is somewhat out of sight, out of mind, because the effects aren’t as dramatic in the places people live,” Houston said.
But below the dam, the river flow can drop to a low of 20 cubic feet per second — only about 1.3 percent of the summertime highs. It was at that low level earlier this fall so crews could work on the dam, but has jumped up to a current rate of about 100 cubic feet per second.
And when the river’s down, it exposes parts of the river bed and banks where water would naturally flow. Vegetation can’t grow along the banks, and the soils freeze and thaw and become unstable, Houston said. Then in the spring, when Wickiup Dam’s gates are opened wider, those unstable sediments are picked up and washed downstream.
“What that means over time is that the river gets wider and shallower,” Houston said.
People have compared pictures of the Deschutes River below Wickiup from 1943 and 1991, and found that over that time period the river has widened an average of 20 percent, said Ted Wise, assistant district fish biologist with the Oregon Department of Fish and Wildlife.
And the sediments from the banks and river beds have to go somewhere, Houston said.
“It’s pretty safe to assume that much of the sediment in Mirror Pond is linked to this erosion in the Upper Deschutes,” he said.
Those fine, eroded sediments are also what algae grows in, he said, so some people believe the algae taking off in Mirror Pond can be linked to the low winter flows.
“It’s not black and white,” he said of the connection. “They’re all things that are exacerbated by the flow regulation out of Wickiup.”
But one more direct connection, Houston said, is that when there’s more water flowing in the winter, the fish population is healthier.
The drop in the river flow means that a big part of what was once covered in water is now essentially exposed mud flats, Wise said.
“Imagine if you’re a fish in that situation,” he said. “You have to accordingly adjust your activities.”
There are fewer deep pools for fish to swim in, Wise said, and there’s more of a chance for a redband trout to be stuck in a small space with a hungry brown trout twice or three times its size. The hiding places are also harder to come by, since much of the overhanging trees or logjams or vegetation are on the dry riverbanks. Other predators, like herons or otters, have an easier time picking off the fish, he said, especially if they get stranded in pools.
The Water Resources Department decides how much water to release based on forecasts for the winter and how much it would take to fill the reservoir, said Kyle Gorman, manager of the south central region with the state department. The goal is to be able to meet the water rights that irrigation districts have held for decades.
“We have to fulfill those water rights,” he said, adding that the Fish and Wildlife Department and the Deschutes River Conservancy are working on ways to increase wintertime flow.
How to generate a steadier Upper Deschutes, while still meeting the water needs of irrigators, is a focus of the Deschutes River Conservancy, said Scott McCaulou with the organization.
The group has previously leased water from irrigators and is interested in releasing water saved through future conservation projects during the winter. Other ideas could come from looking at models of the Wickiup and Crane Prairie reservoirs and water flows, or trying to make sure the dams are managed as efficiently as possible to save water.
“There’s a lot of work going on right now,” he said.
Kate Ramsayer can be reached at 541-617-7811 or firstname.lastname@example.org.
Published Daily in Bend Oregon by Western Communications, Inc. © 2008