Managing River Hazards

Managing River Hazards

IGCSE Geography

Learning objectives

• Explain the advantages and disadvantages of rivers

• Suggest ways how can the impacts of floods be managed

IGCSE Geography

Schedule

• Thursday, May 5 - Managing Floods + Presentation Preps

• Friday, May 6 - no Geography class

• Monday, May 9 - Quizizz review + Presentation Preps

• Thursday, May 12 - no Geography class

• ​Friday, May 13 - Presentation (Travelogue)

• Monday, May ​16 - Quiz 2 (Rivers)

​An overflow of water that submerges land that is usually dry.

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A natural feature of all rivers.​

Flood

Flooding (Double-edged sword)

• Floods bring advantages such as water and fertile alluvium (river deposits or silt), which allows farmers to grow crops.

• Too much water and silt can be devastating​.

Silt - fine sand, clay or other material carried by running water and deposited as a sediment.

Effects of flooding

• Riverbank erosion can cause population displacement and socio-economic impacts.​

• Meghna River, Bangladesh

• Caused major disruptions during the 1990s and 2000s.

• It eroded over 6km of land destroying productive land and causing residents to lose all their possessions.

Open Ended

Describe one impact of floods on humans?

Causes of floods

​The causes of floods are natural, but human interference intensifies many floods:

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• Climatic Forces

  • England - floods are caused by deep depressions (low-pressure systems)

  • India - caused by monsoon and melting snow

Intensifying floods

Topography, vegetation, soil type, rock type and specific characteristics of the drainage basin can also intensify floods.

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The potential for damage by floodwaters increases exponentially with velocity and speeds about 3 meters per second.​

Intensifying floods: Urbanisation

1. highly impermeable surfaces​ (roads, roofs)

2. smooth surfaces served with a dense network of drains, gutters, and underground sewers increase drainage density

3. natural river channels are often constricted by bridge supports or riverside facilities, reducing their carrying capacity

4. Due to increased storm runoff, many sewerage systems cannot cope with the resulting peak flow​

Purposeful clearing of forested land.​

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Increases flood runoff and decreases channel capacity be (due to deposition within the channel)

Deforestation

• Flooding is the most common of all environmental hazards. (1/3 of all natural catastrophe, half of human fatalities, and 1/3 of economic loss).

• People still live in floodplains due to perceived benefits but are fraught with difficulties.

• In China, over 5 million people have been killed in floods since 1860.

increasing impacts of floods (reasons)

• rising global population, including in vulnerable regions

• construction in flood-prone areas

• failure of flood protection systems

• changes in environmental condition (clearance of trees and other vegetation)

​​Low-lying parts of floodplains and river estuaries

​​Small basins subject to flash flood

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​​areas below unsafe or inadequate dam

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Risky areas due to flood concerns

How do we manage floods?

• ​Hard engineering: dams, reservoirs, levées, channel straightening and deepening (dredging), and creating flood relief channels.

• Soft engineering: afforestation, land use zoning and river restoration.​

Afforestation - the process of planting of trees and tree seedlings to increase interception by vegetation.

​​Hard Engineering: Three gorges dam

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​​Soft engineering: the kissimee River restoration project

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Case studies (Next meeting)

EAL ACTIVITY

c/o Ms. Jona

• Same groupings as last week (features of deposition/erosion activity)

• Your pair/trio will play the role of travel guides that will introduce your assigned location.

• Use the website (see MS Teams for more details)​

Travelogue activity (Friday)

• Describe the landscape/location

• Which part/s of the river system does it belong to?

• Which features of erosion and ​deposition, river features are present?

• How do the river features impact humans?

• What kind of hard/soft engineering steps can be made to improve the area?​

• Qujing​ (G1)

• Guilin (G2)

• Xunwu (G3)​

• Shaoguan (G4)​

• Guangzhou (G5)​

• Jiangmen (G6)​

• ​Zhuhai (G7)

Preparations

End of meeting 1

How do we manage floods?

• ​Hard engineering: dams, reservoirs, levées, channel straightening and deepening (dredging), and creating flood relief channels.

