Tidal prism

The volume of water flowing into or out of an estuary between successive high and low tides. It measures the estuary’s tidal exchange.

Tidal range: The vertical difference between successive high and low water levels at a location. A larger tidal range generally moves more water across an estuary’s tidal cycle.
Inlet stability: The tendency of a tidal inlet to maintain its channel position and cross-section over time. Prism volume is compared with inlet size to judge whether tidal currents can keep a channel open.
Tidal volume: The volume of water associated with a tidal movement over a specified area or channel. It is the basic quantity represented by a tidal prism.
Tidal discharge: The rate of water flow through a channel during tidal motion, commonly expressed as volume per time. Discharge is a flow rate; prism is the volume moved over a tidal interval.
Estuary: A coastal water body where river water mixes with seawater and tides influence circulation. The prism is defined by the water exchanged within this coastal setting.
Escoffier diagram: A graph relating tidal-inlet cross-sectional area to the equilibrium tidal prism and flow velocity. It uses prism estimates to identify stable inlet dimensions and possible channel states.
High tide: The stage of the tide when water reaches its greatest height in a tidal cycle. The estuary’s water volume at high tide helps set the prism’s upper boundary.
Residual flow: The net water movement remaining after oscillating tidal currents are averaged over a period. A prism measures gross tidal exchange, not the net transport left after flood and ebb.
Tidal inlet: A channel connecting a coastal lagoon or bay to the open sea, through which tides flow. Its cross-section and flow transmit the water volume represented by the prism.
Empirical relationship: A relationship inferred from observed data rather than derived solely from theory. Empirical formulas connect measured prism volumes with inlet cross-sectional areas.

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