Spring Weather Makes For Tricky River Management

May 9, 2012

Warmer temperatures this week have kept river levels high in Idaho as mountain snow melts. It’s been a challenging year for those who manage the state’s river systems. That’s because the spring runoff happened a month earlier than last year. It's brought flooding along the Boise River and raises questions about water availability next year. Just ask Ron Abramovich. He's a hydrologist and water supply specialist with the Natural Resources Conservation Service in Boise. 

Abramovich peers over the railing of a foot bridge over the Boise River. The water flows fast enough that it can make one dizzy. "Picture what 7,000 CFS (cubic feet per second) is moving down the river," he says. "That would be like 7,000 milk cartons moving by this bridge every second."

The river has inched up higher spilling over its banks in recent weeks. Sections of Boise’s popular green belt remain under water. Tuesday the cities of Star and Eagle declared flooding emergencies. Still, Abramovich says the Boise River actually hit it’s highest peak during the last week in April. Temperatures climbed into the 90s speeding up the snowmelt. That coupled with one to two inches of rain sent streams and rivers rising. "The Boise River at Twin Springs reached 12,500 CFS," explains Abramovich.

He says that’s the second highest flow recorded on the river. That information comes from a stream gauge placed a hundred years ago above Arrowrock Dam. Gauges like the one at Twin Springs show spring runoff times have changed over the years.

"Last year we got an extra month of winter and no spring and summer," says Abramovich. "But this year we’re a month ahead of schedule and it’s just a greater degree of climate variability that is what we’re seeing." Abramovich says that variability makes it hard for water managers who have to regulate reservoir levels.

Forecasters at the National Weather Service office in Boise have left a flood warning in place for the Boise River for two weeks now. That warning will stay in effect through the weekend. After that, Abramovich says it’ll depend on the weather."We won’t exceed the peaks we just had unless mother nature throws us a curve ball with hot weather or abundant rain." 

Overall Abramovich predicts Idaho will have enough water this year. But south of the Snake River concerns are mounting. Reservoirs, including Owhyee, Salmon Falls, and Oakley, are relying on last year’s water storage. That means there could be less money in the bank so to speak for water needs next year and beyond.