Lower Baker Dam - 2: Evaluating Erodibility, Mitigating Leakage, and Addressing Potential Failure Modes at a Concrete Arch Dam through Groundwater Modeling

Abstract Only - A 3D numerical groundwater flow model is being used to help design and implement a leakage mitigation effort and address related potential failure modes at the Lower Baker Dam in Skagit County Washington. Model outputs are being used to identify the magnitudes and distribution of pressure heads and groundwater velocities throughout the rock mass and estimate and rank erodibility along the flow paths. The model simulates flow along and between fracture flow pathways that were delineated by correlating structural surfaces extracted from a 3D geologic model to leakage vectors defined by dye-tracing. Simulated velocities range from as high as 105 feet/day in the fractures to as low as ~10-9 feet/day in the surrounding rock mass. Applied stream powers were calculated using calibrated fracture thicknesses in conjunction with simulated heads and velocities. Erosion potential was determined by comparing model-derived values to critical threshold values derived from cores using the Erodibility Index Method.