High flows revitalize Boise River

For about a month the Boise River has been cresting its banks and flooding low-lying riparian areas, including places like the parking lot at Barber Park. It's important to remember that, while inconvenient, high flows are extremely good for river health. (Photo by Greg Stahl)

The Boise River for the past month has been flowing onto sections of the greenbelt bike path and other low-lying areas in the Treasure Valley. The flow through last weekend was higher that it had been in a number of years, and it is expected to remain high for an extended period. The bike paths, as well as a number of park facilities and some homes, lie in the river’s natural floodplain.

Warm weather and record rainfall in late-April forced federal managers of the Boise River’s dams to increase flows to more than 8,100 cubic feet per second for about five days from May 4 to May 9. It’s only the second time the river hit 8,100 cfs in 30 years. This week, on May 9, the level dropped to about 7,700 cfs. It has been flowing above 5,000 cfs since late-March.

“High-flow events are good for the river,” said Liz Paul, IRU’s Boise River campaign coordinator. “They perform important ecological functions like transporting sediments through the system and recharging side channels, wetlands and flood plains. While these flows are inconvenient for while, it’s important to remember that river health is directly related to fluctuations in flow.”

This year’s high flows are the result of a significant amount of carryover in upstream reservoirs and very little winter water releases, followed by a late but normal snowpack and unusually warm and wet April weather.

Elsewhere in Idaho, rivers are flowing at or slightly above the long-term median flow for this time of year–except for the desert rivers of southwest Idaho where winter snowpack was significantly lower than long-term averages.

The best way to view the Boise River is from the air, and Idaho Rivers United teamed up with LightHawk and Mountain Visions to capture more than 200 photos on June 3, 2011 when flows were 6,670 cfs. Mountain Visions took a small number of the best photos and created an informative Google Earth Tour (kind of like flying).