Deadman's Basin Terminal Outlet Replacement (2010)

Ackley Lake Location

Deadman's Basin Dam History

  • Earthen dam constructed in 1941, raised in 1958
  • Off-stream reservoir with canal from the Musselshell River
  • Dam owned by DNRC, operated/maintained by Deadman's Basin Water Users Association
  • Primary purpose: Irrigation, municipal & recreation
  • Dam Height: 60 feet
  • Dam Storage: 72,218 acre-feet
  • Dam Classification: High Hazard
Ackley Drawdown

Project History

Annual inspections reported numerous issues with the dam and outlet structure including: seepage, erosion behind the outlet structure and outlet structure deterioration.  In 2003, the DNRC performed seepage modeling on the dam and found that high uplift pressures existed at the dam toe and the exit gradient of seepage did not meet Montana Dam Safety Act Standards.  Additional analysis completed by the engineering consultant found that a toe berm and filter significantly increased the factor of safety, rendering the dam compliant to Montana Dam Safety Act Standards. It was decided to move forward with improvements and investigate funding sources for the project.

Work Breakdown

  • Extending the terminal outlet
  • Installation of a filtration and drainage system
  • Construction of a toe berm
  • Canal armoring, articulated concrete blocks
  • Reclamation and erosion control
RCP Installation

 

 

Project Funding

The total cost of the project was $780,000. To finance the project, the DNRC used the following grant and loan programs:

  • DNRC RRGL Grant: $100,000
  • DNRC RRGL Loan: $400,000
    • 20 years @ 4.5%
    • To be repaid by WUA
  • State Funds: $280,000
    • Only utilized on SWP owned projects
  • DNRC In-kind work
CarterFunding

Project Status & Results

  • Construction began in October 2009 and was completed in May 2010
  • Articulated concrete block failure in October 2010. Was replaced with AJAX system, which is working well

 

Project Partners

Owner: DNRC

Lead Design Engineer: WWC Engineering

Prime Contractor: Montana Civil Contractors, Inc.

Construction Oversight: DNRC