Geography: Rivers

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  • Created by: CJame09
  • Created on: 17-04-14 13:24

River features

  • The upper part is usually the steepest.
  • The source is the starting point of the river, it is the highest point.
  • The watershed is an imaginary line that separates one drainage basin from another.
  • The drainage basin is the area from which rainwater drains into the river.
  • Small rivers join the main one. They are called tributaries.
  • The point where two rivers join is called a confluence.
  • All rivers flow down towards sea level, even if they don’t reach the sea.
  • The mouth of the river is where it flows into a lake, sea or ocean. It is the lowest point.
  • The slope flattens out in the lower part.
  • Land that gets flooded when the river overflows is called the flood plain.
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Weathering

  •  Physical weather: Freeze-thaw weathering or frost action is when water gets into cracks in rocks. When the temperature falls below freezing, the water will expand as it turns to ice. This expansion outs pressure on the rock around it and fragments of rock may break off. It’s common in highland areas where temperatures are above freezing in the day and below freezing during the night.
  • Chemical weathering: Rainwater contains weak acids that can react with certain rock types. The carbonates in limestone are dissolved by these weak acids and this causes the rock to break down or disintegrate. This can be seen on limestone statues.
  • Biological weathering: This is the action of plants and animals on the land. Seeds that fall into cracks in rocks will start ti grow when moisture is present. The roots of the young plant force their way into cracks and in time can break up rocks. Burrowing animals, such as rabbits, can also be responsible for the further break up of rocks.
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Mass movement

Slumping: This is common on the banks of rivers. It involves a large area of land moving down a slope. Due to the nature of the slip it leaves behind a curved surface. It's common on clay banks. During dry weather the clay contracts and cracks; when it rains, the water runs into the cracks and is absorbed until the rock becomes saturated. This weakens the rock and, due to the pull of gravity, it slips down the slops on its slip plane. Eventually the river gets wider. It leads to more material in the river and damages river dwelling animals' habitats. It can also block the river and cause flooding.

Soil creep: This is the slowest downhill movement of soil. Gravity will pull the water that is contained in the soil down a slope. The soil will move downhill with the water. As this happens very slowly, it's not possible to see it happening, although it does move more quickly after heavy rainfall. The slope may appear rippled, these ripples are known as terracettes.

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Erosion

  • Hydraulic action: the force of the river against the banks can cause air to be trapped in cracks and crevices. The pressure weakens the banks and gradually wears it away. The water gets into cracks in the rock, it compresses the air in the cracks and this puts more pressure on the cracks and pieces of rock may break off as a result.
  • Abrasion: rocks carried along by the river wear down the river bed and banks as they are thrown against the river bank with force.
  • Attrition: rocks being carried by the river smash together and break into smaller, smoother and rounder particles. In the upper course of a river rocks continually roll around and knock into each other. They chip away at each other until smooth pebbles or sand are formed.
  • Solution: soluble particles are dissolved into the river.It is a chemical reaction between certain rock types and the river water. Particularly evident on limestone.
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Upper course

Upper-course river features include steep-sided V-shaped valleys, interlocking spurs, rapids, waterfalls and gorges.

As the river moves through the upper course it cuts downwards. The gradient here is steep and the river channel is narrow. Vertical erosion in this highland part of the river helps to create steep-sided V-shaped valleys, interlocking spurs, rapids, waterfalls and gorges.

  • As the river erodes the landscape in the upper course, it winds and bends to avoid areas of hard rock. This creates interlocking spurs, which look a bit like the interlocking parts of a zip.
  • When a river runs over alternating layers of hard and soft rock, rapids and waterfalls may form.
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Waterfalls

The formation of waterfalls and rapids (http://www.bbc.co.uk/schools/gcsebitesize/geography/images/riv_009.gif)

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Middle course

Middle-course river features include wider, shallower valleys, meanders, and oxbow lakes.

The river has more energy and a high volume of water. The gradient is gentle and lateral erosion widens the river channel. The river channel has deepened. A larger river channel means there is less friction, so the water flows faster:

  • As the river erodes laterally it forms large bends, then horseshoe-like loops called meanders.
  • The formation of meanders is due to both deposition and erosion. Meanders gradually migrate downstream.
  • The force of the water erodes and undercuts the river bank on the outside of the bend where water flow has most energy due to decreased friction.
  • On the inside of the bend, where the river flow is slower, material is deposited, as there is more friction.
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Oxbow lakes

Over time the horseshoe become tighter, until the ends become very close together. As the river breaks through, eg during a flood when the river has a higher discharge and more energy, and the ends join, the loop is cut-off from the main channel. The cut-off loop is called an oxbow lake.

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Diagram

(http://www.bbc.co.uk/bitesize/standard/geography/images/g514_b.gif)

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Lower course

Lower-course river features include wide flat-bottomed valleys, floodplains and deltas.

  • In the lower course, the river has a high volume and a large discharge. The river channel is now deep and wide and the landscape around it is flat. However, as a river reaches the end of its journey, energy levels are low and deposition takes place.
  • The river now has a wide floodplain. A floodplain is the area around a river that is covered in times of flood. A floodplain is a very fertile area due to the rich alluvium deposited by floodwaters. This makes floodplains a good place for agriculture. A build up of alluvium on the banks of a river can create levees, which raise the river bank.
  • Deltas are found at the mouth of large rivers - for example, the Mississippi. A delta is formed when the river deposits its material faster than the sea can remove it.
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Causes of flooding

A flood occurs when a river bursts its banks and the water spills onto the floodplain. Flooding tends to be caused by heavy rain: the faster the rainwater reaches the river channel, the more likely it is to flood. The nature of the landscape around a river will influence how quickly rainwater reaches the channel.

