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NorthWestern Issues Update on Hebgen Dam Project; Madison River Basin Water Conditions Are Steady

Jun 09, 2017

Butte, Mont. – June 9, 2017 – The rehabilitation of Hebgen Dam is moving ahead and snow/water conditions in the Madison River drainage are changing quickly.

The Natural Resource Conservation Service’s (NRCS) Snotel sites in the Madison Basin indicate the snowpack is 78 percent of median as of June 7, 2017. The Black Bear Snotel site above Hebgen still has 147 percent of median but the lower-elevation snowpack is nearly melted out.

The current reservoir elevation is 6,533.60 feet which is 1.27 feet below full pool. The reservoir has risen 1.5 feet since the beginning of June. Inflows for the month of May averaged 112 percent of normal, and inflows to date for June have averaged 150 percent of normal. Hebgen outflow is currently at 1,440 cubic feet per second (cfs). The Climate Prediction Centers indicate an above-average probability for moisture in June.

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.

Plans are in place to divert Madison River flows to the Hebgen spillway the week of June 12th. This change will allow access to the outlet pipe and downstream area to begin construction work. The construction contractor is scheduled to mobilize to the site to begin work on the outlet pipe project soon after flows are diverted. Early work on the project will focus on constructing access to the outlet pipe and mobilizing labor and equipment to the site to begin work inside the outlet pipe. The project is scheduled for completion in the fall of 2017.

After river flow is diverted to the spillway, currents in the river near the dam will be strong and turbulent. For security and public safety reasons, the dam and shoreline upstream of the spillway are closed. 

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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