Rivers: Uses and Problems+Methods

Question 1

What are the different uses of a river?

Answer 1

WITHRN
1. Water supply
2. Irrigation/agriculture
3. Trade and Transport
4. Hydropower generation
5. Recreation and Tourism
6. Natural Boundaries between countries

Question 2

What are the opportunities and hazards associated with using a river for water supply?

Answer 2

Opportunities:
- Readily available freshwater source (eg. The Thames River in London provides 70% of public water supply after undergoing treatment processes)

Hazards:
- Pollution (Ganges River in India is affected by pollution from industrial, agricultural ad urban sources)

Question 3

What are the opportunities and hazards associated with using a river for irrigation?

Answer 3

Opportunities:
- Allows a larger amount of land to be cultivated-> food security and economic prosperity (eg. According to the Food and Agricultural Organisation, FAO, in 2018, Egypt had 3.7 million square acres of irrigated land for crops)

Hazards:
- Pollution due to chemical fertilisers and waste (eg. Ganges River in India due to plantations along its course/Yamuna River, India as well)

Question 4

What are the opportunities and hazards associated with using a river for trade and transport?

Answer 4

Opportunities:
- Boost economies of certain countries through trade connectivity (eg. The Rhine River connecting European nations such as Switzerland, Germany, France, Belgium and the Netherlands-> in 2019, more than 225 million tonnes of cargo transported)
- More environmentally friendly and reduces congestion on roads

Hazards:
- Pollution such as oil spills
- Navigation can be hindered by obstructions (dams, bridges)

Question 5

What are the opportunities and hazards associated with using a river for hydropower generation?

Answer 5

Opportunities:
- Source of clean energy (The Three Gorges Dam on the Yangtze River, China-> saving about 50 million tonnes of coal and reduces carbon dioxide emissions by 100 million tonnes per year)

Hazards:
- Potential loss of biodiversity as dams disrupt natural flow (Dams on the Mekong River are projected to cause a 40% decline in fish biomass in the lower Mekong basin by 2030)

Question 6

What are the opportunities and hazards associated with using a river for recreation and tourism?

Answer 6

Opportunities:
- River based tourism and recreational activities generate income and creates job opportunities (Danube River in Europe-> attracts millions of tourists yearly-> supports local businesses-> more job opportunities open-> economic growth for the country)

Hazards:
- Pollution due to improper waste management by tourists (Amazon River, South America-> trash is dumped into the ecosystem which causes degradation of the environment)

Question 7

What are the opportunities and hazards associated with using a river for natural boundaries between countries?

Answer 7

Opportunities:
- Clear delineation between countries (Mekong River-> Laos and Thailand; Niagara River-> USA and Canada)

Hazards:
- Tensions between countries as rivers are a shared resource (Mekong River, Asia-> Dams built by China cause water shortages and biodiversity loss in the lower Mekong region-> Lower riparian states suffer)

Question 8

What are the problems of rivers

Answer 8

OCBF
1. Obstruction of flow
2. Channel migration
3. Bank erosion
4. Flooding

Question 9

How is obstruction of flow a problem of a river?

Answer 9

Obstructions such as waterfalls and rapids obstruct the smooth passage of vessels; narrow passages require careful maneuvering to avoid collisions

Question 10

How is channel migration a problem of rivers?

Answer 10

Makes land planning difficult; challanges for infrastructure, land use planning and maintaining a stable habitat

River moves due to meandering

Question 11

How is bank erosion a problem of rivers?

Answer 11

During erosion,
1. The riverbanks loosen and threaten the stability of nearby structures
2. Alluvium soil is deposited in river channels, making them shallower-> more floods
3. When deposition occurs at river mouth, dredging is required to ensure depth of ports remain deep enough-> costly!

Question 12

How is flooding a problem of rivers?

Answer 12

Damage to infrastructure and agriculutral lands, loss of lives, community displacement and spread of water-borne diseases (cholera etc)

Question 13

How can we determine flood risk from a storm hydrograph?

Check notes for drawing

Answer 13

• Take note of lag time and gradient of rising limb
• Short lag time+steep rising limb causes a high influx of water to enter the river-> river cannot cope-> high flood risk (Vice versa)

Question 14

What are the physical factors that can affect the lag time and discharge of rivers?

