The long journey
of one drop of water.
map of the river ready.
The water cycle never ends.
There is no new water being made on Earth. The water in your glass this morning is, more or less, the same water there has ever been — roughly the same amount, moving around and around in a great closed loop the geographers call the water cycle (or the hydrological cycle). The Sun is the engine. The sea, the clouds, the rivers and the ground are the parts. Nothing leaves the system; it only changes shape — from liquid to vapour to liquid again, around and around, for billions of years.
The loop has a small number of moves, and each one has a proper name. The Sun heats the surface of the sea, and water turns to invisible vapour and rises — that is evaporation. Plants add to it: they draw water up through their roots and release it from their leaves as vapour, which is called transpiration. High up, the air is colder, and the vapour turns back into tiny droplets that gather into cloud — that is condensation. When the droplets grow heavy enough, they fall as rain, snow or hail — precipitation. Some of that water soaks into the ground; the rest runs over the surface and downhill — that is surface runoff — gathering into streams and rivers that carry it back to the sea. And then it begins again.
The water cycle
The water cycle is the continuous movement of water between the sea, the air, the land and living things. Its five named moves are evaporation, transpiration, condensation, precipitation and collection / runoff. The Sun provides the energy that drives the whole loop. It is a closed system — water is recycled, never used up.
A single drop of sea water might spend, on average, around 3,000 years in the ocean before it evaporates — but only about nine days in the air as vapour or cloud before it falls again. The cycle has slow parts and fast parts, and the same water has been round it countless times since the oceans first formed.
Every river drains a basin.
A river does not appear from nowhere. It collects the rain that falls on a whole area of land — and that area is called its drainage basin (sometimes a catchment). Picture the land tilted like a very shallow bowl: rain that falls anywhere inside the bowl runs downhill and ends up in the same river. The high ridge of land that separates one basin from the next — the rim of the bowl — is called the watershed. Rain that falls one side of the watershed flows into one river; rain falling the other side flows into a different one.
Inside the basin, the river has its own anatomy. The place where it begins, high up, is the source. The smaller streams that join it are tributaries. A point where two rivers meet is a confluence. And the place where the river finally reaches the sea or a lake is its mouth. These are the words geographers use for every river on Earth, from a moorland trickle to the Amazon.
The parts of a basin
- Source — where the river begins, usually high ground.
- Tributary — a smaller stream that flows into the main river.
- Confluence — the point where two rivers join.
- Mouth — where the river meets the sea or a lake.
- Watershed — the high edge dividing one basin from the next.
What water does in a basin
- Precipitation — rain and snow arriving from the sky.
- Infiltration — water soaking down into the soil.
- Surface runoff — water flowing over the ground.
- Throughflow — water moving sideways through the soil.
- Channel flow — water travelling in the river itself.
A drainage basin, from above
The Amazon drains a basin the size of a continent — about 7 million km², roughly the area of Australia. So much fresh water pours out of its mouth that the Atlantic Ocean is noticeably less salty for more than a hundred miles offshore. Sailors used to fill their water barrels from the sea, out of sight of land.
Source to mouth — a river in three acts.
A river changes character as it travels. Near the source, high in the hills, it is small, steep and fast, tumbling over rocks. By the time it reaches the mouth, it is wide, deep and slow, sliding across flat land to the sea. Geographers split this journey into three parts — the upper, middle and lower course — and each part has its own landforms. Drawn as a side-on slice from source to sea, the shape is called the river's long profile: steep at the start, then flattening out.
The long profile of a river
The three courses of a river
No river runs in a perfectly straight line for long. Even on flat ground a river will start to wander, because the tiniest bend speeds the water on the outside and slows it on the inside — and that difference deepens the bend. Left alone, almost every river on Earth ends up meandering. Straightness, in a river, is unnatural.
Erosion, transport, deposition.
A river is more than water moving — it is water working. Along its whole journey it does three jobs, and knowing the order of them explains almost every river landform you will ever meet. It erodes (wears the land away), it transports (carries the worn-away material along), and it deposits (drops that material when it slows down). Fast water erodes and carries; slow water drops its load.
Erosion itself happens in a few distinct ways, and a KS3 geographer is expected to name them. Hydraulic action is the sheer force of moving water prising at cracks in the bank. Abrasion is the river's load scraping and grinding against the bed, like sandpaper. Attrition is the stones knocking against each other as they travel, slowly smashing into smaller, rounder pebbles. And solution is water quietly dissolving certain rocks, such as limestone, away to nothing.
How a river erodes
- Hydraulic action — the force of the water itself.
