SS2 First Term Geography Lesson Note – Earth External Processes and Landform Development

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WEEK 1:

TOPIC:          EARTH’S EXTERNAL PROCESSES AND LANDFORM DEVELOPMENT 

CONTENT: 

(a) Action of Running Water              

(b) Processes of River Erosion

(c) Processes of River Transportation

SUB-TOPIC 1:   WATER AS AN ENERGY SYSTEM

When rain falls on the earth, it is distributed in various ways. Much of the waters from the rain flow directly off slopes to join streets and rivers, eventually reaching the streams and rivers, oceans and seas. This is a run-off. A great proportion of waters received percolates downward into the soil filling up spaces and joint and pore spaces, and forming what is known as ground water. The source of a river may be spring, lake or marsh, generally rivers flow from uplands to lowlands. The run-off carve out channels as they flow and they transport and deposit materials for very great distances along the course. It becomes great agent of denudation.

The amount of erosion, transportation and deposition a river carries depends on the flow of water through the channel and this flow is determined by several reasons.

The water action in a river flows in two ways; 1. Lamina Flow 2. Turbulent Flow

LAMINA FLOW: This form of flow is found in layers parallel to the bed of the river. This occurs as a result of the slope of river on which the river flows.

TURBULENT FLOW: This flow occurs in a circular form. This is due to interruptions along the course like stacks, rapids and cataracts. Sometimes the loads it carries. The energy of the river decreases when its flow is turbulent because energy has to be used to overcome the friction.

FACTORS AFFECTING THE VELOCITY OF A RIVER

1. SLOPE OF THE RIVER VALLEY: The slope of the river is been determined by the nature of rock bed course of the river. The steeper the slope or gradient, the higher the speed or velocity of flow of the river.
2. THE SHAPE OF THE RIVER CHANNEL OR VALLEY: There are different types of shape in the channel of a river, V-shape, U-shape, and plain shape. The shape determines the amount of energy a river has for erosion and transportation. A river uses more energy to flow through plain shape valley than V-shape and U-shape valley. This is because plain shape has a large surface area.

THE VOLUME OF RIVER AND RIVER REGIMES: The volume of waters in a river

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