The amount of water flowing through the Boise River is expected to reach its highest level so far this year on Friday, after additional water is released from Lucky Peak Dam in two stages.
The federal Bureau of Reclamation and the U.S. Army Corps of Engineers released an extra 500 cubic feet per second beginning late Thursday morning. A few hours later, the agencies announced that an additional 500 cfs will be released beginning at 8 a.m. Friday morning.
That should bring the level at the Glenwood Bridge in Garden City to 9,300 cfs — just 200 cfs below what was recorded in 1983. That year marked the highest river flow since Lucky Peak Dam was built in 1955.
Further increases in the release of water from Lucky Peak could be required over the next week, officials said, as the spring snowmelt continues and the river system’s three reservoirs fill.
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“At 9,500 cfs, additional sections of the Boise Greenbelt adjacent to the river will be submerged, and erosion of riverbanks will continue to be a significant problem. Flooding will continue to occur in areas in Eagle Island, Garden City, Star and Caldwell. Water will cover portions of the Warm Springs Golf Course and Municipal Park in east Boise,” Joe Saxon, a spokesman for the Army Corps of Engineers, said in a written statement.
The extra water could affect some residential properties near the river but should remain below most homes, he said.
The Bureau of Reclamation and the Army Corps expect the river to spill over its banks between 45th and 47th streets in Garden City and reach the warehouse district. However, last month, Garden City Public Works Director Colin Schmidt told the Statesman he was optimistic flooding of streets wouldn’t occur until the flow reached 10,000 cfs.
For much of the spring, river levels have been above flood stage, which occurs at 7,000 cfs at the Glenwood Bridge.
Agricultural water usage had caused the river flow to decrease last week, but as temperatures finally rose into the upper 80s and lower 90s, mountain snow melted in the Boise River watershed and poured into the three reservoirs. As of Thursday afternoon, Lucky Peak was 72 percent full, Arrowrock was 96 percent full and Anderson Ranch was 97 percent full, according to the Bureau of Reclamation.
The National Weather Service in Boise issued a flood warning Wednesday in anticipation of the increased river flows. It urged property owners near the river to take action to protect their belongings.
The summer float season on the Boise River isn’t expected to open until at least sometime next month. The latest the river has opened for floaters and boaters was in 2011, when recreation users weren’t allowed on the river until July 11.