Cottonwood Siphon Rehabilitation Project

Joint Works Project 2020

The Cottonwood Siphon Rehabilitation Project is 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 (C-BT) 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 is the siphon rehabilitation project needed?

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

What is the construction period?

The rehabilitation project must be completed within a short timeframe – beginning in June 2020 and ending in November 2020 – and around the clock construction work may take place. 

What does 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 will the campground and neighboring homes be affected?

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

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

Northern Water and the contractor will minimize impacts as much as possible.  

Who is paying for the project?

The project is a joint works project between Northern Water and Reclamation, so each entity is paying 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.