General characteristics
- Mid-latitude cyclones are also called frontal depressions or extra-tropical cyclones.
- They move from west to east. This is because they occur in the westerly wind belt.
- Air moves in a clockwise direction around the centre of a low pressure in the Southern Hemisphere; but moves in an anticlockwise direction in the Northern Hemisphere.
- They often occur in 'families' of 3 - 4
Areal of formation
- Mid-latitude cyclones develop at the Polar front between 40o and 600 N and S.
- Here the warmer westerly winds meet the cold polar easterly winds.
Conditions necessary for formation
- At about 50o N and S, a transition zone warm tropical air from the cold polar air
- This colder air pushes in underneath the warmer air while the warmer air gets pushed up over the colder air.
- A change in the conditions at the Polar front can be caused by the jet stream, a mountain range or the shape of a coastline. called the Polar front separates the
- The isobars form in a circular pattern and a cell of low pressure begins to form
Convergence: the horizontal movement of air in towards a particular region
Divergence: the horizontal movement of air out from a particular region
Jet stream: a narrow band of very strong, predominantly westerly air currents encircling the globe at altitudes of 10 - 15 km above the earth
Front: the leading edge of an air mass; it can be warm, cold or occluded.
Cold front: where a cold air mass moves against and pushes in under a warmer air mass.
Warm front: where a warm air mass rises gradually up over a cold air mass.
Occluded front: formed when a cold front overtakes a warm front
Stages of development
- The life cycle of a mid-latitude cyclone lasts from two to five days.
Initial stage
- The Polar front separates the cold polar air from the south (polar ea$terlies) and the warmer tropical air from the middle latitudes (westerlies).
- There is no movement across the line of separation between the two air masses.
- The two air masses do not mix easily because of their different characteristics: cold air is heavy and dense; warm air is light and less dense.
Development stage
- A frictional drag occurs between the cold and the warm air masses, disturbing the front.
- The warm, less dense air is pushed up by the cold, dense air. This results in a low pressure forming.
Mature stage
- The air begins to rotate in a clockwise direction around the low pressure (Southern Hemisphere).
- The cold air pushes in under the warm air ahead of it and uplift occurs. A cold front leads the cold air.
- The warm air rises up over the cooler air ahead of it and uplift occurs. A warm front leads the warm air of the warm sector.
- Both fronts are associated with uplift, cooling and possible rain.
Occluded stage
- This stage is reached when all the warm air has been lifted off the surface by the colder air.
- The warm sector becomes narrower as the cold front catches up with the warm sector.
- In time, the warm sector will be displaced above the cold air.
- The front is known as an occluded front.
Dissipating stage
- This is the last stage of a mid-latitude cyclone - the system weakens.
Weather patterns associated with cold, warm and occluded fronts
As a mid-latitude cyclone passes over a weather station on the earth's surface, the following weather conditions can be expected:
Cold front weather conditions
- wind direction changes from west through to southwest (wind backs)
- strong winds
- decrease in temperature
- relative humidity is high during precipitation
- cumulonimbus clouds
- heavy rainfall
- poor visibility
- pressure decreases as the cold front approaches and then increases as the cold sector arrives
- cold front is followed by a rapid rise in air pressure, with scattered showers
Warm sector weather conditions
- pressure continues to decrease
- warm, less dense air
- stratocumulus, altostratus clouds
- northwesterly wind
Warm front weather conditions
- wind direction changes from northwest to west
- temperature increases
- relative humidity is high during precipitation
- nimbostratus clouds
- light rain (drizzle)
- visibility increases
- decrease in air pressure
Occluded weather conditions
An occlusion takes place when the cold front catches up with the warm front. It closes the warm sector and isolates it from the earth's surface. There are cold front occlusions and warm front occlusions.
Cold front occlusion
- Occurs when the coldest air in the mid-latitude cyclone is found behind the cold front. This causes the warm front to be uplifted along the cold front.
- As the air is forced to rise, it cools down, condensation takes place and clouds are formed.
- Rainfall occurs with conditions very similar to a cold front.
Warm front occlusion
- Occurs when the coldest aif in the mid-latitude cyclone is found ahead of the warm front. This causes the cold front to be uplifted along the warm front.
- As the air is forced to rise, it cools down, condensation takes place and clouds are formed.
- Rainfall occurs with weather associated wlth a warm front.
Reading and interpreting satellite images and synoptic weather maps
Weather stations all over South Africa take weather measurements throughout the day. There are also weather stations on ships at sea and on Marion and Gough lslands. This information is then sent to the South African Weather Service.
Satellite images
- Weather satellite images are also used for interpreting and predicting the weather. Photographs taken from satellites are sent to weather stations around the world, including the South African Weather Service.
- These satellite images show detail of cloud cover and frontal syslems. A cold front is identified by a band of cloud and the centre of the low pressure by a swirl of cloud. Land that is free of clouds will typically be dark in colour while clouds appear bright. Thicker clouds have a higher reflectivity and appear brighter than thinner clouds.
Synoptic weather maps
A synoptic weather map shows a range of weather conditions (atmospheric pressure, temperature, precipitation, wind speed, direction, and cloud coverage) for a particular area on a particular day.
On a synoptic weather map there are lines called isobars.
- lsobars join points at equal pressure (all along one isobar the pressure is the same).
- The pressure is measured in hectopascals (hPa).
- The isobars form patterns, indicating low or high pressure.
A cold front shows the leading edge of a cold air mass and a warm front shows the leading edge of a warm air mass.
The weather of a particular place on the synoptic map is seen by referring to the weather station.
- A weather station is indicated by a circle.
- Temperature and dew point temperature are in degrees Celsius.
- Temperature is shown as the top number; the dew point temperature is the bottom number (both in oC).
- Precipitation (if present) is shown by a symbol between the temperatures.
- Wind direction is shown by the 'stick' pointing in the direction from which the wind is blowing.
- Each long line on the stick represents a wind speed of 10 knots. Half lines represent a wind speed of 5 knots.
- Cloud cover is shown in eighths inside the weather station circle
The features of a summer synoptic chart are:
- The date
- Generally high temperatures over the land
- Low pressure over the land
- South Indian High Pressure found south east of South Africa
- Tropical Cyclone
The features of a winter synoptic chart are:
- The date
- Generally low temperatures over the land
- Kalahari High Pressure present over the land
- South Indian High Pressure and South Atlantic High Pressure further north and closer to the land
- Cold fronts present
General characteristics
- Tropical cyclones occur from late summer to early autumn.
- They move from east to west as they form in the tropical easterly wind belt.
- They affect the east coasts of continents.
- They dissipate when they reach cooler latitudes or as they reach land (friction slows the wind and there is less moisture to provide energy).
- They are named alphabetically.
- The first tropical cyclone of the season starts with the letter A, followed by B, C etc., e.g. Cyclone Eline - Sth cyclone of the season.
- The centre of the tropical cyclone is called the 'eye' and has:
- a calm central point
- light or no winds
- no rain , very low pressure (960 hPa)
- a 30 - 50 km area of subsiding air
- high temperatures (32"C)
- towering cumulonimbus clouds surrounding it
Areas where tropical cyclones form
- Tropical cyclones occur between 5o and 30o N and S. They do not develop within 5o of the equator as Coriolis force is zero there.
- They develop over warm tropical oceans where temperatures in the region of27o occur.
- Tropical cyclones are formed in the following areas:
- Atlantic Ocean: West Indies, Gulf of Mexico, south and east coasts of USA - known as hurricanes.
- Indian Ocean: India, Madagascar, Mauritius and southern Africa (Mozambique) - known as cyclones.
- Pacific Ocean: China Sea and Japan - known as typhoons.
- Australia - known as cyclones.
Factors necessary for formation
- Warm oceans: occur in late summer when sea temperatures are warm.
- Hot air temperatures: air rises, a low pressure develops and the rising air cools and condenses. Late summer and early autumn.
- Water vapour: to condense and release latent heat to provide energy.
- Steep pressure gradient: so winds converge on the low pressure and begin to rotate because of Coriolis force.
- Pressure in the centre of the low pressure must be below 1000 hPa
Stages of development
Formative stage
- A low pressure cell develops.
- The atmospheric pressure is still above 1000 hPa.
lmmature stage
- Pressure decreases to below 1000 hPa.
- Gale force winds develop.
- Air circulation is clockwise (Southern Hemisphere).
Mature stage
- Pressure is very low (e.9. 960 hPa) and pressure gradient is very strong.
- Hurricane force winds develop and heavy rain occurs.
- The worst weather is in the forward left-hand quadrant.
Dissipating or degenerating stage
- Pressure starts to rise.
- Winds decrease in speed but heavy rain continues to fall.
- Dissipates over land or if it moves into a higher pressure area.
Associated weather patterns
- Very strong pressure gradient causes hurricane-force winds.
- Torrential rain causes intense flooding.
- Hot, humid and calm weather in the eye caused by descending warm air.
- A storm surge (bulge of sea water) may lead to flooding of the coastal areas. Caused by high winds pushing on the ocean's surface. The wind causes the water to pile'up higher than ordinary sea level
Satellite images and synoptic weather maps
Satellite image of a tropical cyclone
- Typhoon Haiyan was a powerful tropical cyclone that devastated poffons of Southeast Asia, particularly the Philippines, on I November 2013.
- The satellite image shows the tropical cyclone's extensive cloud cover.
- Note that the clouds spiral in an anticlockwise direction (air movement is anticlockwise around a low pressure in the Northern Hemisphere).
- The eye can be clearly seen as an opening in the middle of the cloud mass.
Identification on synoptic weather maps
- a low pressure cellfound between 5o and 30o N and S.
- the date will be late summer or early autumn.
- the name of the tropical cyclone will be present.
Impact of tropical cyclones on human activities and the environment
- Tropical cyclones can cause substantial loss of life and damage to property as a result of:
- the high sea-level and the high waves flooding into low-lying, often densely-populated coastal areas
- strong winds along coastalareas I excessive flooding caused by torrential rain > landslides destroying crops, settlements and infrastructure
- damage to crops, livestock, homes, infrastructure (bridges, telephone lines, electricity)
- lack of clean water, food shortages
Strategies to prepare for and manage the effects of tropical cyclones
- Weather stations can identify and predict the path of tropical cyclones and so issue warnings.
- Disaster management centres have been established to manage crisis situations, such as: food, water and medical supplies and support, temporary housing, rescue operations etc.
- Prepare the community so that people know evacuation procedures and how to prepare themselves and their property.
- Land use planning: limit development in coastalareas.
Location of high-pressure cells that affect South Africa
- Atmospheric circulation over southern Africa is greatly influenced by the Subtropical high pressure belt (30" S).
- This pressure belt is made up of three anticyclones:
- South Atlantic High Pressure
Situated in the Atlantic Ocean, causes southwesterly winds to blow towards the land.
- South Indian High Pressure
Situated east of Durban in the Indian Ocean, causes northeasterly winds to blow towards the land.
- Kalahari High Pressure
Situated over the interior of South Africa.
- South Atlantic High Pressure
General characteristlcs of high pressure cells
- High pressures, also called anticyclones, are associated with descending air. They result in clear skies and no rain.
- Air circulation is anticlockwise around anticyclones in the Southern Hemisphere.
- The anticyclones move north in the Southern Hemisphere summer and south in winter.
- During summer, these cells are weaker due to the warm surface air rising whereas in winter, the cells are stronger due to the cooler air sinking.
Anticyclonic air circulation around SA and its influence on weather and climate
South Atlantic High Pressure
- Causes southwesterly winds to blow towards the land off the cold Atlantic Ocean.
- Originates from subsiding air and the air circulates in an anticlockwise direction.
- lt brings cool, dry, stable air to the west coast.
South Indian High Pressure
- Moves away from the coast in summer but is nearer to the coast in winter.
- The anticlockwise circulation results in northeasterly winds that bring rain to eastern South Africa.
- This is because moisture is picked up as the air moves over the warm Mozambique current.
Kalahari High Pressure
- During winter, the Kalahari High is the dominant pressure cell over the interior. This causes the inversion layer to sink lower than the escarpment and thus no moisture can reach the interior from the east coast.
- The result is that the interior has dry winters and mild days as the descending air is warmed adiabatically.
- During summer, the interior warms up and air rises forming a surface low pressure cell.
