Theeffectoffullysubmergedbouldersontheflowstructureinchannelshasbeenstudiedbysomeresearchers.However,manynaturalstreamshavebedmaterialwithbouldersthatarenotfullysubmergedunderwater.Inmanynaturalstreams,boulderscoverbetween1%and10%oftheareaofthestreamreach.Theeffectofnon-submergedbouldersonthevelocityprofileandflowcharacteristicsisveryimportantforassessingriverbeddeformation.Theobjectivesofthispaperaretofindthepatternofvelocitydistributionaroundanon-submergedboulderandtocompareitwiththeclassicalstudiesonflowresistanceandReynoldsstressdistributioninopenchannels.Also,byconsideringthevariationintheReynoldsstressdistributionatdifferentlocationsaroundanon-submergedboulder,theeffectofanon-submergedboulderontheestimationofshearvelocityandresistancetoflowhasbeeninvestigated.Resultsindicatesthatinsidethescourholecausedbyanon-submergedboulderinarivervelocitydistributionsareirregular.However,velocitydistributionsareregularoutsidethescourhole.ThepresenceofthebouldercausesaconsiderabledeviationoftheReynoldsshearstressfromtheclassicdistribution,showinganon-specificdistributionwithnegativevalues.TheclassicalmethodsforcalculatingshearvelocityarenotsuitablebecausethesemethodsdonotgivedetailedvelocityandReynoldsstressdistributionsinnaturalriverswithalotofboulders.Thus,theeffectofanon-submergedboulderontheestimationoftheresistancetoflowbyconsideringthevariationsinvelocityandReynoldsstressdistributionsatdifferentlocationsaroundanon-submergedboulderisimportantandneedstobestudiedinanaturalriverinsteadofjustinlaboratoryflumes.ThenegativevaluesinReynoldsstressdistributionaroundaboulderindicatethattheclassicalmethodsareunabletopredictresistancetoflow,andalsoshowstrongturbulenceinsidethescourholewherethecomplexflowconditionspresentambi
