A tidal prism is the volume of water in an

estuary An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environment ...

inlet An inlet is a (usually long and narrow) indentation of a shoreline, such as a small arm, bay, sound, fjord, lagoon or marsh, that leads to an enclosed larger body of water such as a lake, estuary, gulf or marginal sea. Overview In marine geogra ...

between mean

high tide Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables can ...

and mean

low tide Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables can ...

,Luketina, D. 1998. Simple tidal prism models revisited.

Estuarine, Coastal and Shelf Science ''Estuarine, Coastal and Shelf Science'' is a peer-reviewed academic journal on ocean sciences, with a focus on coastal regions ranging from estuaries up to the edge of the continental shelf. It's published by Elsevier on behalf of the Estuarine ...

; Vol. 46. pp. 77–84. or the volume of water leaving an estuary at

ebb tide Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables can ...

. The inter-tidal prism volume can be expressed by the relationship: ''P=H A'', where ''H'' is the average

tidal range Tidal range is the difference in height between high tide and low tide. Tides are the rise and fall of sea levels caused by gravitational forces exerted by the Moon and Sun and the rotation of Earth. Tidal range depends on time and location. ...

and ''A'' is the average

surface area The surface area of a solid object is a measure of the total area that the surface of the object occupies. The mathematical definition of surface area in the presence of curved surfaces is considerably more involved than the definition of arc ...

of the basin.Lakhan, V.C. (ed). 2003. Advances in Coastal Modelling. Amsterdam, The Netherlands; Elsevier B.V. pp. It can also be thought of as the volume of the incoming tide plus the river discharge.Hume, T.M. 2005. Tidal Prism. Encyclopedia of Coastal Science. Springer Netherlands. M.L. Schwartz, editor. pp. 981. Accessed via Springerlink database October 13, 2009. Simple tidal prism models stated the relationship of

river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...

discharge and inflowing

ocean The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wo ...

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 Controversy is a state of prolonged public dispute or debate, usually concerning a matter of conflicting opinion or point of view. The word was coined from the Latin ''controversia'', as a composite of ''controversus'' – "turned in an opposite d ...

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

friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction: *Dry friction is a force that opposes the relative lateral motion of t ...

al forces.

Applications of tidal prism

Calculations of tidal prism are useful in determining the

residence time The residence time of a fluid parcel is the total time that the parcel has spent inside a control volume (e.g.: a chemical reactor, a lake, a human body). The residence time of a set of parcels is quantified in terms of the frequency distribution ...

of water (and

pollutant A pollutant or novel entity is a substance or energy introduced into the environment that has undesired effects, or adversely affects the usefulness of a resource. These can be both naturally forming (i.e. minerals or extracted compounds like oi ...

s) in an estuary. If it is known how much

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...

is exported compared to how much of the estuarine water remains, it can be determined how long pollutants reside in that estuary. If the tidal prism forms a large proportion of the water in an estuary at high tide, then when the tide ebbs, it will take with it the majority of the water (this occurs in shallow estuaries) and any pollutants or

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...

s suspended in that water. This means that the estuary has a good

flushing time The residence time of a fluid parcel is the total time that the parcel has spent inside a control volume (e.g.: a chemical reactor, a lake, a human body). The residence time of a set of parcels is quantified in terms of the frequency distribution ...

, or that the residence time of water in that estuary is low. On the contrary, in deeper estuaries, the amount of water that is influenced by the tides forms a smaller proportion of the total water. The difference between high tide and low tide is not as great as in shallower estuaries creating a smaller tidal prism and a longer residence time. The size of an inlet or estuary is determined, according to O’BrienO’Brien, M.P. 1931. Estuary tidal prisms related to entrance areas. Civil Engineer; Vol. 1. pp. 738–739. by tidal prism. Tidal prism

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

can be calculated by multiplying the area of the estuary by the tidal range of that estuary.Davis, R., D.M. Fitzgerald. 2004. Beaches and Coasts. Blackwell Science Ltd. Malden, MA During spring or fall tides, when sea level is relatively high and floods backbarrier areas that are normally above tidal inundation, the cross sectional area at the entrance of the estuary increases as tidal prism increases. Since tidal prism is largely a function of area of open water and tidal range, it can be changed by alterations of the basin area of estuaries and inlets as in dredging; however, if the estuary or inlet is dredged, or the size changed, the channel will fill in with sediment until it has returned to tidal prism equilibrium.

Sand transport

Additionally, there are correlations between tidal prism and amount of sediment deposited and exported in an estuary or inlet. The Walton and AdamsWalton, T.L., W.D. Adams. 1976. Capacity of inlet outer bars to store sand. In Proceedings of the 15th Coastal Engineering Conference, Honolulu, HI: ASCE, pp. 1919–37. relationship shows a strong relationship between the magnitude of the tidal prism and the volume of

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class of s ...

in ebb dominated

deltas A river delta is a landform shaped like a triangle, created by deposition of sediment that is carried by a river and enters slower-moving or stagnant water. This occurs where a river enters an ocean, sea, estuary, lake, reservoir, or (more rarel ...

. The larger the tidal prism, the larger the amount of sand that is deposited in deltas in ebb-dominated estuaries. Inlets with small tidal prisms have too little power to remove sand deposited from adjacent shores. Inlets with large tidal prisms can erode sand and deposit it in ebb-tidal deltas in deeper waters (National Research Council). The size of ebb tidal deltas is proportional to tidal prism. If tidal prism increases, there is an increase in deltas and

shoal In oceanography, geomorphology, and geoscience, a shoal is a natural submerged ridge, bank, or bar that consists of, or is covered by, sand or other unconsolidated material and rises from the bed of a body of water to near the surface. It ...

s formed by sand transport during ebb tide.

Tidal prism models and assumptions

There are assumptions that go along with tidal prism models. The first is that they are applied to smaller estuaries (less than a few kilometers wide) and secondly, that the estuaries are internally well mixed. Additionally, it is assumed that the water entering the estuary is of oceanic

salinity Salinity () is the saltiness or amount of salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal ...

mixing with the fresh river discharge, and that the mixed water will be exported on the ebb tide. Officer provides a model for simple tidal prism theory where the estuary is represented by a box with the

inflow Inflow may refer to: * Inflow (hydrology), the water entering a body of water * Inflow (meteorology) Inflow is the flow of a fluid into a large collection of that fluid. Within meteorology, inflow normally refers to the influx of warmth and moi ...

as the volume of river discharge at a salinity of 0, within the estuary, the river discharge mixes with the volume of the tide flooding in (Vp) from the ocean at oceanic salinity (So) and the mixed VR + VP) water flows out at ebb tide.

References

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