GCSE Geography Revision Guide To waters and rivers

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Water and rivers Quiz

Water and rivers Background to rivers

River profile

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River processe

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River landform

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River flooding and management

issues

Water usage

Too little water - drought

Background to rivers

• The hydrological cycle:The hydrological cycle is also known as the water cycle.Seas and oceans contain 97 per cent of the world's water, and ice holds 2 per cent. That leaves just 1 per cent of the world's water as fresh water on land or in the air. This water is recycled again and again through the process of evaporation, condensation and water transfers such as surface run-off.Terminology for the study of rivers• Drainage basin - the area of land drained by a river. • Catchment area - the area within the drainage basin.• Watershed - the edge of highland surrounding a drainage basin. It

marks the boundary between two drainage basins.• Source - The beginning or start of a river.• Confluence - the point at which two rivers or streams join.• Tributary - a stream or smaller river which joins a larger stream or river.• Mouth - the point where the river comes to the end, usually when

entering a sea.

River profilesCross profiles• Near the source of a river there is more vertical erosion as the river flows

downhill, using its energy to overcome friction (A). As a result the channels are narrow and shallow and may contain large boulders and angular fragments eroded and weathered from the steep valley sides. The sediment in the river creates turbulence and friction.

• As the river approaches the mouth, velocity and energy increase due to increased discharge. The river performs more lateral erosion making the channel wider, and smoother (B) and (C). As a result there is less turbulence and friction, making the flow of water more efficient.

Long profiles• A river changes shape as it flows from its source (where a river starts) to its

mouth (where a river flows into a sea or lake). The shape of both the long profile (a slice through the river from source to mouth) and the cross profile (a slice across the river) changes.

• The source of a river is often - but not always - in an upland area. Near the source, a river flows over steep slopes with an uneven surface. It often flows over a series of waterfalls and rapids. Highland areas are usually composed of hard igneous rocks, which are ideal for forming such features.

• As a river flows down steep slopes the water performs vertical erosion. This form of erosion cuts down towards the river bed and carves out steep-sided V-shaped valleys.

• As the river flows towards the mouth, the slopes become less steep. Eventually the river will flow over flat land as it approaches the sea.

• The discharge (amount of water flowing) will increase as the river approaches the sea.

River processesErosionErosion involves the wearing away of rock and soil found along the river bed and banks. Erosion also involves the breaking down of the rock particles being carried downstream by the river.The four main forms of river 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.• Abrasion - rocks carried along by the river wear down the river bed and banks.• Attrition - rocks being carried by the river smash together and break into smaller, smoother and rounder particles.• Solution - soluble particles are dissolved into the river.

TransportRivers pick up and carry material as they flow downstream. The four different river transport processes• Solution - minerals are dissolved in the water and carried along in solution.• Suspension - fine light material is carried along in the water.• Saltation - small pebbles and stones are bounced along the river bed.• Traction - large boulders and rocks are rolled along the river bed.Rivers need energy to transport material, and levels of energy change as the river moves from source to mouth.• When energy levels are very high, large rocks and boulders can be transported. Energy levels are usually higher near a

river's source, when its course is steep and its valley narrow. Energy levels rise even higher in times of flood.• When energy levels are low, only small particles can be transported (if any). Energy levels are lowest when velocity

drops as a river enters a lake or sea (at the mouth).

DepositionWhen a river loses energy, it will drop or deposit some of the material it is carrying.• Deposition may take place when a river enters an area of shallow water or when the volume of water decreases - for

example, after a flood or during times of drought.• Deposition is common towards the end of a river's journey, at the mouth.• Deposition at the mouth of a river can form deltas - for example, the Mississippi Delta.

River flooding and management issues

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.

The following factors may encourage flooding:• 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 (i.e. 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.

• Flood management techniques include river engineering, afforestation and planning controls to restrict urban development on floodplains.

The impact of flooding• Floods can cause damage to homes and possessions as well as disruption to communications. However,

flooding can also have positive impacts on an area.• Flooding deposits fine silt (alluvium) onto the floodplain, making it very fertile and excellent for

agriculture. People living on or near floodplains may rely upon regular flooding to help support their farming and therefore provide food.

• LEDCs tend to be affected more than MEDCs by the effects of flooding. This is partly because LEDCs have more farms, and farming communities are attracted to fertile flood plains. LEDCs often do not have the resources to prevent flooding or deal with the aftermath of flooding.

PTO

River flooding and management issues

River management• Steps can be taken to manage flooding. Often these steps involve trying to lengthen the amount of time it takes for water to reach the river

channel, thereby increasing the lag time. Flood management techniques can be divided into hard- and soft-engineering options.• Hard options tend to be more expensive and have a greater impact on the river and the surrounding landscape.• Soft options are more ecologically sensitive. The tables summarise the main flood management techniques.Hard-engineering options:• 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.Soft-engineering options:• 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 (also called ecological 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 LEDCs.Different interest groups have different views about flood management techniques:• 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.

