Comparison-of-HYDRUS-2D-Simulations-of-Drip-Irriga

EvaluationofSoilWaterProfileSimulationsinDripIrrigationBasedonSoilHydraulicPropertieswithExperimentalObservationsSinaBesharat1*,NedaKhanmohammadi2,HosseinRezaie1,JavadBehmanesh11WaterEngineeringDepartment,UniversityofUrmia,Urmia,Iran2Ms.C.StudentofWaterEngineeringDepartment,UniversityofUrmia,Urmia,Iran*[e-mail]lpotentialofdripirrigationtechnologyrequiresoptimizingtheoperationalparametersthatareavailabletoirrigators,suchasthefrequency,rate,anddurationofwaterapplication.Numericalsimulationisafastandinexpensiveapproachtostudyingoptimalmanagementpractices.Unfortunately,littleworkhasbeendonetoinvestigatetheaccuracyofnumericalsimulations.ThepurposeofthisresearchisthecomparisonofHYDRUS-2Dsimulationsofdripirrigationwithexperimentaldata.Inthisstudy,asandy-loamsoilwasirrigatedusingT-Tapedriptubing.Threevariousdripirrigationtrials(30,45and75hr)werecarriedout.Attheendofeachirrigation,thewatercontentdistributioninthesoilwasdeterminedbygravimetricsampling.TheresultsshowedthatHYDRUS-2Dhashighabilityinpredictionofsoilwatercontentdistributionandcanuseasausefultoolforinvestigatinganddesigningdripirrigationmanagementpractices.Also,variousmethodsofROSETTAwereevaluatedforhydraulicparametersestimationandresultsshowedthatcompletemodelcanprovidereasonableresults.Keywords:Numericalsolution,HYDRUS-2D,ROSETTAmodel.1.IntroductionRealizingthefullpotentialofdripirrigationtechnologyrequiresoptimizingtheoperationalparametersthatareavailabletoirrigators,suchasthefrequency,rate,anddurationofwaterapplication.Numericalsimulationisafastandinexpensiveapproachtostudyingoptimalmanagementpractices.Unfortunately,littleworkhasbeendonetoinvestigatetheaccuracyofnumericalsimulations.Thus,ananalysisoftrickleirrigationperformanceseemstonecessitatetheapplicationofmoresophisticated,physicallybasedflowmodels.However,thenumericalcharacterofthesesubsurfaceflowmodelsrepresentsoneofthemajorbarriersinusingthemforanobjectiveandoptimalevaluationofirrigationparameters.Soilwettingpatternsundersurfaceandsub-surfacemicroirrigationhavebeenmeasuredand/oranalyzedtheoreticallybyanumberofauthors,includingBresler(1978),Assouline(2002),Coteetal.(2003),Skaggsetal.(2004),Gardenasetal.(2005),Singhetal.(2006),Wangetal.(2006),andLazarovitchetal.(2007),tonameonlyafew.Amongthesestudies,severalofthemorerecentones(e.g.Siyaletal.,2009,Assouline,2002;Coteetal.,2003;Skaggsetal.,2004;Gardenasetal.,2005)haveusedHYDRUS-2D(Simuneketal.,1999)tosimulatesoilwetting.Forexample,Skaggsetal.(2004)demonstratedthatHYDRUS-2Dsimulationsofdripirrigationwereinagreementwithdetailedfieldmeasurements.Numericalsimulationisanefficientapproachtoinvestigatingoptimaldripmanagementpractices(e.g.,Meshkatetal.,1999;Schmitzetal.,2002;Coteetal.,2003).However,therehavebeenveryfew,ifany,studiesshowingthatnumericalsimulationsofdripirrigationagreewithfielddata,thusbringingintoquestionthevalueofconclusionsdrawnfromnumericalsimulations.ThepurposeofthisresearchisthecomparisonofHYDRUS-2Dsimulationsofdripirrigationwithexperimentaldata.AgriculturalEconomyandTechnologyInformationInstitute,XinjiangAcademyofSciences(222.82.246.50)-2013/1/21Download2.MaterialandMethods2.1.FieldexperimentThreevariousdripirrigationtrials(30,45and75hr)werecarriedout.Attheendofeachirrigation,thewatercontentdistributioninthesoilwasdeterminedbygravimetricsampling(Fig.1).FIGURE1:Wettingpatternobservedatthesoilsurface(A)andwithinthesoil(B)and(C).2.2.HYDRUSsimulationsTheHYDRUS(2D/3D)softwarepackage(Simuneketal.,2006)simulatesvariablysaturatedwaterflowinporousmediabysolvingthemixedformoftheRichardsequationusingaGalerkinfinite-elementmethod.ThesoilhydraulicpropertiesinHYDRUSarebasedonthevanGenuchten(1980)model:)h(Kzh)h(Kzxh)h(Kxt(1)whererandsaretheresidualandsaturatedwatercontents(L3L-3),respectively;Ksisthesaturatedhydraulicconductivity(LT-1);aisanempiricalconstantthatisinverselyrelatedtotheair-entrypressurevalue(L-1);nisanempiricalparameterrelatedtothepore-sizedistribution(unitless);lisanempiricalshapeparameter;m=1-1/n(unitless);andSeistheeffectivesaturationgivenby:0h)h1()h(mnrsr(2)ACBAgriculturalEconomyandTechnologyInformationInstitute,XinjiangAcademyofSciences(222.82.246.50)-2013/1/21Download0.000.100.200.300.40020406080Depth(cm)Watercontent0.000.100.200.30020406080Depth(cm)Watercontent0.000.100.200.300.40020406080Depth(cm)Watercontent0.000.100.200.30020406080Depth(cm)Watercontent2mm/1eles])S1(1[SK)h(K(3)n/11m,Srsre(4)3.ResultsTheresultsshowedthatHYDRUS-2Dhashighabilityinpredictionofsoilwatercontentdistributionandcanuseasausefultoolforinvestigatinganddesigningdripirrigationmanagementpractices.Also,variousmethodsofROSETTAwereevaluatedforhydraulicparametersestimationandresultsshowedthatcompletemodelcanprovidereasonableresults.Fig.2showthemeasuredandsimulatedwatercontentdistributionsfor15and75hoursandfor2radial.Inthisfigurecontainscontourplotsofthemeasuredandsimulatedwatercontentprofiles,aswellascomparisonsofthemeasuredandsimulatedwatercontentsalongselectedprofiletra