River processes : Erosion, Transportation and Deposition

Summary

This lesson explores the processes that shape rivers, focusing on erosion, transportation, and deposition. The video introduces key types of erosion—hydraulic action, abrasion, attrition, and solution—demonstrating how water and materials interact with riverbanks. It explains how rivers transport sediment through traction, saltation, suspension, and solution, with particles moving from large to small. Finally, the video covers deposition, showing how materials are dropped in various areas, particularly on the inside bends of meanders. The lesson concludes by highlighting the connections between river processes and coastal features, such as estuaries and landforms like waterfalls.

Takeaways

• 😀 Rivers undergo three main processes: erosion, transportation, and deposition, which shape landforms over time.
• 😀 Erosion can be vertical (in the upper course) or lateral (in the middle and lower courses) depending on the river's flow and landscape.
• 😀 Hydraulic action is the force of water bashing into the riverbank, causing cracks and material to fall into the river.
• 😀 Abrasion occurs when materials in the river hit the riverbank, causing further erosion and widening the channel.
• 😀 Attrition happens when smaller particles collide and break down into finer pieces, becoming smaller as they travel downstream.
• 😀 Solution occurs when slightly acidic river water dissolves materials like clay, contributing to erosion and transportation.
• 😀 Transportation of sediment in rivers occurs through traction (rolling large particles), saltation (bouncing smaller particles), suspension (floating fine particles), and solution (dissolved materials).
• 😀 Deposition occurs when the river's flow slows down, particularly on the inside of meanders, forming features like river beaches and cliffs.
• 😀 Large rocks are deposited in the upper course of the river because they cannot travel far due to their size.
• 😀 Estuaries form where river water mixes with sea water, creating low-energy zones where deposition is prevalent.
• 😀 The long profile of a river shows its varying characteristics from the upper course (steep with waterfalls) to the lower course (wide with meanders and levees).

Q & A

What are the three main processes that occur in rivers?

The three main processes that occur in rivers are erosion, transportation, and deposition.

What is the difference between vertical and lateral erosion?

Vertical erosion happens in the upper course of the river and deepens the riverbed, while lateral erosion occurs in the middle and lower courses, widening the river.

What is hydraulic action, and how does it contribute to erosion?

Hydraulic action is the force of fast-moving water that crashes against the riverbank, causing cracks and eventually eroding the bank.

How does abrasion differ from hydraulic action in river erosion?

Abrasion involves small materials, like sand and pebbles, carried by the river that bash against the riverbank, widening cracks and eroding the bank, while hydraulic action is the direct force of moving water against the bank.

What happens during attrition in a river?

Attrition occurs when particles in the river collide with each other, becoming smaller and rounder as they travel downstream.

How does the acidity of river water contribute to erosion?

The slightly acidic nature of river water can dissolve soluble materials, such as clay, in a process known as solution.

What are the four types of transportation in rivers, and how do they differ?

The four types of transportation in rivers are: traction (large particles are rolled along the riverbed), saltation (smaller particles bounce along the riverbed), suspension (fine particles are carried in the water), and solution (soluble materials are dissolved and carried by the water).

What is the role of deposition in river processes?

Deposition occurs when the river loses its energy and drops the materials it has been carrying. This often happens in areas where the water flow slows down, such as on the inside of meander bends or in estuaries.

Why are large rocks usually deposited in the upper course of a river?

Large rocks are only able to travel short distances due to their weight, so they are typically deposited in the upper course, where the river's energy is higher but still insufficient to carry them further.

What happens to river material when the flow slows down at meanders?

When the river flow slows down on the inside of meander bends, deposition occurs, forming features like river beaches. The fastest flow occurs on the outer bend, where erosion takes place instead.