Cottonwood Siphon Rehabilitation Project

Joint Works Project Complete

UPDATE: Oct. 23, 2020 

The Cottonwood Siphon Rehabilitation Project is complete and the resulting outage on the 930 Section of the Hansen Feeder Canal (between Flatiron Reservoir and the Big Thompson River Siphon) has been lifted. As the Cameron Peak Fire threatened to move south of Highway 34, there was a need for alternate electricity resources to be made available to Estes Park. Due to construction activities on some C-BT features, including the Cottonwood Siphon, the hydropower plants between the Adams Tunnel and Flatiron Reservoir had been out of service. Northern Water and the U.S. Bureau of Reclamation made the decision to conclude maintenance activities which would allow water to flow and hydropower generation to commence. As of Oct. 17, the Cottonwood Siphon and related features were fully operational. 

What was the Cottonwood Siphon Rehabilitation Project?

The Cottonwood Siphon Rehabilitation Project was a joint works project between Northern Water and the U.S. Bureau of Reclamation. The siphon was constructed in the 1950s and carries Colorado-Big Thompson Project water from Flatiron Reservoir underneath Cottonwood Creek and Larimer County Road W 18E (Pole Hill Road), approximately 2/10-mile west of South County Road 31. The water is delivered to water users and ultimately to Horsetooth Reservoir.   

Why was the siphon rehabilitation project needed?

The siphon is more than 60 years old. It was determined that it was structurally distressed beyond serviceability limits and required rehabilitation to provide continued service for the C-BT Project.  

What was the construction period?

The rehabilitation project timeframe was June 2020-November 2020. 

What did the project include? 
  • Slip-lining the existing concrete siphon with a ¾-inch thick, 142-inch outside diameter steel pipe
  • Placing grout between the new steel pipe and the existing concrete pipe
  • Lining the interior of the steel pipe and valve  
  • Installing a new bridge over the open canal upstream of the siphon
How were the campground and neighboring homes affected?

Impacts to campers at Flatiron Reservoir Campground and neighboring homes may have included: 

  • Construction activities
  • Noise
  • Lighting
  • Intermittent and short lane or road closures

Northern Water and the contractors minimized impacts as much as possible.  

Who paid for the project?

The project was a joint works project between Northern Water and Reclamation, each entity paid an equal share of the cost. 

Who do I contact if I have questions? 

If you have questions regarding the project or construction activities, call Northern Water at 800-369-7246. The Flatiron Reservoir campground host and the Larimer County Parks office can also provide information.