An air infiltration system for a hydroelectric plant includes a spillway gate and a linearized cone valve coupled to the spillway gate, the linearized cone valve having a pivotable plate assembly. The spillway gate may be a tainter or Stoney gate and the pivotable plate assembly may have a deflection plate. A method of infiltrating air in water released from an impoundment may include: lifting a spillway gate from a resting position proximate a bottom of a spillway; and pivoting a deflection plate coupled to the gate proximate the bottom of the spillway; wherein water flows through an opening disposed between the deflection plate and the gate and is sprayed into an atmosphere to be oxygenated.