Rivers flow downhill — Earth science, 4–6 years
Water on land can gather into streams and rivers, moving from higher ground towards lower ground.
Water finds the lower way
Rain and melting snow can collect on the ground. If the ground slopes, the water moves downhill, joining other water to make a stream or river. Rivers may twist and turn, but their overall journey is usually from higher land towards lower land.
Why does river water move?
People wanted to know where streams came from and where they would go, especially when finding drinking water or crossing a river. Watching water spill from a tilted cup gives the first clue: gravity pulls it towards a lower place. The river’s route is shaped by the land, rocks and bends in its channel.
Three cups of water
Place three cups in a line: one on a chair, one on a low box and one on the floor. Pour a little water into the chair cup. First it spills down to the box level, then towards the floor cup. A real river behaves similarly: water starts higher, follows the sloping ground and ends in a lower place such as a lake or sea.
A river does not always look straight
It is reasonable to think a river cannot be going downhill when it turns left, right or even seems to flow sideways. The water follows the lowest available path, and the land can bend that path around rocks, banks and hills. Look at the whole route, not just one short bend.
Water in towns and fields
Rivers carry water to farms, towns, lakes and seas. People build bridges where roads cross them and dams where they need to store or control water. When heavy rain falls, knowing which land is lower helps people understand where water may collect or flow quickly.
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