- This rising air meets the descending air from the Kalahari cell at a point higher than the top of the escarpment.
- The point where the two cells meet, is called the inversion layer.
- Because the inversion layer is higher than the escarpment, moist air from the east coast (South Indian High Pressure) can be fed into the interior where it brings rain.
Travelling disturbances associated with anticyclonic circulation
Moisture front and Line thunderstorms
- A moisture front is formed at the convergence zone of air masses from the Atlantic and the Indian Ocean.
- The South Atlantic High Pressure brings in SW winds from the Atlantic Ocean. This air is cold and does not hold much moisture. The Atlantic Ocean (Benguela current) is cold, so cold, dry air is fed onto the land from the west.
- The South Indian High Pressure brings in NE winds from the Indian Ocean. This air is warm and moist. The Indian Ocean (Mozambique current) is warm, so warm, moisl air is fed onto the land from the east.
- The cold, dense Atlantic air (SW) moves in underneath the warm, moist Indian air (NE), forcing it upwards. This results in a moisture front and causes condensation and convection clouds to develop.
- The moisture front brings a Iine of thunderstorms and heavy rainfall over the central parts of South Africa. Also called a 'storm line'.
Coastal Low Pressure systems
- Coastal low pressures develop over the coast of Namibia and move around the coast.
- The circulation is clockwise and this causes onshore winds on the one side and off-shore winds on the other side.
South African berg winds
- A berg (mountain) wind usually occurs during winter.
- lt is a hot, dry wind and is followed by a cold front and cold, wet weather.
- Formation of a berg wind:
- High pressure over the interior, low pressure on the coast.
- Cold front approaches the land and sets up a pressure gradient between the interior high and coastal low pressure.
- This causes warm air to move from the interior towards the coastal area.
- As these winds blow from the plateau/mountains to the coast, they heat up adiabatically and bring warm, dry conditions.
- Berg winds usually occur along the east coast and move along the coast towards KwaZulu-Natal.
- Berg winds bring warm, dry conditions and consequently a threat of veld fires.
Microclirnate: The weather conditions within a small local area such as a valley or urban settlement.
VALLEY CLIMATES
Aspect of slope
- In the Southern Hemisphere, the slopes that face north are warmer as the sun's rays are more direct.
- South-facing slopes are cooler, as the sun's rays strike them at an oblique angle.
Katabatic and Anabatic winds
Katabatic winds
- Occur at night.
- Valley slopes cool down as a result of terrestrial radiation.
- The air in contact with the slope cools down and the dense, cool air sinks down the valley slopes.
- These winds are also called mountain breezes, e.g. the Mistral In the Alps, Swi2erland and the Bora along the Adriatic Coast (east coast of llaly).
Anabatic winds
- Occur during the day.
- Mountain slopes are heated and the warm air rises up the valley slopes.
- These winds are also called valtey breezes.
Temperature inversions
- A temperature inversion is an atmospheric condition where temperature increases with height. The warmer air lies above the cooler air.
- There is an increase in temperature with height.
- Occurs on clear, stillwinter nights.
- Air resting on the surface of upper slopes cools down and becomes more dense and sinks.
- Cool air moves down the slope and collects on the valley floor.
- Results in a warmer air layer above a cold air layer: a temperature inversion.
Thermal belts
- A thermal belt is a zone on the side of a valley where night-time temperatures remain relatively mild. Temperatures above and below the thermal belt are much colder. There is little frost damage in this zone.
Frost pockets
- Frost pockets are found where cold air collects on the valley floor.
- In the early morning, if the dew point temperature is below OoC; water vapour condenses directly into ice crystals, and frost occurs.
- This lower part of the valley then becomes known as a frost pocket.
Radiation fog
- Radiation fog generally forms when the air near the surface cools due to terrestrial radiation.
- It occurs on cold, cloudless nights.
- In the morning, the earth's surface heats up and the fog evaporates, clearing the valley of fog.
Influence of local climates on human activities
Settlements
- In rural areas in the Southern Hemisphere, people will settle on the more temperate, middle, north-facing slopes to avoid the cold valley floor and frost pockets in winter, or the low temperatures on the higher slopes.
- In urban areas in the Southern Hemisphere, people prefer to settle on the north-facing slopes to get maximum insolation from the sun, especially in the cold winter months.
Farming activities
- Crops that are affected by frost are cultivated on valley slopes to avoid the frost pocket that occurs at the bottom of the valley.
- An example is in the Western Cape where the frost-resistant crops are grown on the lower valley slopes, while vineyards and other frost-sensitive deciduous fruit is grown on the warmer middle and upper slopes.
URBAN CLIMATES
Differences between rural and urban climates
Temperature differences
- Cities have higher average temperatures and a smaller difference between day and night temperatures than rural areas.
- The reasons are:
- Artificial surfaces such as tar roads and concrete buildings absorb and retain heat longer than the natural surfaces of rural areas.
- Glass and steel in cities reflect the heat.
- More air pollution in cities which prevents maximum terrestrial radiation, especially at night.
- Heat islands over cities trap heat so less radiation takes place. > Steep thermal gradient between cities and surrounding areas reduces air flow, so less heat is lost, enhancing a greenhouse effect.
- Human activities in cities, e.g. people, machines, vehicles, air conditioners, etc., generate heat.
- Ultraviolet radiation is 30% lower in cities than in surrounding areas in winter.
Rainfall/precipitation differences
- Cities have more fog and rainfallthan the surrounding rural areas.
- The reasons are:
- A higher concentration of hygroscopic particles brought about by pollution results in more fog developing.
- Less moisture in the air due to less surface water to evaporate, while runoff is higher due to artificial surfaces and drains.
- Higher rainfall (particularly convectional rainfall) with cloud cover 5 -'10% higher over cities.
Greenhouse effect: the rise in temperature that the earth experiences because gases in the atmosphere (carbon dioxide, nitrous oxide and methane) trap energy from the sun.
Ultraviolet radiation: shortwave rays that are part of the energy that comes from the sun.
Hygroscopic particles: small particles such as dust or sea salt on which water vapour can condense.
Wind differences
- A city has lower wind speeds because of the friction of buildings, etc., however the winds are more turbulent than in the surrounding areas.
- The reasons are:
- High-rise buildings cause more turbulence.
- Buildings channel high-speed winds and gusts occur at corners of buildings.
Pollution differences
- Cities have higher pollution levels than surrounding areas.
- The reasons are:
- Trapped smoke/fog is more concentrated.
- Gaseous pollution from cars, engines and industry cannot escape
- Development of heat islands.
- Acid rain more frequent.
- Poor visibility due to fog.
- Greenhouse effect caused by pollution.
URBAN HEAT ISLANDS
- Hot air rises above a city and cool air moves in from the surrounding suburbs and rural areas.
- Warmer air over the city rises so a heat island mushrooms over the city.
- The heat island encloses the built-up area.
- The heat island is less concentrated during the day.
- City surfaces lose heat more rapidly at night than the surrounding rural natural surfaces.
- The city cools at night, therefore upward-moving air currents are not so strong.
- The heat island becomes shallower and the air forms a denser layer.
- Temperature differences are not so great, making air movement in the city less strong.
- Pollution is more concentrated at night resulting in a pollution dome developing.
Strategies to reduce heat island effect
- A number of steps can be taken to reduce the heat island effect:
- Increase tree and vegetative cover.
- Create green roofs - rooflop gardens or eco-roofs.
- Install cool, reflective roofs. Urban planners may also paint structures white or other light colours or use reflective materials to build houses, pavements and roads thus increasing the overall albedo of the city.
Drainage basin: area that is drained by a river system - the river and all its tributaries,
Catchment area: total area that provides water to the drainage basin.
River system: the main river and its tributaries and channels.
Watershed: area of high-lying land separating two river valleys - high ridges, hills or mountains. A watershed will influence the direction of water flow and determine into which drainage basin the water will flow.
Tributary: a stream that flows into the main river. River mouth: point where the river ends - the sea or a lake.
Source: place where a river starts. Confluence: point where two rivers meet.
Water table: the upper level of the underground water. Below the water table the rock is saturated.
Surface runoff (overland flow): water that flows over the ground. This sometimes happens during heavy rain or when the soil is already saturated.
Groundwater: water that is found underground in the pores and cracks of a rock.
Interfluve: ridge of high ground between individual channels (also called a spur).
Surface runoff and groundwate
- Rainfall is the main source of water in a drainage basin.
- Water that flows over the ground is called surface runoff.
- Water infiltrates into the earth's surface through the pores in the rocks.
- It moves downwards under the influence of gravity.
- The upper level of the satur;ated zone is called the water table.
- Afler heavy rain, the water table will rise and if it reaches the surface it results in surface water or a lake.
- Where the water table intersects the earth's surface at the bottom of a river channel, it is called base flow.
- The water table is usually situated a few metres below the surface.
- The line of a water table generally follows the shape of the land surface.
- Water located below the water table is called groundwater.
- Rock layers that allow water to infiltrate are called aquifers whereas those that cannot be infiltrated by groundwater are called aquicludes.
- Where the water table intersects the earth's surface on the side of a hill, it forms a spring.
Factors influencing infiltration
- Amount and nature of precipitation - soft, soaking rain will result in more infiltration than with heavy rain.
- Rate of evaporation/ - dry, hot and windy conditions will reduce the amount of water available for infiltration.
- Gradient - gentle slopes will result in dow runoff and greater infiltration.
- Vegetation - vegetation traps the rain water and so infiltration is greater.
- Amount of moisture already in the soil - soils that are already saturated are unable to absorb any more moisture.
Types of rivers
- Periodic river A river that flows only during the rainy season.
- Episodic river A river that flows only after heavy rain. lt may remain dry for several years.
- Exotic river A river that flows through a desert. lt is fed by rainfall from a high rainfall area and flows through an arid region.
Drainage patterns
The rock structures underlying the relief of an area will determine the drainage pattern. The streams flowing over an area will create a variety of patterns on the surface.
Dendritic pattern
- Most common pattern with a tree-like appearance.
- Rivers flow over uniform rock layers that have uniform resistance to erosion.
- Develops where the underlying rocks are massive igneous rocks or there are horizontal layers of sedimentary rock.
Trellis pattern
- Has parallel streams with short tributaries.
- Tributaries meet the main stream at right angles.
- Found where there are folded sedimentary rocks or where there are alternating layers of hard and soft rocks.
- Parallel valleys are formed in the softer layers of rock.
- The shorter streams ofien erode poorts or gaps through the mountains.
Rectangular pattern
- Similar to trellis paftern, but different because rectangular pattern streams have a 90o bend in their own courses.
- This is due to the presence of intersecting fault lines and joints.
- Found in joints and faults of igneous rocks and horizontal layers of sedimentary rock.
Radial pattern
- Streams radiate outward from a central high point.
- Found mostly around buttes, domes and volcanoes.
Centripetal pattern
- Opposite to radial pattern, because streams flow in towards a central basin or low-lying area such as a lake.
- This system is not connected to the sea and is often found in add regions.
Deranged pattern
- Found mostly in areas of glacial erosion where surfaces have been scoured flat by glaciers leaving glacial debris.
- Characterised by small streams following irregular routes, swampy depressions and many small lakes.
Parallel pattern
- River and its tribularies flow down slope nearly parallel to one another.
- Develops on a surface that slopes uniformly but is fairly steep on strata with uniform resistance to erosion.
Drainage density
- This is the ratio between the total length of all the streams in a river system and the area of the drainage basin that it drains,
- Drainage density is used to measure and compare drainage basins.
- Drainage density is classified as low, medium, high or very high.
Factors that influence drainage density
- Drainage density depends on the amount of runoff along the surface. High evaporation rates will reduce the amount of runoff. This causes lower drainage density. > Areas with high rainfall usually have a high drainage density.
- The rate of infiltration is also an important factor as a high infiltration rate will reduce the runoff.
- The hardness of the underlying rock can also affect the drainage density. Hard rock will prevent infiltration and increase runoff.
- Climate: high rainfall can contribute to a high drainage density because of a higher runoff, e.g. dry areas cannot support a large number of permanent rivers. The type of vegetation (dense or sparse), determined by climate, will also influence the type of ruhoff.
- The gradient of a slope wlttlalso influence the drainage density. A steep slope will promote rapid runoff and therefore a higher drainage density.
Stream order
- Topographical maps can be used to identifiT stream order and drainage density.