- Abrasion — load scraping against the bed and banks.
- Attrition — stones knocking each other smaller and rounder.
- Solution — water dissolving soluble rock away.
How a river transports its load
- Traction — big rocks rolled along the bed.
- Saltation — pebbles bounced along in small hops.
- Suspension — fine mud carried within the water.
- Solution — dissolved minerals carried invisibly.
Fast water erodes and transports; slow water deposits. That single sentence explains why the upper course (fast) carves valleys and the lower course (slow) builds floodplains and estuaries. Whenever a river loses speed — meeting flat ground, the sea, or a lake — it drops whatever it was carrying.
Pick up a pebble from a beach or a river mouth and it is almost always smooth and round. That roundness is attrition at work — thousands of journeys knocking the corners off. A jagged rock high in the mountains and a round pebble at the sea can be the very same stone, hundreds of years and many miles apart.
The rivers of Middle-earth are real rivers.
Tolkien drew Middle-earth the way it is because he had walked in the places it is made of. The great rivers of his maps — the Anduin running the length of the land, the Bruinen below Rivendell — behave like real ones: they rise in mountains, gather tributaries, swing into meanders on the flats, and reach the sea at a wide mouth. He knew his physical geography, and it shows.
The most famous landform of all in his world is a piece of real physical geography too. Mount Doom — Orodruin — is a stratovolcano: a tall, cone-shaped mountain built up in layers from many eruptions, with a chamber of molten rock — magma — beneath it. When it erupts, that magma reaches the surface as lava. The fire and the smoke at the heart of the story are a real volcanic process, the same one that built Vesuvius and Mount Fuji.
The water cycle, in motion.
You've followed the loop on paper — evaporation, condensation, precipitation, runoff. Now watch it move. As the film runs, try to name each stage as it appears, and notice how the Sun is the engine behind every part of it.
Name the stages of the water cycle.
Four stages of the water cycle are numbered on the diagram. Pick a label from the pool, then drop it on the matching pin. Two of the chips are not stages of the water cycle at all — read each one before you place it.
Match each label to its pin
Show what you know.
The plant's part in the cycle.
What drives the whole loop?
Where does a river begin?
Which course makes a waterfall?
A little further.
The looping bends.
The rim of the bowl.
Fast water, slow water.
Stones knocking stones.
Explain why.
This is the kind of question that rewards full sentences and developed points — say something, then say why, then say so what. Aim for 100–150 words. No bullet points.
Explain why a river is fast and narrow in its upper course but wide and slow by the time it reaches its mouth.
Use the words source, steep, erosion and deposition somewhere in your answer.
A few thoughts on what you wrote, Florence
strong Your opening line ties the steep ground near the source straight to fast water cutting downwards — that cause-then- effect chain is the move a six-mark answer is built on. You kept erosion in the upper course and deposition at the mouth, which is exactly where each one belongs.
try this The word flat turns up three times in two sentences. When the picture is hard to hold you reach for the same word — let two of them go and reach for something that does more work (the gradient eases, the land levels out, the slope gives way). One precise word carries further than three plain ones.
to add One sentence on why slow water deposits — because it no longer has the energy to carry its load — would close the loop between the two ends of the river. That is the link to reach for next time you write this kind of answer.
Rivers, oceans and the moving water.
Sit down with Dad for one of these. They follow water from the mountain to the sea, and they're filmed the way only the best nature series manage. Pick an episode, not a whole series.
The words from today.
- Water cycle
- The continuous, closed loop water moves through — sea, air, land and back again — driven by the Sun.
- Evaporation
- Liquid water turning into invisible vapour and rising, as the Sun heats the sea and the land.
- Transpiration
- Water released as vapour from the leaves of plants, after being drawn up through their roots.
- Drainage basin
- The whole area of land that a river and its tributaries collect their water from.
- Meander
- A looping bend in a river's middle course, eroding its outer bank and depositing on its inner bank.
- Estuary
- The wide, tidal mouth of a river, where fresh river water mixes with the salt of the sea.
You've followed the water all the way round.
You know the water cycle and its five named moves, and that the Sun drives the lot. You know a river drains a whole basin, and the words for its parts — source, tributary, confluence, mouth. You can take a river from steep upper course through meandering middle to wide, slow lower course and estuary. And you know the three jobs water does to the land: erosion, transport, deposition. Next time it rains, Florence, you'll know exactly where that water is going.
Video — “Water Cycle: How the Hydrologic Cycle Works”, National Science Foundation (YouTube). Used for educational reference; rights remain with the NSF.
Film recommendations are factual reference only — see each title's own copyright owner.