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1、EnglishForWaterResourcesSoilerosionandsoilconservationAbstract:Themajormovementofsoilerosionandsoilerosion,soilerosionhazardstohumansistheerosionofthefirstoverofthelandbarrenexception,andthereforecannotgrowcrops,farmersbankruptandhadtomovetoabetterplace.Themainmetho
2、dstopreventsoilerosionisagoodmethodofcultivation.BasedonU.S.soilasanexampleabouthowtobuildterracesandothermethods.1IntroductionAllcivilengineersknowtwomaintypesofsoilmovement,soilcreeportheslowflowofsoil,andthefasterflows,calledslides,slipsoravalanches.Thefastermove
3、mentgenerallymoveslayersthataredeeperthanthosemovedbysoilcreep.Butmoreimportantthaneitherofthesetwotypes(atleastinthequantityofsoilremovedeveryyear)aresoilerosion,theremovalofsoilbyflowingwaterfromgroundthatisusuallydry,andscourtheremovalofsoilorrockfromthebedorbank
4、ofariverorstream.Forestsoilundergrowingtreesgenerallydoesnoterodebecausetheleavesanddeadorbrokenwoodholduptherainlikeblottingpaperandpreventitsattackingthesoil.Themainactionofdeadleavesindelayingrunoffisthattheyholdopenthedrainagechannelsintothesoil.Inbaresoilthatis
5、notprotectedinthisway,thesoilporesarequicklyblockedduringrainbythefinesoilgrainsflowingintothem.Therainrunsoverthesurfaceandnotintoit,smallchannelsform,tobedeepenedeventuallyintothereallydamagingdeep,scouredditchescalledgullies.Thefirstdisadvantageofsoilerosiontoman
6、kindisthaterodedlandissopoorthatcropswillnotgrowonit,farmersareruined,andhavetomovetobetterland.ThishashappenedtomanythousandsoffarmersintheUnitedStates,whichinthelasthundredyearshasprobablysufferedmoreformerosionthananyothercountry.Theseconddisadvantageisthatsoiler
7、osionmakesfloodingbothmoresevereandmorefrequentsincethewaterrunsoffthesoilmorequickly.Inforestareas,95percentoftherainfallisabsorbedwhileonbaresoilabout95percentmayrunoff.Thisproportioniscalledtherunoffcoefficient.Nearlyallcivilengineeringstructures,roofs,roads,anda
8、nyconcreteworkhavearunoffcoefficientofabout95percent.Thedamagecausedbythesoildepositedduringfloodinginacitystreethasoftenbeencalculated,bu
