Tidal intrusion and mixing in the highly stratified Palmiet Estuary are discussed as an example of a typical small bar-built estuary. The flux of salt through the estuary is dominated by advection owing to the strong gravitational circulation. This vertical circulation pattern is characterized by four processes. The dense saline water enters the estuary as a hydraulically controlled flow through a constricted entrance channel. Beyond an internal hydraulic jump, landward of the flood tidal delta, the saline intrusion propagates as a non-mixing bottom density current and eventually replenishes deep basal reservoirs of saline water in the upper estuary. On the ebb tide this lower saline layer is prevented from flowing seaward by the presence of the sill at the mouth (upstream blocking)-upward entrainment of halocline water occurs via subcritical shear and the sub-halocline water is not removed. The entrained salt is exported to sea by way of the outflowing buoyant surface layer This pattern of circulation is expected to be present in countless small bar-built estuaries around the world. While these systems are generally characterized by micro-tidal and high wave-energy coasts, they are observed in a variety of other situations. In the Palmiet Estuary this pattern occurs during both the drier summer and the wetter winter, exhibiting a certain robustness to seasonal changes. These estuaries are generally classified as highly stratified, although the actual stratification varies as a function of season, tide and position in the estuary. Of consequence is the long residence times expected, and observed, for the deep saline water found in the scour holes of the upper estuary. With decreasing river flow and more constricted connections with the sea, tidal mixing decreases and this deep basal water can be resident long enough to become anoxic.