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NorthWestern Issues March 2017 Update on Hebgen Dam Project; Madison River Basin Snowpack in Good Shape

Mar 23, 2017

Butte, Mont. – March 23, 2017 – The rehabilitation of Hebgen Dam is moving ahead and snow/water conditions in the Madison River drainage are above the typical seasonal levels.

Snowpack for the Madison basin is currently at 109 percent of median levels. The Natural Resource Conservation Service’s (NRCS) Snotel sites above Hebgen are well above average at 123 percent, while the remaining sites in the basin average 99 percent.

The NRCS latest volume runoff forecast issued on March 6th estimated the volume runoff for the April to July period to be 122 percent of normal at Hebgen and 108 percent of normal for Ennis.

The Hebgen reservoir elevation is currently at 6,527.78 feet which is 7.09 feet from full pool and slightly higher than the 10-year average of 6,527.45 feet for the same time frame. Inflow for March to date has averaged 101 percent of normal. Outflow has increased to 1,180 cubic feet per second in an attempt to draft the reservoir for the above-average snowpack.

The Hebgen and Madison hydro projects are subject to constant monitoring, re-evaluation, and collaboration with applicable agencies. Appropriate operational changes will be made, as necessary, taking into account our FERC license requirements.

In 2009, the Federal Energy Regulatory Commission (FERC) required safety repairs to the Hebgen Dam intake, spillway and outlet pipeline to meet current dam-safety standards and reflect advances in earthquake seismology. The approximately $40 million project is expected to be finished by the end of 2017. 

The spillway replacement project is now substantially complete. Removal of the spillway cofferdam is complete. The new gates operate under power and the control system has been completed. New security lights and cameras have been installed. Fine grading, topsoil, and seeding of the disturbed areas will be accomplished in the spring along with the replacement of security fencing. 

The outlet pipe rehabilitation project at Hebgen is scheduled to begin this spring. Plans for the project are currently under review by FERC. New permit applications and permit modifications with the appropriate federal and local agencies have been submitted.

NorthWestern Energy is working to secure a construction contract for the project in the coming weeks. Work on the project will begin as soon as the reservoir elevation and conditions allow. River flows will be diverted to the new spillway during the work, which is expected to be complete in 2017 before winter.

A public meeting intended to update stakeholders on the Hebgen Dam rehabilitation project and related matters is scheduled for Monday, March 27, at 7 p.m. at the Ennis Fire Hall.

The meeting will include representatives from NorthWestern Energy, the Madison River Foundation, Trout Unlimited, Montana Fish, Wildlife & Parks and the U.S. Forest Service. Along with presentations, there will be a question-and-answer session.

NorthWestern will work to provide monthly public updates on the schedule and progress of Hebgen outlet-pipe repairs, snowpack and runoff forecasts and related Madison River biological and recreational issues.). 

About NorthWestern Energy (NYSE: NWE)
NorthWestern Energy provides electricity and natural gas in the Upper Midwest and Northwest, serving approximately 701,000 customers in Montana, South Dakota and Nebraska. More information on NorthWestern Energy is available on the company's website at

Media Contact:
Butch Larcombe
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