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AS Geography: River Environments - Yangtze Basin, China |
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Drainage basin modification by human activity
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Yangtze River, China
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Background
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The Yangtse River in China is prone to flooding. In the mid 1990’s 4,00 people drowned whilst 400,000 people live with the risk of flooding.
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How has the risk of flooding been increased by human activity?
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Deforestation
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In the upper catchment, the area still contains large areas of mixed forest. The tree roots stabilise the soil so that water can infiltrate into the soil. Without the forests, the large amounts of rainwater that fall in the mountains would run-off quickly into the river.
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People living in the area use the forests for firewood, food and for living in. There is plenty of fallen dead wood to be used. In towns, large amounts of timber are used for building. Since the floods of 1998 felling has been banned in the upper basin. In Huize County, the original 40% forest cover has been reduced by 50% in 40 years. There is now a policy of afforestation on denuded land, but it will take time for the trees to grow.
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Industry
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Using land for pasture does not allow the vegetation to regenerate. The land is left as scrub vegetation. Due to Mao Tse Tung’s policy of building steelworks in the mid-1950’s, large areas of land were deforested to provide fuel to power the furnaces. Since the closure of the steelworks, land has been terraced, but only buckwheat is grown, as the soil is so poor. Many of the terraces are poorly constructed. Consequently, during periods of heavy rain, water runs off the hillsides quickly, taking the nutrient-rich topsoil with it. When the heavy rain falls on the hillside, minimum interception and infiltration takes place. As a result, the likelihood of flooding increases.
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What is being done to reduce the risk of flooding?
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In 1985, the region suffered major flooding. As a result, the tobacco crop was lost and animals were swept away. After the flood the County Policy Bureau tried to implement several flood prevention policies
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Afforestation
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The government invested money, whilst the local people provided the labour. The government provides the seedlings and expertise whilst the locals plant them. Any profits are shared. As a result, the area has not flooded since. However, because only one species is being cultivated, little vegetation grows beneath the pines. They were chosen because the seedlings were cheap. However, the acidic soil does not allow other vegetation to grow below. Locals also had to give up their Buckwheat fields and now only have a small amount of land to live off.
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Education
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Education has meant that high yielding varieties are being grown under polythene to make land more efficient. Inter-cropping has also decreased erosion rates. Now trees are interspersed with crops. As Chestnut trees mature, the yield of beans will be reduced, but this should be compensated by the Chestnut crop.
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D.Drake 2011
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