July 11, 2002
Larry Wolf
(208) 378-5220
Dick Bauman
(307) 739-8765
Grassy Lake Draft Environmental Assessment Issued
The Bureau of Reclamation is seeking comments on an environmental assessment released this week on proposed safety of dams modifications for Grassy Lake Dam. Comments will be accepted until August 15.
Grassy Lake is located on Grassy Creek, about a half mile upstream of Falls River, in a remote area of northwestern Wyoming just south of Yellowstone National Park.
Significant damage has occurred to the spillway floor. Spillway discharges could cause uplift of the failed floor slabs resulting in erosion and undercutting that would eventually lead to dam failure. In addition, several seepage areas have been discovered over the years indicating drain blockage and pipe damage. The drain design does not meet today’s standards and is ineffective in controlling seepage and preventing piping of embankment material.
The preferred alternative would replace a 557-foot section of the concrete-spillway chute and replace the drainage system in the embankment. Construction would occur during the summers of 2004 and 2005. The estimated cost of the project is $5 million.
Other alternatives include:
* No action
* Dam remova
* Project abandonment
* Reservoir restriction (with modifications)Grassy Lake Dam and reservoir provides 15,200 acre-feet of storage for irrigation within the Fremont-Madison Irrigation District. The Fremont-Madison Irrigation District operates and maintains the dam which is owned by Reclamation.
An interim operating restriction was placed on Grassy Lake Reservoir in 1999 restricting the winter-spring time operation 5 feet below normal pool, and the summer operation 1 foot below normal pool to safely pass a 100-year flood event.
Repairs to Grassy Lake Dam are part of Reclamation’s safety of dams program which examines and evaluates the structural integrity of its dams and identifies potential public safety risks.
To obtain a copy or to comment on the Draft Environmental Assessment or provide written comments contact Dick Bauman, Bureau of Reclamation, PO Box 1493, Jackson WY 83001, or FAX (307) 739-8794, or telephone at (307) 739-8765.