Why do rivers enthrall us?
Maybe it's because they're teeming with life—everything from nibbling midges to
flashing kingfishers and trout and salmon wiggling beneath the
ripples. Perhaps it's because water is so central to our existence
and so vital to life. Possibly it's to do with the tranquility of a
river; in countryside or in cities, the sight of water has an
instantly calming effect. All these things come to mind,
instinctively or very consciously, whenever we think of rivers or
spend time near them swimming, fishing, boating, or canoeing. Let's
take a look at what makes rivers so amazing!
Photo: The River Itchen, England. Photo courtesy of UK Rivers Network published under a Creative Commons Licence.
Water is constantly circulating between
Earth's surface (the land
and oceans that make up our planet) and the atmosphere up above in a
never-ending conveyor belt called the water
cycle.
Rivers are the main parts of the conveyor that carry water from the higher parts of
Earth (the mountains and hills that we call uplands) to the lower
parts (lakes and seas).
You can think of rivers as drains, if you like:
channels with fairly well defined banks,
carved through millennia,
that can be thin and shallow or very deep and wide. Powered by
gravity, rivers are always flowing downhill (even when they look
absolutely flat, they're really flowing down a gentle incline). Unlike
seas, which are salty, rivers are filled with freshwater to which the lives
of many different creatures (insects, animals, and humans too) have
become perfectly adapted. Far from the oceans, rivers bring the land
to life.
Photo: Aerial view of the Black River Yukon Flats National Wildlife Refuge. Photo by M. LeFever courtesy of US Fish and Wildlife Service and Wikimedia Commons.
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The path of a river
You might think a river is a dead thing, because it's not a living
organism. But you can think of a river as a living thing in at least
three important ways. First, it's full of living creatures like
otters and fish: it may not be alive, but it's certainly full of life.
Second, it's living in the sense that it's
constantly adapting to Earth's changing climate, geology,
ecology—and even the changes that humans bring. Third, it's living
because it changes its character from the place in the uplands where
it begins its life (known as its source)
to the place where it ends
its life (known as its outlet
or mouth, where it flows into
the sea).
The path that a river takes in its journey over Earth's surface is a
bit like the
life a human leads between birth and death but, where a human's life
is spread out in time, a river's spreads out in geographical space.
Upper river courses (youthful stage)
Photo: Tower Falls. A waterfall is a typical feature of the upper reaches of a river. Photo by Bruce Halstead courtesy of US Fish and Wildlife Service.
A river begins life high in the hills or mountains. In a cold
region, a river may be created by melting snow or a
glacier. In warmer places, rivers typically form when water drains from
a whole series of upland slopes known as a basin. Water drains from
each slope to form a small trickle called a rill. Rills from many
slopes combine to form brooks,
which join together to make creeks
(small streams) and larger streams,
before all these things eventually merge into a river.
The brooks, streams, and creeks that form a river are called its
tributaries. Flowing down from
high hills and mountains, the upper
part (or course) of a river is usually narrow, steep, and marked by
sharp valleys and abrupt, zig-zag changes of direction. The steepness
means the water flows quickly, often forming dramatic features such
as white-water rapids and waterfalls (great for canoeists).
Rapid flow means the
water has high energy to cut through rocks, wearing away deposits in
a process called erosion.
Middle river courses (mature stage)
As rivers leave the hills and mountains where they're created,
they take on the classic pattern of the mature rivers we see in the
landscapes around us. They're wider, slower, less steep, and change
course more gradually. The features they form are bigger and more
substantial: wider lakes,
wandering S-shaped bends called meanders,
and deeper, broader cuts in the landscape called valleys. Sometimes two rivers will join together
at a point called a confluence.
Photo: Meanders occur in the middle and lower reaches of a river.
These meanders are at the confluence (joining point) of the rivers Alatna and Koyukuk near Allakaket. Photo by Steve Hillebrand courtesy of US Fish and Wildlife Service.
Sediment carved from the upper reaches of the river and carried downstream can build banks called levees that keep the water level higher than the landscape around it. When
flows are high, water spills over the banks carrying mud and sediment
with it and creating marshy floodplains.
