Edexcel IGCSE Geography Chapter 1 - Pearson Schools

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Tonnes of industrial and human waste will also be trapped behind the dam.A major concern is whether the dam will be able to withstand the earthquakesthat often occur in this part of China. If the dam were to collapse manymillions of people would die.<strong>Chapter</strong> 1: River environmentsMake a list of the disadvantages of theThree Gorges Dam project.Figure 1.34: The completed Three Gorges DamEnvironmentalists have questioned the wisdom of the whole project. Theyargue that a series of smaller hydro-electric dams on the tributaries of theYangtze would have been a more efficient way of generating electricity andmanaging the flood-prone river. However, one long reservoir does offerimproved, year-round navigation, as well as water for industry and agriculture.Any domestic use of the reservoir’s water will require proper treatment.1.8 Flooding – causes and controlFlooding occurs when the amount of water moving down a river exceeds thecapacity of the river’s channel. The excess water overflows the banks and spills outacross the flood plain. Flooding is a hazard that can cause great damage to theenvironment and people.CausesRivers usually flood as a result of a combination of causes. This combination caninvolve both natural (physical) and human factors. In many cases, natural floodingis made worse by people and their activities.Most flooding is related to spells of very heavy rainfall. The critical factor is howquickly this rainfall reaches the river from where it falls on surrounding land andmountains. The shorter the lag time (see Figure 1.8 on page 6) and therefore thefaster it does so, the greater the chances of flooding.26
FACTORPhysicalWeatherRockSoilReliefDrainagedensityVegetationHumanDeforestationUrbanisationAgricultureClimatechangeTable 1.3: Factors causing floodingImpactIntense rainfall greater than the infiltration capacity of the ground.Prolonged rainfall leading to saturation of the ground.Rapid snow melt as temperatures suddenly rise above freezingImpermeable rocks limiting percolation and encouraging rapidsurface run off or overland flowLow infiltration rate in certain soils, e.g. claysSteep slopes causing fast run offHigh drainage density means many tributary streams carry therainwater quickly to the main riverLow density vegetation absorbs little water and does notseriously impede run offCutting down trees reduces interception and speeds up run offConcrete and tarmac surfaces together with drains mean quickerdelivery of rainwater to the riverThe risk of flooding increased by leaving the soil bare, overgrazing,monoculture and ploughing down rather than across slopesIncreasing temperatures, partly due to the burning of fossil fuels,cause more melting of ice sheets and glaciers, as well as morerainfall and more frequent stormsTable 1.3 lists some of the factors that reduce the lag time and therefore increase thechances of flooding.Which of the factors in Table 1.3 are likelyto have the greatest effect on lag times? Itwould help if you were to look back topage 6 about the storm hydrograph.<strong>Chapter</strong> 1: River environmentsFlooding can also result from persistent rain over a relatively long period of time.Gradually, the water table (level of water underground) rises and the soil becomessaturated. Downward infiltration ceases and water simply accumulates in shallowdepressions and on low-lying land.Figure 1.35: Floods in Sheffield, June 200727
Page 1 and 2: Section A:The natural environment a
Page 3 and 4: ●●●●overland flow - most of
Page 5 and 6: shows the channel networks of two d
Page 7 and 8: There are a number of factors affec
Page 9 and 10: ErosionThere are several different
Page 11 and 12: KeyDifference inheight betweenX and
Page 13 and 14: As lateral erosion continues, the b
Page 15 and 16: The height of the drainage basin an
Page 17 and 18: ●●●The rising standard of liv
Page 19 and 20: uses less water (now 14%) (Figure 1
Page 21 and 22: 1.7 Water qualityIn Part 1.6, we lo
Page 23 and 24: Agriculture●●●Liquid from far
Page 25: There is a fourth and relatively ne
Page 29 and 30: In the longer term, there is the co
Page 31 and 32: the monsoon climate with its heavy

Edexcel IGCSE Geography Chapter 1 - Pearson Schools

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