- Stream order is a simple ranking system used to describe river systems.
- A 1st order stream has no tributaries and has the lowest rank order.
- When two 1st order streams join, they become a 2nd order stream. When two 2nd order streams join, they become a 3rd order stream and so on.
- Only when two streams of equal order join, is a new, higher stream order created.
Discharge of a river
Laminar and turbuleni flow
- Laminar flow: occurs when the river bed is level and smooth. The friction is low so it results in a fast-flowing river. The water flows in thin layers.
- Turbulent flow: occurs when the river bed is uneven. The speed of the water is fast and this results in an irregular and whirling flow. Turbulent flow causes erosion and is also effective in the transportation of sediment.
River profiles
- The profile of a river is determined by:
- the amount of energy available for erosion (back-cutting and down-cutting);
- the transportation and deposition of sediment;
- the landforms that are shaped in this process. > The steeper the gradient, the more rapid the stream flow, and therefore the greater the erosion process. > Deposition lakes place when the flow of the river decreases.
Transverse profile (cross-profile)
- A transverse profile is a cross section of a river from one banklside to the other banldside. It is also known as the cross-profile of the river.
- In the young stage (upper course), the gradient is steep and there is more downward erosion. A deep and narrow valley is formed.
- In the mature stage (middle course), the gradient is less steep and lateralerosion takes place. The valley widens with less steep river banks.
- In the old stage (lower course), the gradient is very gentle and deposition takes place.
Longitudinal profile
- A profile along the length of a river from its source to its mouth.
- A longitudinal profile indicates the gradient of a river.
- The ideal longitudinal profile is concave in shape - steep in the upper course and more gradual in the lower course.
Permanent or ultimate base level: the lowest level to which a river will erode (sea level).
Temporary base level: the vertical erosion of the river is slowed down temporarily e.g. rapids, waterfalls, lakes and dams.
Identification and description of fluvial landforms
Meander
- A bend or curve in the course of a river.
- When a river flows around a bend, the flow is faster on the outer bend, so erosion occurs there forming an undercut slope. On the inner bend, the speed is slower so material is deposited there forming a slip-off slope.
Ox-bow lake
- A small lake which was originally part of a meander of a river
- Formed when a river beaks through a meander neck.
- Sediment is deposited and the meander becomes cut off from the river to create a lake.
- When an ox-bow lake dries up, it becomes a meander scar.
Braided stream
- A stream or river which splits into two or more smaller channels due to the deposition of silt and then rejoins further downstream.
- In some rivers there is so much deposition that the river blocks its own course. Small rivulets develop and weave their way around sand banks.
Flood plain
- A lowland area next to a river that has been built up by the deposition of alluvium (silt) in times of flood.
Natural levee
- A natural embankment formed alongside a river by the deposition of silt when the river is in flood.
- When repeated flooding takes place, the flood plain gradually fills with silt deposits many metres deep.
Waterfall
- A steep or vertical descent of the water in a river.
- Formed when a hard rock layer covers underlying soft rock layers.
- The river erodes upstream (headward erosion) undercutting the softer layers faster than the harder layers.
- When the undercut softer rock can no longer support the harder rock above, the top rock collapses.
- As the waterfall moves upstream, a gorge may form.
Rapid
- A small waterfall with turbulent water along a stretch of the river.
- Develops when a hard rock layer dips downstream.
- There is an increase in the water velocity and turbulence of the river.
Delta
- An accumulation of silt deposited at the mouth of a river.
- A river's speed is reduced when it flows into the still waters of a sea or lake.
- Large scale deposition occurs and a delta may form under certain conditions:
- there must be sufficient and constant supply of silt.
- the sea or lake must be shallow.
- there must be no strong ocean currents at the mouth.
- there must be a minimal tidal effect.
River grading
- Graded river: a balance has been achieved between erosion and deposition. The gradient, volume and channel shape are in equilibrium so that the river has just sufficient energy to flow.
- Overgraded river: the river erodes the channel. lt has a lot of energy.
- Undergraded river: the river deposits some of its load. lt does not have enough energy to flow and transport its load.
Rejuvenation of rivers
Rejuvenation: renewal of the erosive power of a river because of a change of gradient in the river's long profile or due to an increased volume of water.
- The energy levels of a river can change because of an added volume of water or because there is a change in gradient. A change in gradient may be caused by:
- a drop in sea level
- isostatic uplift (rising of the land)
- The river has renewed energy and begins eroding downwards again.
- The river is said to be rejuvenated.
Reasons for rejuvenation
- The sea level is lowered or the land is raised by isostatic uplift. This changes the base level of erosion.
- The volume of the river increases as a result of increased rainfall, river capture or increased runoff.
Features of rejuvenation
- Knickpoint waterfall The point at which increased erosion begins. lt creates a break in the long profile of the river. A waterfall is usually found here.
- Terraces The river may cut down to a new and lower level, leaving the old flood plain abandoned at a higher level. This creates a river terrace.
- Valleys within valleys When rejuvenation takes place very rapidly and the base level of erosion is lowered, a valley within a valley is formed. The new valley usually has steep slopes.
- Incised/entrenched meanders Increased verticalerosion takes place and the old meander is deepened and is cut down into the landscape.
River capture (stream piracy)
Abstraction
- Abstraction occurs when a watershed is altered. This happens when a watershed is cut back and lowered by very erosive rivers (headward erosion). It alters the position of the watershed.
- Abstraction occurs in South Africa where the escarpment forms the main watershed. The short, fast-flowing rivers that flow down the eastern escarpment towards the Indian Ocean are very erosive and cut back towards the Orange River basin.
River capture
- River capture or stream piracy is the capture of a river's water supply by another river.
- River capture can occur when a river on one side of a watershed is more energetic than on the other side because of a:
- steeper gradient
- larger stream volume
- As a result it erodes by backcutting towards the watershed (headward erosion). In this way, a river cuts through the watershed and intercepts the flow of the other river.
- River capture may also occur if a river flows at a lower level and erodes through the watershed and intercepts the course of a river on a higher flow level.
Features associated with river capture
Captor stream (pirate stream)
This is the capturing stream that cuts back through the watershed towards the other river. It is the more energetic river.
Captured stream (captive stream)
The stream that has lost its water and has been captured. lt now flows in a valley that is too big for the stream. lt is the river that is diverted by the captor and is the less energetic river.
Misfit
The stream that has lost its source waters. Also called the beheaded river.
Elbow of capture
The bend in the river where river capture has taken place.
Wind gap
A dry river valley with river gravel. The area between the elbow of capture and the misfit river.
Superimposed and antecedent drainage patterns
- In some areas, stream networks display a pattern that has nothing to do with the underlying structures or relief.
- In these cases, the drainage pattern is either superimposed or antecedent.
Superimposed stream
- In this drainage paftern, it looks like the river has been placed on top of the landscape.
- In such a landscape, the river eroded the original surface to reach the underlying rocks.
- Instead of altering its course due to older rock structures, the river kept its course.
- Therefore, through erosion the river has superimposed its current flow pattern on to the newly-exposed rock layer. e.g. Vaal River near Parys.
Antecedent stream
- In this drainage pattem, the river developed its course over an earlier landscape that was later uplifted due to some form of tectonic activity.
- The river maintains its original course through the uplifted obstruction.
- This happened because the rate of down-cutting by the river was greater than the rate of uplift.
- e.g. Orange River on western escarpment before reaching the sea.
Superimposed stream: younger than the structure it flows over.
Antecedent stream: older than the structure it flows over.
There is a direct relationship and interaction between humans and the natural environment. All human socio-economic activities depend on drainage basins for the constant provision of water. However, if there is poor management of drainage basins, it puts enormous pressure on the ability to supply sufficient water for both the physical and the human environments.
Importance of managing catchment areas
- Primary water source: Rivers in a drainage basin are a primary source of water for domestic, agricultural and industrial use.
- Communication and infrastructure: Many large rivers provide communication (shipping) and infrastructure on adjacent land. Railways and roads are more easily built in river valleys and on flood plains. Trade and transport Navigable rivers form main routes for trade and transport, e.g. Mississippi (USA) and Rhine (Germany).
- Dams: Dams constructed in drainage basins store water for human consumption; generate hydro-electricity; supply water for irrigation; help with flood control; and are also used for recreational purposes.
- Boundaries: Rivers serve as boundaries between countries.
- Fertile soil for agriculture: Flood plains of large rivers contain enormous quantities of fertile soil and are therefore very important agricultural areas. ln some countries the flood plains accommodate large populations and many large cities in Europe and Asia are situated on the banks of such rivers.
- Fishing: Fishing is an important activity in many rivers and lakes.
Impact of people on drainage basins and catchment areas
- Vegetation: Overgrazing and clearing of vegetalion in a drainage basin decrease infiltration, so there is less groundwater available to feed the rivers during the dry seasons. Less vegetation means that there is greater runoff and more erosion and the loss of valuable topsoil.
- Polluted runoff water: Runoff water in agricultural areas often contains nutrients, pesticides and salt from fertilizers. This runoff pollutes the river and its catchment area.
- Mining activities: Can cause pollution of groundwater, e.g. acid mine water in Witwatersrand basin.
- Boreholes: Remove water from the groundwater zone so that less groundwater can flow into the rivers.
- Urban areas: Natural surfaces are replaced with tar and concrete in the cities. As a result, infiltration is less and the runoff is greater. Together with the loss of natural vegetation, this is responsible for a shorter lag time and higher flood peak. This leads to increased flooding in the urban settlements. Domestic, agricultural and industrial use: Riverflow is decreased because water is removed for inigation, domestic, industrial and mining use. This has a negative influence on the ecological process of the river and the quality of the water.
- Misuse of wetlands: Wetland areas have been widely used for crop farming, timber plantations, waste disposal sites, pastures, etc. Often these wetlands are polluted by industries, mining and sewage, and used as dump sites. Wetlands are also destroyed when they are reclaimed for building sites.
- Riparian zones: Buildings and recreational activities in the riparian zones disrupt the ecology and this results in various forms of pollution. These activities are often too close to the banks of a river, or on a flood plain. The natural flow of the river is disrupted and often river banks break during floods.
- Dams and water schemes: Water transfer schemes and the construclion of dams cause an unnatural flow in rivers, and can destroy the ecology of a river system.
- Artificialflood control: Flood control methods such as constructing canals in the river channels, building artificial embankments (lev6es) and cutting through meander loops also change the flow of the river and often prevent natural flooding, a necessary process in a river environment.
Management strategy in South Africa
Today, very few rivers and drainage basins in South Africa are still in their natural state - most are being changed by human activity.
Monitoring and management
- Rivers and drainage basins need to be carefully monitored and managed so that everyone can have access to water. River ecosystems need to be maintained and flooding controlled to provide sustained support for the environment.
- For economic development to take place, it is necessary to use the water from drainage basins. Such usage must be carefully managed so that river systems can remain sustainable.
Legislation
- One of the most serious problems encountered in drainage basins is that of pollution. Normally, the ecology of a river is capable of breaking down small amounts of waste. However, if there is a lot of pollution, the processes cannot cope.
- Legislation is therefore required to control what is discharged into rivers. > Legislation is also necessary to control the use of underground water; building of new dams; and sinking of boreholes. Alien vegetation needs to be removed.
Education
- Farmers and the general public must be educated to conserve and use waterwisely.
Agreements
- Entire drainage basins need to be managed. Mismanagement of a channel upstream has an impact on the other rivers downstream. Where rivers form international boundaries, international agreements are necessary so that the water is accessible to all countries concerned.
Flood control
- Flooding is a natural process and can be beneficial as the silt deposits enrich soils. However, floods can cause tremendous damage to property, the environment and even loss of human life.
- Flood control is therefore a very important management strategy.
- Flood damage can be minimised in a number of ways:
- Enlarge river channels to hold more water.
- Build artificial banks alongside the river (artificial lev6es).
- Build channels and install flood gates to lead the water away from settlements.
- Build reservoirs to store water.
- Prevent the building of settlements on sites where flooding is likely.
- Protect natural vegetation.
- Protect wetlands.
Concept of settlement
- A settlement is a place where groups of people live in either a rural or urban environment.
- It is a place where there are buildings used for specific functions.
- People in a settlement regularly interact with each other, and with the surrounding environment.
- A settlement is categorised as either rural or urban.
