Rivers Case Studies

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Bangladesh, 2004

During July and August, approximately 38% of Bangladesh's land was flooded, including 800,000 acres of agricultural land and the capital city of Dhaka. 3.6 were made homeless, and disease meant that by September, the death toll was 800. 2 billion dollars of damage was caused. The government provided supplies such as rice, clothing, medicine, and towels.

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River Adur, Sussex

Its annual maximum flows are in winter due to high precipitation and low temperatures causing saturated soil. There are lower flows in summer due to high evapotranspiration and less soil saturation. Most years, however, summer precipitation isn't much lower than winter.

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  • A village in a valley. The valley is very steep, with rainwater falling directly on the hills above the valley. The water runs very quickly down the valley sides. Rainwater becomes concentrated in the narrow valley space.
  • There was an increase in runoff speeds and discharge volume.
  • The ground was saturated due to stormy weather on the days leading up to the 6th August.
  • The 6th August was a very hot day with clear skies in the morning. Warm moist air travelled upwards quickly. Storm clouds formed and it rained in the early afternoon.
  • Within hours, 5 inches of rain fell. The volume of water burst the river's banks.
  • Westerly/South Westerly winds blown from the Atlantic were slowed by friction.
  • Meanwhile, winds from the North and South met in a convergence zone.
  • There were heavy showers and thunderstorms due to the Brown Willy effect - the hill near Boscastle which causes precipitation to fall into the valley. 
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Boscastle, 2

  • There was a lack of a flood control system. There were no raised banks or emergency ditches, and inadequate drainage.
  • Structures obstructed the river and increased the spread of floodwater. This partially blocked the river and water had to flow around a bridge.
  • Roads were blocked off by floodwater, making emergency access difficult.
  • Properties were destroyed by debris such as trees/vehicles.
  • People were trapped in/on buildings.
  • A burst sewage main damaged buildings.
  • Boscastle was mostly inaccessible.
  • Flood waters damaged properties and repairs had to be made and rubble and debris had to be secured.
  • Home insurance became far more expensive.
  • Tourism effectively closed, leading to a massive loss of revenue.
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3 Gorges Dam, China

  • A project on the Yangtze river. A dam, intended to generate hydroelectric power and reduce the flood risk for 15 million people.
  • A 600km long and 1km wide reservoir has also been created.
  • Creating the reservoir forced the resettlement of 1.2 million people from over 100 villages.
  • The dam is 2.3km long and over 100m high. It cost £25 billion to build.
  • Cultural monuments were lost and there was increased erosion downstream.
  • Sediment behind the dam needs regular dredging.
  • Afforestation was needed on the drainage basin slopes in order to reduce the amount of sediment washed into the river and reservoir.
  • There has been an increased landslide risk and species habitats have been disrupted.
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River Quaggy, South East London

  • Heavily managed since the 1960s with artificial channels.
  • They allowed the river to be brought above ground, cutting a new channel through Sutcliffe Park.
  • This improves flood management and the park's quality: a new lake has been created, the park was lowered and sloped to create a floodplain.
  • A wetland environment has been created.
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