LI: To understand river processes
- Discuss the flow of a river
- Discuss each of the three processes in turn to determine what each does
- Draw three simple diagrams showing the processes
- Write what each one does under the diagrams
Last week, we looked at the three courses of the river. Can you remember what they are and what characterises them?
upper course – this is the beginning of a river (which starts at the source), when it flows quickly with lots of energy. The river here is smaller and usually has a rapid, tumbling flow that cuts a narrow channel through rocky hills or mountains.
middle course – when a river gets wider and slows down. Rivers often meander (follow a winding path) along their middle course. The current of the river no longer has the force to carry stones or gravel. This material drops to the riverbed, where it forms bars of sand or gravel or builds islands.
lower course – this is when the river reaches the end of its journey. Here, the river is deep and wide and the flow is much slower. The end of the river is called the mouth. At the mouth, there is often a river delta, a large, silty area where the river splits into many different slow-flowing channels that have muddy banks.
This week, we will look at what happens in the river as it flows from its source to the mouth.
Rivers don’t run in straight lines because there may be obstacles to avoid as they flow downhill. Another reason is due to the following processes.
There are three processes that happen as a river flows: erosion, transportation and deposition.
These three processes can change the shape of a river.
What do you think erosion means? Discuss with a partner.
- When a river is fast-flowing, its energy causes erosion to take place. Erosion involves the wearing away of rock. Rivers break rock down into small, rounder and smoother pieces. The bed and banks can be eroded making it wider, deeper and longer. Vertical erosion can cause waterfalls to be formed.
Once material has been eroded, there is then the process of transportation. What do you think this involves?
- Transportation is when material that has been loosened by erosion (e.g rocks, stones and soil) is picked up by the river and moved or transported downstream.
Finally, deposition happens. What do you think this might be? Discuss the root of the word if this helps.
- Deposition is when the river drops its load. This is usually when the river loses energy towards the end of its course. (draw the cross-section diagram below to show the materials deposited).
Research more on these processes at home and then draw your own three simple, labelled diagrams showing erosion, transportation and deposition. Write a few lines explaining each process.
How do you think these processes can also create meanders (bends in the river)?