Site and situation
Site
- Site is the actual place on which a settlement is built.
- Factors that influence the site of a settlement:
- Physicalfactors, e.g. water, fertile soil, grazing
- Economic factors, e.g. minerals
- Trade and transpo( factors, e.g. natural harbour, bridging point of a river
- Social factors, e.g. lsraeli moshav which is a planned settlement for communal living and agriculture
- Politicalfactors, e.g. government policies such as communism
- Historicalfactors, e.g. defensive sites
Situation
- The situation is the position of a settlement in relation to the surrounding gnvironment, e.g. Hex River Valley, Western Cape
Rural and Urban settlements
- Rural: areas in the countryside where people are engaged in primary activities such as farming, fishing, mining, forestry.
- Urban: a built-up settlement, like a city or town, where people are involved in secondary, tertiary and quaternary activities.
- Secondary activities: manufacturing of finished goods, e.g. textiles, chemicals, metalworking, construction.
- Tertiary activities: provision of services including banking, tourism, media, entertainment, sales, etc.
- Quaternary activities: intellectual activities linked to government, research, education, etc.
- Rural settlements are located in the countryside and are usually unifunctional.
- Urban settlements are located in towns or cities and are multifunctional.
Settlement classification according to size, complexity, pattern and function
Size and Complexity
Pattern
- The pattern of a settlement is either dispersed or nucleated.
Function
- All settlements have a function. This determines its main activities.
- The original function of many settlements has changed over time.
How site and situation affect the location of rural settlements
- A good site will have the availability of:
- drinking water with rivers or natural springs
- arable land
- grazing (pasture) for livestock
- building materials
- fuelfor cooking purposes
- transport routes
- Other influencing factors are
- quality of the soil
- relief and drainage
- defence - usually on high vantage points
- political and administrative needs - where village becomes residence of local governorlchief or regional headquarters of central government
- minerals - a mine attracts people to the area
Classification of rural settlements according to pattern and function
- The following patterns will emerge:
- Rural settlements show a dispersed pattern (displayed on maps as a square or dot that consists of the main house and outbuildings), or a nucleated pattern (squares or dots that show buildings grouped together, as in a village).
Reasons for different shapes of settlements
- Most nucleated settlements are classified according to their specific shape.
- Many physical, human and cultural factors influence these shapes.
- These include the:
- relief of the area (mountains, rivers, plains)
- transport routes (roads)
- safety (defence), etc.
There are four basic shapes:
Round or circular
Round villages develop for defensive reasons or around a central feature, e.g. common land, village green, a well or church.
Linear
Linear villages develop along a road or river.
Crossroad
Crossroad villages develop at a crossroad (intersection) and develop in a star shape.
T-shaped
T-shaped villages develops at a T-junction in a road.
Land-use in rural settlements
- The land-use depends on the function and the type of primary activities that occur in and around the settlement.
- Environmentalfactors (soiltype, climate, topography) determine the types of crops or animals that can be farmed.
- Economic factors may influence the land-use, sugh as the size of land required to make a living, the distance to market for the sale of goods and so on.
- Social factors and culture may influence how the rural land is used, e.g. in communities where cattle represent wealth, they may be the main rural activity. Many rural areas are becoming more urbanised.
- The land-use for a settlement involved in agriculture could include houses in which people live, storage buildings and sheds, grazing land, roads, water storage facilities etc.
Rural-urban migration
Rural-urban migration: People leave the rural areas to live in urban areas. This is taking place on a global scale, especially in developing countries.
Causes and consequences of rural depopulation on people and the economy
Rural depopulation: Rural areas become depopulated, resulting in a decline of functions and services. Towns become 'ghost towns'.
Causes of rural depopulation
- Poverty is the mosl important reason for rural depopulation.
- ln developing areas, the rural poor are very isolated because of :
- distance from urban services
- lack of basic services (electricity and clean water)
- poor health care
- few educational opportunities
- few employment opportunities
Push factors
These factors push people dway from rural areas and include:
- Natural disasters e.g. droughts, famine. > Crop failures due to droughts or floods, famine.
- Limited food production because of overgrazing, misuse of arable land, resulting in soil erosion or soil exhaustion.
- Lack of jobs due largely to mechanisation (modern machinery) - means that farms need fewer labourers.
- Basic services close down, i.e. medical, educational (schools), and banking services.
- Low standard of living and poor quality of life.
- Lack of safe (clean) water.
Pull factors
These factors pull people towards the urban areas and include:
- Employment
- Education - better schools and educational opportunities.
- lndustries and services in cities offer employment opportunities.
- Better services such as health care and entertainment.
- Expectation of better housing and better quality of life.
- More reliable sources of food.
- Factory workers paid more than farm workers and are not as atfected by natural disasters, e.g. drought.
- Expectation of a constant supply of clean water and sanitation.
Consequences of rural depopulation
- Farmers and residents spend less in the smaller service centres as they prefer to shop in the larger service centres.
- As a result, the smaller centres struggle to survive economically.
- Young men usually leave first and the women and elderly remain behind.
- The rural population starts to become older.
- As a result, the process of rural decline and decay sets in.
Strategies to address the effects of rural depopulation
Developing countries all over the world have problems with rural depopulation and dwindling economies. South Africa is no exception, and also suffers from the inequalities of apartheid policies that kept rural people in a state of poverty.
Rural settlement problems in South Africa
- Rural depopulation is a global phenomenon, but many of the problems in South Africa stem from discriminatory legislation and neglect of the majority black population during apartheid.
- Forced removals led to overpopulation in the rural areas and deprived people of basic needs.
- High population growth put further pressure on limited family incomes, social services and on the natural resources.
Reconstruction and Development Programme (RDP) - 1994
The focus was on:
- meeting basic needs
- developing human resources
- building the economy
- creating a democratic slate and socie$
GEAR
GEAR: Growth, Employment and Redistribution
It replaced the RDP in 1996. This economic reform plan was directed towards:
- growing an economy to create sufficient jobs
- redistribution of income opportunities in favour of the poor
- ensuring the availability of good health, education and other services
- creating environments where homes and places of work are safe
Comprehensive Rural Development Programme (CRDP)
CRDP is presently being implemented in South Africa.
It aims to
:- eliminate rural poverty and food insecurity
- maximise the use and management of nalural resources
- create sustainable rural settlements
This aims to be achieved by the implementation of land reform policies, stimulating agricultural production, improving service delivery and rural infrastructure, skil ls development, development programmes for ru ral transport and so on.
Social justice issues in rural areas, such as access to resources and land reform
- Socialjustice is the principle that all individuals are entitled to their basic human needs:food, water, clothing, shelter, health care and education.
- The Native Land Act of 1913 had a major impact on rural areas in South Africa. Black South Africans were assigned 13,6% of the land. These areas were called reserves and later became known as homelands.
- ln the 1950s the government passed laws stating that all black South Africans had to live in a homeland unless they had a pass allowing them to leave.
- The previous homeland areas have very poor soil conditions caused by overuse of the land which has lead to severe degradation.
- Many of the social injustices in the rural areas are caused by the lack of easy access to resources.
- Poverty is a huge problem in these areas. Subsistence farming is practised. Poor soil fertility and unsuitable climate contribute to poverty.
- Gender inequality and lack of basic education have increased the unemployment rates.
- Access to primary healthcare is limited. HIV/Aids and tuberculosis (TB) are widespread in South Africa's rural areas.
- Rural infrastructure is poor. There is limited access to sanitation and water in many rural areas.
In South Africa the current land ownership and development patterns still reflect much of the economic and political conditions of apartheid. The government believes that granting land ownership to communities and people in rural areas can help to alleviate poverty.
Here are some of the strategies used in this plan
Land redistribution
Land owned by the government is allocated to disadvantaged and poor people (especially in rural areas) for settlement and farming.
Land restitution
Land that was forcibly removed from people under various discriminatory laws is returned to them. People lodge claims through the Land Claims Court who decide on an outcome.
Land reform
People are given the security of land tenure/occupancy, including communal land ownership and informal ownership (by farm workers and labour tenants), as some labour tenants have lived on the same land for generations and have no other home.
Origin and development of urban settlements
- All settlements were originally rural.
- The low productivity of agriculture meant that towns could not prosper on the income derived from farming and so they had to manufacture goods to trade.
- Villages became established and eventually grew into towns and then cities.
- The earliest urban settlements were established 6 000 years ago.
- Initially the proportion of the world's population living in urban settlements was very small but in recent times this has risen dramatically.
- 50% of the world's population was urban by 2010.
- One of the main reasons for urbanisation is the transition from an economy based on primary activities to a system where secondary and tertiary activities become more important.
Urbanisation Process where the ever-increasing percentage of the total population lives in urban rather than rural settlements.
Urban growth The increase in the number of people living in a city
Urban expansion Refers to the physical or real growth of an urban settlement linked to the increase in the urban population numbers.
Urban sprawl Refers to the haphazard expansion of low-density residential developments.
Rate of urbanisation The amount by which the level of urbanisation takes place from year to year and is expressed as a percentage.
Level of urbanisation The percentage of the total population living in urban settlements at a given time.
How site and situation affect the location of urban settlements
Several factors influence the site and situation of urban settlements:
Human factors
- historical, e.g. defence
- social, e.g. need for social interaction
- political, e.g. nucleated for safety in times of war or political instability or nucleated as a result of policy, e.g. Communism
- cultural, e.g. communal living
Economic factors
- transport and trade
Physical factors
- climate
- relief
- Water supply and drainage of the land
Classification of urban settlements according to function
An urban settlement can be classified according to its function. However, this original function may change over time as new needs and services are provided.
Types of urban settlements Central places
- Develop because of the surrounding rural population's need for certain goods and services, usually found in urban areas.
- These services include social, economic, health, education and religious needs.
- Most towns in the interior of South Africa (e.9. Karoo and Free Sate) originated as central place towns.
Trade and transport cities
- Cities originate where transport routes meet. They are often along transport routes such as navigable rivers, major road transport routes or where one form of transport is replaced by another, e.g. sea to rail.
There are 3 types of trade and transport cities:
- Break-of-bulk towns Develop at a point where the type of transport changes, e.g. at a harbour where the transport changes from sea to road or rail.
- Junction towns Originate where important transport nodes meet, such as road, river or railway junctions, e.g. De Aar (rail junction).
- Gateway/gap towns Originate at places where there are physical barriers, such as mountain passes or low-water river crossings, e.g. Worcester.
Specialised cities
- Usually have one dominant function, e.g. mining, recreation, military, industry, e.g. Sasolburg (oilfrom coal), Phalaborwa (copper mining).
- Resources are generally strongly localised.
- Tend to originate in clusters, e.g. along safe beaches, coalfields, gold fields, etc.
Hierarchy: a number of levels ranging from low to I high. Each level offers a similar set of functions. I However, each levelwill be ranked ther.
Central Place Theory
- ln 1933, the German Walter Christaller developed the Central Place Theory.
- He observed that the towns in northern Germany displayed a regular distribution pattern.
- His Central Place Theory explained the number, location, size, distribution and function of the urban setllements.
- There are four main principles to this theory:
- People prefer convenience.
- People want to pay the cheapest price for goods.
- Businesses want to make as much profit as possible.
- People prefer to pay the minimum travelling costs when making a purchase.
Central place: an urban settlement that provides goods and services to the surrounding population.
Threshold population: the minimum number of people required to support a business or service.
Sphere influence : the area from which a business draws its customer.
Range: the maximum distance a person will travelto buy goods.
- The smaller the settlement, the smaller the threshold population, the range and sphere of influence.
- The larger the population of a settlement, the more able that population is to support a larger variety of services and functions.
- There are more small settlements than large settlements.
Lower and higher order functions and services
- Low-order goods/services are generally cheaper convenience goods needed on an everyday basis located in local convenient outlets, e.g. bread and milk.
- High-order goods/services are more specialised and expensive goods and services needed less frequently and generally located only in larger centres.
Lower and higher order centres
- Urban settlements can be arranged in a hierarchy (system of ranking) according to their size and functions - lower and higher order centres.
- A South African geographer, Professor RJ Davies, used some of the ideas of the Central Place Theory to classify South African cities into an urban hierarchy.
- In 1967 he classified urban settlements into eight hierarchical categories.