As rivers cross floodplains, they snake from side to side eroding the
landscape in some places and building it up other places through a
process called deposition. Rivers are often surrounded by lush
grassland areas called meadows.
Lower river courses (old-age stage)
Photo: Deltas occur at the lowest part of a river's course. Or, to put it another way a delta is the last stage in a river's life before it meets the sea. Aerial view of the Noatak River Delta in Alaska. Photo courtesy of US Fish and Wildlife Service.
There are no strict boundaries between the upper, middle, and lower
courses of a river, and many middle-course features (like meanders) are also
found in the lowest reaches of a river. But the lower course of a
river is less steep again than the middle course and the water runs
even more slowly. Rivers finally reach the sea at estuaries (wide,
deep, open river mouths) and triangular-shaped deltas (where a river
deposits sediment at its mouth creating many narrower channels called
distributaries instead of a
single, wide mouth).
Artwork: The upper, middle, and lower courses of a river and some of the features they contain. The upper course is the steepest. That's where you'll find things like rapids and waterfalls.
The middle and lower courses are more shallow than the upper course and rivers form things like meanders, oxbow lakes, and floodplains there. In the lower courses, rivers meet the sea in estuaries and deltas.
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How rivers flow
Think of a huge torrent of water flowing under the power of
gravity, for thousands of years. Like the water from a pressure washer, it has enough energy to cut sediment
from the hills of its upper reaches and carry it down to the middle
and lower reaches. Rivers gradually slow down because the water has to
overcome
friction as it flows—friction as the moving water rubs against the
banks and bottom of the
river channel itself and friction as layers of water flow past one
another. The rate at which a river flows is also affected by the
climate and the seasons. Some smaller streams (known as winterbornes)
dry up entirely in summer. Humans also have a huge effect on river
flows through
abstraction (removing water for
many different uses),
from irrigation (watering crops in the countryside) to supplying
factories and homes with the water they need.
Why do rivers matter to people?
Photo: Villagers gather on the banks of a river
in Bangladesh waiting for humanitarian aid.
Photo by Anthony J. DeCapite courtesy of US Marine Corps and
Wikimedia Commons.
Thousands of years ago, human settlements grew up around great
rivers such as the Tigris and Euphrates in the Middle East—and this
was how modern civilization began. Rivers remain, in a sense, the "open
pipes" that supply many towns and cities with the
water people need. Rivers have also been hugely important in helping
people travel across Earth, especially before modern roads were
constructed, both for exploration and trade.
People have been harnessing the energy in rivers since ancient times
and
modern-day environmental problems such as global warming have led to
renewed interest in such things as hydroelectric power (made by
damming rivers and forcing them to flow at high-speed past turbines
to generate electricity).
Rivers are incredibly important to people,
but we've not always looked after them properly. Removing sand and
gravel from river beds for building materials can damage them, for
example, while pouring untreated sewage and other wastewater into
rivers causes pollution, lowers
water quality, and reduces how much
life they can support. Thankfully, many people recognize just how
important rivers are.
Lots of people use them for recreation, from fishing and canoeing to
walking their dogs along riverbanks. Many people have formed
themselves into community groups to help keep their rivers clean and
protect them from damaging industrial developments. Rivers give us
life and help to look after us—and it's vitally important that we
return the favor!
Chart: The world's ten longest river systems (some are made up of two or three rivers "joined" together). At over 6650km (4100 miles), the Nile is long enough to stretch the width of the United States from New York City to Los Angeles (roughly 4500km or 2800 miles)... and halfway back again! Data from the Wikipedia article List of rivers by length.
Rivers: A Natural and Not-so-Natural History by Nigel Holmes and Paul Raven. Bloomsbury, 2019. A detailed, well-illustrated overview of British rivers aimed at general readers. Though focused on the UK, it will also be of interest to readers in other countries.
Rivers: A Very Short Introduction by Nick Middleton. Oxford, 2012. A basic introduction to the science of rivers and how we use and abuse them.
Thames: Secret River by Peter Ackroyd. Knopf, 2009. How the River Thames has dominated London life from ancient times to the present day.
