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As Tenmile Creek rises, County has new infrastructure to reduce potential flooding

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Posted at 6:21 PM, Jun 30, 2020
and last updated 2020-06-30 20:21:45-04

HELENA — The Helena Valley has yet to see a significant flooding event in 2020, but the County says the infrastructure in place should one occur.

The $2.4 million Helena Valley Flood Mitigation Project on North Montana Avenue and Sierra was completed this April.

It’s designed to handle approximately 400 cubic feet of water per second. In 2018 the area saw flooding with 80 cubic feet of water per second overflowing ditches and culverts. The costly flooding forced Rossiter Elementary to hold class at Carroll College for the remainder of their year.

Lewis and Clark County Engineer Dan Karlin says the project turned out well, but he’d prefer there to be more established vegetation in the area to reduce the chance of any scours forming with yearly runoff.

“We’ve seen stream levels come up, but really the key is vegetation that we see in a project like this,” explained Karlin. “That root structure is really vital and critical to hold all of that material in place.”

The project included purchasing an easement to use the Trap Club gravel pit as a stormwater retention pond, creating a formal diversion and flow control structure into the pit and saw the replacement of 13 undersized culverts between Forestvale Road and Rossiter School.