Bureau of Reclamation opens spillway at Arrowrock Dam

Water released from spillway at Arrowrock Dam

BOISE - Starting Monday, water managers will increase flows along the Boise River to 9,500 cubic feet per second. It will be the highest flows on the Boise River this year. The Army Corp of Engineers says the increase in flows is due to a wet pattern that has been forecasted for this week.

Ada County spokeswoman Kate McGwire tells KTVB they're expecting more debris in the river due to these higher flows. They will continue to monitor the river, but are asking people if they do spot debris in the river to report it to authorities, don't try and retrieve it yourself.

The record runoff has also forced the Bureau of Reclamation to open up Arrowrock Dam’s spillway in order to maintain space in the system. It’s the first time since 2006 the spillway has been used.

“Right now we’re using all of the outlets just because we have a lot of water to move down from the upper reservoirs,” Brian Sauer with the Bureau of Reclamation said.

Sauer tells KTVB that water was coming into the Boise Reservoir System faster than what they were able to release using the ten outlets at the dam.

“Very high inflows in the upper system, including Anderson Ranch and the tributaries, the Middle Fork of the Boise River. So we filled Arrowrock fairly quickly,” Sauer said.

Currently, Anderson Ranch and Arrowrock reservoirs are nearly at capacity, and Lucky Peak Reservoir is almost two-thirds full.

“The runoff into the reservoirs has dropped substantially in the last couple of days. One thing is primarily due to the cooler temperatures,” Sauer said.

Experts say water in the spillway is nothing to be alarmed about, as it was built to do exactly what it’s doing.

The Bureau of Reclamation can also control the amount of water going through the spillway using six different gates.

“We can regulate how much water we do spill down on to Lucky Peak,” Sauer said.

Lucky Peak will fill up faster because of water going over the spillway, but Sauer added they can always pull back if needed.

“What you're seeing is a controlled release,” Sauer said. “We can pull back and store more water in the upper reservoir.”

Sauer tells KTVB they don’t’ want to bring the flows along the Boise River any higher that what we’re going to see this week; any other increases above 9,500 cfs is really up to Mother Nature and the sort of temperatures and precipitation that we’ll see.

© 2017 KTVB-TV


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