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Rockfall Mitigation - Project Life Cycle

Hydroelectric projects are often located within very steep, high-relief canyons with numerous geohazards. These hazards often include a risk of rockfall from natural and/or excavated rock slopes that may impact operations, damage facilities, or pose serious safety risks to project personnel or the public.


During the 2022/2023 winter, California was hit with multiple atmospheric rivers that caused widespread damage due to flooding, landslides, and rockfalls. The most significant atmospheric rivers occurred in late December 2022 and triggered a large rockfall above the Hell Hole Dam spillway near the crest of the Sierra Nevada mountains. The rockfall blocks traveled downslope and impacted a flexible rockfall barrier system, which successfully retained the material and prevented rockfall impacts to the roadway, bridge, and spillway below.


This webinar will focus on the rockfall mitigation project life cycle for the flexible rockfall barriers installed above the Hell Hole Dam spillway. The content will summarize the project activities from the initial slope investigation utilizing SPRAT rope access techniques and in-field/computerized rockfall simulations to the selection, design, and construction of the flexible rockfall barrier system. The presentation will also include an overview of the post-rockfall barrier damage and repairs, a summary of LiDAR change detection following the rockfall event, and back-analysis rockfall simulations used to estimate the energy absorbed by the 5-meter-tall 2,000 kJ barrier during the 2022 rockfall strike.

Analysis tools for rockfalls image

Presented By:

Ellen Yeh photo

Casey Smith, PG, CEG

Principal Geologist, Gannett Fleming, Inc.

Casey Smith is a Principal Engineering Geologist with over sixteen years of experience. His experience has focused on evaluating geologic conditions for projects throughout the western United States. These projects have included geologic mapping, subsurface explorations, rock mass characterization, landslide/rockfall assessments and mitigation, instrumentation installation/monitoring, and condition assessments. Casey has performed numerous condition and geohazard assessments of many dams, spillways, penstocks, and hydroelectric tunnels for the purposes of identification and prioritaization of maintenance and repairs. He has also performed numerous projects that include rope access including¬ assistance with surveying, installing instrumentation, and performing rockfall evaluations and mitigation construction support.