An assembly for a high output hydrodynamic separation unit includes, in one form, several components or parts. Top and bottom plates serve as caps for and distribute force through layers of separation channels. The compressive forces seal the channels and prevent leakage from the channels. An optional middle plate may also be provided to create smaller subsets of the layers of separation channels. At least one connector is provided to the combination of components to compress the layers of separation channels. In a variation, an optional outer shell may encase the unit to provide support and compress the stack with a unique threaded configuration.