Water movement, due to tides and surface waves, is the basic forcing mechanism for nutrient fluxes, sediment dynamics and the fate of pollutants within the Exmouth Gulf. The dominant hydrodynamic process in this shallow basin is tidal motion, with a predominant semi-diurnal constituent. Large surface waves are only generated during tropical cyclones but their development is limited by water depth and bottom friction. Therefore, our hypothesis is that long-term water mass balance is predominantly governed by tidal motion and wind-induced currents. To estimate the water mass balance within the Gulf, field observation and numerical modelling were carried out in parallel. During the first stage of the field study, waves, wave-induced velocities and tidal elevations were measured at various locations in the Gulf. This study revealed that outside of cyclone episodes, wind-generated waves are only important at the entrance to the Gulf and wind-induced velocities are less than 0.5 m sec-'. The second stage of the field study involved measuring water velodties along sixteen transects widely distributed throughout the Gulf. Both vertical and horizontal velodties were recorded from the surface to the bottom at a resolution of 0.25 metres, every 10 seconds. Tidal elevations were aiso observed at two locations. The data collected during the field studies are now used for calibration of a computer model of tidal circulation in the Gulf. It is expected that this model will provide a long-term water mass balance for the Gulf and quanhfy the net fluxes of various suspended organic and non-organic substances into and out of the Gulf. The distribution of water flow intensity, also provided by the model, will indicate areas of potential erosion and areas vulnerable to potential pollution.