Idaho wrestles with water issues
The Boise River’s 3-dam system was built for flood control, but Otter wants to expand it for
irrigation.
BY ROCKY BARKER
rbarker@idahostatesman.comFebruary 2, 2014
Because of water rights, raising Arrowrock Dam would add a bunch of storage capacity but not a large amount of excess water for irrigation.
IDAHO STATESMAN FILE
Idaho Gov. Butch Otter touted a study in his State of the State address to look at raising the height of the nearly century-old
Arrowrock Dam to increase the Treasure Valley’s water supply.
But if the 348-foot dam is raised, it will be flood control that drives the decision and the millions of dollars in federal spending
the project would need. That’s because the federal dam was built for flooding, and an estimated $10 billion worth of homes,
buildings and other structures lie in the Boise River flood plain.
Water supply is a future concern for Idaho’s farmers, but flooding is an every-year worry for anyone living along the river.
In April 2012, two days of record-high temperatures and two days of record rainfall sent 26,000 cubic feet per second surging
into the Boise River dam system. That forced federal river managers to increase flows to more than 8,100 cfs (flood stage is
about 7,500 cfs). That was the highest flow out of Lucky Peak Dam since 1998 — and just the second time it hit 8,100 cfs in 30
years.
The river plowed through its bank into a small canal downstream of Boise, which could have failed and caused widespread
flooding. Just above Eagle Island, the river nearly “captured” an active gravel pit, which could have turned the river out of its
channel and caused massive Eagle-area flooding, said Ellen Berggren, the U.S. Army Corps of Engineers Boise Project
manager.
“I don’t know if we were lucky so much as we haven’t been unlucky,” she said.
Otter is asking the Idaho Legislature for $15 million in one-time payments for various water projects across the state, including
$1.5 million to study expanding Arrowrock.
On Friday, the Joint Finance-Appropriation Committee unanimously backed the request. The full Legislature still must vote.
The U.S. Army Corps of Engineers already is doing a feasibility study of flood control options for the Boise River, which
includes looking at raising the height of Arrowrock Dam by 70 or 80 feet. Otter’s $1.5 million, which would come through the
Idaho Water Resource Board, would cover the 50 percent local match to add examining the benefits of more water supply.
“What the state is trying to do is guide the project so there is a water-supply component,” said Brian Patton, director of the
board’s planning bureau.
The Corps is required to study alternatives that would be cheaper and more environmentally friendly and would reduce damages
when the inevitable flood does come. These could include rejuvenating old, out-of-use floodways; building new flood channels;
widening the New York Canal and building an outlet from Lake Lowell to the Snake River; or even building levees in some
areas.
Such projects could delay the inevitable flood. Other measures the Corps will consider are those that could reduce the damage if
a flood does arrive. One example is fixing low bridges; a flood can alter the river channel dramatically if large trees and other
debris get trapped against them.
The Corps is putting together its list of alternatives and working with its partner in the Boise dams, the U.S. Bureau of
Reclamation.
“It’s like building something out of Legos, with many different colors and sizes,” Berggren said.
PROJECT GENERATES CONTROVERSY
Conservation groups were generally supportive of the Corps study when it was launched, because it was supposed to include
looking at environmental restoration projects to reduce flood risks and restore natural ecological function to the Boise River.
One example is restoring lost cottonwood trees and other riverside species.
A century of dams has dramatically reduced the sediment that flows down the river. Cottonwood seeds find fertile ground for
sprouting in freshly laid sediment left by floods in the Boise River plain. Fewer floods means fewer new cottonwoods to sprout,
and fewer trees to provide bird and animal habitat. And fewer sources of shade to cool the river water in which fish thrive.
But the environmental restoration segment of the study was dropped 15 months ago because the Corps wanted to get it done in
three years for $3 million.
Idaho Rivers United, which advocates for passive flood control measures, wants to change that. Campaign coordinator Liz Paul
plans to organize Treasure Valley residents later this year to get involved in the process to make sure that environmentally
friendly alternatives, such as restoring historic water channels, are considered.
She also wants managers to consider conservation measures that she says would make the river and water systems more reliable
and secure whether there are floods or droughts. She’d like this environmental infrastructure designed with both existing and
new development in mind — adding wetlands and ensuring that development occurs in such a way that floodwaters could flow
through the Valley with less damage.
“I want attention to be paid for water security, get more storage off the table, and make sure our river and our economy can
continue because we are good water planners and good managers,” she said.
TICKING CLOCK
On Sept. 5, Tim Page had to make a tough decision. The project manager of the Boise Board of Control, which oversees the
New York and other Boise River canals tied to the reservoir system, had to shut off the canal when its stored water ran out. That
meant cutting off the water that irrigates most of the crops in the Treasure Valley weeks before the usual mid-September
shutdown.
Page and most of the farmers he serves say storing more water in the dams would give them insurance against such events.
Raising Arrowrock 72 feet would add an additional 300,000 acre-feet to the 949,700 acre-feet of storage capacity at the
Arrowrock, Anderson Ranch and Lucky Peak reservoirs. That sounds like an increase of more than 30 percent, but it’s
misleading.
Although more water would be captured in big water years, most of it is already spoken for by existing water-rights owners. So
just about 60,000 acre-feet of new water would be made available for uses ranging from drinking to irrigation.
The Bureau of Reclamation, which operates Arrowrock and Anderson Ranch in cooperation with the Corps of Engineers, also
wants the Corps to consider raising Anderson Ranch up to 6 feet, said Jerry Gregg, the bureau’s Snake River Area manager.
Whatever the Corps decides, the clock is ticking. In recent years, which have featured dry winters and warmer springs, the
mountain snowmelt and river runoff have come earlier in the year, and growing variations in flows are making the job of water
managers more complicated.
Rocky Barker: 377-6484
BOISE FLOODS: THE PAST IS A GUIDE
Lucky Peak was built in 1955. The flood that prompted it came in 1943, with Boise River flows rising to 16,000 cfs.
In 1983, dam operators had to allow the river to flow at 9,500 cfs, the highest since the dam was built.
In the winter of 1997, water managers ran the river at 7,000 cfs — just below flood stage — from January to spring to avert a
flood after a New Year’s Day rain-on-top-of-snow storm. That’s a treacherous weather combination that frequently leads to
floods.
One flood not included in federal officials’ calculations weighs heavily on their minds nonetheless.
The year was 1862. The story was chronicled by Idaho historian Merle Wells: Homesteader I.N. Coston reported that on July 4,
floodwater in the valley bottom extended “from bluff to bluff and from the present site of Boise westward to the canyon near
the present site of Caldwell.”
Engineers estimate that the river ran at 100,000 cfs, nearly 15 times today’s flood-level flows.