NorthWestern Energy updates rehab progress on Hebgen Dam

NorthWestern Energy said Nov. 16 that reconstruction of the intake structure at the Hebgen Dam in Montana, which is an operation it bought last year, is near completion and that the second phase of the multi-year rehabilitation projection got a strong start in 2015.

A third and final phase of the project, the rehabilitation of the wood outlet pipe that takes water from the intake structure through the dam to the Madison River, is tentatively scheduled to begin in May 2017. The details of the outlet pipe rehabilitation, duration and specific schedule are not yet finalized.

In recent weeks, concern has been expressed about the timing of the project’s final phase. “While the multi-phase plan has not changed, we acknowledge that the 2017 outlet pipe project has needed to be more effectively communicated to the public over the last few years while the work on the intake structure has been in progress,” said John VanDaveer, manager, Hydro Generation for NorthWestern Energy. “We will be working to improve the communication on the remaining Hebgen project as we move forward.”

NorthWestern Energy will also continue to consult with Montana Fish, Wildlife and Parks and other appropriate agencies on issues affecting downstream river and recreation resources.

The overall Hebgen project stems from the 2008 failure of the dam’s original wood stoplogs that were used to control flow in the original intake structure. After making emergency repairs, an extensive rehabilitation project, that included a significant seismic upgrade, was launched in 2009 as required by the Federal Energy Regulatory Commission.

The dam’s intake tower has been completely rebuilt, with gates and operating mechanisms scheduled to be ready for operation by the end of this year. The intake gates will be fully automated with control established at NorthWestern Energy’s Madison hydroelectric project north of Ennis. The automation is expected to help NorthWestern more efficiently manage operations, including downstream flow requirements.

The second phase of the project involves the removal and reconstruction of the dam’s spillway. During this work, downstream flows will be provided through the dam’s new intake gates from a reservoir depth of approximately 40 feet. The work will replace the spillway gates and deteriorated concrete and increase the spillway capacity. The spillway work is expected to be finished in the fall of 2016.

While NorthWestern Energy considered alternative schedules for the outlet pipe work, a fully functional intake structure gate system was first necessary to allow the outlet work to be conducted safely. Those gates will be completed this fall. In addition, the outlet pipe is required for reservoir operation and maintaining Madison River flows in winter months.

NorthWestern Energy assumed ownership of Hebgen Dam and the Madison hydroelectric project in November 2014 as part of its purchase of PPL Montana’s hydro facilities. Between the two companies, more than $40 million will be spent on the Hebgen rehabilitation project, which will bring the dam into compliance with the FERC seismic guidelines. NorthWestern planned for these expenditures as it sought regulatory permission to buy the hydroelectric facilities in 2014.

Said the company website about this facility: “South of Madison Dam, just north of the Idaho border near Yellowstone National Park, is our Hebgen Lake storage reservoir, which is used to store water from a 905-square-mile drainage area at the headwaters of the Madison-Missouri river system, home to eight Montana hydroelectric plants — Black Eagle, Cochrane, Hauser, Holter, Madison, Morony, Rainbow and Ryan. Hebgen is used to regulate the flow of water into the Madison-Missouri system.”

NorthWestern Energy provides electricity and natural gas in the Upper Midwest and Northwest, serving approximately 692,600 customers in Montana, South Dakota and Nebraska.

About Barry Cassell 20414 Articles
Barry Cassell is Chief Analyst for GenerationHub covering coal and emission controls issues, projects and policy. He has covered the coal and power generation industry for more than 24 years, beginning in November 2011 at GenerationHub and prior to that as editor of SNL Energy’s Coal Report. He was formerly with Coal Outlook for 15 years as the publication’s editor and contributing writer, and prior to that he was editor of Coal & Synfuels Technology and associate editor of The Energy Report. He has a bachelor’s degree from Central Michigan University.