003 - River Processes

Geographic Knowledge and Understanding

River processes of erosion, transportation and deposition and spatial and temporal factors influencing their operation, including channel characteristics and seasonality.

Concept

Physical processes of fluvial erosion, transportation and deposition interact within a drainage basin system.

Aims

To be have knowledge and understanding of the river processes of erosion, transportation and deposition, specifically:

Erosion - attrition, hydraulic action, solution, abrasion and vertical erosion

To have knowledge and understanding of the spatial and temporal factors associated with river processes:

Channel characteristics - The inside of a meander vs. the outside

Seasonality - summer meltwater from glacial environments / seasonal differences in deltas

Key Terminology

    • Meander
    • Flood Plain
    • Dredging
    • Silt
    • Natural Flood Defence
    • Bog

Define the words above using your Freshwater text book by Codrington.

Activity One - Explain

Image One - River Processes

Time For Geography - River Processes

Rivers help create a range of landforms due to its very specific processes. We can not begin to look at the landforms found in the different areas of the river without knowing what the processes are and how they move the sediment and bedload. Using the slide show below explain how the following processes work:

                      1. Hydraulic Action
                      2. Attrition
                      3. Corrasion/Abrasion
                      4. Corrosion
                      5. Vertical Erosion
                      6. Horizontal Erosion

Useful Resource

Activity Two - Transportation

You have already learnt how a river transports its material so this should just be a review (hence the distinct lack of resources). On a A4 white board draw a diagram to show the four ways in which a river transports is material (bedload and sediment). Remember that using the correct terminology is crucial!

Activity Three - Draw

Below is a digram which represents Hjulstrom's theory. Hjulstrom's theory illustrates how fast the water needs to be to carry a certain size of sediment. If the velocity of the river falls then heavier material will be deposited. If the velocity increases then more sediment can be transported and the greater chance that erosion will take place. For us in Switzerland we have seen the impact that snow melt has on the velocity of our rivers and the large boulders the rivers can then carry.

            1. Copy out the diagram below.
            2. Describe what the image represents.

Image Two - Hjulstrom's Theory

Taken from Greenfield Geography

Taken From:

http://greenfieldgeography.wikispaces.com/floodplain+management

Activity Four - Channel Characteristics

When we discuss a channel's characteristics we think about its shape and size. The discharge and velocity of a river can impact those characteristics. A bend in a river is called a meander and this helps to show how a channels shape can change due to erosion and deposition.

        1. Looking at image three describe how the meander has changed its location in the valley.
        2. Draw out image four and explain how a meander impacts a channels shape.

Image Three - Changing Channel Flow

Taken From: https://earthobservatory.nasa.gov/IOTD/view.php?id=6887

Taken From -

https://earthobservatory.nasa.gov/IOTD/view.php?id=6887

Image Four - Meander

Taken From: http://web.gccaz.edu/~lnewman/gph111/topic_units/fluvial/16_23.jpg

Taken From -

http://web.gccaz.edu/~lnewman/gph111/topic_units/fluvial/16_23.jpg

Activity Five - Seasons

Seasons can have a huge impact on the discharge of river depending on the precipitation rates and temperature. By reading the article below and using your Freshwater text book by Codrington write down how the different seasons can impact discharge.

Exam Style Questions

State two river transport processes and outline how each process operates. [2 +2]

Explain how stream discharge is related to channel size and shape. [6]

Describe two processes involved in the transport of a river’s load. [2 + 2]