theme 1 - case study geography

hydrology

Chang Jiang River importance

China’s largest river and the third largest river in the world. Around 400 million people live along it.

Main natural cause of flooding in the Chang Jiang basin

Monsoon rains.

How snowmelt contributes to flooding

Snowmelt from the Himalayas increases river discharge.

Natural hazards threatening the Chang Jiang basin

Earthquakes and typhoons.

1998 Chang Jiang flood – reason monsoon rains lasted longer

Because of the El Niño effect.

How global warming contributed to the 1998 flood

Increased snowmelt from the Himalayas.

How population growth worsened the 1998 flood

Cities were built beside the river.

How land use changes worsened flooding in 1998

Factories were built on old flood plains.

How deforestation contributed to the 1998 flood

Reduced interception and evapotranspiration.

Height reached by some floodwaters in 1998

45 metres.

Number of Chinese provinces affected in 1998

Seven provinces.

People affected by the 1998 Chang Jiang flood

240 million people.

Deaths in the 1998 Chang Jiang flood

About 4,000 people drowned.

People left homeless after the 1998 flood

14 million people.

Location of the Three Gorges Dam

Downstream on the Chang Jiang River.

Why the Three Gorges Dam is significant

Largest construction project ever undertaken on a river.

Size of the Three Gorges Dam

2.3 km long and 200 metres high.

Cost of the Three Gorges Dam

Over $40 billion.

People protected from flooding by the Three Gorges Dam

Around 50 million people.

People receiving water security from the dam

Around 13 million people.

Percentage of China’s electricity produced by the dam

About 10%.

Electricity output comparison of the dam

Equivalent to 15 nuclear power stations.

How the dam improved trade

Ships can navigate the river more easily and river traffic increased by 500%.

Jobs created by the Three Gorges Dam

Around 22,500 jobs.

People resettled because of the dam

About 1.2 million people.

Towns and cities flooded by the reservoir

150 towns and cities.

Location of Boscastle

Cornwall in southwest England.

Population of Boscastle during the flood

Around 2,000 people.

Date of the Boscastle flood

16th August 2004.

Type of flood in Boscastle

Flash flood.

Rainfall in Boscastle in one hour

89 mm.

Why the ground could not absorb water in Boscastle

It was already saturated from previous rainfall.

How Boscastle’s landscape worsened flooding

The steep V-shaped valley funnelled water into the village.

Peak discharge during the Boscastle flood

140 m³/s.

Homes and businesses destroyed in Boscastle

About 100.

Cars washed away in Boscastle

75 cars.

How people were rescued in Boscastle

Helicopters rescued over 150 people from roofs and trees.

Deaths in the Boscastle flood

No one died.

Environmental benefit of flooding in Boscastle

Replenished soil and groundwater stores.

Flood defence introduced after Boscastle flood

A £10 million defence scheme.

Number of tourists visiting Oxford every year

Around 7 million.

Why Oxford is economically important

One of the UK’s fastest-growing economies with 5,000 businesses and 135,000 jobs.

Why flood risk is increasing in Oxford

Climate change is increasing flooding.

Main aim of the Oxford Flood Alleviation Scheme

To divert water into underdeveloped floodplains away from homes and businesses.

Hard engineering methods in the Oxford scheme

Deeper channels, culverts and bunds.

Purpose of the deeper channel in Oxford

To direct 5 km of new channel along flood plains.

Soft engineering methods in the Oxford scheme

Tree planting and landscape creation.

Why trees were planted in Oxford flood plains

To increase natural protection and create wildlife habitats.

Cost of the Oxford Flood Alleviation Scheme

£150 million.

Level of flooding the Oxford scheme is designed to withstand

A 1-in-100-year flood.

Homes and businesses expected to be protected by the Oxford scheme

Over 1,000.

Largest flood on the Yangtze since 1998

The 2020 Yangtze flood.

Why the 2020 Yangtze flood was surprising

The Three Gorges Dam was meant to help prevent major flooding.

How the Three Gorges Dam responded before the flood

Opened 3 floodgates after warnings about extreme weather 5 days before the rainfall event.

Comparison between the 2020 flood and 1997 floods

Rainfall was higher in 2020 but the impacts were less severe.

Location of the 2020 flooding

Downstream from the Three Gorges Dam.

Main cause of the 2020 Yangtze flood

Heavy monsoon rains in June 2020.

Weather pattern linked to the 2020 flood

An anticyclone over the northwest Pacific.

How El Niño contributed to the 2020 flood

It caused much higher rainfall than expected.

Public reaction to flood management on the Yangtze

Many questioned whether the river had been managed effectively.

Chinese officials’ response about flood management

They said management reduced impacts and delayed flooding, allowing evacuations.

Rainfall during the 2020 Yangtze flood

Exceeded 300 mm, the biggest rain event in two decades.

Role of climate change in the 2020 flood

Climate change was blamed for the extreme weather event.

How COVID-19 affected flood management

The dam was understaffed.

Deaths caused by the 2020 Yangtze flood

141 people.

Homes destroyed in the 2020 Yangtze flood

28,000 homes.

Crop damage from the 2020 Yangtze flood

3.53 million hectares of crops were affected.

Economic cost of the 2020 Yangtze flood

11.76 billion dollars.

People affected by the 2020 Yangtze flood

63 million people.

Impact on rivers and dams during the 2020 flood

Nearly 700 smaller rivers and tributaries flooded, straining older dams and levees.

Cultural landmark threatened during the 2020 flood

The Leshan Giant Buddha.

Why the Leshan Giant Buddha is important

A 1,200-year-old sculpture carved into the mountainside and a UNESCO World Heritage Site.

Bluff case study

Pecos River, Texas.

Braided channel case study

Yellow River, China.

Additional Yellow River landforms

Hokou waterfall and rapids.

Channel straightening case study

Kissimmee River, Florida.