Embodiments provide a method and apparatus to lower the temperature and heat content of the ambient air at the inlet to a gas combustion turbine to enhance power generation. Embodiments can use multiple, staged direct contact air chillers, variable flow secondary water chilling systems, constant flow primary water chilling systems with water chilling units arranged for parallel chilled water flow, and a coolant water circulation system used for heat rejection with open cooling towers. Alternatives can use a chilled water thermal storage system, and/or waste heat to drive at least part of the water chilling process. With the included apparatus a method to allow adiabatic air chilling is available for operation during periods of lower ambient air conditions when needs for power augmentation may not be as great.