Rollinsford Hydroelectric Project Modifications for Downstream Fish Passage Facility Construction

Strategic Insights -

Green Mountain Power Corporation has submitted a report to the Federal Energy Regulatory Commission detailing modifications made to the Rollinsford Hydroelectric Project to accommodate downstream fish passage facility construction. The project, located on the Salmon Falls River in New Hampshire and Maine, was required to deviate from its mandatory operating conditions to facilitate the construction of downstream fish passage facilities. The modifications involved a planned drawdown of the project impoundment to remove a bulkhead on the spillway crest, as well as the placement of a downstream fish bypass flume and installation of fish guidance boom anchors on the dam.

Key Takeaways:

  • The Rollinsford Hydroelectric Project underwent impoundment level and run-of-river flow modifications from June 22 to June 26, 2025, to accommodate downstream fish passage facility construction.
  • The project impoundment was drawn down from 92.15 feet, NGVD 1929, to approximately 69.9 feet, NGVD 1929, during the drawdown period.
  • The minimum bypass flow was reduced to approximately 16 cfs from the required 35 cfs during the drawdown period.
  • Green Mountain Power Corporation consulted with multiple state and federal agencies and received comments from the New Hampshire Fish and Game Department.
  • No adverse impacts to fish or wildlife resources or water quality in the Salmon Falls River were reported as a result of the modifications.
  • No additional incidents or safety concerns arose from the event.

Statistics:

  • The project impoundment was drawn down by approximately 22.25 feet.
  • The minimum impoundment level reached during the drawdown period was 69.9 feet, NGVD 1929.
  • The minimum bypass flow was reduced to approximately 16 cfs from the required 35 cfs.
  • The drawdown period lasted from June 22 to June 26, 2025.
  • The project refill started on June 27, 2025, at 0815 hours.

Sources:

  • Federal Energy Regulatory Commission, "Rollinsford Hydroelectric Project (FERC No. 3777); Run-of-River and Impoundment Level Modifications to Accommodate Downstream Fish Passage Facility Construction"
  • Green Mountain Power Corporation, "Report to the Federal Energy Regulatory Commission: Rollinsford Hydroelectric Project (FERC No. 3777); Run-of-River and Impoundment Level Modifications"