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Public Comments Sought for GAOA Mitchell Dam Project on the Mystic Ranger District
Release Date:
Contact(s): Media Contact: Scott Jacobson, 605-440-1409
Rapid City, SD, February 29, 2024 — The Black Hills National Forest is proposing a project to address the deferred maintenance of the dam at Mitchell Lake, located on Spring Creek just east of Hill City along Highway 16. The project is called the Great American Outdoors Act Mitchell Dam Project.
The proposal is to either decommission (remove) the dam or repair the dam and remove the built-up silt. The current state of the dam does not meet requirements to protect life and property downstream for a probable maximum flood event where over 56,000 cubic feet of water per second flows at the dam. Significant damage and potential loss of life could result in the event of a dam failure.
If the dam is decommissioned, riparian habitat would be restored, and the stream would be designed to enhance the recreational fishing experience. Through decommissioning, the dam would be removed completely, and thus would no longer pose a threat to downstream populations and infrastructure. The natural Spring Creek river channel is proposed to be restored through the existing reservoir pool area to match the natural channel materials and features prior to creation of the reservoir.
The entire sediment pool would also be revegetated with a native seed mix. The existing floodplain of the channel would be restored with native shrubs, trees, and grasses. Graveled parking areas and walking trails would be considered to provide better access to the restored floodplain and channel for the public.
If the dam is repaired, the overall height would be reduced slightly. Rehabilitation would include removal and reconstruction of the existing auxiliary spillway and outlet works, as both are significantly deteriorated and not capable of routing the design storm events. Sediment removal to restore the original storage capacity of the dam is also proposed. The primary spillway outlet intake, control, and conduit would also be reconstructed. The overall lake size would remain relatively the same.
Nearly two-thirds of the reservoir’s capacity has been filled with sediment since construction. The original 1937 drawings for the dam show storage of 53.35 acre-feet at the auxiliary spillway crest, and the most recent bathymetric survey shows only 17.8 acre-feet of storage. To restore the reservoir to its previous capacity, approximately 35 acre-feet of sediment would need to be removed. Onsite disposal is likely not feasible as the reservoir is constricted by steep canyon walls and Highway 16.
The third option is a No-action Alternative: Categorized as a high hazard dam, if left alone, the estimated damages and loss of life are high. The costs of no action range up to $14.9 million with an additional $2 million or more in deferred maintenance and sediment removal costs.
The Mystic Ranger District has a public involvement plan identifying specific public involvement objectives, including collaborative efforts, methods to achieve the objectives, estimated times and dates for any activities and the people organizations to involve. A public meeting is planned for this project on March 13 from 6-8 p.m. at the Community Center in Hill City.
The scoping document is now available for the proposed Great American Outdoors Act (GAOA) Mitchell Dam Project. The preliminary assessment is to evaluate this proposal as a categorical exclusion (CE), 36 CFR 220.6 (e)(18), categorically excluded from documentation in an Environmental Analysis or Environmental Impact Statement. The scoping document is currently available for a 30-day agency and public review period. Documents relating to this project can be found on the Black Hills National Forest website: https://www.fs.usda.gov/project/blackhills/?project=65637.
Forest Service specialists will analyze potential effects on resources such as water, wildlife, cultural resources, recreation, and timber. Required consultation with other federal, state, and tribal entities, such as the U.S. Fish and Wildlife Service, South Dakota State Historic Preservation Office, and Tribal Historic Preservation Offices, will also occur prior to the decision.
Electronic comments are preferred and must be submitted to the Comment Reviewing Officer online at https://cara.fs2c.usda.gov/Public/CommentInput?Project=65637. An automated response should confirm your electronic comment has been received. Comments can also be sent via U.S. mail to Mystic Ranger District Office, Attn: GAOA Mitchell Dam Project, 8221 S. Mount Rushmore Rd., Rapid City, SD, 57702 or by fax at 605-343-7134.
While the Forest welcomes comments on this proposal at any time, it would be most helpful if the comments are received by March 29, 2024. It is the responsibility of the sender to ensure timely receipt of any comments submitted. Comments submitted, including names and addresses of commenters, are public information.
For additional information, or if there are questions on this proposed project, please contact Brittany Coupe, Civil Engineer, at (605) 642-4622 or Jim Gubbels at the Mystic Ranger District office in Rapid City, SD, at (605) 343-1567, Monday through Friday between 8:00 a.m. and 4:30 p.m., mountain daylight time.
For more information on the Black Hills National Forest, visit www.fs.usda.gov/blackhills or follow Facebook: https://www.facebook.com/blackhillsnf and/or Twitter: https://twitter.com/BlackHillsNF.
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