Abstract

  
This Happy Isles Gauging Station Bridge Removal Project Environmental Assessment is intended to guide the future of the Happy Isles Gauging Station Bridge Removal Project. The project alternatives and this environmental assessment, which evaluates the potential impacts of the alternatives, are integrated in this document and are referred to collectively as the Happy Isles Gauging Station Bridge Removal Project Environmental Assessment. The environmental assessment identifies and analyzes two alternatives: Alternative 1 – the No Action Alternative, and Alternative 2 – Controlled Demolition (the preferred alternative).  
Alternative 1, the No Action Alternative, represents conditions and management practices as they currently exist at the Happy Isles Gauging Station Bridge. It provides the basis of comparison for the action alternative. The action alternative (Alternative 2) is based on the purpose and need for the project and conforms with the goals of Yosemite National Park’s General Management Plan, the goals and management elements of the Merced Wild and Scenic River Comprehensive Management Plan, and goals of the Yosemite Valley Plan.  
Alternative 2, Controlled Demolition, would partially remove the Happy Isles Gauging Station Bridge. The river-right abutment, which is located on a large boulder on the riverbank, would be retained to protect the historic Happy Isles Gauging Station. Alternative 2 would involve separating the bridge into liftable segments and removing the segments using equipment located on the riverbank. A temporary containment system (e.g., a reinforced tarp, netting, cage, or floating barge) would be installed beneath the Happy Isles Gauging Station Bridge to catch small amounts of debris during partial bridge removal. This containment system would prevent slurry from concrete saws, as well as small debris, from falling into the Merced River. However, not all demolition debris would be prevented from falling into the river; masonry debris greater than 2 inches in any dimension and all metal debris would be removed from the river. A temporary structural support system (e.g., scaffolding, jacks, or mechanical lifts) may be installed to prevent uncontrolled collapse of the bridge structure during demolition or to anchor the containment system. Once the river-left abutment has been removed, the bank would be shaped and contoured and riparian vegetation would be planted to match conditions of adjacent portions of the riverbank.
  
If you have questions or comments regarding this document, you may contact:
  
Superintendent, Yosemite National Park
ATTN.: Happy Isles Gauging Station Bridge Removal Project
P.O. Box 577
Yosemite, California 95389
  
or call: 209-372-0261
or fax: 209-379-1294
or visit the planning web site: www.nps.gov/yose/planning  or email YOSE_Planning@nps.gov