简介:Longtermmorphologicalsimulationsusingcompletecoupledmodelsleadtoverytimeconsumingcomputations.Latteux(1995)presentedmodellingtechniquesdevelopedfortidalcurrentsituationsinordertoreducethecomputationaleffort.Inthispapertheapplicabilityofsuchmethodstosmallscaleproblemsisinvestigated.Itispointedoutthatthesemethodscanbetransferredtosmallscaleproblemsusingtheperiodicityofthevortexsheddingprocess.
简介:南部的山麓陆地受苦当时,节制到严重侵蚀在单身者下面的farmed?庄稼,到由犁板耕作,disking或耙地组成的系统为止常规。这主要由于高土壤侵蚀度,高精力春天?夏天暴风雨,低残余盖子,和差的管理因素。没有庄稼的一个冬季季节经常从降雨影响让土壤没有防卫。最小化耕种并且在夏天和冬季两个都把成长庄稼和庄稼残余留在表面的保存收割系统保护土壤免受腐蚀效果的伤害并且支撑生产率。在这篇论文我们在场并且讨论土壤损失,流量和残余生产数据从26年一2.71哈典型地代表小南部的山麓分水岭的集水。集水首先从1972~1974在夏天大豆(Glycine最大(L.)Merrill)和冬季休闲的常规耕种系统被管理。它然后被变换成收割夏天大豆的系统的保存,蜀黍(蜀黍二色(L.)Moench),或棉花(Gossypiumhirsutum(L.))和冬季大麦(Hordeumvulgare(L.)),小麦(Triticumaestivum(L.)),或继续了到礼品的苜蓿(Trifoliumincarnatum(L.))。立即的有的保存收割系统和在在夏天和冬季控制侵蚀和流量的剩余效果。破坏土壤侵蚀,从高精力,暴风雨显著地被减少。在保存收割下面在常规耕种下面从大约2Mgha-1yr-1增加到9.88Mgha-1yr-1的残余生产在20年的系统。
简介:TheblacksoilregionofnortheastChina,whichcoverstheProvincesofHeilongjiang,JilinandtheInnerMongoliaautonomousregionwithblacksoil,chernozemandmeadowsoil,hasexperiencedsoilerosionsinceintenseagriculturalreclamationbeganapproximately100yearsago.However,thesedimentdeliveryratio,definedasthefractionofgrosserosionthatistransportedfromagivenareainagiventimeinterval,isstillunclear.Inthisstudy,wecalculatedthedeliveryratioandanalysedchangesinerosiveprocesseswithinHebeicatchmentfrom1977to2007basedonananalysisofsedimentsoftheLiuduireservoir.Theoriginalvegetationlayerclearlyidentifiedthebottomofthereservoirwhenitwasconstructedin1977;thus,thereservoirsedimentscouldbepreciselydated.Thedeliveryratio,calculatedbycomparingthesedimentdepositioninthereservoirwiththetotalsoilerosionintheupstreamcatchment,wasfoundtobeexponentiallycorrelated(r~2=0.95,P<0.01)withdecreasinggrainsize,exceptforthefraction<0.002mm.Thedeliveryratiofortheclays(<0.002mm)waslow,averaging0.10duringthestudyperiod,whichindicatedpartialremovalofclaysfromthereservoir.Thechangesinthereservoirdepositionratereflectedthetemporalchangesintheerosionprocesses.Theexceptionallyhighrainfallin1998wasconfirmedbythedistributionsof~(137)Cs,~(210)Pb,andthegrain-sizeofthesediments.Beginningfromthepositionoftheoriginalgrasslayer,wedefinedthreeperiodsfrom1977to2007basedondepositionrates:2.40cmyear~(-1)from1977to1997,5.60cmyear~(-1)in1998duetounusuallyhighrainfall,and1.55cmyear~(-1)from1999to2007.Theoverallaveragedepositionratefortheentireperiodwas2.26cmyear~(-1).Precipitationwasfoundtobethemainfactoraffectingthesoilerosionofthestudyarea.
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