A small barrier breach in Kouchibouguac Bay, New Brunswick, is examined with respect to: (a) origin, (b) morphological development, and (c) hydraulic characteristics. The small tidal inlet was formed in 1970 by storm conditions which have a return period of between 5 and 12 years, based upon two different storm intensity indices. Barrier breaching is not a catastrophic event in the temporal sense in the bay and the return period of the initiating storm conditions is close to the average interval between breaching episodes for this barrier system. A threshold barrier morphology is suggested as a more important variable than storm magnitude. Traced from its inception to closure (a period of 6 years), the barrier breach cited revealed: (a) flood domination generating a transfer of large volumes of sedimentary material from the littoral drift system into the lagoon, (b) gradual reduction in tidal prism associated with flood delta growth and infilling of tidal channels, and (c) migration (30 m year−1) and increasing reorientation of the inlet neck under a strong preferred littoral drift direction.