Conurbation: a continuous urban area, e.g. Witwatersrand (linking Johannesburg, Boksburg, Brakpan, Benoni, Randburg, Sandton, Soweto, Midrand, Pretoria).
Megalopolis: formed when conurbations join together, e.g. eastern seaboard of the USA - over I 000 km linking New York, Boston, Philadelphia, Baltimore, Washington DC.
Internal structure and patterns of urban settlements
Land-use zones
Land-use zone: refers to a type of function (or service) that is found in that area.
CBD: Central Business District
Commercial zone (CBD) (A)
- Located near city centre where land is scarce and land values are very high.
- Concentration of high-rise buildings (skyscrapers) due to limited space.
- The CBD is the most accessible area because all roads and railways converge here.
- Very intensive land-use creates high volumes of traffic.
- Predominantly high-order functions,
- Commercial and financial activities.
Transition zone (zone of decay) (B)
- Most often located around the older parts of the CBD.
- Different functions, including retail, commercial and residential.
- Buildings are'run down'.
- High land values.
High-density residentia! zone (G)
- Found on the perimeter of the CBD and sometimes in neighbouring suburbs.
- Generally consists of high-rise buildings (flat complexes), e.g. Hillbrow.
- Due to urban decay, some are overcrowded, poorly maintained, and a source of crime.
Light industrial zone (D)
- Small to medium industries, e.g. manufacturing of furniture, electronic equipment, printing, bakeries.
- Require good transport networks and quick access to the CBD or shopping centres. > Do not produce much pollution.
Low-income residential zone (E)
- Generally located near the CBD.
- Also located on the outskirts of a city (if planned, called dormitory towns, if not planned, called squatter camps).
- Legacy of apartheid and urbanisation created these zones.
Suburban shopping zone (F)
- Generally situated in residential areas away from lhe CBD.
- Customers require parking areas and road networks for maximum accessibility.
- Trend is to locate these functions on fringes of city with rooftop parking or parking garages.
Suburban office parks (G)
- Office parks located away from the CBD with sufficient parking, sometimes in the rural-urban fringe.
- Attractive zones with landscaped environments, accessible by road transport, e.g. Century City near Cape Town.
Heavy industrial zone (H)
- Located far away from the CBD and high-income residential areas because of air and noise pollution, industrial hazards and dangers.
- Require heavy transport (rail and mass road transport). > Buildings require large areas with lower land values.
Informal housing zone (l)
- Usually in rural-urban fringe.
- High density informal houses with limited access to basic services, such as clean water and sanitation.
High-income residential zone (J)
- Located far away from the CBD and industrial zones.
- Associated with high land values and single dwellings on large plots with pleasant environments and views.
- ln South Africa, crime has given rise to cluster housing in security complexes and golf estates.
Rural-urban fringe (K)
- On the outskirts of urban areas.
- Mixed functions need large spaces with lower land values, e.g. golf courses, nu rseries, market g ardens, cemeteries, airports.
Greenbelt (L)
- Area of parks, farmland or uncultivated land surrounding (or within) a city.
Urban profile
- An urban profile shows the vertical shape of a city skyline when viewed from the side.
Reasons for shape of urban profile
- A concentration of high-rise buildings is usually located towards the centre of the city. Buildings are tall and vertical because of high land values and the scarcity of land for building purposes and extension.
- Many cities have a second concentration of high-rise buildings away from the city centre. This is usually the flat and hotel district.
- Towards the outskirts of the city, land values are lower. Large buildings extending horizontally are located in these areas comprising of warehouses, factories and office parks.
- Residential areas consisting mostly of single storey houseslinformal settlements.
- Vacant areas may also be located in between because of building restrictions; conservation areas; green belt zones; and recreation zones (golf courses).
Factors influencing the morphological structure of a city
- The shape of cities is largely dependent on the physical site of the city, land values, transport routes and economic factors.
- Most cities tend to be roughly circular in shape as it means that the total amount of movement within the city is kept to a minimum.
- However, some cities have different shapes that often reflect their origin, growth and functions. These shapes can be directly linked to some form of relief barrier or human activity:
- The geometrical shape was characteristic of the Middle Ages and the Renaissance and planned as fortress cities.
- Access to private motor vehicles has been the most significant influence on the shape of cities.
- ln the 20th century, many urban settlements developed a roughly stellar/star shape with new extensions radiating in several directions along main roads and transport routes.
- Other settlements have linear shapes due to relief barriers such as along rivers, at a coastline or in valleys between two parallel mountains.
Street patterns
- Streets can be regarded as the skeleton of an urban settlement.
- Streets can be used to identify different zones, and the age of the settlement.
- Most urban settlements have a combination of different street patterns.
- This is the result of the age of the city, planning and relief.
Grid or gridiron pattern
- Streets intersect at right angles to each other.
- Typical of older settlements and in the CBD because pedestrian traffic was important.
- Positives:
- Easy to survey, plan and extend.
- Easy to subdivide land into plots and to construct buildings.
- Easier to lay down networks for water, electricity and telephones.
- Negatives:
- The many intersections can lead to traffic congestion.
- Not suitable where the land is steep.
Irregular (planned or unplanned)
- Planned irregular patterns are more typical of the modern era; they were used to break the monotonous gridiron pattern.
- Newer suburbs have circles and circular drives, especially in hilly areas where the relief influences such planning.
- Positive: Allows for smooth and uninterrupted flow of tratfic.
- Unplanned iregular pattern is the result of a lack of planning, resulting in a maze of streets with various widths and directions. Slreet blocks of all shapes and sizes, found especially in older cities of Europe, rural areas and informal settlements, e.g. centre of Kimberley.
- Negative: Streets may be very steep along steep gradients and result in pedestrian and transport flow problems.
Radial pattern
- All roads lead to a central accessible point.
- Many old cities of Europe have this pattern. Boulevards replaced the old city walls.
- Positive: Ensures smooth flow of traffic.
- Negative: Confusing, easy to get lost.
Models of Urban Structure
- Geographers have attempted to explain land-use zones in urban places by means of models. Planning for future growth is done using models of existing cities.
- There are three classic models of land-use zones:
Modern American - Western city
- All Western cities have an orderly structure, where we can find the different functions and particular zones in more or less lhe same part of the city.
- Most are a multi-nodal city with an old CBD, new secondary urban cores and large suburbs, gated estates and edge cities.
- Many businesses move aiway from the inner city to the secondary nodes and suburbs.
The Third World city
- The CBD is the main urban core and i$ surrounded by housing and industrial areas.
- Large informal settlements are located on the outskirts of the city.
The South African city - changing urban patterns and land-use
- South Africa has an unnatural system of land-use as a result of the apartheid policies. These have Ieft a racial imprint on South African cities.
- The Group Areas Act (1952) divided South African cities into separate racial areas. Black people were removed from their homes and relocated in outlying townships. Large townships and informal settlements are found in most parts of South Africa.
- Many South African inner city areas are in decline with the groMh of secondary nodes and suburbs.
Recent urbanisation patterns in South Africa
- South African cities are growing rapidly - especially Johannesburg, Cape Town and Durban.
- 62% of South Africans live in urban settlements and this percentage is increasing.
- The average rate of urbanisation is 1,ZYo per year.
- The increase in urbanisation is due to both intemal migration from within South Africa and also the natural growth of urban populations.
- South African urbanisation rates have also increased due to migrants from other African cities.
Urban issues related to rapid urbanisation
- Rapid urbanisation can lead to many challenges or problems:
- Lack of planning
Rapid urbanisation can result in many unplanned settlements, e.g. informal settlements or building extensions. New urban developments need to be properly planned and managed.
- Housing shortages
The growing size of urban populations leads to a shortage of houses, overcrowding, inadequate services etc.
- Overcrowding Many cities have high population densities, slums develop and services such as schools and hospitals are under pressure.
Traffic congestion Rapid urbanisation has resulted in traffic jams, delays, shortage of parking.
- Problems of service delivery
Growing cities need services like water, electricity, sewerage and refuse removal. Services providers struggle to meet the growing demand.
- Lack of planning
Growth of informal settlements and associated issues
Informal settlement: an unplanned residential settlement where people have occupied land illegally and built shacks there.
- South Africa's population is becoming increasingly urbanised. There is a shortage of housing resulting in many people living in informal settlements.
- Most informal settlements lack basic services such as water, electricity and sanitation.
- There is an increasing number of backyard shacks - informal dwellings built alongside formal houses.
Informal settlement issues
- Shacks are usually made of corrugated iron and are very hot in summer and cold in winter.
- Many settlements are in low-lying areas and are prone to flooding.
- Fires occur frequently - caused by candles, paraffin stoves and open fires. They spread rapidly as the shacks are close together. Fire engines cannot gain access as the spaces between the shacks are very narrow.
- Services are lacking. Taps and toilets are often outside and some distance from the houses.
- Unhealthy living conditions.
- Poverty and unemployment.
New towns
- Such settlements are planned right from the start and built on new sites and include all aspects of development before construction begins. This means that:
- suburbs, roads, allthe land-use zones, parks and amenities are planned in advance
- all socio-economic features are integrated, e.g. schools, roads, shopping centres
- transport systems such as wide roads, traffic circles, and street patterns are planned to be functional
- allfunctions are regulated by laws ' some new towns are built in poorer areas to boost the economy. Others are self-sustainable providing employment, education and health care services, recreation, etc.
- New towns include garden cities and greenbelt towns. > These new towns are intended to limit the groMh problems of large cities, stimulate economic growth, and provide housing for the growing urban populations. They also help to decentralise urban populations to lessen overcrowding and the pressure on limited city resources.
Self-help cities
- Communities initiate a 'self-help'approach when local authorities or central governments fail to improve the quality of life of the inhabitants.
- In South Africa, a substantial number of foreign and local organisations and volunteers are assisting potential home owners to build their own homes by providing the basic material and helping with the building, e.g. Habitat for Humanity. lnhabitants become skilled in the building trade.
Future urban settlements
Urban settlements in the future need to become more sustainable by:
- planting more trees, creating parks and greenbelts
- recycling urban waste
- using cleaner fuels and energy sources
- using environmentally friendly building materials
- establishing food gardens, growing vegetables
- managing the use of urban water
The economy can be divided into four sectors: the primary sector, secondary sector, tertiary sector and quaternary sector.
Economic sectors
Primary
- Allthe economic activities in which products come directly from nature.
- For example: mining, fishing, forestry, agriculture (farming)and hunting, etc.
Secondary
- Raw materials are processed or manufactured into products which are more useful, e.g. building and construction, metalworking, food production.
Tertiary
- The provision of services.
- No tangible products, e.g. health, education, entertainment, recreation, law and order, financial services, retailing, goods transport, garbage removal.
Quaternary
- Associated with the IT sector, and linked to processing and distribution of knowledge and information, e.g. information technology services, research and management (services rendered by professionals).
GDP (Gross Domestic Product): total value of all goods and services produced in a country in one year.
Economic sectors'contribution to the South African economy
Primary activities
- Mining and agriculture are the two most important primary contributors.
- Mining has decreased substantially, but international demand for raw materials makes it an important commodity.
- Agriculture is under strain due to the fluctuating market and rand-value; rising production costs; low income due to weather inconsistencies; and competitive international market.
- Fishing and forestry activities contribute much less.
- Approximately 11% of all workers are employed in primary activities.
Secondary activities
- The metal and engineering industry and construction are the most important contributors, e.g. the motor industry.
- Approximalely 24% of allworkers are employed in secondary activities.
Tertiary activities
- Finance, transport, communications, tourism, real estate and government are the major contributors to the GDP.
- Approximately 65% of all workers are employed in tertiary activities.
- Agriculture is a primary economic activity.
- Land is cultivated for crop production and livestock is farmed for food production.
- Food production has changed as a result of mechanisation, improved irrigation, the use of chemicals and fertilizers, hybridisation and genetically modified crops.
- These new methods enhance food security and limit the risks and vulnerability experienced in this economic sector.
Contribution of agriculture to the South African economy
- Agriculture only contributes 3,1% (approximately R40 billion) to the GDP, compared to the larger contribution of the secondary and tertiary sectors.
- Agriculture supports the development of services in the secondary and tertiary sectors because it requires transport and delivers raw materials for manufacturing.
- South Africa is self-sufficient In most basic food crops, and also contributes to the GDP by exporting some of these crops.
- Agriculture is an employer of labour.
