DOWNWARD AND UPWARD APPROACH FOR ENTROPY VELOCITY PROFILE M. Greco, D. Mirauda Basilicata University Department of Environmental Engineering and Physics Via della Tecnica, 3, 85100 Potenza Italy ABSTRACT. The use of the entropy velocity profile in the field of Applied Hydraulics allows describing the local flow condition through the use of simple parameters easily to derive. The features of the law, based on the mean and maximum velocity, as well as the recent results concerning the relationship between the mean and the maximum cross section velocity, suggest employing the velocity profile at both local and global scale. That is, downward and upward approaches are proposed in order to describe the flow energy budget at the small scale and the morphological river characteristics at the high scale respectively. 1. Introduction A relevant challenge for hydraulic engineers has been and still is to give a suitable description of flow field in terms of velocity distribution inside the current. Sediment transport processes as well as pollutant diffusion are classic hydraulic examples in which the knowledge of cinematic assessment of the flow plays a fundamental role for prediction and design purposes. The real needed is to handle an easy velocity law which gives suitable results basing on few parameters simple to measure or derive. Recent studies outline the opportunity to relate the local energy budget to the informational content hold into the point velocity measurements through a velocity distribution profile derived by an entropy-probabilistic approach (Chiu, 1987; 1989; 1991). These analyses allow an easy employment in the field of the Applied Hydraulic Engineering due to the use of simple derivable parameters instead of very difficult and hardly measurable ones. The use of a velocity profile law, defined through a few data set collected in situ or obtained via the knowledge of the mean cross velocity (Chiu et al., 1995; Xia, 1997), plays an important role in the study of open channel flow. That is a clever contribute to obtain more suitable information about the flow field and relative processes ongoing with respect to the application limits and suitability of the results. The entropy model has been tested in several regular flows giving good performance for the body current description particularly, while seems to be inconsistent for representation of the motion acting in “delicate” region of the flow field (i.e. boundary layer) requiring further boundary condition “mechanically based” in order to calibrate and efficaciously correct the velocity profile as well (Pulci Doria, 1992). Nevertheless in the study of natural current with high relative submergence (water depth over roughness typical dimension) the boundary effects are constrained in a bounded zone, small with respect to the flow field generally, so that the motion of the fluid particles can be though as a turbulent kernel at whole. Through this assumption the entropy model can take place giving a satisfactory description of the velocity field. In the paper velocity data sets referred to natural flows are described by the use of entropy model. Further, stressing the representative scheme of the flow, a scaling approach for the entropy law is proposed obtaining a better description of the velocity field features with respect to the geometry consistence and variation of the flow field. Computed velocity profiles are compared to the measured ones for different river cross section at different water discharge stages allowing an evaluation of the entropy model consistence.