Summary

Drainage basins are open systems, with inputs, stores and outputs. The main input is precipitation which is regulated by various means of storage. Outputs include channel runoff, evapotranspiration and groundwater flow.

The Drainage basin system

TASK

1. Complete the system diagram using information from the flow chart

2. Identify and annotate a feedback loop on your system diagram

3. Explain how human activity can modify 3 named processes on the diagram

PLENARY

Match the words with the definitions to create a circle

Add post-it notes to the board to identify the different inputs, processes, stores and outputs involved in the drainage basin system. How might human activity affect these?

RIVER DISCHARGE

River discharge is the volume of water flowing through a river channel. This is the total volume of water flowing through a channel at any given point and is measured in cubic metres per second (cumecs). Discharge is calculated as follows:

River discharge = mean velocity of water x cross sectional area of a river

1. Describe three relationships shown on the diagram above e.g. as discharge increases, velocity increases

HYDRAULIC RADIUS & RIVER EFFICIENCY

The wetted perimeter of a river refers to that part of the channel that is in contact with water. It represents the friction that slows down the river velocity. The longer the wetted perimeter, the more friction between channel and water.

The hydraulic radius is a measure of efficiency in a river channel. It is calculated by comparing the wetted perimeter with the cross-sectional area of the channel. The higher the hydraulic radius, the more efficient the river.

Hydraulic radius = cross-sectional area / wetted perimeter

Calculate the hydraulic radius for the two rivers below. Which river is more efficient?

ACTIVITIES

1. Make simple sketches of the diagram above

2. Read pp 7-10 (River Discharge) and make detailed notes under the different headings.

PLENARY

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

Award [1 mark] for defining/calculating discharge.

Award [1 mark] for establishing a link between discharge and channel size (e.g. higher discharge in a larger/lower course channel).

Award [1 mark] for establishing a link between discharge and channel shape (lower discharge in wide, shallow or deep, narrow channels, or equivalent point made).

The remaining [3 marks] should be awarded for explanatory points, such as:

• role of hydraulic radius

• importance of wetted perimeter

• idea of friction in relation to stream efficiency

• further development of width/depth or shape explanation.

TASK 1

1. Watch the video and read the overview above

2. Describe two ways that rivers erode (2 + 2 marks)

3. Describe two ways that rivers transport matieral (2+2 marks)

river landforms

TASK 2

1. Watch video above

2. Read pp 120-122 Core book

3. Complete the grid