Edexcel IGCSE Geography Chapter 1 - Pearson Schools

More documents

Recommendations

Info

layers of deposits build upin great thicknessthe river’s energy is reduced when itleaves the channelleveeleveeriver in floodsilt or alluviumFigure 1.15: The formation of a floodplain and levees<strong>Chapter</strong> 1: River environmentsslowerflow oninsidebendsfastestflow onoutsidebendsdeposits of sandand silt in channelDuring its lowland course, the river is still an agent of erosion. However, verticalerosion is less important because the river is too close to sea level. More importantis lateral erosion where the river wears away the sides of the channel, especiallyon the outside of meanders. The river becomes an agent of deposition as well.Such a large load of material has been picked up that, once the river loses energy, itdrops some of that load, usually mud, stones and other organic matter. Thegreatest thickness of river-deposited material, known as alluvium, is on the floodplain. As its names suggests, the flood plain is an area of flat land formed byflooding. Every time the river leaves its channel, its velocity (speed) decreases. Oncethis happens, alluvium is deposited across the valley floor. A great thickness ofalluvial material builds up. The largest amount of deposition is always on the banksof the channel, which builds up to a greater height than the rest of the floodplainto form levees (Figure 1.15).steep river bankslip-off sloperiver cliffox-bowlakecut offoutside benderodedmore sharplyby river currentsealed bydepositsnarrow neckof landriver nowflows straightxmuchlargermeanderyABCdeposited materialon the slip-off slopeChannel cross-section x–yxfastest waterflow hererivercliffyFigure 1.16: Formation of meanders and oxbowsA study of the formation of meanders and ox-bow lakes shows how the riverboth deposits and erodes laterally (Figure 1.16). The force of the water undercutsthe bank on the outside of a bend to form a steep bank to the channel, called ariver cliff or bluff. An underwater current with a spiral flow carries the erodedmaterial to the inside of the bend where the flow of water is slower. Here thematerial is deposited to form a gentle bank, called a slip-off slope or point bar.12
As lateral erosion continues, the bend of a meander becomes even more pronounced(Figure 1.16). Especially in times of flood, when the river’s energy is much greater,the narrow neck of the meander may be breached (broken and crossed) so that theriver flows straight again. The redundant meander loop retains some water andbecomes an ox-bow lake. Deposition during the flooding helps to seal off the edgesand ends of the lake.Figure 1.17: Mississippi meanders and ox-bow lakesLateral erosion on the outside banks of meanders helps to widen the flood plain.Flood plains have great value for people. Flat land with rich, thick alluvial soils andnearby, plentiful water is attractive to agriculture, industry and urban settlements.Rivers meander naturally. The meanders migrate across the flood plain as theoutside of the meander erodes laterally (sideways). Figure 1.17 shows a small partof the complicated meander pattern of the Mississippi River.Try researching two facts about theMississippi River:• the actual length of the river from itssource to the sea• the straight-line distance from itssource to the sea.What does this tell you about the amountof meandering the river does?<strong>Chapter</strong> 1: River environmentsFigure 1.18: Satellite image of part of the Ganges−Brahmaputra delta. It also showshuge amounts of silt being deposited in the waters of the Bay of Bengal.13
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: KeyDifference inheight betweenX and
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 and 26: There is a fourth and relatively ne
Page 27 and 28: FACTORPhysicalWeatherRockSoilRelief
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

Create successful ePaper yourself

Delete template?

Save as template?