GCSE

Geography

Unit One: Water on the

Land.

Question 5.

Water on the Land Revision Checklist:

1. Read through your notes and tick off whether you have notes on the topics that have been covered. If not, you must

copy up ASAP.

2. For each topic you must provide a score to reflect how well you think you understand what you’ve covered. This will

help you focus your revision. Provide a score of 1-5.

3. Identify the topics you most need to revise – and do this as a priority!

1 = Don’t understand 3 = Understand some 5 = Understand all

Section of Topic Pages: Notes? Understanding?

RIVER PROCESSES:

Erosional processes: hydraulic action, abrasion, attrition, solution, vertical & lateral erosion.

Transportational processes: traction, saltation, suspension & solution.

Depositional processes: The reasons for deposition, the long profile, and the changing cross profile.

42/43

RIVER LANDFORMS:

Erosional landforms: waterfalls & gorges.

Erosional & depositional landforms: meanders and ox-bow lakes.

Depositional landforms: levees and floodplains.

44/45

DISCHARGE:

Factors affecting discharge: amount & type of rainfall, temperature, previous (antecedent) weather conditions, relief, rock type (i.e. permeable, impermeable, porous, pervious) and land use.

47

FLOODING:

Physical causes: prolonged rain, heavy rain, snowmelt, relief.

Human causes: deforestation, building construction..

Frequency: the frequency and location of flood events in the UK over the past 20 years.

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FLOODING CASE STUDIES:

Case study: of flooding in a rich part of the world.

Case study: of flooding in a poor part of the world.

NB: With a focus on the different effects and responses.

49

THE COSTS & BENEFITS OF DIFFERENT TYPES OF MANAGEMENT:

Hard engineering: dams & reservoirs and river straightening.

Soft engineering: flood warnings, preparation, flood plain zoning, ‘do nothing’.

50

WATER AS A RESOURCE:

The UK: The increasing demand for water, areas of deficit & areas of surplus, the need to transfer water.

Case study: A dam/reservoir to consider the resulting economic, social, and environmental issues and the need for sustainable water supplies.

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Rivers Revision Checklist and Guide

Weathering – 4 types – mechanical/physical/biological weathering – freeze thaw, chemical ( solution, carbonation), exfoliation

Erosion – Hydraulic Action, Abrasion, Attrition, Solution

Transportation – Traction, Saltation, Suspension, Solution

How a river changes from source to mouth – long profile and cross profile

Formation of waterfalls + gorges

Formation of meanders and ox-bow lakes

Formation of flood plains and deltas

Hydrological cycle

Storm hydrographs

Factors that affect discharge (river flow) – soil type, land-use etc

Causes of flooding – physical and human

Differences between floods in richer and poorer countries

Solutions to flooding – soft and hard engineering

Water supply where is there stress and surplus

Ways of managing water supply – reservoirs, water transfer, sustainable approaches

Rivers

http://www.bbc.co.uk/learningzone/clips/topics/secondary/geography/rivers.shtml

What are the key features of a Drainage Basin?

Factors affecting drainage basins:

Relief – the steeper the relief, the faster surface run-off of the rain

Rock type - Impermeable rock will cause more surface run-off whereas permeable (porous) rock will allow through flow and ground water flow. This slows the water down, increasing the lag time and reducing the peak discharge of the river.

Soil – the deeper the soil, the greater the infiltration

Vegetation - trees & shrubs provide interception & reduce surface run off

Land use - Urbanisation of an area means an increased amount of tarmac and drains therefore surface run-off will be increased.

Use of rivers by man - If water is extracted for industry, domestic use, or irrigation, this will reduce the amount of water flowing down the river all at once. Building a dam means that water can be stored and the river's water level can be regulated.

Drainage density - A large network of smaller streams to collect water more quickly will mean that the water will flow very quickly to the bottom of the river which could cause a dramatic increase in the water level over a short period of time.