Answer 14

1. Drainage basin (Shape, size, slope)
2. Ground type (permeability)
3. Presence of vegetation
4. Precipitation

Very similar to factors affecting volume of flow

Question 15

What are the human factors affecting lag time and discharge?

Answer 15

1. Urbanisation
2. Deforestation
3. Climate change

Self-explainatory based on VOF notes

Question 16

What are the soft engineering methods to manage river flooding?

Answer 16

FWRP
1. Floodplain zoning
2. Weather forecast and flood warnings
3. River restoration
4. Planting vegetation

Question 17

How does floodplain zoning work? What are pros and cons?

Answer 17

Implementation of restrictions to prevent buildings being built on land prone to flooding

• Areas more prone to flooding-> farms
• Less prone to flooding-> housing, industry, transport

PROS:
- Without permanent buildings on flood prone areas, lower damage to locals and environment during flooding
- Provides recreational opportunities

CONS:
- Restricts development-> not enough land for housing
- Cannot be implemented on already developed land

Question 18

How does weather forecasts and flood warnings help manage river flooding? Pros and cons?

Answer 18

People are warned about possible floods through the media should water levels reach undesirable levels

PROS:
- People given the chance to evacuate before floods come
- Reduction in damage as measures can be taken (sandbags)

CONS:
- Floods may still occur too quickly
- People who cannot access media networks do not get notified

Question 19

How does river restoration help manage river flooding? What are pros and cons?

Answer 19

Allowing a river to flood naturally by removing artifical levees

• As a river floods on a floodplain, discharge decreases and reduces the risk of flooding downstream

PROS:
- Little maintainance needed
- Provides a better habitat for wildlife
- Protect settlements downstream

CONS:
- Local floodrisk can increase if nothing is done to prevent major flooding
- Requires land that can be flooded

Question 20

How does planting vegetation help to manage river flooding? What are the pros and cons?

Answer 20

Growing vegetation like mangroves along the river to minimise bank erosion

PROS:
- Banks are stabilised due to roots-> lower erosion-> lower risk of floods due to sediments
- Vegetation lowers river discharge

CONS:
- Plant debris may obstruct flow of river-> flooding
- Weight of vegetation may cause bank collapse
- High maintanance cost to clear plant debris

Question 21

What are the various hard engineering methods to manage river flooding?

Answer 21

1. Re-alignment of river
2. Re-sectioning of river
3. Bank protection
4. Dam building

Question 22

What is river re-alignment and what are the pros and cons?

Answer 22

Straightening and shortening of river channel by removing meanders of a river

PROS:
- Increases SOF-> river does not reach flooding height
- Washes away sediments-> channel is deeper

CONS:
- Doing this upstream may lead to major flooding downstream
- Doing this reduces wetland area as river flows over a smaller area

Question 23

What is river re-sectioning and what are the pros and cons?

Answer 23

Widening and deepening different sections of river channel by dredging

PROS:
- Channel can hold more water
- Riverbed and banks can be smoothened by cement and granite-> increased SOF

CONS:
- Expensive and large manpower needed
- Higher SOF-> more sedimentation downstream and hence shallower channel downstream

Question 24

What is river protection and what are the pros and cons?

Answer 24

Building artificial walls to raise banks and increase channel depth

Can use gabions to divert flow from the river banks to the centre of the channel

PROS:
- Artificial levees create deeper channels, contain more water
- Gabions protect riverbanks from erosion-> reduce sediments flowing in the river-> hold more water

CONS:
- Levees may break after heavy rainfall, massive flooding
- Sedimentation still occurs in channel-> shallower channel

Refer to notes for drawings

Question 25

What is dam building and what are the pros and cons

Answer 25

Controls discharge in the river by holding water back behind the dam in a reservoir

PROS:
- Water stored can be released to generate hydropower
- Water in reservoir can be used for irrigation, especially during dry seasons

CONS:
- Dam may burst with heavy continuous rainfall
- Good farming land will have to be permanently flooded for the dam (wasted!)