Project Name:
Seismic and Hydraulic Rehabilitation of Big Tujunga Dam
Los Angeles, California, United States
Region: Americas
Service Offering: Engineering & Design, Construction & Construction Management
Market Sector: Water & Wastewater
Client Type: Public & Private Utilities
Status: Complete
Description:

MWH provides optimized and efficient design solutions to upgrade one of California’s largest dams to protect against seismic and flood concerns

ENR Best Project 2011 Winner

The 244-foot-tall Big Tujunga Dam, nestled in the San Gabriel Mountains northeast of Los Angeles, Cali., was originally completed in 1931. MWH worked with the Los Angeles County Department of Public Works (LACDPW) to perform rehabilitation and spillway modification to help meet the updated standards for Maximum Credible Earthquake (MCE) and Probable Maximum Flood (PMF) scenarios.

LACDPW commissioned MWH to conduct studies to re-analyze both the seismic and hydraulic issues related to the dam, which was operating at 25 percent storage capacity due to seismic safety concerns for more than 30 years. The studies confirmed the dam’s inability to handle MCE and PMF, and proposed a number of alternatives for both the seismic and hydraulic rehabilitation.

MWH proposed a number of alternatives for both the seismic and hydraulic rehabilitation. Ultimately, LACDPW selected the alternative design recommended by MWH to strengthen the dam by adding concrete against the downstream side of the dam to create a “thick arch” in combination with construction of a new ogee crest spillway with flip-bucket. MWH provided optimized and efficient design solutions for the rehabilitation of both the dam and spillway, and provided engineering services during construction.

Construction began in early 2008, with the last concrete block placed in January 2011, and the project re-dedicated on July 21, 2011. 

Project Highlights

  • 2012 Award of Excellence in the Constructed Project from the United States Society on Dams
  • 2012 Public Works Project of the Year for projects over $75 million from the American Public Works Association
  • Named 2011 Best Civil Works/Infrastructure Project in California by Engineering News-Record
  • Awarded 2011 National Rehabilitation Project of the Year by the Association of State Dam Safety Officials
  • Design refinements led to savings of approximately 40,000 cubic yards of concrete, or about $25 million
  • Increased water supply will save Los Angeles County nearly $2 million per year in otherwise imported water costs
  • Validation of design for PMF and MCE requirements
  • Addition of 70,000 cubic yards of concrete on the downside stream of the thin arch dam to create a thick arch dam to reduce stress under MCE loading
  • Unique radial curved overtopping spillway design that discharges and flips overtopping flows away from the dam to a central point downstream
  • Had the dam not been rehabilitated and a significant seismic or flooding event to the level of MCE or PMF scenarios were to cause a dam failure, it would likely have resulted in:
    • Injury and/or loss of life
    • $175 million in damage to homes, buildings, facilities and roads, including a portion of the Interstate 210 freeway
    • More than 100,000 people impacted by disruptions to utilities, services and commerce
    • Loss of water storage and supply for the City of Los Angeles
Services Provided
  • Seismic and Hydraulic Studies and Analysis
  • Optimized and Efficient Design Solutions
  • Geotechnical engineering services
  • Structural engineering services
  • Hydraulic engineering services
  • Mechanical and electrical engineering services
  • Engineering Services During Construction