• Soft engineering: afforestation, land use zoning and river restoration.​

Afforestation - the process of planting of trees and tree seedlings to increase interception by vegetation.

​​Hard Engineering: Three gorges dam

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​​Soft engineering: the kissimee River restoration project

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Case studies

Three gorges dam

• over 2 km wide and 100 m high and the lake behind it is over 600 km long

• the Yangtze basin provides 66 % of China's rice and contains 400 people

• the river drains 1.8 million km and discharges 24,000 m³/sec of water annually.​

While watching the clip, make an advantages/disadvantages table.​

Three Gorges dam

Advantages

• It generates up to 22,500 megawatts, 50% > previous largest HEP dam

• It enables China to reduce its dependency on coal

• It supplies energy to Shanghai (population over 17 million) and Chongqing (3 million)

• It protects 10 million people from flooding

• It allows shipping above the Three Gorges: water is raised by 90 m and turned rapids into a lake​

Three Gorges dam

DisAdvantages

• Over 1.25 million people were removed to make way for the dam and the lake

• It cost $25 billion to build​

• Most floods in recent years have come from rivers that join the Yangtze below the Three Gorges Dam

• The region is seismically active and landslides are frequent​

Three Gorges dam

DisAdvantages

• The port at the head of the lake may become silted due to increased deposition

• Much of the land available for resettlement is over 800 m above sea level, and is cold, with thin, infertile soils on relatively steep slopes

• Dozens of towns were evacuated: e.g. Wanxian (population 140,000) and Fuling (80,000), and then were drowned by rising waters​

Three Gorges dam

DisAdvantages

• Up to 530 million tonnes of silt are carried through the gorge annually: the first dam on the river lost its capacity within 7 years, and one on the Hwang He filled with silt within 4 years

• To reduce the silt load, afforestation is needed, but resettlement of people will cause greater pressure on the slopes above the dam

• The dam interferes with aquatic life -- the Siberian crane and the white flag dolphin are threatened with extinction

• Archaeological treasures have been drowned, including Zhang Fei Temple​

Open Ended

How many people live in the Yangtze basin?

Open Ended

What is the energy potential of the Three Gorges Dam?

Open Ended

How many people could it supply with energy?

Open Ended

How much did it cost?

Open Ended

How many people had to be resettled as a result of the building of the Three Gorges Dam?

​​Hard Engineering: Three gorges dam

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​​Soft engineering: the kissimee River restoration project

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Case studies

Kissimmee river restoration project

Between 1962 and 1971 the 165 km meandering Kissimme River in Florida, USA and its adjoining floodplain were channelised and thereby transformed into a 90 km, 10 m deep drainage canal.

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The river was channelised to provide an outlet canal for draining floodwaters from the developing upper Kissimmee lakes basin, and to provide flood protection for land adjacent to the river.

Kissimmee river restoration project

Between 1962 and 1971 the 165 km meandering Kissimme River in Florida, USA and its adjoining floodplain were channelised and thereby transformed into a 90 km, 10 m deep drainage canal.

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The river was channelised to provide an outlet canal for draining floodwaters from the developing upper Kissimmee lakes basin, and to provide flood protection for land adjacent to the river.

Impacts of channelisation

• the loss of 12,000-14,000 hectares of wetlands

• a reduction in wading bird and waterfowl usage

• a continuing long-term decline in game fish population

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Concerns about the sustainability of existing ecosystems led to a restoration study, supported by the state and national authorities. The result was a massive restoration project, on a scale unmatched elsewhere.​

The Project

The project will benefit over 320 fish and wildlife species, including the endangered bald eagle, wood stork and snail kite. It will create over 11,000 hectares of wetlands.

​Goal: restore over 1000 km² of​ the river and associated floodplain wetlands.

The Project

Dechannelisation

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The backfilling of approximately half of the flood control channel and reestablishing of the flow of water through the natural river channel.

