A large proportion of estuaries present along microtidal, wave-dominated coastlines, both in Australia and globally, are Intermittently Closed/Open Coastal Lakes and Lagoons (ICOLLs). These estuaries are periodically closed by longshore drift along the coast and onshore wave driven sediment, and then opened again by high river discharges.  Prolonged closure has important management implications, such as flooding and decreased water quality.  In both Victoria and NSW many hundreds of thousands of dollars are spent each year artificially opening these estuaries. The basic geomorphology of these estuaries is poorly understood.  Fundamental questions include: what mix of processes lead to closure and opening; and does artificial opening make them more likely to close in the future?  This study explores these questions, but begins with a classification of ICOLLs on the Victorian coast.   A long-term objective is to develop a robust understanding of ICOLL morphodynamics and how they may respond to human intervention or environmental change. A critical aspect is the degree to which fluvial or marine processes affect entrance condition. To address this, the present study explores the influence of these processes by linking their effect to the frequency of entrance closures. As a result, a model of ICOLL geomorphology is created to classify and describe dynamics of microtidal, wave-dominated estuaries. The position of ICOLLs within this is based on their geomorphic characteristics and the dominant processes controlling the entrance state. Local wave conditions, fluvial discharge and sediment transport characteristics, along with the inherited topography of the embayment, are exert a major control on estuary type. This model has applications for coastal management, in particular understanding the estuary response to artificial opening to confirm whether it is physically and financially worthwhile. A further step is to test the national and global applicability of this model, with case studies exemplifying each class of estuary.