Flow in the Boise River set a record low this week. According to the U.S. Geological Survey, flow Thursday at the Glenwood bridge on Boise’s west side was the lowest ever recorded on May 8.
Flow dippedbelow 500 CFS Thursday and Friday mornings. That’s about half the flow rate late last week, and less than a third of flow in early April. Over the past three decades, median flow for this time of year is about 1,500 CFS.
Melissa Jayo is a hydrologic technician with the Bureau of Reclamation, which helps manage the reservoir system. She says flow out of Lucky Peak has been steady the last several weeks. The river level has fallen, she says, because more water is being diverted into irrigation canals. The largest of those are located east of Boise. That means the river is carrying less water through the city.
Jayo says relatively cool weather of late has meant the basin’s snowpack has been melting slowly.
“It’s coming off nice and slow and steady,” she says. “That’s good for the ground, the river and the reservoirs.”
Jayo says a slow melt means a steady flow into the reservoir system, which allows water managers to let lakes fill without having to increase outflows. Unusually warm weather early in the spring – like in 2012 – can lead to large influxes of runoff that force water managers to raise the river’s levels, sometimes aggressively. In early May 2012, the river was running at about 8,000 CFS through Boise.
“We’re not seeing big flushes of water this year,” Jayo says. “We’re able to be proactive instead of reactive. Lots of time in the spring we’re reactive.”
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