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1、EnglishForWaterResourcesSoilerosionandsoilconservationAbstract:Themajormovementofsoilerosionandsoilerosion,soilerosionhazardstohumansistheerosionofthefirstoverofthelandbarrenexception,andthereforecannotgrowcrops,farmersbankruptandhadtomovetoabetterplace.Themainmethodstopreven
2、tsoilerosionisagoodmethodofcultivation.BasedonU.S.soilasanexampleabouthowtobuildterracesandothermethods.1IntroductionAllcivilengineersknowtwomaintypesofsoilmovement,soilcreeportheslowflowofsoil,andthefasterflows,calledslides,slipsoravalanches.Thefastermovementgenerallymovesla
3、yersthataredeeperthanthosemovedbysoilcreep.Butmoreimportantthaneitherofthesetwotypes(atleastinthequantityofsoilremovedeveryyear)aresoilerosion,theremovalofsoilbyflowingwaterfromgroundthatisusuallydry,andscourtheremovalofsoilorrockfromthebedorbankofariverorstream.Forestsoilund
4、ergrowingtreesgenerallydoesnoterodebecausetheleavesanddeadorbrokenwoodholduptherainlikeblottingpaperandpreventitsattackingthesoil.Themainactionofdeadleavesindelayingrunoffisthattheyholdopenthedrainagechannelsintothesoil.Inbaresoilthatisnotprotectedinthisway,thesoilporesarequi
5、cklyblockedduringrainbythefinesoilgrainsflowingintothem.Therainrunsoverthesurfaceandnotintoit,smallchannelsform,tobedeepenedeventuallyintothereallydamagingdeep,scouredditchescalledgullies.Thefirstdisadvantageofsoilerosiontomankindisthaterodedlandissopoorthatcropswillnotgrowon
6、it,farmersareruined,andhavetomovetobetterland.ThishashappenedtomanythousandsoffarmersintheUnitedStates,whichinthelasthundredyearshasprobablysufferedmoreformerosionthananyothercountry.Theseconddisadvantageisthatsoilerosionmakesfloodingbothmoresevereandmorefrequentsincethewater
7、runsoffthesoilmorequickly.Inforestareas,95percentoftherainfallisabsorbedwhileonbaresoilabout95percentmayrunoff.Thisproportioniscalledtherunoffcoefficient.Nearlyallcivilengineeringstructures,roofs,roads,andanyconcreteworkhavearunoffcoefficientofabout95percent.Thedamagecausedby
8、thesoildepositedduringfloodinginacitystreethasoftenbeencalculated,bu