The role of small-scale farmers and large-scale farmers
Commercial farming: farming for profit where food is produced on a large scale.
Subsistence farming: takes place on a small scale and agricultural products are produced to be consumed by family and community.
Main products produced
South Africa has a wide range of climates. This makes it possible to farm a range of crops and livestock.
Main agricultural products:
- Deciduous fruits - grapes (wine), apples, pears, peaches, plums, apricots
- Subtropical fruits - bananas, pawpaws, mangoes, avocados
- Citrus - oranges, grapefruit, naartjies
- Grains and seeds - maize, wheat, oats, sunflowers, canola
- Livestock - beef, lamb, mutton, pork, ostrich
- Dairy
- Sugar
Home market
- South Africa has increased its food production in the last few years.
- Most grains, vegetables and seasonal fruit are grown for local consumption.
- Meat and poultry products are also produced for the home market.
Export market
- South Africa has increased its export of agricultural products and is a leading exporter of deciduous fruits, avocados, grapefruit, maize and ostrich products.
- Processed agricultural products such as wine and rooibos tea bring in valuable foreign exchange.
Factors that favour and hinder agriculture in South Africa
Factors favouring agriculture in South Africa
- Climate
- South Africa has a range of climates and natural vegetation. This makes it possible to farm a range of crops and livestock.
- The eastern wetter and warmer parts of South Africa support farming of sugar cane and subtropical fruit. The winter rainfall areas in the southwestern parts support deciduous fruit and wheat farming. Livestock farming is more suited to the drier northwestern parts.
- Most arable areas are frost-free and this supports a longer growing season.
- Relief
- Much of the country is flat or has an undulating landscape with low hills.
- This feature supports extensive crop farming (wheat and maize) and livestock rearing (sheep and cattle).
- Rivers provide irrigation water in the drier western parts of the country.
- Research
- New drought and pest-resistant hybrid seeds are used, producing higher yields.
- Climate research can predict hazards more accurately (droughts, floods, hail storms) and disaster management strategies are more effective.
Factors hindering agriculture in South Africa
- Only a small portion of arable land is suitable for crop farming.
- In many parts of South Africa the soil is very thin and, due to over-cultivation and overgrazing, the damaged soil is less fertile. Erosion (water and wind) is a serious problem.
- Farming methods are often poor. Poverty makes it difficult for farmers to buy machinery and introduce modern methods. They cannot afford fertilizers and pest control.
- Many areas are too densely populated for commercial farms to develop. Too many people have to share the land.
- Some areas have poor transport networks. Training and education in new farming practices are neglected.
The importance of food security in South Africa
Food security: food security exists when all people have enough food in order to sustain a healthy life.
- At present, South Africa produces enough food. However, the population is increasing, which means that food consumption is also increasing. At the same time the production of some basic foods is decreasing.
- Agricultural products are mainly exported to the countries of the European Union (EU) and Southern African countries. ln times of shortfalls due to droughts, South Africa can afford to supplement food by importing it.
- There are some urban and rural areas where people do not have enough food to eat, and so food insecurity/shortage exists. A national nutrition programme has been introduced in primary schools to feed learners.
- Most of the poorest households are in the rural areas where subsistence farmers cannot produce food enough for their own consumption.
Contribution of mining to the South African economy
- Mining contributes 1B% to South Africa's GDP (8,6% direct and 10% indirect).
- Mining also brings additional economic development as it has resulted in other industries, transport links and services.
- Mining earns more than 50% of South Africa's foreign exchange. Minerals are exported either in their raw state or after they have been processed.
Beneficiation: minerals that are processed into a higher value product, e.g. iron ore into steel.
- Mines are a major source of employment.
- Mining companies contribute billions in taxes to the economy.
- Mining activities have attracted huge foreign investment to South Africa.
- Coal mines in South Africa provide about 90% of the electricity generated.
Significance of mining to the development of South Africa
- The discovery of diamonds and gold resulted in the development of South Africa's infrastructure, e.g. railways.
- Mining led to the opening of universities and educational institutions as there was a need for training in geology, engineering and other fields.
- Mining resulted in huge investment in South Africa to develop new mines and related industries.
- Link industries were developed to supply products to the mines.
Link industries: industries that supply materials or equipment to another industry or which depends on another industry for its own processes.
- Mines and link industries provide employment for many people.
- The export of minerals has resulted in valuable foreign exchange for South Africa.
Factors that favour and hinder mining in South Africa
Factors favouring mining in South Africa
- South Africa's mineral resources are estimated to be the largest in the world. South Africa also has a wide range of different minerals.
- The mineral seams are often thick and near the surface so are more easily mined.
- The low geothermal gradient in South African mines reduces the cost of cooling the air that is pumped down into the mines
Geothermal gradient: the rate at which the rock temperature increases with increasing depth below the surface
- South Africa has a large source of unskilled labour.
- Many countries have invested capital in South African mines.
- South Africa has a developed infrastructure - railways, roads, water and electricity.
- South Africa's huge coal resources are used to make electricity. This helps to keep costs lower^
Factors hindering mining in South Africa
- Mining of both gold and platinum is labour intensive and expensive.
- Cooling underground requires a great deal of energy which has become costly and Eskom is struggling to keep up with the demand.
- Labour unrest and violent protests combined with rumours of possible nationalisation of mines have been a deterrent for many foreign investors.
- Fluctuations in the rand exchange rates have had serious effects on the gold mines and some have had to close when prices fell too low.
- Many of South Africa's mineral deposits are located far inland. This means that transport costs are high.
- The mining industry uses large amounts of water. ln addition, mining produces huge amounts of waste and contaminated water which threaten the environment and water supplies.
- Huge costs are involved in minimising the negative effects of mining and in rehabilitating old mine sites.
Contribution of secondary and tertiary sectors to the South African economlr
- The secondary and tertiary $ectors of South Africa's economy are both larger than the primary sector in terms of their contribution to the gross domestic product (GDP).
- In 2011 the secondary sector contributed 21% lo the GDP and the tertiary sector contributed 6'l %.
Secondary sector: includes manufacturing, construction and util ities (supply of water, electricity and gas)
Tertiary sector: includes a great range of occupations. People who work in the tertiary sector provide a service of some sort. As the South African economy matures, the tertiary sector continues to grow.
Types of industries
Heavy industry
- uses large quantities of raw materials
- may emit much waste and pollution
- requires mass transport
- requires large areas - usually located on the urban edges
- e.g. steel plants, petro chemicals
Light industry
- manufactures smaller products
- does not produce pollution
- located in industrial areas within the city
- e.g. clothing, packaged food
Raw material orientated
- located close to the source of raw materials
- produces periqhable goods
- e.g. butter and cheese near dairy farms, wine near vineyards
Market orientated
- industries that manufactures bulky or perishable products
- factories are placed close to where the buyers are, e.g. bakeries making bread
- If the industry produces heavy or bulky products, e.g. furniture or if the product is expensive to transport, e.g. big machines, then the factory needs to be located close to the market.
Footloose industries
- industries that are not tied to any specific location
- e.g. upholstery factory
Ubiquitous industries
- industries that are found everywhere
- e.g. bakeries, butchers
Bridge industries (break of bulk points)
- Set up where cargo is transferred from one mode of transport to another, e.g. at a port.
- Motor car manufacturers Ford and General Motors in Port Elizabeth established where necessary components arrived by ship.
Factors influencing industrial development in South Africa
Raw materials
- South Africa mines a wide range of minerals. Many of these are used in heavy industry.
- Agriculture supplies raw materials for food manufacturing.
Labour supply
- Many unskilled workers.
- Need for more skilled workers.
Transport infrastructure
- South Africa has a good infrastructure - rail, road, flight networks, harbours.
- Allows for transport of raw materials and finished products.
Power
- South Africa has huge coal reserves. There is an abundance of coal in Mpumalanga which provides thermal electricity and has helped to keep power costs lower.
Water
- Most industries need water to operate. South Africa has numerous dams and also inter basin transfer schemes.
Political intervention
- Since the late 1990s the government has started programmes to help manufacturers to set up new factories.
- E.g.IDZs (lndustrial Development Zones) SDIs (Spatial Development lnitiatives)
Competition and Trade
- South Africa is accessible to sell to local, regional and foreign markets.
South Africa's industrial regions
GAUTENG (Tshwane-Witwatersrand-Vaal complex)
Main industries
- Metals, iron and steel plants (Vanderbijlpark, Vereeniging)
- Motor vehicles (BMW, Nissan)
- Chemicals (explosives)
- Petrochemicals (SASOL at Sasolburg and Secunda)
- Machinery
Factors influencing location
- Availability of water - Vaal River. lnter basin transfer from the Tugela-Vaal Project and the Lesotho Highlands Water Project
- Gold provided the initial stimulus
- Well-developed transport network
- Raw materials available - minerals and agricultural products
- Availability of labour force - skilled and unskilled
- Energy resources available - mines provide coal to the thermal power stations
- Good and plentiful agricultural land
- Large market - fast-growing population provided a market for a huge range of industries
DURBAN-PINETOWN (eThekwini metropolitan region)
Main industries
- Oil refining (making petrolfrom crude oil)
- Sugar processing (Huletts)
- Chemicals
- Paint
- Textiles
- Motor vehicles (Toyota)
- Shoes (Bata)
Factors influencing location
- High rainfall region, which means a good water supply
- Location of Durban harbour close to large markets in Gauteng
- Large local market
- Unskilled and skilled labour available. Linked to Gauteng by road and rail
PORT ELIZABETH-UITENHAGE (Nelson Mandela metropolitan region)
Main industries
- Motor vehicle assembly plants (Volkswagen, Mercedes Benz, Delta)
- Supporting industries (motor parts, tyres)
- Textile (wool)
- Leather (shoes)
- Fruit canning
- Salt works
Factors influencing location
- Water available - Orange River Project
- Port Elizabeth harbour
- Plenty of labour (although mainly unskilled)
- Equalised rail tariffs (costs are the same as the rest of the country)
- Central location to markets
- lndustrial Development Zone: Coega, near Port Elizabeth
SOUTHWESTERN CAPE
Main industries
- Food processing (fish, fruit)
- Clothing and footwear
- Oil refining (Milnerton)
- Link industries (printing and packaging) > Wine making
Factors influencing location
- Enough water from dams
- Raw materials available, e.g. fruit, fish, wheat, vegetables, dairy, chickens > Cape Town harbour, as well as good transport links
- Foreign tourist market and local market
- Higher level of education than national average and specialised skills, e.g. clothing industry
- Historicalfactors - Cape Town (first city in SA); parliament
- Energy - negative factor. Far from the coal fields so high cost of electricity
Apartheid industrial development strategies
- Apartheid was a system of racial segregation enforced by the National Party governments from 1948 - 1994.
- One of the aims of the government was to decentralise industrial development by creating black national states, called homelands, outside the main centres.
- Growth points were developed in the areas surrounding the homelands so that workers could work at growth point industries and yet remain living in the homelands.
- Deconcentration points were industrial development sites located outside the main centres, e.g.Atlantis near Cape Town.
Post-Apartheid lndustrial Development Strategies
- Since 1994, the post-apartheid government has supported the development of the manufacturing sector and a revised Regional Industrial Development Programme (RDP) was introduced.
- The government has developed strategies to increase investment in certain areas. ln 1996 the government implemented the Spatial Development lnitiatives (SDls). These were aimed at attracting investmenl in underdeveloped areas.
Concept and distribution of of Industrial Develooment Zones (IDZ)
- In 1996 the government introduced a new development plan. lt was based on two initiatives:
- Spatial Development lnitiatives (SDls)
- lndustrial Develooment Zoncs (lD7s'l which are r:nras wiihin the SDlq
Industrial Development Zones (IDZs)
- Eight IDZs were selected for advanced development. These IDZs were either at ports or near to airports.
- The main objective of an IDZ is to develop infrastructure and services of certain areas and to promote investment there.
- By 2013, four IDZs were operating: Richards Bay, East London, Coega (near Port Elizabeth) and Saldanha Bay.
- The government aims to make IDZs more attractive to foreign investors by offering tax incentives. The government is revising the concept of IDZs into a new strategy of Special Economic Zones (SEZs)which focus on Foreign Direct lnvestment (FDl).
