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NorthWestern Issues January 2017 Update on Hebgen Dam Project; Madison River Basin Snowpack Below Normal

Jan 11, 2017

Butte, Mont. – Jan. 11, 2017 – As of Jan. 1, 2017, the Montana Natural Resources Conservation Service water supply outlook report indicates a snowpack for the Madison River basin of 79 percent of normal. October and November offered a slow start to the snowpack with mild temperatures and weather, but December brought well-above-average snowfall. It is still early in the water year, and additional precipitation in the Madison basin is expected in the near future.

Construction work on the spillway replacement project at Hebgen Dam continued through the end of 2016 and is now nearly complete. As was the goal from the beginning of the project, all concrete pours and replacement of the dam embankment were completed by the end of the year. Remaining work now includes the completion of the spillway gate electrical and control systems and removal of the spillway cofferdam. Seeding and revegetation of the disturbed areas surrounding the spillway will occur in the spring.

In 2017, NorthWestern Energy will undertake the planned project to rehabilitate the outlet pipe. The outlet pipe is a 500-foot long, 12-foot diameter concrete pipe with a wood-stave lining that serves as the conduit for normal river flow from the intake structure. The outlet pipe traverses through the dam itself and is over 100 years old so requires rehabilitation. 

 In the spring, as early as the reservoir level and runoff allows, NorthWestern will divert the normal Madison River flow to the newly completed spillway, which will allow work inside the outlet pipe. The wood-stave lining of the pipe will be removed and a new lining consisting of reinforced concrete applied as shotcrete will be installed. The project is anticipated to require four to six months to complete. 

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. NWE also proposes public meetings on these same topics in mid-March (Ennis) and in late April or early May (Ennis and West Yellowstone). 

About NorthWestern Energy
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
(866) 622-8081

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