Platinum Geography Grade 12 Learner's Book

Platinum Geography Grade 12 Learner's Book




Chapter 1:

Chapter 2:

Chapter 3:

Drainage systems in South Africa

Fluvial processes

Catchment and river management




drainage systems in south Africa

Key wOrds

surface run-off – water

flowing downslope over the


groundwater– water found


saturated zone – part of the

crust where all air spaces are

filled with groundwater

water table – upper limit of

the saturated zone

aerated zone – part of the

crust above the water table

where there are open air


Unit 1: Important concepts

Geomorphology studies how Earth’s surface is changed, either as a result of

internal forces, such as volcanoes, or due to external forces, such as erosion.

The Grade 12 section of geomorphology covers the role of rivers in shaping the

landscape. Refer back to the opening photograph of this chapter on the previous

page to see how the work of rivers has affected the landscape.

In order to understand the role of rivers, we will investigate how a river works,

where the water comes from, what controls the energy of a river, and what

we need to do to manage our precious water resources. To start, we need to

understand some basic terminology and concepts.

Water in the river may come directly from rainfall or snowmelt, or indirectly

from surface run-off (water flowing downhill over the land surface, towards the

river). It may also come from groundwater bubbling to the surface at a spring,

or from groundwater feeding into a river valley as base flow. This concept will be

discussed shortly.

indirect runnoff (over surface)

aerated zone

(unsaturated zone)

direct runnoff (stream channel)



water table

ground water

(saturated zone)

Figure 3.1 Terms relating to ground water

When it rains, some water will seep into the soil,

moving through the air spaces in the soil. When all

the air spaces are filled with water, the crust is said

to be saturated. This is illustrated in Figure 3.1 as the

saturated zone. The water table is the upper limit of

the saturated zone. Above the water table, there are

some open air spaces, and this is called the aerated

zone. When there is heavy rain, excess water will

flow over the surface as surface runoff, indirectly

contributing to the water in the river. Find all these

terms labelled on Figure 3.1.

Figure 3.2 Basic concepts

114 Topic 3 Geomorphology

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