Long and Cross Profiles of a text book river

The different types of 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

Long

Profile

Cross

Profile

The different types of erosion

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.

Deposition

Deposition is when a river loses its 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 Nile Delta.

A Feature of the Upper Stage

The formation of a Waterfall and Gorge

1. A waterfall is most commonly found in the upper stage of a river

2. A layer of resistant rock crosses the river channel and stops vertical (downward) erosion

3. The river cuts down when it meets less resistant rock

4. Hydraulic action and abrasion wear away a plunge pool at the foot of the falls and undercut the

resistant rock above

5. In time, gravity causes the overhanging resistant rock to collapse & the waterfall retreats upstream

leaving a gorge

6. An example of a waterfall is Niagara Falls - USA

A Feature of the Middle Stage

The formation of a meander

The Long profile of a meander

Cross-section of a meander

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.

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 to

form a slip-off slope.

The formation of an Oxbow Lake

1. Over time the meander becomes tighter with its neck narrowing.

2. Eventually the neck of the meander becomes very narrow.

3. The river eventually breaks through, often during a period of flood when the river has a higher discharge and

more energy.

4. The meander loop is cut-off from the main channel. The cut-off loop is called an oxbow lake. In time

deposition occurs and dams up the oxbow lake, which becomes colonised with plants and eventually dries

up leaving a meander scar

Features of the Lower Stage

The lower stage of the river is characterised by;

The river has a high volume and a large discharge

The channel is now deep and wide and the landscape around it is flat.

Energy levels are low and deposition takes place.

The river now has a wide floodplain.

Floodplains a good place for agriculture.

A build-up of sediment on the banks of a river can create levees which raise the river bank and the level of

the water in the channel above the floodplain

The formation of Levees

Levees are depositional features and are formed when rivers flood repeatedly

Larger sediments are deposited along the banks, while finer sediments are deposited along the floodplain

When the river is not in flood, deposition occurs along the river bed

Successive periods of flooding and normal flow raise the level of both the levees and the river bed. This

results in the water level of the channel being higher than the ground level of the surrounding floodplain

As a result, the water table on the floodplain rises and leads to marshy land

The formation of a Delta

A Fan-Shaped Delta - 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.

The Niger Delta

For a delta to form:

The river needs to have travelled a considerable distance in order to collect sufficient sediment

The river needs to join a shallow sea with weak currents and small tides

As the River currents meet the gentle currents of the sea, the currents cancel each other out, causing the

flow of the water to come to a standstill and for material to be deposited causing deltas to form.

The small channels which take water to the sea through the deposited material are known as distributaries

E.g. River Nile Delta in Egypt

The importance of Deltas

Deltas are often densely populated due to fertile soil.

Rising sea level is posing a problem as it causing increasing salinity and reducing fertility

NB. there are no deltas in the UK as UK rivers do not meet any of the above criteria

The Water Cycle

Evaporation

Condensation

Surface Run Off

Ground Water Flow

PrecipitationTranspiration

Water Cycle

L.O. To understand why the amount of water fluctuates in a river

Throughflow

Infiltration

Percolation

1

2

3

4

Output

Input

Flow (transfer) Storage

1. Interception

2. Surface storage

3. Soil moisture

4. Groundwater

Storm Hydrographs

Interpreting Storm Hydrographs

Impermeable

Heavy thunderstorm

Urban Area

Steep river basin

Bare ground

Moist soil

Small catchment area

High drainage density

Permeable

Light drizzle

Farmland

Shallow river basin

Wooded area

Dry soil

Large catchment area

Low drainage density

The Causes of flooding

A flood occurs when a river bursts its banks and the water spills onto the floodplain.

