Big Hole River: Diversion Dam Improvement

The Big Hole diversion dam replacement project is complete.  On November 7, 2010 the city and county of Butte-Silver Bow finished the replacement of the 80-year-old diversion dam in the Dewey Canyon of the Big Hole River.  This diversion dam is used for pumping water from the Big Hole River to the city of Butte, Montana for a portion of the cities drinking water.    After nearly a century of existence, the diversion dam is no longer an impediment to fish and boater passage, and the security of Butte Silver Bow’s ability to draw water from the Big Hole River is ensured.

The old diversion dam and intake structure was outdated, and structurally failing, which has a threat to the River, and the ability for Butte to get one of their sources of drinking water.  The previous structure was a safety issue for recreational floaters on the Big Hole River.  Over the years the dam has been the cause for flipping many boats as floaters tried to navigate over the concrete structure.  As a guide on the Big Hole River I would only run the diversion at certain safer flows, and would remove my gear and clients from my boat as I navigated over the diversion.  This dam was unsafe for the most experienced floaters, and novices.  The 80-year-old diversion dam also restricted fish passage.  Spawning rainbow trout in the spring would try to jump the 5-foot high concrete structure to spawning grounds upriver.

The rebuilt diversion dam has taken recreational use on the Big Hole River into consideration when designing the new diversion.  The new diversion has a rock weir dam, which has a boat and fish passage channel.  The boat and fish passage channel width is wide enough to keep your oars extended while going through it.  The spillway is designed for boater safety.  There are two rest pools for boaters while they are losing elevation down the rock face.  These channels and rest pools are constructed from native rock.

The completion of the diversion dam on the Big Hole River is a great example of a community working together to improve a structure that benefits all uses.  Silver Bow County now has a better functioning diversion that ensures a source of their drinking water.  Recreationalists now have a safe, unrestricted passage in the river that promotes the health and migration of fish.  Boat traffic is going to be more spread out on the Big Hole as a result of the new diversion dam.  Previously there was a dead-zone for floating recreationalists.  You either had to take out above the diversion dam at Silver Bridge or risk your life going over the diversion.  Now since the diversion has a slough to safely navigate, boat traffic will be spread out with more floating sections to choose from on the Big Hole River.  The completion of this project has resulted in significant improvements to one of our highest valued and treasured resources in the West.  May this set the precedent of all diversion improvements on western rivers.