Variable renewable energy resources will play an increasingly prominent role in electricity systems as global economies pursue ambitious decarbonization and electrification targets. Power system flexibility will become a valued asset as more variable renewable energy resources are integrated into energy systems. The extent to which power systems can provide flexibility services to accommodate increased net load variability depends considerably upon the constraints of the existing energy resources in the generation mix. Jurisdictions whose electricity supply is predominantly hydroelectric operate within a unique set of operational, environmental, and regulatory constraints specific to large storage hydro systems. The constraints associated with large hydro systems may limit the extent to which hydro-dominant electricity systems can accommodate VRE resources. This thesis presents a model for cascaded hydro generation resources that is compatible with the SILVER production cost model and presents a case study of future VRE integration into the British Columbia electricity system. Modelling results indicate that a fully decarbonized BC electricity system is feasible assuming that hydro generation assets have a high degree of operational flexibility and adequate transmission capabilities.