Spatial Development Initiatives (SDIs)
- A Spatial Development lnitiative is a programme to initiate and support a series of development corridors stretching across parts of South Africa and also into neighbou ring countries.
- The aim of SDls is:
- to develop and improve existing transport infrastructures
- to initiate and support economic activities along transport corridors
- to create an attractive environment for private sector investment
- e.g. Maputo Development Corridor - connects the economic centre of Gauteng with the harbour of Maputo, Mozambique.
Issues associated with industrial centralisation and decentralisation
South Africa's wealth and industry is concentrated in the four core industrial areas. As these areas develop and get richer, the rest of the country (called the periphery) becomes less developed and poorer. The advantages and disadvantages of centralisation are summarised in the diagram below:
- At present South Africa faces the problem of growing unemployment. As a result, people create their own employment in the informal sector, the so-called 'hidden part' of the economy.
- Informal trading generally refers to market traders, hawkers or street vendors, spazas and house shops. These traders operate in city streets, and in highdensity areas such as townships and informal housing settlements.
- Generally, the following goods and services are provided:
- Selling of fruit, vegetables, clothing, handcrafted goods, cheap imported goods (sunglasses, shoes, belts, handbags), traditional herbs
- Pavement hair salons, car guards, car washers or any other casual labour
Informal sector: Consists of self-employee people. People work for themselves from their own homes or as vendors on the streets, generally without a license or a business permit.
Formal sector: All jobs with normal hours and regular wages and are recognised as income sources on which income taxes must be paid.
Characteristics of the informal sector
- Lack of access to financial services such as credit.
- Limited business skills.
- Self-employed.
- Inadequate or no links with supplies from formal businesses.
- Very limited access to infrastructure and basic services such as water, electricity and rubbish removal.
- Limited access to government regulations on how space can be acquired and the issuing of trade licensing.
- Unwillingness to undergo formal trading as they will lose out on trading hours.
- Incomes are low and uncertain and long working hours.
- Profit margins are low.
- Mostly unskilled or semi-skilled workers.
- Small-scale services provided mostly on the streets.
- Some goods made from recycled materials.
- Workers have no protection by trade unions.
- Many problems: Iitter; unhygienic environments; congested pavements; petty crime; and urban decay
Reasons for high informal sector employment in South Africa
- Inadequate training and low literacy levels mean that many people moving towards the cities and towns from the rural areas are not equipped to enter the job market.
- Urbanisation: new arrivals in towns and cities outnumber the available job opportunities.
Challenges facing South Africa's informal sector
- In South Africa, the informal economy offers employment to 15% of the employment force.
- Some 3,8 million people were employed in the informal sector in 2005,
- Informal-sector traders lack access to credit.
- Frequently infringe the city's trading regulations.
- To develop businesses to the next level, traders need to obtain licenses and undergo training.
TOPOGRAPHICAL MAP A type of map with large-scale detail that shows topographical features of the earth (mountains, valleys, rivers and vegetation),
ORTHOPHOTO MAP A type of aerial photograph that has contour lines and various features indicated.
Direction
- Direction is expressed using the points of a compass (North, South, West, East) and the points between them.
- These are known as the 16 cardinal points.
Worked Example
Refer to the map extract below. What is the direction of the farm De Hoek from trig beacon 30?
Answer: southwest>
Contour lines
- The brown lines on a topographical map are called contour lines.
- They join places of equal height in metres.
- The height is the same along one contour line.
- The closer together the contour lines are, the steeper the slope.
Position/Coordinates
- Coordinates are a set of values that show the exact position of an object or point.
- They consist of a latitude and a longitude coordinate.
- Latitude is the coordinate that specifies the north-south position of a point.
- Longitude is the coordinate that specifies the west-east position of a point, Latitude and longitude are given in degrees (symbol o), minutes (symbol ') and seconds (symbol ").
- When giving the position in the correct format, latitude (south) is given first followed by longitude (east).
To determine position more accurately, each minute can be subdivided into seconds (symbol").
1o = 60'(minutes) 1'= 60" (seconds)
1'can be divided into 6 equal parts, each part representing 10 seconds
- On all 1 : 50 000 topographical maps coordinates are shown on the edges of the maps.
- The latitude (south) values are shown down the sides; the longitude (east) values are shown along the top and bottom of the map.
- The latitude and longitude values are subdivided into 1 minute (1') intervals.
- To determine the precise location of a place, the lines of latitude and longitude that pass through the place need to be read off the map.
Method
The method of finding the coordinafes of a specific , point is exptained by using the following exampte.
Determine the coordinates of the spot height .277 on the map extract below.
- Draw imaginary horizontal and vertical lines that meet at spot height .277 and extend to the side (latitude) and top (longitude)where the values are indicated.
- The latitude value of .277 is read on the side of the map.
- The degree value is 32o.
- The minute value falls between 0' and 1'. The correct minute reading is 0'.
- The seconds (") value falls between 0' and 1'. The minute bar is divided into 60 seconds.
- Lightly divide the minute bar in half, then divide each half into three equal spaces (10" each). This will help you to read the position in seconds.
- The correct seconds reading is 50".
- Latitude = 32o 00' 50" S
- The longitude value of .277 is read at the top of the map.
- The degree value is 18o E.
- The minute value falls between 45'and 46'. The correct minute reading is 45'.
- The seconds value is between 45'and 46'. Divide the minute bar as you did for the latitude reading.
- The correct seconds reading is 30".
- Longitude = 18o 45' 30" E
Answer: 32o 00'50's 18o 45', 30' E
Test Your Understanding 1
Determine the coordinates of trig beacon 212 on the map extract below.
Map sheet reference
- The map sheet reference is the title of the map and refers to the area that the map covers.
- The map of South Africa is divided into squares that are one degree by one degree (1o x 1o).
- Each map has a code which indicates its position on a grid covering South Africa.
- The map sheet reference is found at the top of the map in front of the name of the place shown on the map.
Example:
- The map of Mapungubwe has a map sheet reference code of 2229AB.
- This code can be broken down as follows:
- 22 = 22o South (latitude)
- 29 = 29o East (longitude)
- AB refers to squares A and B
The area of (1o x 1o) within these lines of latitude and longitude is divided into 4 big squares, labelled A, B, C and D. Each big square is subdivided into 4 smaller squares, also labelled A, B, C and D. (AB in the map sheet reference of Mapungubwe therefore refers to big square A and small square B).
- The map sheet reference of Mapungubwe 2229A8 is shaded on the grid above.
Worked Examples
1. Give the map sheet reference of the map immediately to the east of Mapungubwe 2229A8. Answer:22298A
2. Give the map sheet reference of the map immediately to the north of Mapungubwe 2229A8. Answer:2129CD
Test Your Understanding 2
The map sheet reference of Clan william is 32188B.
1. Give the map sheet reference of the map directly to the south of 321BBB.
2. Give the map sheet reference of the map directly to the east of 321BBB.
Bearing
- Bearing is an accurate way of giving the direction of one place in relation to another. lt is a compass point measured in degrees from 0o to 360o.
- We distinguish between true bearing and magnetic bearing.
True bearing
- True bearing (TB) is the angle measured clocl$vise from lrue north to a specific point or position.
Method
- Draw a north-south line through the place from which the measurement is to be taken (e.g. A).
- Draw a straight line between the fuo places, e.g.A and B.
- Place a protractor along the north-south line with 0o on the north-south line.
- Measure the angle in a clockwise direction from the true north line to the bearing line A to B.
- The answer will be in degrees, e.g. 129o.
Worked Example
Study the map extract below and calculate the true bearing of:
1. spot height .339 from trig beacon 30.
2. trig beacon 30 from spot height .339.
Answer:
1. 105o
2. 180o + 105o = 285o
Test Your Understanding 3
Study the map extract below and calculate the true bearing of:
1. the farmhouse at De Hoek from trig beacon 30.
2. the trig beacon 30. from the farmhouse at De Hoek.
Magnetic declination
- Magnetic declination (MD) is the angle between true north and magnetic north.
- This angle is calculated when the map is drawn, but the position of magnetic north changes, so the angle between true north and magnetic north (the magnetic declination) will also change.
- The magnetic declination for the year the map was drawn appears at the bottom of the map.
Example: Information on the Mapungubwe map
Mean magnetic declination 12o 21' West of True North (July 2001).
Mean annual change 3'westwards (1995 - 2000).
- July 2001 refers to the mbnth and year that the mean magnetic declination was recorded.
- Mean annual change refers to how much the magnetic declination changes each year.
- (1995 - 2000) refers to the years that were used to calculate the mean (average) magnetic declination.
- Magnetic declination can change in a westerly direction and the angle between true north and magnetic north increases.
OR
- Magnetic declination can change in an easterly direction and the angle between true north and magnetic north decreases
- It is necessary to calculate the magnetic declination for the current year.
Method
- You will need the following information from the map:
- Mean magnetic declination
- The year that the declination was recorded
- The mean annual change
- Mean annual change westwards or eastwards?
- Calculate the difference in years between the current year and the year that the magnetic declination was recorded.
- Multiply the mean annual change by the difference in years.
- If the mean annual change is westwards add the change to the given magnetic declination.
- If the mean annual change is eastwards subtract the change from the given magnetic declination.
Worked Example
Use the given information from the Mapungubwe map and calculate the magnetic declination for Mapungubwe in 2014.
Answer:
- Present year = 2014
- Mean magnetic declination = 12o
- Year magnetic declination was recorded = 2001
- Mean annual change = 3'westwards
- Difference in years: 2014 - 2001 = 13 years
- Multiply mean annual change by difference in years: 13 x 3'= 39'
- Mean annual change is westwards, therefore add to lhe given mean magnetic declination.
12o 21'+ 39' = 12o 60
Rememher: there are 6A'in 1o
Therefore the final answer is:
13o 00' west of true north
What to do if:
1) Your answer has minutes greater than 59', e.g.24o 71'
- you need to convert the minutes to degrees
- 71' = 1o 11
- add the 1o to 24o
- final answerwill be 25o 11'
2) You have to subtract a larger number of minutes from a smaller number,
e.g. mean magnetic declination = 22o 13'W
mean annual change = 23'
- if the mean annual change is eastwards, it needs to be subtracted from the mean magnetic declination:
22o 13',W - 23'
- before subtracting, convert 1o into minutes so that
22o 13' = 21o 73'
- continue subtraction:
21o 73'-23'
= 21o 50'
.'. Magnetic declination = 21o 50'W
Test Your Understanding 4
Use the following information to calculate the magnetic declination for 2014.
- 1. Mean magnetic declination 21o 15' west of true north (1991 .02). Mean annualchange 2'westwards (1990 - 1995).
- 2. Mean magnetic declination 21o 54' west of true north (1986.05). Mean annual change 2' eastwards (1980 - 1985).
Magnetic bearing
- Magnetic bearing is the angle between magnetic north (MN) and a given point.
- Calculate the magnetic bearing by using the following formula:
Magnetic Bearing = True Bearing + Magnetic Declination
Method
- Calculate the true bearing as explained on p. M4.
- Calculate the magnetic declination as explained on p. M5.
- Add the true bearing to the magnetic declination.
Take note that the answer must not have direction (N, S, f or W) as it is an angle measured in degrees and minutes.
Map scales are expressed in three ways:
Distance
- Distance on a map is calculated between two points.
- Use the following formula to calculate distance on a map:
Actual distance = distance on map x scale
When doing distance calculations, you will be asked to give your answer in kilometres or metres. The calculations for a topographical map and an : orthophoto map differ, because their scales differ
Straight line distance
Method
- Use a ruler to measure the distance between two points in cm.
Note: Measure accurately from the middle of the one point to the middle of the other.
Remember the following:
Worked Example
1. On a topographical map (scale 1 : 50 000)
Calculate the actual distance between point A and B in kilometres.
Answer:
Distance measured on topographical map in cm: 2,5 cm
Scale: 1 cm represents 0,5 km in reality
.'. Distance = 2,5 x 0,5 = 1,25 km
2. On an orthophoto map (scale 1 : 10 000)
Calculate the actual distance between point C and D in kilometres.
Answer:
Distance measured on orthophoto map in cm: 2,5 cm
Scale: 1 cm represents 0,1 km in reality
.'. Distance = 2,5 x 0,1 = 0,25 km
Curved line distance
Method
- Place the straight edge of a piece of paper along the feature to be measured, e.g. road.
