002 - Discharge

Syllabus Point

Define (AO1) stream discharge.

Examine (AO3) its relationship to stream flow and channel shape.

Key Terminology

Define the terms below using your 'IB Geography. Course Book' by Cooke and Nagle, the command term posters in the classroom and the links below.

• Define
• Examine
• Bed
• Bank
• Channel
• Cross-sectional area
• Discharge
• Velocity
• Wetted Perimeter

Useful Links

1. USGS - water glossary
2. Also have a look at the classic Geography text books; 'Geography. An Integrated Approach' by Waugh and 'Planet Geography' by Codrington.

Activity One - Watch

Watch the following clip and answer the following questions:

1. Define stream gradient.
2. How is stream gradient measured?
3. Define stream discharge.
4. How is discharge measured?
5. Draw the sediment transport diagram.
6. What is bedload?
7. Define the three ways that the river can move the sediment in the river.
8. There are actually four ways that a river can move sediment, Traction is missing from this clip. Traction is when the force of the water can only push or roll sediment on the bed of the river as it is too heavy for the water to pick up. Write your own definition of traction.
9. What impacts the amount of sediment that can be carried within the channel of the river?
10. Define competence and capacity.

Activity Two - 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.

Activity Three - Turbulent and Laminar Flow

Look at the two diagrams below.

1. Describe how the water is moving?
2. What impact do you think these different environments have on the velocity of the river?
3. Write a definition of turbulent and laminar flow.

Diagram 1

Diagram 2

Activity Four - Channel Shape

The shape of the river will effect its efficiency. The efficiency of the river is measured by calculating its hydraulic radius.

Hydraulic radius - This is the ratio between the length of the wetted perimeter and the cross section of the river.

1. Using the diagram below, describe how channel shape impacts the velocity of the river channel.

Activity Five - The Bradshaw Model

The Bradshaw Model illustrates the changing characteristics of a river through its three courses; upper, middle and lower. You will be using this model to help justify your hypotheses for the Internal Assessment.

1. Describe what you think is happening to the river's characteristics as it moves away from its source towards the mouth. If you need a bit of help there is a slide share clip kindly made by Mr. Allaway below to help you.

IB Geography: Drainage Basins: Bradshaw Model from geographyalltheway.com

Exam Style Question

Explain the relationship between stream flow and channel shape. (6 marks)