The seasonal closure of tidal inlets is a common and important coastal phenomena. However, studies which have been specifically geared to identify processes governing seasonal inlet closure are almost non-existent. Hence, this study was undertaken to gain insight into processes governing seasonal inlet closure. To determine the processes governing this phenomenon, Wilson inlet, Western Australia, a typical seasonally open tidal inlet is taken as a case study. The study comprised of a field experiment over the summer of 1995, and a numerical modeling exercise employing a molphodynamic model. Results of the field study imply that longshore processes may not be the cause of inlet closure, but that onshore sediment transport due to persistent swell wave conditions in summer may govern seasonal closure of the inlet. Application of a morphodynamic model, which includes both cross-shore and longshore processes, to Wilson Inlet conclusively shows that seasonal closure of the inlet is due to onshore sediment transport under typical summer conditions. The effects of summer streamflow and storm events, which are not uncommon, are also examined using the morphodynamic model. The effect of both streamflow and storm events on the 'open duration' of the inlet is shown to be dependent on the intensity and timing of the event. (C) 1999 Elsevier Science B.V. All rights reserved.