The following factors may encourage flooding:

PHYSICAL FACTORS HUMAN FACTORS

Heavy or prolonged rainfall

Snowmelt

Steep-sided drainage basin

High density drainage basin

Impermeable rock

Urbanisation

Deforestation

Failure to manage rivers effectively

e.g. lack of dredging

SHORT TERM EFFECTS LONG TERM EFFECTS

Positive effects

Flooding deposits fine silt (alluvium) onto the

floodplain, making it very fertile and excellent

for agriculture ( Bangladesh)

Construction companies derive business from

flood damage

Negative Effects

Destruction of property

Loss of crops & seed for following year (Sri

Lanka 2011)

Damage to infrastructure – roads, bridges, rail,

power etc.

Loss of life

Pollution of drinking water

Loss of shelter

Damage to local economy

Higher insurance premiums in richer countries

Flood management schemes

Migration from increasingly flood prone areas

in poorer countries into shanty towns

Spread of disease

Cycle of poverty enforced

Increased frequency of flooding

General Rules: The bigger the flood, the less frequently they occur

The poorer the country, the greater the impact

• Flooding in countries like Bangladesh becoming more severe due to sea level rise & climate change

• Serious flood incidents reported worldwide with greater frequency – so far in 2011 there were significant

floods in – Sri Lanka, Queensland, Brazil

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.

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.

Levees Strengthening levees along banks of rivers (Mississippi, USA)

Barrage Used during periods of peak flow and high tides, barrages open and close like gates holding back flood water. (The Tees barrage)

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.

Floodplain zoning / 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 poorer counrties

Dredging The river channel may be deepened allowing it to carry more water. The sideiment can be spread on local farmalnd or used to build up Levees (Cuckmere

River, East Susex)

Interest Groups and their views towards River Management:

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 electric 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.

2004 BANGLADESH FLOODS

A case study of floods & flood management in a poorer country

LOCATION:

is one of the world's most densely populated countries!

has a population of 125 million inhabitants

is one of the poorest countries in the world with a GNP of $330 per head

has three of the world's most powerful rivers passing through its country - The Ganges, the Meghna & the Brahmaputra

contains virtually no raw materials or rock

experiences floods and tropical storms every year – serious floods in 1998, 2004 & 2007(Cyclone Sidr) – interval between severe floods getting shorter

threatened by sea-level rise

CAUSES OF FLOODING IN 2004

The Physical Causes of the Floods

70% of country is less than 1m above sea level

Over 700 waterways in the country

10% of the land is fresh water

It lies on the Ganges-Brahamaputra floodplain

increased surface run off & silt in rivers due to farming & deforestation

Rising sea levels due to global warming – some areas flooded for up to 9 months a year

Monsoon climate

Tropical cyclones from the Bay of Bengal – Cyclone Sidr 2007

Summer snow-melt in the Himalayas feeds the Ganges

2004 saw the heaviest rainfall in 50 years – 35cm on 13 / 09 / 2004he main cause was the above average & long period of heavy rain which caused all 3 rivers to have their peak flow at the same time!!!

Human Causes of the Floods

Deforestation in Nepal and the Himalayas – 50% lost since 1950 = increases run off and adds to deposition and flooding downstream

Urbanisation of the floodplain has increased magnitude & frequency of floods

the building of dams in India has increased the problem of sedimentation in Bangladesh

Global warming is blamed for sea level rise, increased snow melt & increased rainfall in the region

Poorly maintained embankments (levees) leak & collapse in times of high discharge

Ineffective warning systems in rural areas

SHORT TERM EFFECTS

Over 60% of the land area was flooded

LONG TERM EFFECTS

Loss of habitable land increases population density

40% of Dhaka flooded Over 600 people were killed 30 million homeless out total pop. of

140 million There was a serious shortage of

drinking water & dry food Diseases spread such as bronchitus

and cholera/diarrhoea – 100,000 diarrhoea cases in Dhaka

As the waters receded - it left fields of rotting crops, wrecked roads and bridges and destroyed villages

