Modifications Proposed for New Fork Lake Dam in Pinedale

Pinedale, Wyo.—March 13, 2020 The New Fork Lake Irrigation District (NFLID) has proposed a modification to the New Fork Lake Dam located on the Pinedale Ranger District of the Bridger-Teton National Forest. The NFLID is holding an Open House in Pinedale at the Sublette County School District #1 Administration Building, on March 26, 2020 from 5:00 – 7:00 pm, to share information and hear from interested members of the public.

A series of studies by Wyoming Water Development Commission revealed a shortage of state-permitted irrigation water for the NFLID on their currently irrigated acres. The modification proposed would increase access to existing storage at New Fork Lake by lowering the outlet structure in the existing dam to access currently stored but inaccessible water in New Fork Lake. Lowering the outlet structure would effectively increase the amount of water actively stored at New Fork Lake without increasing the surface area of the existing lake.

Additionally, the New Fork Lake Dam does not meet current regulations and standards of the State Engineer’s Office (SEO) Safety of Dams Program.  Currently, a probable maximum flood would overtop the existing dam up to seven feet for six consecutive days and the current spillway is only capable of conveying 20 percent of the flood water.  The project would address these deficiencies in the reconstruction of the New Fork Lake Dam.

The New Fork Lake Dam and associated waterworks have been permitted, operated, and maintained since 1933.  The NFLID holds valid State of Wyoming water rights for irrigation and stock water, and is currently permitted by the United States Forest Service to operate and maintain the dam and associated structures.

The proposed construction-specific actions include:

  • Construction is currently estimated to begin in 2022 or 2023 and take approximately 24-months, with winter shutdowns.
  • The first year of construction could begin either in late spring as soon as the site is accessible, weather permitting, or after the irrigation season.  At a minimum, one irrigation season would be impacted because of construction.
  • Prior to and throughout construction, the water level in New Fork Lake would be lowered to the elevation of the existing outlet structure, 7810.1 feet, which is approximately 17 feet lower than the normal high water level of New Fork Lake.  This is required for construction safety.
  • During construction, water would be diverted and continually pass into the New Fork River and may result in higher river flows than typically observed during runoff periods or storm events because the water is not being stored by the dam.
  • Once construction begins, there would be no public access to the active construction areas (e.g., dam site and Narrows).
  • Construction access to work areas would be provided by temporary access roads.
  • Alternative and temporary road alignments to provide public access around construction areas to the various campgrounds and boat ramp would be developed.  Public access to these areas may be temporarily impacted during active construction periods.
  • Depending on construction traffic routes and activities, public access to the campground and at the dispersed campsites at the southern end of New Fork Lake may be inaccessible throughout all or most of the construction period.
  • Construction at the Narrows would require removal and disposal of material.  Disposal areas would be located on private property downstream of the dam.  The plan for transportation of the excavated material from the Narrows to the disposal areas is still being developed.  Two options currently being considered are: along the exposed northern shoreline rim of lower New Fork Lake, or through the existing Narrows campground and along USFS Road 730.  Temporary access through the Narrows campground may require tree removal and straightening portions of the road alignment.  The Narrows campground would be inaccessible to the public during active construction at this site, which is anticipated to take approximately 2 months.

As a result of the proposed action and the resulting change in the lower operational water level, it is anticipated that the following mitigation measures may be required:

  • Extension of the beach on the east side of New Fork Lake to accommodate the proposed lower water level.
  • Extension of the boat ramp on the west side of New Fork Lake to accommodate the proposed lower water level.

Additional information on the New Fork Lake Dam Modification Project is also available on the webpage:  https://www.fs.usda.gov/project/?project=57080.  Official 30-day scoping period will begin at publication of Legal Notice in the Casper Star-Tribune, also expected on March 26, 2020.

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