The source of a river is often, but not always, in an upland area. Near the source, a river flows over steep slopes with uneven surfaces. It often flows over a series of waterfalls and rapids. As a river flows down steep slopes, the water performs vertical erosion. This form of erosion cuts down towards the river bed and carves out steep-sided V-shaped valleys. How rivers change from source to mouth.
Rivers change immensely on their journey from Source areas where they start to their finishing point at their mouths. There are 4 major concepts here;. The drainage basin The water cycle The changing characteristics of rivers from the mountains The changing valley shape Tasks.
The drainage basin This is the area of land drained by a river system a river and its tributaries. It includes the surface run-off in the water cycle , as well as the water table. Drainage basins are separated by watersheds.
A drainage basin is an example of an open system because it is open to inputs from outside, such as precipitation, and is responsible for outputs out of the system, such as output of water into the sea and evaporation of water into the atmosphere.
You can see a diagram of the drainage basin below. The water cycle This is a series of processes by which water is evaporated from the sea and eventually condenses and precipitates over the land.
It is the main input to the drainage basin and you can read detailed notes on this process at the Met Office's website. There are many changes that occur in rivers as a result of changes within the water cycle and drainage basin.
Width and depth increases as more water is added from tributaries. Gradient the slope of the land decreases as rivers flow because the river meanders across the land rather than erode into it and follow a straight path as it does in the source. As a river flows down steep slopes, the water performs vertical erosion. Eventually the river will flow over flat land as it approaches the sea.
As the river moves from the source to the mouth — both the depth of the river and the width of the river will both increase. This means it covers a decrease in height over a longer distance the further downstream you get. As a river flows downstream, its velocity increases. Additionally, less water is in contact with the river bed, which results in less energy needed overcome friction.
The larger mass of water causes wider and deeper water channels in order to allow water in the river to flow more freely. This is because the further downstream material is carried then the greater the time available for it to be eroded by attrition and abrasion which makes rocks and stones smaller and rounder.
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