In February 2017, Oroville Dam’s main and emergency spillways were damaged. NHC provided technical assistance to the California Department of Water Resources (DWR) as part of a collaborative team that included DWR, other consultants, and regulatory agencies including the California Division of Safety of Dams and the Federal Energy Regulatory Commission (FERC). NHC’s work started with initial emergency support to understand the hydraulic conditions that led to the failure of the spillways and providing input on the necessary repair strategies for the spillways over a range of forecasted flow conditions. NHC supported the repair effort as part of the Technical Advisory Committee and with development of FLOW3D Computational Fluid Dynamics (CFD) models of the emergency and broken main spillway. NHC used these intricate models to provide the design team information on depths, velocities, shear stresses, and hydraulic characteristics to support the proposed repairs and improvements of the spillways.