A tidal river is a

river A river is a natural flowing watercourse, usually freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the ...

whose flow and level are influenced by

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 ...

s. A section of a larger river affected by the tides is a

tidal reach A reach is a segment of a stream, river, or arm of the sea, usually suggesting a straight, level, uninterrupted stretch. They are traditionally defined by the capabilities of sailing boats, as a stretch of a watercourse which, because it is stra ...

, but it may sometimes be considered a tidal river if it has been given a separate name. Generally, tidal rivers are short rivers with relatively low discharge rates but high overall discharge, which generally implies a shallow river with a large coastal mouth. In some cases, high tides impound downstream flowing freshwater, reversing the flow and increasing the water level of the lower section of river, forming large

estuaries 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 environme ...

. High tides can be noticed as far as upstream. Oregon's Coquille River is one such stream for which that effect can be noticed.

Overview

The area of a tidal river can be difficult to define. The term "tidal river" generally encompasses the area upriver of the maximum limit of salinity intrusion and downriver of tidal water level fluctuations. This classification is based on both tidal trends and salinity. By this definition, a tidal river will be affected by tides, surges, and sea level variation, though its water may not have a high salinity content. If that is the case, this section of river can be known as a "tidal freshwater river" or a "river reach." In terms of tides, tidal rivers are classified as microtidal (<2 m), mesotidal (2-4 m), and macrotidal (>4 m). Areas of brackish water seaward of the tidal river section are often called

. A phenomenon commonly associated with tidal rivers is a

tidal bore Tidal is the adjectival form of tide. Tidal may also refer to: * ''Tidal'' (album), a 1996 album by Fiona Apple * Tidal (king), a king involved in the Battle of the Vale of Siddim * TidalCycles, a live coding environment for music * Tidal (servic ...

, where a wall of water travels upriver during a flood tide. Freshwater tidal rivers discharge large amounts of sediment and nutrients into the ocean. This is a necessary influx for the global water balance. Rivers contribute about 95% of sediment entering the ocean. Discharge estimates from freshwater tidal rivers are important for informing water resource management and climate analyses. These discharge amounts can be estimated using tidal statistics. Some challenges to estimating discharge amounts include reversing tidal flow, compensation flow for Stokes drift, spring-neap water storage effects, lateral circulation, and multiple distributaries or ebb and flood channels.

Threats

Tidal rivers face threats due to climate change and other human-caused impacts. In tidal rivers' deltas, mineral and water extraction, reduced sediment input, and floodplain engineering are causing the sinking of deltas. This, combined with

rising sea levels Rising may refer to: * Rising, a stage in baking - see Proofing (baking technique) *Elevation * Short for Uprising, a rebellion Film and TV * "Rising" (''Stargate Atlantis''), the series premiere of the science fiction television program ''Starga ...

, is causing tidal rivers to become deeper, which amplifies the tidal motion and increases the extent of salt intrusion. Increasing salinity in tidal rivers could have a detrimental impact on freshwater organisms and alter tidal river ecosystems significantly. The increasing effect of deltaic subsidence, which is due to the removal of gas, oil, and water from deltas, will also increase the risk of flooding.

Tidal river examples

Rio de la Plata

The

Rio de la Plata Rio or Río is the Portuguese, Spanish, Italian, and Maltese word for "river". When spoken on its own, the word often means Rio de Janeiro, a major city in Brazil. Rio or Río may also refer to: Geography Brazil * Rio de Janeiro * Rio do Sul, a ...

is a tidal river on the border between

Uruguay Uruguay (; ), officially the Oriental Republic of Uruguay ( es, República Oriental del Uruguay), is a country in South America. It shares borders with Argentina to its west and southwest and Brazil to its north and northeast; while bordering ...

and

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, t ...

. It is classified as microtidal, as its tidal range is less than 1 meter. This river is significant mostly due to its size, as more than one tidal wavelength can be accommodated in this river's estuary. Similarly to most tidal rivers, saltwater does not extend far up the river, due to its large volume of freshwater discharge.

Amazon River

The Amazon River has the highest flow, largest volume of sediment discharge, and largest drainage basin of any river in the world. Because of its large flow volume, saltwater never enters the mouth of the Amazon River, and the limit of salinity is 150 km seaward of the river mouth. The Amazon River is classified as macrotidal, as its tidal range is 4 to 8 meters at the mouth of the river. During low-flow periods, this river's tidal area may extend over 1,000 km into the Amazon depression.

Navigation

The tidal behaviour of a river is an important consideration in

riverboat A riverboat is a watercraft designed for inland navigation on lakes, rivers, and artificial waterways. They are generally equipped and outfitted as work boats in one of the carrying trades, for freight or people transport, including luxury u ...

navigation. For major rivers, such as the

Saint Lawrence River The St. Lawrence River (french: Fleuve Saint-Laurent, ) is a large river in the middle latitudes of North America. Its headwaters begin flowing from Lake Ontario in a (roughly) northeasterly direction, into the Gulf of St. Lawrence, connecting ...

(and the associated

Saint Lawrence Seaway The St. Lawrence Seaway (french: la Voie Maritime du Saint-Laurent) is a system of locks, canals, and channels in Canada and the United States that permits oceangoing vessels to travel from the Atlantic Ocean to the Great Lakes of North Ameri ...

), publications such as an atlas of surface currents (or tidal currents) may be available, based on sophisticated

hydrodynamic In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids—liquids and gases. It has several subdisciplines, including ''aerodynamics'' (the study of air and other gases in motion) and ...

models, subject to empirical validation.

Images

File:Tidal Suites at the Norseman Resort - view of the Ogunquit River at high tide IMG 2299 right FRD.jpg,

Ogunquit River The Ogunquit River is a U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map, accessed June 30, 2011 tidal river in southern Maine. It flows to the Atlantic Ocean at the town of Ogunquit. Images Fi ...

at high tide File:Tidal Suites at the Norseman Resort - view of the Ogunquit River at mid tide IMG 8804 right FRD.jpg, Ogunquit River at mid tide File:Tidal Suites at the Norseman Resort - people walk on river bed at low tide IMG 2490 FRD.jpg, Ogunquit River at low tide

References

{{DEFAULTSORT:Tidal River Rivers Tides