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In residential areas, the flood control channel will remain in place.

cost The Project

• The project will cost $980 million (initial channelisation cost $20 million), with the bill being shared by the state of Florida and the federal government

• Long-term project: began in 1999, will not be completed until 2015

• Higher losses of water due to evapotranspiration during wet periods

benefits of restoration

• Higher water levels should ultimately support a natural river ecosystem again

• The re-establishment of floodplain wetlands and associated nutrient filtration function is expected to result in decreased nutrient loads to Lake Okeechobee

• It is possible that restoration fo the floodplain could benefit the population of key avian species, such as wading birds and waterfowl, by providing increased feeding and breeding habitats.

Potential revenue associated with increased recreational use (such as hunting and fishing) and ecotourism on the restored river could significantly enhance local and regional economies.

Open Ended

Where is the Kissimmee river?

Open Ended

Describe the changes to the Kissimmee river between 1962 and 1971.

Open Ended

Identify one benefit of river restoration.

Open Ended

How much did the Kissimmee river restoration cost?

Open Ended

When was it completed?

How do we manage floods?

• ​Hard engineering: dams, reservoirs, levées, channel straightening and deepening (dredging), and creating flood relief channels.

• Soft engineering: afforestation, land use zoning and river restoration.​

Afforestation - the process of planting of trees and tree seedlings to increase interception by vegetation.

​​Hard Engineering: Three gorges dam

​

​​Soft engineering: the kissimee River restoration project

​

Case studies

Event modification

• attempts to reduce floods and divert them from settlements

• reducing floods involves decreasing the amount of runoff, thereby reducing the flood peak in a drainage basin which can be achieved by weather modification and/or watershed treatment.

Event modification strategies

• ​reforestation

• reseeding of sparsely vegetated areas to reduce evaporative losses

• mechanical land treatment of slopes, such as contour ploughing or terracing to reduce runoff

• comprehensive protection of vegetation from wildfires, overgrazing, clear-cutting of forests, or any other practices likely to increase flood discharge and sediment load

Event modification strategies

• clearance of sediment and other debris from headwater streams

• construction of small water - and sediment- holding areas

• preservation of natural water detention zones

Event modification strategies

Flood diversion

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Construction of levées, reservoirs, and the modification of river channels.​

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Channel improvements include enlargement which increases the carrying capacity of a river.​

Loss sharing and insurance

• Loss sharing includes disaster aid and insurance.

• Refers to any aid -- such as money, equipment, staff and technical assistance -- that is given to a community following a disaster.

• Taxpayers are commonly argue that they cannot fund the losses that should have been insured.

This practic​e is more common in developed countries. Not all flood-prone areas are insured.

Hard-resistant design

• Floodproofing includes any adjustments to buildings and their contents that help reduce losses.

  • Short-term: blocking up entrances, use of shiled to seal doors and windows, removal of damageable good to a higher level levels, and use of sanbags.

  • Long-term: moving the living spaces above the likely level of the floodplain and building home on stilts.

Hard-resistant design

Forecasting and warning

• Flood forecasting is more accurate and widely used by many to reduce the problems caused by flooding.

• In developed countries, flood warnings and forecasts may reduce economic losses by as much as 40%.

• In most developing countries there is much less effective flood forecasting.

  • Example: in Bangladesh, they give 72 hour flood warning when events in Himalayas happen

land use planning

• Land-use zoning involves allowing compatible land uses on land that might flood.

  • A land that floods regularly (once a year) could be used for pastoral agriculture, as animals can be moved to higher ground.

  • Recreational use

  • Not to meant for industrial, commercial or residential land use, as valuable equipment and possession would be damaged or destroyed

Preparation: Presentation

The presentations will take place on Friday, May 13.

Travelogue activity (Friday)

• Describe the landscape/location

• Which part/s of the river system does it belong to?

• Which features of erosion and ​deposition, river features are present?

• How do the river features impact humans?

• What kind of hard/soft engineering steps can be made to improve the area?​

• Qujing​ (G1)

• Guilin (G2)

• Xunwu (G3)​

• Shaoguan (G4)​

• Guangzhou (G5)​

• Jiangmen (G6)​

• ​Zhuhai (G7)