Farecdl Ahmed. Md et.al.SHIVAKUMAR, A.2018-07-172018-07-172017CAES 30http://krishikosh.egranth.ac.in/handle/1/5810060576Reservoirsortankscanbecontrolledbynumberofhydraulicstructures,such assluicegates,weirs,pipesandorifices.Thesetypesofstructuresmaybeclassified intotwogroups.Inonegroup,the flowtakesplaceunderpressurethrougha fixed crosssectionasisthecasefororifices,nozzles,shorttubes,sluicewaysandgates.The second group includes cases in which the flow occurs through an initially undeterminedcrosssection,suchasoverweirs,spillways,chutesanddropstructures (Simon,1981). . In this studythe determination ofcoefficient ofdischarge, coefficient of velocityand coefficientofcontractionoforifices and coefficientofdischarge of differentmouthpiecesaretakenintoconsideration. Themeanvalues ofcoefficientofdischargeby constanthead method of Bourda,Converging-diverging,mouthpiecewith1/d=4,mouthpiecewith1/d=2.5are 0.79, 0.75, 0.8, 0.82 with Coefficient ofvariation 3.11, 3.98, 7.2, 6.7 percentage respectively.ThemeanvaluesofcoefficientofdischargebyTimefallmethodof Bourda,Converging-diverging,mouthpiecewith1/d=4,mouthpiecewith1/d=2.5are 0.84,0.81,0.86,0.86withCoefficientofvariation168, 1.97,4.77,3.18percentage respectively. Themeanvalues ofcoefficientofdischargeby constantheadmethod of Orificeof12mmandOrificeof10mmare0.78and0.66withCoefficientofvariation 7.04and3.86respectively.ThemeanvaluesofcoefficientofdischargebyTimeof fall method ofOrifice of 12mm and Orifice of10mm are 0.65 and 0.66 with Coefficient ofvariation 1.90 and 2.49 percentrespectively. Themeanvalues of CoefficientofvelocityofOrifices of12mm and 10mm are0.98 and 0.98 with Coefficientofvariation 1.82 and 1.64percentrespectively. Themean values of CoefficientofcontractionofOrificesof12mmand 10mmare0.79and0.67with Coefficientofvariation8.0and4.19percentrespectively. The Coefficient ofvariation is lowerin Bourda Mouthpiece followed by Converging-diverging, mouthpiece with 1/d=4, mouthpiece with 1/d=2.5. The CoefficientofvariationislowerinOrificeof101nmcomparedtoOrifice12mm. Keywords: Orifice,Mouthpiece,coefficientofdischarge,Coefficientofvelocity, Coefficientofcontraction.ennullTechnical Report