V-SHAPED VALLEY
- Features of the upper course of a river include a very steep sided v-shaped valley on either side of the river. A diagram of this is shown below.
INTERLOCKING SPURS
- The streams flow around the foot of mountains causing interlocking spurs shown below:
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WATERFALLS
- Waterfalls are frequent occurrences in the steep upper course of rivers. These contain many processes, which constantly change the waterfall due to natural erosion.
- In the Upper Course, the river is not only eroding vertically (down) but towards its source (HEADWARD EROSION). This means the feature shown in the diagram below is created. The river erodes the softer rock underneath the harder rock on top faster, and this means the level of the land along the river's
course becomes lower over time and the waterfall retreats back towards the source. Successive positions of the waterfall are shown on the diagram. The movement backwards leaves a second feature called a GORGE.
COURSE OF A RIVER
As the river approaches the middle and lower courses, the channel gradually widens and flattens as it experiences lateral erosion due to the gentler gradient.
MEANDERS & OXBOW LAKES
The river becomes wider and travels from side to side, bending. These bends are called meanders. The erosion processes are demonstrated in the diagram below.
As the water flows down a river, its speed is faster on the outside of the meander causing erosion and slower on the inside of the meander resulting in deposition. When the river slows on the inside of the meander it loses energy so that it can no longer carry suspended fragments. This will, over a period of time accentuate the curve of the meander. Sometimes this can even result in an oxbow lake, when the bend of the meander is so extreme that it joins with its adjacent bend to form a new route for the water, excluding the cut off meander.
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U-SHAPED VALLEYS
- A U- shaped valley is also a prominent feature of the middle course of a river. This is a valley whose typical cross section is shaped like a 'u'.
A glacier, which is much bigger and more powerful than a river, shaped this and so glaciers deepen and widen the v-shaped valleys formed by rivers in mountain areas. These glacial formed valleys have flat bottoms and steep sides and are called u-shaped valleys.
- As ice is not so flexible at turning corners, so the former spurs are truncated (cut off) straightening the former v-shaped valleys.
If a u-shaped valley is at the coast and the sea floods it, then it is known as a fjord.
FORMS OF EROSION
Abrasion-the way rocks in rivers or glaciers scrape and erode the rocks they are moving over.
Attrition - the way that rocks in rivers are worn down by rubbing against each other.
Corrosion - the way which rivers use the rocks that they carry to batter the land.
Corrasion/ abrasion: process where rocks on the bed erodes the banks of the river in a ‘sand papering’ action. This swears away the bottom of the riverbank, forming a small river cliff.
FORMS OF TRANSPORTATION
Traction: where large rocks are moved along the riverbed in a rolling action.
Saltation: where smaller stones move along the riverbed in a ‘leap- frog’ movement.
Suspension: where the river carries small material. This process discolours the water in the river.
Solution: where material is dissolved by acids and other chemicals in the river, and carried along as water is discharged. This process also discolours the water.
LOWER COURSE
In the Lower Course (Old Age or Plain Stage), the river slows down, as the gradient is almost flat. The river is no longer able to erode and therefore deposits its load and landforms in this course are features of deposition. The volume is the largest on the river's course. This part of a river is liable to .
Flood plains and levees (a.k.a. bluffs): River overflows banks during a flood and spills onto the land. This sudden increase of friction lowers the velocity. When the river retreats it leaves a deposit of material. The coarsest material is deposited first as it is heavier, forming levees (natural extension of River bank to prevent floods - a.k.a bluffs). Alluvium is then deposited. Each time the river floods a new layer is added, eventually forming a floodplain.
Braiding – this is where the river channel is broken up into a number of distributaries. The river slows as it reaches where it joins the sea – this results in further deposition. As a river slowly meanders across its flood plain, it often deposits material in the 'middle' of its channel. Sand and shingle banks often form small islands in this way.
Deltas - Formed at the mouth of a river. It is a result of the reduction of river velocity as it enters the sea. A delta is formed when deposits of sediment cause a river to divide at the mouth.