2 million tonnes of rice was destroyed + cash crops like jute & sugar

1/2 million cattle and poultry were lost

Increased rural-urban migration = growth of shanty towns

Economy suffers = increasing reliance on foreign aid

Cycle of poverty continues

Poorest most affected

IMMEDIATE RESPONSES TO 2004 FLOOD

Government asked for international help

UN appeal for $74 million -received only 20% by Sept

Water Aid sent water purification tablets & posters showing sanitation risks

LONG TERM RESPONSES - FLOOD MANAGEMENT: In 1987 the government of Bangladesh & the World Bank began working with a number of international agencies to produce a Flood Action Plan. SHORT TERM FLOOD MANAGEMENT

Rescue boats

Emergency supplies for food, water, tents and medicines in warehouses

Fodder for livestock

Repair and rebuild houses, as well as services - sewage etc

LONG TERM MANAGEMENT –Flood Action Plan

Build 7 large dams in Bangladesh to store excess water $30-$40 Billion & 40 yrs to complete

Build 5000 flood shelters to

Build 3500km of embankment - 7 metres high at a cost of $6 billion to reduce flooding Create 15 flood water storage areas

Reduce Deforestation in Nepal & Himalayas

effective Flood Warning Scheme

River Flooding in Boscastle

A case study of floods & flood management in a richer country

Boscastle – Flash Floods 2004

Where: Boscastle is a small village in Cornwall What: The village was hit by an extreme thunderstorm, which produced 200mm of rainfall in 5 hours, an amount far exceeding the monthly average of 75mm. The rainfall poured down the steep valley slopes, swelling the normally small River Valency, causing it to burst its banks. The area which the River drains is heavily tarmaced, with open countryside covered with few trees. The rock in the area is slate, which is impermeable, causing the water to runoff quickly down the steep slopes. When: This all happened in the afternoon of Monday 16 August 2004

Effects:

58 buildings were flooded

25 businesses properties were destroyed

Businesses closed resulting in a loss of income

84 wrecked cars

32 cars were lost, after being washed out to sea

Several roads and bridges were damaged

Local people and tourists were left traumatised

Trees were uplifted

Five people had to be airlifted to safety

Nobody was killed

The cost of repair exceeded £15 million

Responses:

People fled the swelling river

An RAF helicopter was deployed to airlift people to safety

Police were deployed to direct people to safety and try to oversee a safe evacuation of the area

People without homes were put up in emergency shelters away from Boscastle

Eventually people were relocated to temporary housing

The village was cleared up with debris removed and cars pulled from the harbour.

The roads, bridges and property that was damaged needed to be restored, using traditional building techniques in many cases

Flood defences were reviewed and new defences installed to avoid a repeat of the flood event.

UK Water Management

• Rainfall varies over time and place as does water stress

• Areas of high water stress have a deficit while those of low stress have a surplus

• High water stress = insufficient rainfall on a permanent basis e.g. Drought

• Low water stress = abundant rainfall, small population

• We use between 127 & 177 litres / day

Demand for water

Expected to rise due to:

1. UK population increase – 60+million today, 66million by 2031

2. Increased use of dishwashers etc.

3. Demand for out of season foodstuffs

UK Water Stress

Sustainable Water Use

• Conservation strategy:

Houses & appliances designed to be more water efficient

Use of grey water – rainwater etc

Smaller cisterns

Water meters

Showers as opposed to baths

Where does our water come from?

Reservoirs – Arlington on the River Cuckmere, East Sussex

natural lakes,

rivers – London gets its water from the Thames

aquifers - an aquifer is an underground layer of permeable rock, gravel or sand which is soaked with water.

Eg. Willingdon from Downs aquifer

Water transfer - traditional solution to supply water to areas of high stress from areas of surplus eg The

Kielder reservoir in Northumberland was built to supply Tyneside, Wearside & Teeside. In 2004 gov decided

that such projects were too expensive & to use like Arlington

Reservoirs

BENEFITS DRAWBACKS

• Can be used as part of flood management strategy

• Create HEP • A leisure attraction • A source of drinking water / irrigation in drier

climates

• Expensive to build • Require loss of settlements & / agricultural land • Affects the flow within the river &

sedimentation • Can raise the local water table