Potential consequences of a pit capture

What happens when the river gets diverted.

BOISE - Over the last several weeks KTVB has reported about the possibility of a pit capture at the Sunroc gravel pit. But what exactly does that mean for nearby neighborhoods and infrastructure?

We spoke with Ada County engineer Angie Gilman to find out what areas could be affected if this were to happen.

Back in 2011, the Boise River was diverted into Quinn's Pond, then back into the Boise River, to help create a whitewater park. That was an intentional pit capture.

South of Eagle Island is the 90-acre Sunroc gravel pit.

Emergency officials fear that a saturated river wall could give way, filling the gravel pit and creating an unintentional pit capture.

“So when the river gets diverted and channeled into the gravel pit then at some point it will come out of this gravel pit, and in this situation we are hoping we can reroute that water back into the south channel of the Boise River quickly if that happens,” Gilman said.

Gilman says if the river can’t be rerouted in time, water could flow west, going through subdivisions until it hits and floods Eagle Road.

MORE: Ada County installing flood barriers on Greenbelt

Three different types of barriers and a ditch have been put in the past week to help prevent this from happening, but Gilman says there are many unknowns and other scenarios that could also happen.

“We’re trying to address all of them and we are seeing things arise, we had no idea that we would have flooding in Garden City because of a tree, so we are responding to those and looking at other potential situations that could happen,” Gilman said.

Aside from building barriers, emergency officials from various city and county agencies have been meeting every day to evaluate the worst case scenarios.

“We are looking at all issues along the river from Boise and Garden City, Eagle, all these areas," Gilman said. "What if a road was flooded?  What if there was a tree that got stuck like in Garden City? Where would we evacuate? What would we do with school children if they were in school?

Gilman added that the Sunroc company is also making efforts to prevent a capture. They have two water pumps in place to suck out water in the event of an emergency.

© 2017 KTVB-TV


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