Dam spillways are the structures that lead rightly and safely the outflow downstream, so that the dam integrity can be guaranteed. Many accidents with dams have been caused by an inadequate spillway design or insufficient capacity. This situation is particularly important in embankment or rockfill dams, because the possibility of overtopping failure of the dam. The morning glory spillway may be used when there is not available space for a conventional spillway. Engineers use physical modeling to design this kind of structures, and therefore scale effects can cause a difference between model and prototype discharge rating curve. This paper has the objective of analyze the discharge flow rating curve in a vertical shaft with morning glory inlet and to correct scale effects for low heads. An experimental study has been carried out, using the spillway model of Paraitinga Dam in 1: 51, 02 scale. As a result equations are proposed in order to correct the discharge coefficient in the discharge rating curve for low heads. 20412046China Society for Hydropower Engineering,Chinese Hydraulic Engineering Society,et al.,Int. Assoc. Hydraulic Eng. Res. (IAHR),National Natural Science Foundation of China,State Key Lab. Hydrology-Water Resources Hydraulic Eng.Chanson, H., Hydraulics of retangular dropshafts (2004) Journal of Irrigation and Drainage Engineering, 130 (6), pp. 523-529(1987) Design of Small Dams, , EUA-Bureau of Reclamation Washington, D.CFais, L.M.C.F., (2007) Experimental Analysis of Bend in Vertical Shafts with Morning Glory Inlet, , Doctoral Tesis, Civil Engineering, Architecture and Urbanism College, UNICAMP, Campinas, Brazil (in portuguese)Ferreira, L.M.C., (2001) Vortex Formation in Vertical Intakes, , Master degree tesis, Civil Engineering, Architecture and Urbanism College, UNICAMP, Campinas, Brazil (in portuguese)Ferreira, L.M.C., Genovez, A.I.B., Analysis of air entrainment in vertical shaft with different inlets (2005) Water Resources Brazilian Symposium, 26. , 2005, João Pessoa, Paraíba, Brazil. (in CD-ROM), 20 a 24 nov 2005 (in portuguese)Genovez, A.I.B., (1991) Scale Effect Study in Air Entrainment in a Shaft with Morning Glory Entrance, , Doctoral Tesis, USP, São Paulo, Brazil (in portuguese)Genovez, A.I.B., (1997) Evaluation of Limit Lenght in the Study of Air Entrainment in Shaft with Morning Glory Entrance, , Associate Professor Tesis, UNICAMP. Campinas, SP (in Portuguese)Heidarpour, M., Chamani, M.R., Velocity distribution over cylindrical weirs (2006) Journal of Hydraulic Research, 44 (5), pp. 708-711Kobus, H., Fundamentals (1980) Hydraulic Modelling, , German Association for Water Resources an Land Improvement, Bulletin 7, Cap. 1Kolkman, P.A., Considerations about the accuracy of discharge relations of hydraulic structures and the use of scale models for their calibration (1984) Symposium on Scale Effects in Modelling Hydraulic Structures, , Esslingen, Germany: 2.1-1 to 2.1-12Mussalli, Y.G., (1969) A Study of Flow Conditions in Shaft Spillway, 158p. , Atlanta, EUAPinto, N.L., Neidert, S.H., Model-prototype conformity in aerated spillway-flow (1982) International Conference on the Hydraulic Modelling of Civil Engineering Structures, , Coventry, England sep 22-24, 1982Ribeiro, A.A., Tomas, T.D.L.G., (1976) Vertical Dropshafts, , Porto (in portuguese)(1971) Tecnological Hydraulic Center, , São Paulo (State) DAEE Spillway of Paraitinga Dam. Model study of Paraitinga Dam. Report, reviewedSarginson, E.J., The influence of surface tension on weir flow (1972) Journal of Hydraulic Research, 10 (4), pp. 431-445Sarginson, E.J., Scale effects in model tests on weir (1984) Symposium on Scale Effects in Modelling Hydraulic Structures, , Esslingen, Germany: 3.3-1 to 2.3-4Zhao, C., Experimental study of flow in a vortex drop shaft (2006) Journal of Hydraulic Engineering, 132 (1), pp. 61-68