Flooding in South Africa

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Assignment

GEO 234

D Sonnekus

2011042526

Flooding In South-Africa

A Deeper Insight to What Happens Around Us

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Photo: Ivan Sonnekus 2012

Index

Page Number

1. Introduction3

2. The Nature Of Flooding3

3. The Main Causes Of Flooding In South-Africa4

4. The Effect Of Development On Flood Hazards in SA5

5. The Effect Of The Economic Status Of People -
Regarding Flood Hazards6

6. Conclusion7

7. Bibliography8

1. Introduction

Floods play a major role in our everyday lives, and how we react to the daily changing climate is of course our way of surviving our planetary conditions. Floods determine our building styles and play a very large role in the economy by means of devastating destruction and environmental engineer specialists in terms of flood prevention. The hydrological definition for a flood states that a flood is a rise in water level in a stream to a peak point where after the water level will recede at a slower rate (UNESCO-WMO 1974). A flood event can be described as a flow of water in a stream constituting a distinct progressive rise, culminating into a crest, together with the recession that follows the crest (Linsley, 1942).

In this Assignment I will be explaining some key features about flooding regarding a South-African point of view.

2. The Nature of Flooding.

Floods can be broken down into different classes or divisions between different types of floods in this section I will explain the main flood types and their nature. Floods can be divided between major floods, minor floods and flash floods.

Major Floods:

In the event of a major flood the flooding is caused by the overflowing of rivers and dams by means of breaks in dikes, levees, dam walls and other protective structures; by uncontrollable releases of impounded water in reservoirs and by the accumulation of excessive runoff. In the case of a major flood the floodwaters will cover a wide spread contiguous area and will spread rapidly to adjoining areas of relatively lower elevations. The flooding will be deep in most parts of the total flooded area and there is a highly perceptible current as the flood spreads to a greater extent.

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Minor Floods:

In the cause of a minor flood the inundation may or may not be due to overbanking. If there is no bank overflow, flooding happens due to the accumulation of excessive surface run-off in lower lying flat areas. In these cases flooding will mostly be restricted to flood plains along a river channel or low-lying areas or terrain depressions around the direct source of the flood. The flood water will be shallow and there may not be a perceptible flow apparent or present.

Flash Floods:

Flash floods is as the name states a flood that happens relatively quick, normally no more than 6 hours to a normal flooding time of 12 to 24 hours or longer. Flash floods is the result of a short concentration time of the drainage catchment or a steep river slope, this means that the precipitation falling on a point in the catchment farthest from the river takes a very short time to reach the river itself and become a part of the stream flow. Thus the amount of flow will rapidly increase and the water level will rise, when the capasity of the river/stream is exceeded the channel overflows and the result is a flash flood.

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3. The Main Causes of Flooding in SA.

South Africa was subject to some intense floods over the last couple of years mainly as the result of cloud breaks and very heavy precipitation in very short time periods which leads to flooding of most small streams and rivers, what then leads to the larger rivers to flood.

South Africa is also a victim of the Southern Oscillation which leads to El-Nino: dry conditions with high surface pressure and; La-Nina: low air surface pressure...
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