Dam Safety Engineering for Wanapum and Priest Rapids Dams, Beverly, Washington
Grant County Public Utility District (GCPUD) owns and operates the Priest Rapids Hydroelectric Project on the mid-Columbia River which consists of the Wanapum Development and Priest Rapids Development. The CCI-LT team has provided dam safety engineering services in support of GCPUD operations since 2017.
 
Our services have included 34 task assignments to date including seismic embankment stability and liquefaction evaluations, internal erosion and seepage evaluations, automated instrumentation and monitoring system development and implementation, FERC Part 12 inspections and safety reviews, independent technical review, dam safety training courses for GCPUD staff, breach modeling with consequence evaluation support, and risk analysis.​ 
Project Highlights
​The Wanapum and Priest Rapids dams were completed in the early 1960’s. Their location in the mid-Columbia River Valley brings a unique set of geotechnical challenges. During the last ice age, a lobe of the Cordilleran Ice sheet blocked a large valley around the area that is now Missoula, Montana. This ice dam impounded a lake over 2,000 feet deep within the valley. This ice dam broke and flooded the area that is now eastern Washington with catastrophic mega-floods. The ice dam broke and reformed perhaps as many as 100 times, and shaped the character of the alluvium upon which the dams are founded. This complex geologic assemblage, combined with 1960’s era construction practice, has created challenges for characterizing and understanding the behavior of the dams, especially with the modern understanding of the hazard posed by Cascadia Subduction Zone earthquake.
 
Our recent work for GCPUD has included a study focused on the seepage characteristics, filter compatibility, and internal erosion mechanisms of the Wanapum Dam left embankment. The left embankment is a zoned earth and rockfill dam constructed upon megaflood deposits of generally coarse-grained alluvium. Nearly 1,000 construction gradations were compiled, digitized, and evaluated using custom programming solutions to efficiently evaluate and display the gradation data. This included an evaluation of internal instability in the unique megaflood deposits of the mid-Columbia valley, using a variety of state-of-the-art methods.  
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The Priest Rapids Dam is a major electricity producer for Washington and provides energy for data storage centers and regional energy distribution.
Owner: Grant County Public Utility District (GCPUD)
More Information: Grant PUD: Priest Rapids Dam History