Meanders and oxbow lakes - Pearson...
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6 The natural environment (Section A) Downstream changes in river channels and landforms: Lowland landforms Lowland landforms are associated with deposition because here the river is closer to sea level. The river’s long profile is gentler and smoother. Meanders and oxbow lakes Meanders are formed by erosion and deposition. Lateral erosion is more significant here because the river is close to sea level. On the outside of the bend, lateral erosion forms a river cliff. On the inside of the bend the water flow is slower and deposition forms a slip-off slope. Figure 1.7 shows this process and how oxbow lakes can form. fastest flow on outside bends slip-off slope river cliff much larger meander fastest water flow here river cliff sealed by deposits narrow neck of land river now flows straight steep river bank x y deposits of sand and silt in channel outside bend eroded more sharply by river current oxbow lake cut off deposited material on the slip-off slope Channel cross-section x–y x y C B A slower flow on inside bends Figure 1.7 Formation of meanders and oxbow lakes Floodplains and levees When a river floods, the water rapidly loses velocity as it spreads over the land, so it deposits its load. Over thousands of years this forms a floodplain. Lateral erosion on the outside banks of meanders helps to widen the floodplain. The flooding river drops its heaviest load (the biggest particles) first and this gradually forms banks along the side of the river. These are levees. silt or alluvium levee levee river in flood layers of deposits build up in great thickness the river’s energy is reduced when it leaves the channel Figure 1.8 Formation of floodplains and levees Make sure you know how the following lowland landforms are formed: meanders, oxbow lakes, floodplains and levees. TOP TIP ✓ ✓ Practise drawing annotated diagrams to show how these lowland landforms are formed. PRACTICAL SKILLS Make sure you know a case study of the physical features of a drainage basin. You should know physical characteristics of the drainage basin and how they affect the river regime. Make sure you know how the river channel changes downstream and that you can describe landforms along the river’s course. TOP TIP ✓ ✓
Transcript of Meanders and oxbow lakes - Pearson...
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Downstream changes in river channels and landforms: Lowland landformsLowland landforms are associated with deposition because here the river is closer to sea level. The river’s long profi le is gentler and smoother.
Meanders and oxbow lakes
Meanders are formed by erosion and deposition. Lateral erosion is more signifi cant here because the river is close to sea level. On the outside of the bend, lateral erosion forms a river cliff. On the inside of the bend the water fl ow is slower and deposition forms a slip-off slope. Figure 1.7 shows this process and how oxbow lakes can form.
fastest�ow onoutsidebends
slip-o� slope
river cli� muchlargermeander
fastest water�ow here
rivercli�
sealed bydeposits
narrow neckof land
river now�ows straight
steep river bank
x
y
deposits of sandand silt in channel
outside benderodedmore sharplyby river current
oxbowlake
cut o�
deposited materialon the slip-o� slope
Channel cross-section x–y
x y
CBA
slower�ow oninsidebends
Figure 1.7 Formation of meanders and oxbow lakes
Floodplains and levees
When a river fl oods, the water rapidly loses velocity as it spreads over the land, so it deposits its load. Over thousands of years this forms a fl oodplain. Lateral erosion on the outside banks of meanders helps to widen the fl oodplain.
The fl ooding river drops its heaviest load (the biggest particles) fi rst and this gradually forms banks along the side of the river. These are levees.
silt or alluvium
leveelevee
river in �ood
layers of deposits build up in great thickness
the river’s energy is reduced when itleaves the channel
Figure 1.8 Formation of fl oodplains and levees
Make sure you know how the following lowland landforms are formed: meanders, oxbow lakes, fl oodplains and levees.
TOP TIP ✓✓
Practise drawing annotated diagrams to show how these lowland landforms are formed.
PRACTICAL SKILLS
Make sure you know a case study of the physical features of a drainage basin. You should know physical characteristics of the drainage basin and how they affect the river regime. Make sure you know how the river channel changes downstream and that you can describe landforms along the river’s course.
TOP TIP ✓✓
Geog_Rev_Guide-Book.indb 6 14/01/2013 11:38
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Water uses, demand and supplyWater is essential for life and is used for many purposes: agriculture, industry, hygiene and sanitation, and leisure. Figure 1.9 shows how the proportion of water that is used in homes, in industry and in agriculture changes between countries. Ninety per cent of people in Malawi farm land, so water for agriculture is very important there. Less than 1 per cent of Americans work in agriculture, but the USA uses a huge amount of water for irrigation of farmland. In the UK, industry uses most water: the majority of this is in energy production – water is used as a coolant in power stations.
Water-defi cit areas are places where water demand exceeds water supply. Water-surplus areas are places where there is more water available than there is demand for it.
Global demand for water has doubled every 20 years for the last 100 years.
Waterde�cit
Watersurplus
Figure 1.10 Areas of water defi cit and areas of water surplus
Areas of water surplus are
typically remote, mountainous
areas with high rainfall and small
populations.
Areas of water de� cit may be
areas that receive little precipitation
all year.
Areas of water de� cit are also
often areas that have large
populations and rising
development (e.g. India).
UK USA Malawi
Agriculture
Industry Domestic
2.9%
21.7%
75.4%
Agriculture Industry
Domestic
9%
22.3%
68.7%
Agriculture Industry
Domestic
5%
14.9%
80.1%
The increase in demand comes from population growth and development. As countries develop:
• more water is used in industry (e.g. for power generation)
• more water is used in agriculture to feed growing populations
• more water is used as standards of living improve: fl ush toilets, showers, washing machines, etc.
Water can be transported from areas of surplus to areas of defi cit, e.g. in pipelines or tankers. But water is heavy and expensive to transport.
Make sure you know a case study of the rising demand for water in one country. The UK is an interesting example because population growth is happening fastest in the south and east of the country, which receives the least precipitation, while the areas of highest water supply are in the north and west.
TOP TIP ✓✓
Figure 1.9 Water use in three different countries
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