A washing machine appliance, such as a consumer washing machine, includes a casing, and a tub disposed within the casing. A wash basket is received within the tub and is configured for receipt of articles to be washed. A diffuser plate defines a continuous bottom of the wash basket and includes a plurality of passages defined therethrough. An impeller system is operably configured within the tub below the diffuser plate and includes at least one impeller that is rotationally driven during a wash cycle to direct high velocity wash water through the passages with sufficient energy to move and wash articles within the wash basket.