  • A steep-sided channel - a river channel surrounded by steep slopes causes fast surface run-off.
  • A lack of vegetation or woodland - trees and plants intercept precipitation (ie they catch or drink water). If there is little vegetation in the drainage basin then surface run-off will be high.
  • A drainage basin, consisting of mainly impermeable rock - this will mean that water cannot percolate through the rock layer, and so will run faster over the surface.
  • A drainage basin in an urban area - these consist largely of impermeable concrete, which encourages overland flow. Drains and sewers take water quickly and directly to the river channel. Houses with sloping roofs further increase the amount of run-off.
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Soft engineering

Afforestation: Trees are planted near to the river. This means greater interception of rainwater and lower river discharge. This is a relatively low cost option, which enhances the environmental quality of the drainage basin.

Managed flooding: The river is allowed to flood naturally in places, to prevent flooding in other areas - for example, near settlements.

Planning: Local authorities and the national government introduce policies to control urban development close to or on the floodplain. This reduces the chance of flooding and the risk of damage to property. There can be resistance to development restrictions in areas where there is a shortage of housing. Enforcing planning regulations and controls may be harder in LICs.

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Home » GCSE Revision » Geography » River Landscapes » Managing Rivers and Flooding

Managing Rivers and Flooding

Quick revise

Short Term

  • Sand bags - to prevent further damage to property

Medium Term

  • Afforestation - trees are planted to absorb water (additional information)
  • Managed flooding - the river is allowed to flood in some places to avoid destruction close to large settlements
  • Planning - governments and local councils implement plans to help prevent damage to property in future

Long Term

  • Dam building - dams are built in order to control the amount of discharge released
  • River engineering - the river channel may be widened or deepened to allow water to flow more quickly

- See more at: http://www.revisionworld.com/gcse-revision/geography/river-landscapes/managing-rivers-and-flooding#sthash.Sy9x2btj.dpuf
Read more at http://www.revisionworld.com/gcse-revision/geography/river-landscapes/managing-rivers-and-flooding#ZE77VEEdRYWLVY

You are here

Home » GCSE Revision » Geography » River Landscapes » Managing Rivers and Flooding

Managing Rivers and Flooding

Quick revise

Short Term

  • Sand bags - to prevent further damage to property

Medium Term

  • Afforestation - trees are planted to absorb water (additional information)
  • Managed flooding - the river is allowed to flood in some places to avoid destruction close to large settlements
  • Planning - governments and local councils implement plans to help prevent damage to property in future

Long Term

  • Dam building - dams are built in order to control the amount of discharge released
  • River engineering - the river channel may be widened or deepened to allow water to flow more quickly

- See more at: http://www.revisionworld.com/gcse-revision/geography/river-landscapes/managing-rivers-and-flooding#sthash.Sy9x2btj.dpuf
Read more at http://www.revisionworld.com/gcse-revision/geography/river-landscapes/managing-rivers-and-flooding#ZE77VEEdRYWLVYfT.99

You are here

Home » GCSE Revision » Geography » River Landscapes » Managing Rivers and Flooding

Managing Rivers and Flooding

Quick revise

Short Term

  • Sand bags - to prevent further damage to property

Medium Term

  • Afforestation - trees are planted to absorb water (additional information)
  • Managed flooding - the river is allowed to flood in some places to avoid destruction close to large settlements
  • Planning - governments and local councils implement plans to help prevent damage to property in future

Long Term

  • Dam building - dams are built in order to control the amount of discharge released
  • River engineering - the river channel may be widened or deepened to allow water to flow more quickly

- See more at: http://www.revisionworld.com/gcse-revision/geography/river-landscapes/managing-rivers-and-flooding#sthash.Sy9x2btj.dpuf
Read more at http://www.revisionworld.com/gcse-revision/geography/river-landscapes/managing-rivers-and-flooding#ZE77VEEdRYWLVYfT.99

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Hard engineering

Dam construction:

  • Dams are often built along the course of a river in order to control the amount of discharge. Water is held back by the dam and released in a controlled way. This controls flooding.
  • Water is usually stored in a reservoir behind the dam. This water can then be used to generate hydroelectric power or for recreation purposes.
  • Building a dam can be very expensive.
  • Sediment is often trapped behind the wall of the dam, leading to erosion further downstream.
  • Settlements and agricultural land may be lost when the river valley is flooded to form a reservoir.

River engineering:

  • The river channel may be widened or deepened allowing it to carry more water. A river channel may be straightened so that water can travel faster along the course. The channel course of the river can also be altered, diverting floodwaters away from settlements.
  • Altering the river channel may lead to a greater risk of flooding downstream, as the water is carried there faster.
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Views

  • Governments and developers often favour large hard engineering options, such as dam building. Building a dam and a reservoir can generate income. Profits can be made from generating electricity or leisure revenue.
  • Environmental groups and local residents often prefer softer options, such as planting trees. Soft options cause little damage to the environment and do not involve the resettlement of communities.
  • Effective flood management strategies should be economically, environmentally and socially sustainable. Sustainable strategies allow management without compromising the needs of future generations.
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Impacts of flooding

  • Buildings and property washed away or damaged by water and mud
  • People and Animals can drown in fast flowing water
  • Transport can be interrupted - airports can be closed, road and rail networks submerged and river traffic closed down
  • Crops ruined and farmland saturated for months afterwards preventing new planting
  • Sewage contaminates drinking water supply and causes diseases such as cholera & typhoid
  • Economic impacts on individuals, industries, insurance companies and governments
  • Positive impacts of flooding include - deposition of fertile silt, washing away of pollutants and repleneshing groundwater
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