Poudre Dam Inundation Study

Seaman Reservoir Labrynth Spillway

Halligan Dam Northwest of Fort Collins, CO

Seaman Reservoir Dam

Poudre River 2D model simulation of flood inundation due to dam failure.

Project Summary

The Dam Safety Branch of the Colorado Division of Water Resources provides financial assistance to dam owners for projects to develop dam breach flood inundation mapping necessary for Emergency Action Planning (EAP). The Dam Safety Branch office recognized an opportunity to reduce costs by combining multiple projects for ten dams located within the Cache la Poudre Canyon. Anderson Consulting Engineers provided dam breach flood inundation mapping for the following dam owners and corresponding reservoirs:


City of Fort Collins Dams

  • Joe Wright Reservoir
  • Halligan Reservoir

Water Supply and Storage Company Dams

  • Long Draw Reservoir
  • Chambers Lake Reservoir

City of Greeley Dams

  • Barnes Meadow Reservoir
  • Comanche Reservoir
  • Seaman Reservoir
  • Hourglass Reservoir
  • Peterson Lake Reservoir
  • Twin Lakes Reservoir

Dam breach parameters including geometry and time to failure were developed using empirical equations recommended by the Colorado State Engineers Office Dam Safety Branch. Breach modeling was conducted using the USACE’s HEC-RAS 1D Unsteady Flow Model to produce an outflow hydrograph. Flood routing and inundation mapping was conducted along 135 miles of river using the USACE’s HEC-RAS 2D Model.



  • Client/Owner: Colorado Department of Natural Resources-Dam Safety, City of Fort Collins, City of Greeley, Water Supply and Storage Company
  • Project Location: Cache la Poudre watershed west of Fort Collins, Colorado
  • Approximate Project Cost: $118,000
  • Project Completion Date: June 2019
  • Project Components:
    • Poudre Canyon 2D Hydraulic Model – covers approximately 30 miles of the Poudre River upstream of the North Fork confluence, 16 miles of the South Fork, 6 miles of Beaver Creek, 2 miles of La Poudre Pass Creek, and 7 miles of Joe Wright Creek.
    • North Fork 2D Hydraulic Model – includes the lower 23 miles of the North Fork Poudre River between Halligan Reservoir and the Main Stem.
    • Poudre 2D Hydraulic Model – includes approximately 25 miles of the Poudre River downstream of the North Fork Confluence.
    • Final deliverables of the project, produced individually for each dam, included an Inundation Mapping Report, inundation mapping, digital inundation boundaries and critical facilities shape files, and HEC-RAS modeling files.

Ready to start a project?

Talk to our team of experts to get started today.