New Bullards Bar Dam Updates
New Bullards Bar Dam is owned and operated by the Yuba County Water Agency. At 645 feet tall, it is the 5th tallest dam in the United States. The dam is a double-curvature concrete arch dam comprised of the following features: a main concrete arch dam, a gated spillway, intake and conveyance systems, powerhouses, and a low-level outlet. The gated spillway is located on the left abutment and includes three radial crest gates. A selective water intake directs water into a series of penstocks and a tunnel to a 340 MW powerhouse with two Pelton-type turbines. The dam also provides flood control in coordination with the US Army Corps of Engineers.
The first Part 12D Comprehensive Assessment (CA) for the project is currently being conducted in accordance with FERC’s updated Engineering Guidelines. The consultant’s Independent Consultant Team prepared the Part 12D Inspection Plan (PIP) and the Pre-Inspection Preparation Report (PIPR), as well as supporting evaluations including a probabilistic hydrologic hazard curve, HEC-RAS 2D dam breach modeling, and consequence estimates using LifeSIM. The IC Team performed a thorough review of design, construction, operation and maintenance, surveillance and monitoring, and all analyses of records as required by FERC. Work included development of updated potential failure modes and a Level 2 Risk Analysis (L2RA). The team reviewed dam and public safety records (EAP, DSSMP, ODSP, STID), operation and maintenance data, extensive instrumentation data, and evaluation of the concrete arch dam and radial spillway gates.
Prior to the CA, Schnabel developed a digital 3D model of the dam and foundation. The model included the current dam configuration, internal galleries, all instrumentation, and foundation excavations and treatments. Given the foundation complexities at the site and the importance understanding these features in relation to the stability of the dam, the 3D model was updated for the CA to include projections of foundation rock discontinuities. This was used to better visualize the potential for moveable rock block wedges under the dam. During the L2RA and other risk assessments, this model has been used extensively to visualize the spatial relationship of the between the foundation and the dam.