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Transcript of Rivers
The water in rivers comes from rainfall, from snow and ice melting, and from water inside the Earth,called groundwater. Rivers carry the water downhill, along with vast amounts of rock, sand, soil and mud, to lakes and oceans. Rivers can carve through solid rock, eroding deep gorges and huge waterfalls.
A river changes as it flows downhill along it's path, or course. The beginning of a river is called a source. Many rivers begin in mountain areas, where rain and melting ice run into steep, clear streams. These streams cut narrow, deep valleys and join together as they follow downhill. Smaller streams and rivers that flow into a bigger are called tributaries
Away from mountains, the water flows in broader channels and larger valleys. As the land levels out, the river starts to form large bends, or meanders. Finally, the river widens out into a broad estuary, or splits to form a network of channels called a delta, before flowing into the sea or lake. The art of a river where it meets the sea is called a river mouth.
rivers at work
As a river flows, the water sweeps along any rocks on its way. The rocks slide and bounce along, chipping away at the riverbed and making it deeper and wider. They also grind against each other, which wears them down and breaks them into smaller pieces.
A river's course
As a river flows downstream, the riverbed becomes smoother, so the water flows slightly faster. It starts to drop or deposit, sand, silt and then mud. This is why the slower sections of a river have muddy riverbeds. Near the sea, the sediament may build up to form whole islands. This is when the river splits up to forms a delta.