LANDSLIDES CAUSED BY RAPID DRAINING OF TETON RESERVOIR, IDAHO

The rapid release of 17-mile-long Teton Reservoir due to the sudden failure of Teton Dam on June 5, 1976, produced an extreme example of the "rapid drawdown" condition in a reservoir. This resulted in many landslides in those parts of the canyon wall of the Teton River that previously were submerged by the reservoir. Studies of these slopes indicate that approximately 3.6 million cu yd. of soil and rock slid from the canyon walls between the times of ponding of the reservoir and of post-failure aerial photography taken on June 19, 1976. Undoubtedly most of the landslides occurred during rapid drawdown. The total map area of landslides on the formerly submerged canyon slopes is approximately 500 acres (21.8 million sq ft.), or some 34 percent of the 1,460 acres (63.5 million sq ft.) of valley slopes submerged by the reservoir. In spite of the large area subjected to landsliding, damage costs were small because of lack of development along the shoreline of the reservoir; however, both the river and the canyon sustained enviornmental damage. The rock that forms the canyon walls throughout the original reservoir area is a highly fractured, rhyolitic, welded ash-flow tuff, the Pleistocene Huckleberry Ridge Tuff. The upland is covered by a layer of loess; canyon walls are largely obscured by loess or colluvium consisting of loess and/or fragments of welded tuff. These materials proved to be very unstable when saturated by the reservoir and then subjected to rapid drawdown. Usually the unstable materials were only a few feet thick and the sliding was mainly translational, often exposing bedrock at the rupture surface. In some places they were thicker and failed by slumping or a combination of slumping and translation. Locally rock falls and rock slides occurred in the welded tuff, but these failures were on a considerably smaller scale than failures in the loess and colluvium. Sliding was enhnced in both the unconsolidated materials and the bedrock by return of bank storage water to the river after drawdown. (Author)

• Supplemental Notes:
  • Proceedings of the Eighteenth Annual Engineering Geology and Soils Engineering Symposium, held at the Red Lion Inn, Boise, Idaho.
• Corporate Authors:

  Idaho Transportation Department

  3311 W State Street, P. O. Box 7129
  Boise, ID  United States  83707-1129

  University of Idaho, Moscow

  Department of Geology and Geological Engineering
  Moscow, ID  United States  83844-3025

  Boise State University

  Department of Geology and Geophysics
  Boise, ID  United States 

  Idaho State University, Pocatello

  Department of Geology
  Pocatello, ID  United States  83201

  Idaho State University, Pocatello

  Department of Geology
  Pocatello, ID  United States  83201
• Authors:
  • SCHUSTER, R L
  • Embree, G F
• Conference:
  • Proceedings of the Eighteenth Annual Engineeing Geology and Soils Engineering Symposium, held at the Red Lion Inn, Boise, Idaho.
• Publication Date: 1980-4

Media Info

• Features: Figures; References;
• Pagination: p. 1-14

Subject/Index Terms

• TRT Terms: Canyons; Colluvium; Drainage; Landslides; Loess; Reservoirs; Rockfalls; Rockslides
• Subject Areas: Geotechnology; Highways; Hydraulics and Hydrology; I42: Soil Mechanics;

Filing Info

• Accession Number: 00334055
• Record Type: Publication
• Files: TRIS, STATEDOT
• Created Date: Sep 16 1981 12:00AM