Rivers of America by Tim Palmer. Abrams, 2006. A glossy guide to America's greatest rivers, including 200 photos.
Data and statistics
Rivers of Europe by Christiane Zarfl, Christopher T. Robinson, Klement Tockner (eds). Elsevier, 2021. A companion volume to Rivers of North America, presenting similar data for 180 of Europe's most important rivers.
Rivers of North America by Arthur C. Benke and Colbert E. Cushing (eds). Elsevier, 2005. Biological, hydrological and other data for over 200 North American rivers.
Rivers for Life: Managing Water for People and Nature by Sandra Postel and Brian D. Richter. Island Press, 2003. Two leading water experts consider whether human demands for water are placing the world's rivers in peril.
Silenced Rivers by Patrick McCully. Zed Books, 2001. A classic examination of how large hydroelectric dams have damaged some of the world's greatest rivers and the communities who depend on them.
For older students
The Biology of Streams and Rivers by Paul S. Giller, Björn Malmqvist. Oxford, 1998/2004. A good general introduction to river ecosystems for undergraduates (or interested older readers—it's quite readable and accessible).
A River by Marc Martin. Chronicle Books, 2015. A beautifully illustrated story of a river journey that will inspire readers aged 5–7.
Eyewitness: Pond and River by Steve Parker. DK, 2011. This colorful introduction explores the idea that freshwaters are seasonally changing ecosystems, going into more details about plants and animals than most other children's "river" books (ages 8–10). Later editions include a companion CD-ROM containing clip-art from the book.
Rivers (Natural Wonders) by Alyse Sweeney. Capstone, 2010. An introduction for very young readers (ages 4–8).
Rivers by Laurie Burnham. Chelsea House, 2007. A reasonably detailed introduction for teenaged readers. Begins with a basic introduction to the geography of rivers before considering 10 of the world's greatest rivers in more detail (including the Nile, the Amazon, the Yangtze, and the Mississippi).
In a Warming West, the Rio Grande Is Drying Up by Henry Fountain. The New York Times, May 24, 2018. Why is the famed river on the US-Mexico border turning to sand? An interactive feature.
The Ganges Water Crisis by Anthony Acciavatti. The New York Times, June 17, 2015. Is there any solution for the water scarcity afflicting India's Ganges river?
Taps Start to Run Dry in Brazil's Largest City by Simon Romero. The New York Times, February 16, 2015. How São Paulo, the world's largest city, has been plunged into water crisis, despite (theoretically) ample water resources.
'Millions at risk' as deltas sink by Richard Black. BBC News, 21 September 2009. Sinking rivers and rising water levels place up to half a billion people at risk.
World's major rivers 'drying up' by Matt McGrath. BBC News, 21 April 2009. How the growing problem of water scarcity is becoming more obvious through dwindling river flows.
Half of world's rivers at risk by Alex Kirby. BBC News, 29 November 1999. Pollution and water extraction are driving rivers to the brink.
The Guardian: Rivers: An archive of recent river articles (mostly about the UK, but with some worldwide coverage too).
Videos
For older students
NOAA Fisheries: You'll find lots of inspiring river restoration projects on the NOAA YouTube channel.
River Management and River dynamics: Narrated by Mike Kline and produced by James Valastro. Two short introductions (one lasting 13 minutes, one 10 minutes) to how rivers work, by themselves and for us, and how people use and abuse them. Uses the rivers of Vermont as an example.
River restoration on the Hampshire Avon: An uplifting 6-minute video from bioengineer Simon Cain, illustrating how a poorly managed river can be revived and restored to its original glory.
The Yamuna, India's most polluted river: The Guardian, July 7, 2017. Correspondent Michael Safi journeys down the Yamuna river from the Himalayas, investigating how it becomes polluted as it flows through urban centers like Delhi.
The World's Dirtiest River: Unreported World/Channel 4, November 15, 2017. A look at pollution problems affecting the Citarum river on the island of Java, Indonesia.
For younger students
Streams and Rivers: Hazen Audel and Rob Nelson explain rivers the best way—from the water! A short introduction to how a river's ecosystem works.
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