The necessity of updating the numerical models inputs, because of geometrical and resistive variations in rivers subject to solid transport phenomena, requires detailed control and monitoring activities. The human employment and financial resources of these activities moves the research towards the development of expeditive methodologies, able to evaluate the outflows through the measurement of more easily acquirable sizes. Recent studies highlighted the dependence of the entropic parameter on the kinematical and geometrical flow conditions. They showed a meaningful variability according to the section shape, dimension and slope. Such dependences, even if not yet well defined, could reduce the difficulties during the field activities, and also the data elaboration time. On the basis of such evidences, the relationships between the entropic parameter and the geometrical and resistive sizes, obtained through a large and detailed laboratory experience on steady free surface flows in conditions of macro and intermediate homogeneous roughness, are analyzed and discussed., {"references":["C. L. Chiu, \"Entropy and probability concepts in hydraulics,\" Journal of Hydraulic Engineering, vol. 113, no. 5, pp. 583-600, May 1987.","C. L. Chiu, \"Entropy and 2-D velocity distribution in open channels,\" Journal of Hydraulic Engineering, vol. 114, no. 7, pp. 738-756, July 1988.","C. L. Chiu, \"Velocity distribution in open channel flow,\" Journal of Hydraulic Engineering, vol. 115, no. 5, pp. 576-594, May 1989.","C. L. Chiu, \"Application of entropy concept in open-channel flow,\" Journal of Hydraulic Engineering, vol. 117, no. 5, pp. 615-628, May 1991.","C. L. Chiu, and D. W. Murray, \"Variation of velocity distribution along non uniform open-channel flow,\" Journal of Hydraulic Engineering, vol. 118, no. 7, pp. 989-1001, July 1992.","M. Greco, and D. Mirauda, \"Experimental analysis for the entropic parameter evaluation,\" in Proc. 2nd Int. Conf New Trends in Water and Environmental Engineering for Safety and Life: Eco-compatible Solutions for Aquatic Environments, Capri (Italy), June 2002.","M. Greco, and D. Mirauda, \"Valutazione globale del parametro entropico di velocitk\" L 'Acqua, vol. 5, pp. 17-23,2002.","T. Moramarco, C. Saltalippi, and V. P. Singh, \"Estimation of mean velocity in natural channels based on Chiu's velocity distribution equation,\" Journal of Hydrologic Engineering, vol. 9, no. 1, pp. 42-50, January/February 2004.","R. Xia, \"Relation between mean and maximum velocities in a natural river,\" Journal of Hydraulic Engineering, vol. 123, no. 8, pp. 720-723, August 1997.\n[10] C. L. Chiu, and C. A. A. Said, \"Maximum and mean velocities and entropy in open-channel flow,\" Journal of Hydraulic Engineering, vol. 121, no. 1, pp. 26-35, January 1995.\n[11] M. Greco, and D. Mirauda, \"Expeditive methodology for river water discharge evaluation,\" in Proc. 2nd Int. Conf on Fluvial Hydraulics, River Flow 2004, Napoli (Italy), June 2004.\n[12] C. L. Chiu, and N. C. Tung, \"Maximum velocity and regularities in open-channel flow,\" Journal of Hydraulic Engineering, vol. 128, no. 4, pp. 390-398, April 2002.\n[13] C. L. Chiu, and S. M. Hsu, \"Probabilistic approach to modeling of velocity distributions in fluid flows,\" Journal of Hydrology, vol. 316, pp. 28-42,2006.\n[14] A. Bumelli, D. Mirauda, T. Moramarco, and V. Pascale, \"Applicability of entropic velocity distributions in natural channel,\" in Proc. 4th Int. Conf on Fluvial Hydraulics, River Flow 2008, Izmir-Cesme (Turkey), September 2008.\n[15] T. Moramarco, A. Ammari, A. Bumelli, D. Mirauda, and V. Pascale, \"Entropy Theory Application for Flow Monitoring in Natural Channels,\" in Proc. of the iEMSs 4th Biennial Meeting International Congress on Environmental Modelling and Software, Barcelona, Spain, July 2008.\n[16] D. L. Rosgen, \"A classification of natural rivers,\" Catena, vol. 122, pp. 169-199,1994.\n[17] H.\tSchlichting,\t\"Experimentelle\tUntersuchungen\tzum \nRauhigskeitsproblem,\" Ingenieur Archive, vol. 7, no. 1, February 1936.\n[18] H. Rouse, \"A classification of natural rivers,\" Journal of Hydraulics Division, vol. 91, no. 4, pp. 1-25,1965.\n[19] H. M. Morris, and J. M. Wiggert, Applied hydraulics in engineering, New York, USA, John Wiley & Sons, inc., 1971.\n[20] ISO 748, Measurement of liquid flow in open channel - Velocity-area methods, 1997."]}