Lesson 4: River Processes

What you should know by the end of this lesson:

Key processes involved in river erosion
Key processes involved in river sediment transportation

Background

Rivers are one of the main ways that material is eroded, transported and deposited. This is essential in the formation of sedimentary rocks. Rivers have energy which they use to move water downstream. They use this energy to overcome friction with the bed (bottom) and banks (sides) of the river.

If there is an excess of energy (e.g. during times of flood, or when two rivers join at a confluence), that energy can be used to erode the bed and banks. The eroded material is transported by the river as its load.

Hydrosphere Workbook

Digital Workbook and Paper Jotter

Work Booklet Task 7-8 (Page 13)

Read through the processes below
Complete your workbook tasks 7, 7B and 8

River Erosional Processes

There are 4 main ways which a river erodes and wears away at the river banks and valley around it. As they involved water they are the same erosional processes that are found in the Coastal Features topic with the same explanations:

Hydraulic Action
Abrasion
Attrition
Solution

Reminder

Fully explained processes will gain you double marks. 1 mark for naming the process and 1 for explaining the term but you NEED to do both to get both marks.

Directions of Erosion

The 4 erosional processes do have a slightly different effect on rivers than it does on the coast. Erosional processes in rivers occur in 3 different directions. This is important to know as river features only form due to this variation in direction of erosion.

Task 7b: copy the definitions for each direction to your table on page 12

Transportation Processes

A river transports sediment and material downriver in 4 main ways: traction, saltation, suspension, and solution. This varies depending on the energy within the river and the size of the material being transported. The more energy contained within the river the large the material can be transported.

Task 8 Page 13:

Complete the diagram below by adding the correction transportation method to the diagram.

Rivers Energy

A river’s energy is affected by how much water is in the river and how fast it is flowing. These together are measured as the river’s discharge (usually measured in m3/second). The river’s velocity (speed) usually increases downstream, as there is less friction with the river’s banks, bed and load.