Tidal prism

A tidal prism is the volume of water in an estuary or inlet between mean high tide and mean low tide, or the volume of water leaving an estuary at ebb tide.

The inter-tidal prism volume can be expressed by the relationship: P=H A, where H is the average tidal range and A is the average surface area of the basin. It can also be thought of as the volume of the incoming tide plus the river discharge. Simple tidal prism models stated the relationship of river discharge and inflowing ocean water as Prism=Volume of ocean water coming into an estuary on the flood tide + Volume of river discharge mixing with that ocean water; however, there is some controversy as to whether traditional prism models are accurate. The size of an estuary’s tidal prism is dependent on the basin of that estuary, the tidal range and other frictional forces.