Advances in estuarine physics.

Recent advances in our understanding of estuarine circulation and salinity structure are reviewed. We focus on well- and partially mixed systems that are long relative to the tidal excursion. Dynamics of the coupled system of width- and tidally averaged momentum and salt equations are now better understood owing to the development of simple numerical solution techniques. These have led to a greater appreciation of the key role played by the time dependency of the length of the salt intrusion. Improved realism in simplified tidally averaged physics has been driven by simultaneous advances in our understanding of the detailed dynamics within the tidal cycle and across irregular channel cross-sections. The complex interactions of turbulence, stratification, and advection are now understood well enough to motivate a new generation of physically plausible mixing parameterizations for the tidally averaged equations.