Rivers case studies

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  • Created by: Lilly
  • Created on: 24-04-13 18:23

Three Gorges Dam, China- Hard engineering

  • Dam spans the Yantze river, hydroelectric dam

Advantages:

1) Could power 1/3 of Chinese households from hydroelectric power- 100 million tonnes of CO2 no put into atmostphere

2) Jobs created, working in hydroelectric plant, cleaning river, and working on river retaurants, which will boost the economy

3) It will reduce the flood risk for 15 million people

4) Improve water navigation, river has been deepended due to the dam, going to rise to 175 metres which will allow larger ships to navigate it, also means that larger ships can travel to and from shanghai

5) Is thought that the dam has reduced major flooding events from every 10 years to every 100 years

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3 Gorges, Disadvantages

Disadvantages:

1) Mass relocation of people as water level in the resevoir has risen. Thought that between 1,3 and 2 million people in total will have to relocate by the time the reservoir is full- 13 cities and 1352 villages will be submerged

2) Will flood farmland, 657 factories and 1300 sites of cultural and historical interest, e.g. Temple og Zhang Fei will be submerged

3)Sediment that is usually carried down Yantzee river will be trapped by the dam, which could cause the failure of the dam- flooding

4) Can destoy habitats and endangered species, e.g. endangered Siberian Crane spends winter in wetlands below the dam, are expected to be affected by less flooding. Fewer than 100 baiji dolphins are lefy in the Yantse, dam could reduce their food supply

5) Dam won't reduce flood risk for everyone, reservoir will increase flooding along tributaries- Daning river- increased water levels in tributaries will increase erosion of river banks, causing collapses and landslides

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River Restoration- Kissimmee River, Florida

  • Was being straightened, would reduce distance from Lake Kissimme to Lake Okeechobe to just 56 miles
  • Realised it was having detremental effects:

1) 40,000 acres of floodplain below Lake Kissimmee dried out- reduced quality of waterfoul habitats by 90% 

2) Number of heros, egrets and wood storks by 2/3s

3) Reduced catchment areas of largemouth bass

4) 45,000 acres of wetlands was turned into pastureland- loss of habitats, migration of birds away from the area

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Kissimee river, resoration

After the authorities realised that the striaghtening of the channel was having detrementral effect on the river, they stopped and allowed the river to return to its natural state

Benefits:

1) Birds such as black-necked stilt retunring

2) Water quality improving

3) Fish stocks booming

4) Flower and plant population began to increase- pink-tipped smartweed, horsetail

5) Flooding and continous flow of dissolved oxygen in the water, creates near perfect conditions for aqautic vertebrates, such as insects, mollusks, works, crayfish and fresh water shrimp

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Flooding in Bangladesh- 2004

Location:

  • South Asia, on delta of 3 rivers
  • Moonsoon climate, wet season between may and septermber
  • Affected by cyclones
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Bangladesh floods

Human causes:

  • Deforestation in headwater areas and Himalays due to population increase in Tibet, Nepal and Dhaka- trees cleared to become fuel and grazing land for cattle- less interception, also less evapouration due to decreased vegetation meant delay between precipitation and water reaching river has increased

-Greater amount of surface run off and soil erosion- increased land slides

  • 80% of Bangladesh lives on flood plain and delta of 3 rivers, most is 1m a bove sea level
  • Much of the Ganges has been diverted for irrigation purposes, removes some of the silt, prevening the floodplains further downstream from bulding up, increases risk of flooding
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Bangladesh flood

Natural causes:

  • Moonsoon climate- heavy precipitation, increases river discharge- soil saturated with time, infiltration impossible leading to increased surface runn off- decreases time between precipitation falling and reaching river
  • Source of 3 rivers, Himalays, spring snow melt results in soil erosion and a rapid increase in river discharge
  • Rivers silt up due to increased soil erosion- raises river bed- reduces capacity of channel, resulting in an increased liklihood of flooding
  • Cyclones, frequnetly hit Bangladesh, severly affect the discharge of the three riversm making flooding more likli
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Effects and impacts of Banfladesh floods

Environment:

  • Soil erosion
  • Water logging in urban areas
  • water contamination with associated health risks
  • Approx 48% of total land area looded
  • River bank erosion
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Social impacts

  • 800 epeple died- many from water born diseases, didnt have access to clean water
  • Value of damage estimated at being $2.2 bullion, was 5% of GDP for 204
  • Damage to infrastruture- roads, bridges, eirrigation systeems
  • 36 million made homeless
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Response to floods

Short term

  • Provision of rice, clothing, medicines, blankets and towels from government and NGOs

Long term

  • Flood shelters and early waning systems put into place
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Bostcastle floods- 2004

Location

  • North coast of cornwall, UK- MEDC
  • Between confluence of three rivers

 Human causes:

  • Did little, was freak storm event, however there are steps that could have prevented the extent of te damage caused
  • River Valency lacks any flood prevention system
  • Sewers and drainage systems in area could not handle small capacity, added volume destroyed system
  • Bridges along river, clogged debris- wood and cars- water had to go around it- flooded town
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Bostcastle floods

Natural causes:

  • Ground already saturated from previous rain- infiltration reduced, increased surface run-off, precipitation reaches river faster than it would have if the ground hadn't been saturated
  • Town was on a confleuce
  • Conerging winds trapped storm abover Bostcastle, high intensity rainfall- over 60mm of tain fell in 2 hours
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Bostcastle

Economic effects:

  • 75 cars, 5 caravans, 6 buildings and several boats washed into sea
  • Approx 100 homes and bussinesses destroyed- damage estimated to require £15,00 and £30,000 for repairs
  • Flood led to insurance claims of £4milion
  • About 90% of economy is tourism, and about 2/3 comes from summer holidays- tourism fell as 20 acconodation proviers had to shut down- detremental to ecnomy

Social effects:

  • 150 people had tombe resuced from roof tops
  • No oone died, but some were injured
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Bostcastle

Respsonse

  • Relief channel of River Jordan made bigger
  • £4.5 million scheme put in place to inprove flood defences- stretched along valley, incorporating drainage, sewage systems and alnd re-grading

Car park at raised level- will stop river bursting banks so easily

River channel has been made deeper and wider by 6ft- increases river capactiy

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