- Mark the beginning point of the feature on the edge of the paper. Hold the paper steady with the point of a pencil.
- Swivel the paper to follow the road.
- Mark where the paper intersects with the road.
- Mark the end point of the road on the paper.
- Measure the distance marked off on the paper.
- Calculate the distance in reality by using the scale of the map.
Worked Example
Calculate the distance along the international boundary from A to B, on the topographical map extract below, in kilometres.
Answer:
Distance measured on map in cm: 7,5 cm
Scale: 1 cm represents 0,5 km in reality
.'. Distance = 7,5 x 0,5 = 3,75 km
Test Your Understanding 6
1. Calculate the following distances on the topographical map extract below.
1.1 Calculate ihe distance from spot height .604 to spot height .542 in kilometres.
1.2 Calculate the distance from spot height .586 to spot height .525 in metres.
2. Calculate the distance from A to B in kilometres on the orthophoto map extract below.
Area
'- Area is the measurement of the size of a surface.
Area of a regular shape, e.g. square or rectangle
- If the area to be determined is a square or a rectangle, use the following formula:
Area (A)= length (L)x breadth (b)
Method
- Measure the length in cm and convert to km or m.
- Measure the breadth in cm and convert to km or m.
- Multiply the length by the breadth.
- Write the answer in kilometres squared (km2) or metres squared (m2).
Worked Examples
1. Topographicalmap calculation (scale 1 : 50 000)
Answer in km2
:L = 5,6cm x 0,5 = 2,8km
b = 2,6cm x 0,5 =1,3km
A = L x b
= 2,8 x 1,3
= 3,64 km2
Answer in m2:
L = 5,6 cm x 500 = 2800m
b= 2,6cm x 500 =1300m
A = L x b
= 2800m x 1300m
= 3 640 000 m2
2. Orthophoto map calculation (scale 1 : 10 000)
Answer in km2
:L = 5,6cm x 0,1
b = 2,6cm x 0,1
A = L x b
= 0,56 x 0,26
= 0,1456 km2
Answer in m2:
L = 5,6cm x 100 = 560m
b = 2,6cm x 100 = 260m
A = L x b
= 560 x 260
= 145 600 m2
Test Your Understanding 7
Area of an irregular shape
- lf the shape is irregular, e.g. lake, dam, the area can be calculated by using the grid method.
Gradient
- Gradient is the relationship between vertical height and horizontal distance.
- It is the measure of steepness of a slope.
- Use the following formula to calculate gradient:
Worked Example
Calculate the gradient of trig beacon 23 to spot height .598.
Take note:
Trig beacons are numbered; do not get confused with the nutnber of the beacon and the height. The height is written below the /_\.
Answer:
VI = 842m - 598m
= 244m
HE = 2,3 cm x 500 = 1150m
Test Your Understanding
Cross sections
- A cross section is a drawing of the side view of a landform, e.g. a hill or a mountain.
Method
- Draw a straight line between the points, e.g. point A and point B.
- Use a strip of paper and place it along the line.
- Mark off each contour line and record its height in metres.
- Transfer the data to graph paper or draw a grid with a vertical and a horizontal axis.
- The vertical axis shows the height and the horizontal axis shows the distance.
- On the vertical axis mark off a scale, e.g. 1 cm :20 m. The horizontal scale is the length between points A to B, e.9.4,5 cm.
- Place the strip of paper on the horizontal line and plot the heights to correspond with the heights on the vertical axis. Mark the position with a dot.
- Join the dots to complete the cross section.
Worked Example
Draw a cross seclion from point A to B shown on the map extract below.
Answer:
Vertical exaggeration
- If the vertical and horizontal scales of a cross section are the same, the differences in slope is not easily distinguished.
- To make the slope more obvious or clear, the profile is drawn with a degree of vertical exaggeration.
- It is necessary therefore to calculate the vertical exaggeration (VE) of a cross section, by using the following formula:
Test Your Understanding 9
1. Calculate the vertical exaggeration of a cross section drawn from a topographical map 1 : 50 000 with a vertical scale of 1 cm representing 10 m.
2. Calculate the vertical exaggeration of a cross section drawn from an orthophoto map 1 :10 000with a verticalscale of 1 cm representing 30 m.
Intervisibility
- lntervisibility refers to whether one place is visible from another place.
Method
- Draw a line on the cross section joining the points between the two places.
- If the line cuts through any part of the cross section, there is no intervisibility. lf it does not cut through, the two points are intervisible.
Worked Example
Study the following and determine if:
1. points A and B are intervisible.
2. points C and D are not intervisible.
Answer:
1. Points A and B are intervisible.
2. Points C and D are not intervisible.
Speed, Distance and Time
Speed is measured as distance travelled per unit of time.
Use the following formula to calculate the speed at which an object moves:
Speed = distance / time
The formula triangle below is a helpful tool to remember how to calculate the time it would take to travel a given distance at a given average speed.
Note: Always use both the orthophoto map and the topographical map when answering questions in your exam.
Shadows
- The direction of shadows can determine the time of day that the orthophoto was taken, while the length of the shadow can help to determine the time of the year.
Time of day
- Look at the shadows of trees or high buildings. lf the shadow lies in a southwesterly direction it indicates that the sun is still lying relatively far to the east. The photo was thus taken in the morning.
- If the shadow lies to the south the photo was taken at +12 noon.
- If the shadow lies to the southeast the photo was taken in the afternoon.
Time of the year
- Use the date on the photo (if provided).
- Look for signs of rainfall. (ls it a summer or winter rainfall area?)
Tone and texture
- If the cultivated lands are light in colour, then crops have been sown or are still very young, signifying winter time in a summer rainfall area or summer in a winter rainfall area.
- If the crops are darker in colour then they are fully grown, signifying the middle of summer in a summer rainfall area or the middle of winter in a winter rainfall area.
- Where plantations reveal regular ordered planting, these are obviously planted by man.
- Crops show a regular colour and texture and often follow the contours.
- Orchards have a dotted appearance and regularly spaced rough appearance.
- Vineyards also have a dotted appearance; smaller of texture than orchards with a clear linear form. With trellised vines it is possible to detect the connecting wires together with the dotted appearance.
Urban areas
CBD
- This is the part where the densest development and highest buildings occur.
- The street fattern is usualty a grid pattern,
Flats/Apartments
- These are usually just on the outskirts of the CBD adjacent to parking areas.
- Big and high buildings (not as dense as the CBD).
High income residential areas
- Houses of varying sizes, selectively positioned on large plots (occasionally with swimming pool and tennis court).
Low income residential areas
- Houses are uniform, neatly arranged in rows on very small plots. (Modern RDP-houses).
Informal settlements
- Shacks randomly positioned usually with no obvious street pattern.
Industries and factories
- Normally outside residential areas with access to road and railway facilities.
- Large plots with large single story buildings.
Schools
- Found in residential areas. Large buildings often with significant sports grounds.
Different features found on a topographical map are indicated by specific symbols. The key showing these symbols is found at the bottom of the map. Memorise the most important symbols to make interpretation of the map easier.
Relief
- Relief influences the land-use in an area.
- In the Southern Hemisphere the north-facing slopes are warmer than the southfacing slopes. People build houses and grow crops on north-facing slopes.
- Forestry often takes place on steeper slopes and crops are grown on gentle slopes.
Rivers and llYater
- Non-perennial rivers and the presence of dams indicate seasonal rainfall in an area.
- The drainage patterns of rivers depend on the features of the landscape. You may be asked to determine the drainage pattern, e.g. dendritic, trellis.
- The total length and number of rivers in an area gives an indication of the drainage density.
- To determine the direction in which a river flows:
- Rivers flow from the highest to the lowest point. Look at the spot heights and contours at various points along a river.
- The contour lines point upstream in a valley.
- Look at the tributaries joining the river. The direction in which they join the main river indicates the direction of flow.
- Wind pumps indicate seasonal rainfall. Often found in dry areas, e.g. sheep farming areas.
- Lrrigation systems, furrows and canals indicate lower rainfall in a region.
Agriculture
Commercial Farming
- Indications of commercial farming:
- Farm nafnes
- Well-developed infrastructure - road systems, electricity, railways
- Farm buildings, e.g. sheds, workers' homes
- Irrigation systems, dam
GIS involves the use of computers to make maps. These maps can be made to suit the individual user's own purposes as he or she can select the data that they want to use or analyse.
This information can be used in numerous fields and by people such as scientists, meteorologists, traffic controllers, town planners, environmentalists, businessmen, government departments, companies etc. Basically it can be used in any field that has a spatial component.
How can GIS help you?
- You decide what question you would like answered. The geographicaldata is then collected, put in the computer which analyses the information before giving you a visual representation of the data on a map.
Why use GIS?
- Computers make it easy to store large amounts of information, as information is digital compared to analogue (paper format).
- Once saved on the computer the data/material can be manipulated or changed.
- You do not have to print and store large paper maps.
- Being electronic, maps are easy to copy and send.
Components of GIS
GIS consists of five components:
- Computer hardware - computer, screen, keyboard, mouse, etc.
- Software - the programme that will allow you to enter information, edit, manipulate and put the information into map format.
- Geographical data (information) - it must be correct and accurate.
- Personnel - people operating the computers, entering the information and extracting the relevant information.
- Methods or application of the material - how the data is stored on the computer, e.g. raster or vector system.
Remote sensing
- This is the collection of information by a recording device that is not in direct contact with the area.
- Examples of remote sensing are observations taken from aircraft, satellites or an aerial photograph.
- Remote sensing is usefulfor collecting information from inaccessible and isolated places.
Data structures
Vector data
- The data/information shows geographic features in the form of points, lines or polygons. The information (e.9. coordinates)on each is stored separately in its own file.
- Point features - indicate small features, e.g. spot heights, buildings, trig beacons.
- Line features - indicate narrow linear features, e.g. rivers, roads.
- Polygon features - include cultivated land, built-up areas and dams.
Raster data
- Data is displayed as patterns within a grid system.
- The data is allocated in rows and columns on the map by the computer.
- The size of the cells will determine the accuracy of the map (pixels).
- The storage of raster data can use a lot of space on a computer system.
Data management
- Spatial data - data which describes the position of geographical features, e.g. towns, rivers, roads .'. its coordinates.
- Spatial resolution - how clear and easy the detail is to see. lt describes the size of the picture elements (pixels) that make up the image.
- Attribute data - information which describes or gives the characteristics of a geographical feature (object). These characteristics can be qualitative andlor quantitative. Usually shown in table format and include numbers, length, area etc.
- Buffering - to demarcate (mark off) an area around an object. lt is used for identifying areas surrounding geographical features.
- Querying - map features can be retrieved on the basis of attributes to se lectively retrieve information.
- Data layering - when different kinds of data (vector or raster data) are placed one on top of the other to produce a map for a particular area. Layers of data may include: vegetation, e.g. farrn land; contour lines; roads; power lines; built-up areas and rivers.
- Maps are a representation of the earth on a flat surface and are used to find direction, distance and area.
- When maps are drawn from the spherical earth onto a flat surface, the shape, distance, area and direction change; these are called distortions
Parallels: lines of latitude or horizontal lines (east - west)
Meridians: lines of longitude or vertical lines (north - south)
Mercator Projection
- ln 1569 Mercator invented a projection that got directions right but exaggerated areas towards the poles.
- lt was good for navigation but not for showing topography and countries to scale.
Transverse Mercator Projection
- In 1772 Lambert adapted Mercator's idea to show the spherical earth as if a cylinder of paper had been wrapped around it, touching it along a particular meridian (line of longitude).
- For this projection:
- Scale is constant along the central meridian - but increases to the west and east.
- Areas bemme exaggerated towards the eastern and western edges of the map.
- Shapes become distorted toward the western and eastern edges.
- Directions are confusing but are accurate at the central meridian.
- This projection is excellent for mapping countries that are long from north to south. lt can be used quite well for maps of Africa.
- For maps of smaller parts of the world, the projection was modified by having more than one central meridian.
Gauss Gonformal Projection
- Gauss developed Lambert's idea further.
- His calculations recognised the earth as not a perfect sphere but elliptical (slightly flattened at the poles).
- It was drawn on strips or zones that were only 20 wide.
- This projection is usefulfor mapping countries that are long from north to south.
- Since 1999, South Africa has used a coordinate system based on the Gauss conformal projection.