The volume of water exchanged between a lagoon or estuary and the open sea in the course of a complete tidal cycle. McBride et al. (2007) Geomorph. 88, 3–4 argue that tidal prism and the quantity of littoral sediment transport are the most important factors controlling inlet stability. The tidal prism is also significant in the size and configuration of ebb-tidal deltas (Fitzgerald et al. (2002) Geomorph. 48, 1–3).