Water usageWhy are there so many differences in the way water is used?Agriculture• In MEDCs irrigation is mechanised. Sprinklers or timed irrigation feeds are used. Where agriculture is common,

vast amounts of water can be released at a touch of a button.• In LEDCs irrigation channels are prone to loosing water through evaporation.Industrial use• Cow dung soap production, India• many women mixing ingredients to make cow dung soap in India.• Industries in MEDCs can be on a large scale, and so demand a lot of water. Corus Steelworks in South Wales is

an example of an industry which needs a large water supply.• LEDCs have smaller scale cottage industries. They demand less water in the production of items. However as

more multinational companies locate in LEDCs there will be more demand on water. For example in India Coca-Cola uses over a million litres of water a day to produce drinks.

Domestic water use• In MEDCs there are a lot of facilities which demand water use. For example showers, baths, washing machines

and swimming pools.• In LEDCs many people do not have access to piped water and so use it more sparingly. Water may be brought

to the home from a well or stream.As a country becomes more wealthy, there will be an increase in its demand for water. Higher levels of industrialisation and more domestic goods such as washing machines all lead to an increase in demand for water. With greater wealth there is also more demand for spas, golf courses and even baths and showers.

Too little water - droughtDroughts occur when a long period of abnormally dry weather leads to a severe water shortage. Droughts are also often caused by the activity of humans and can have devastating effects.Human activities causing drought• Human activities that can help trigger droughts include:• Widespread cutting down of trees for fuel reduces the soil’s ability to hold water - drying

out the ground, triggering desertification and leading to drought.• Constructing a dam on a large river may help provide electricity and water to irrigate

farmland near the reservoir. However, it may also cause drought downstream by severely reducing the flow of water.

Effects of drought• Droughts endanger lives and livelihoods through thirst, hunger (due to crops dying from

lack of water) and the spread of disease.• Millions of people died in the 20th century due to severe drought and famines. One of the

worst hit areas was the Sahel region of Africa, which covers parts of Eritrea, Ethiopia and the Sudan.

• Droughts and famines can have other geographical impacts. If drought forces people to migrate to a new home it could put pressure on resources in neighbouring countries.

• Droughts can have a severe impact on MEDCs as well as LEDCs. Droughts have caused deaths in Europe in recent years - especially amongst the elderly. In the UK in summer 2006, there were hose-pipe bans and campaigns to make people save water.

River landformsUpper-course river features include steep-sided V-shaped valleys, interlocking spurs, rapids, waterfalls and gorges.• Middle-course river features include wider,

shallower valleys, meanders, and oxbow lakes.• Lower-course river features include wide flat-

bottomed valleys, floodplains and deltas.Upper course features• 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. P.T.O

River landforms Middle course features• Meanders• In the middle course the river has more energy and a high volume of

water. The gradient here is gentle and lateral (sideways) erosion has widened the river channel. The river channel has also deepened. A larger river channel means there is less friction, so the water flows faster:

• As the river erodes laterally, to the right side then the left side, it forms large bends, and then horseshoe-like loops called meanders.

• The formation of meanders is due to both deposition and erosion and 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.

• Over time the horseshoe become tighter, until the ends become very close together. As the river breaks through, e.g. 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.

P.T.O

River landforms Lower course features• 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.

Floodplains• 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• 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. There are three main types of delta, named after the shape they create:

Type of delta Example

Arcuate or fan-shaped - the land around the river mouth arches out into the sea and the river splits many times on the way to the sea, creating a fan effect.

Cuspate - the land around the mouth of the river juts out arrow-like into the sea.

Bird's foot - the river splits on the way to the sea, each part of the river juts out into the sea, rather like a bird's foot.

Quiz

Quiz 1

What is a Drainage basin?

A Drainage basin is the area of land drained by a river.

A Drainage basin is when the river drains into a sea.

A Drainage basin is when a river drains into a reservoir.

Quiz 2

What is a river Source ?

A river Source is the beginning or start of a river.

A river source is the river leading to the sea.

A river source is the end of the river.

Quiz 3

What are the four main forms of river erosion?

The four main forms of river erosion are Hydraulic action, Abrasion, Attrition and Solution.

The four main forms of river erosion are rain, storms, snow and ice.

The four main forms of river erosion are Solution, Suspension, Saltation and Traction.

Quiz 4 What are the four different river transport processes?

The four different river transport processes are Solution, Suspension, Saltation and Traction.

The four different river transport processes are Hydraulic action, Abrasion, Attrition and Solution.

The four different river types processes are water, river currents, fast flow and slow flow.

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