Tidal river

Key takeaways

Tidal river belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Tidal river to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Tidal river from memory before moving on to harder problems.

Reference excerpt

A tidal river is a river whose flow and level are caused by tides. A section of a larger river affected by the tides is a tidal reach, but it may sometimes be considered a tidal river if it has been given a separate and another title 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. High tides can be noticed as far as 100 kilometres (62 mi) 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 estuaries. A phenomenon commonly associated with tidal rivers is a tidal bore, 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, 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 is a tidal river on the border between Uruguay and Argentina. 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 kilometres (93 mi) 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 kilometres (0 mi) into the Amazon depression.

Navigation The tidal behaviour of a river is an important consideration in riverboat navigation. For major rivers, such as the Saint Lawrence River (and the associated Saint Lawrence Seaway), publications such as an atlas of surface currents (or tidal currents) may be available, based on sophisticated hydrodynamic models, subject to empirical validation.

Images

See also Estuary Ria Tidal reach Tidal bore Tidal creek

References

Illustrations

Worked examples

Example 1 — a first encounter with Tidal river

Start with the simplest possible case. Write down what Tidal river claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Tidal river before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Tidal river ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Tidal river

In research: Tidal river appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Tidal river in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Tidal river is common in secondary-school and first-year university syllabi. It links to neighbouring topics Rivers, Tides, so understanding it makes those chapters shorter.
In everyday life: Look for Tidal river outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Tidal river in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Tidal river means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Tidal river out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Tidal river in simple terms?

A tidal river is a river whose flow and level are caused by tides. A section of a larger river affected by the tides is a tidal reach, but it may sometimes be considered a tidal river if it has been given a separate and another title name.

Why does Tidal river matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Tidal river?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Tidal river.