This paper presents numerical solutions for the flowfield transients with a single jet of cold liquid entering horizontally at the bottom of a tall tank initially filled with hotter liquid which is removed at the top of the tank. Accurate solutions of the unsteady two-dimensional Navier-Stokes and heat equations are computed for laminar flow conditions with the coupling between the flow and the temperature modeled through the Boussinesq approximation. Early in the filling process, the inflow of the higher density liquid produces a gravity current which propagates across the tank floor. When turned by the wall opposite the jet, the gravity current generates a range of internal wave phenomena which are apparent in oscillations of the thermocline. The region below the thermocline is initially filled with a complex pattern of recirculation cells, which evolves to a pattern dominated by the jet vortex as the thermocline moves away from the inlet.