Estler Dam Rehabilitation

Estler Lake Dam is a remote mountain dam located in the East Pioneer mountain range in the Beaverhead National Forest near Dillon, MT. It is an on-stream storage reservoir located on Estler Creek, a tributary of Rattlesnake Creek. The dam has an earthen embankment that is roughly 330 feet long and an embankment height of 35 feet. The reservoir has a normal storage volume of 470 acre-feet. The dam is owned and operated by Rattlesnake Reservoir and Water Company who holds an easement from the United States Forest Service. The site is accessed by foot or ATV. The dam was built over a hundred years ago and required several upgrades to increase its longevity.

AESI first evaluated the dam for the required 5-year engineer inspection. After producing and submitting the inspection report to the DNRC and USFS, AESI completed a feasibility study to evaluate alternatives for rehabilitation.   The feasibility study involved close coordination and collaboration with the Owner as well as the DNRC and USFS. Next, AESI completed final design and permitting for the preferred alternative. AESI also provided assistance to the Owner through the construction phase of the project. Highlights of the project are provided below.

• Feasibility Study
  • Embankment stability analysis using the computer program Slope-W
  • Spillway capacity analysis
  • Development and evaluation of alternatives for embankment and outlet works rehabilitation
  • Selection of a preferred alternative and cost estimate for preferred alternative
• Outlet Works Rehabilitation
  • Replace 40-feet of corrugated metal pipe with reinforced concrete pipe
  • Replace inclined slide gate with a 4-ft square concrete outlet tower with a vertical control gate
  • Slipline 80-feet of concrete arch pipe with high-density polyethylene pipe
• Embankment Rehabilitation
  • Raise embankment elevation
  • Add rock fill on downstream embankment – ~1,000 cubic yards of rock
  • Add toe drain and diaphragm filter on downstream embankment to address seepage
• Permitting
  • US Army Corp Clean Water Act – exemption request granted
  • Montana Natural Streambed and Land Preservation Act (310)
  • Short-Term Water Quality Standard for Turbidity (318)
  • US Forest Service – various permits
  • General Permit for Stormwater Discharges Associated with Construction Activity
  • DNRC High Hazard Dam Construction Permit