Awards

• 2000 Engineering Excellence Award American Consulting Engineers Council
• 2000 and 2001 Outstanding Civil Engineering Award American Society of Civil Engineers
• Best of 1999 for Outstanding Large Civil Engineering Category Intermountain Contractor
• 1999 National Rehabilitation Project of the Year Association of State Dam Safety Officials
• 1999 Concrete Excellence Awards First Place Montana Contractors' Association

The 60-year-old Tongue River dam experienced a large flood in 1978 during which the existing spillway was severely damaged and nearly overtopped. This near failure and increased storage requirements from a recent water rights compact settlement spurred a major design and construction effort to implement dam safety rehabilitation and reservoir enlargement measures.

Features

• 109,000 cfs roller-compacted concrete (RCC) stair-step emergency spillway (largest capacity over-the-embankment RCC spillway in the world at the time of construction)
• 41,000 cfs labyrinth-crest conventional concrete service spillway
• Design to accommodate full irrigation deliveries throughout construction
• Impact mitigation included creating 50 acres of new, high-value wetlands
• A new, nine-foot horseshoe tunneled outlet works with 1,500 cfs capacity

SEH Services

• Field investigations and laboratory testing
• Comprehensive geotechnical evaluations and analyses
• Alternatives analyses of spillway and outlet works schemes
• Final design and preparation of complete construction documents and cost estimates
• Full-service construction-phase support from bidding through acceptance