TRANSPORT OF GRADED SEDIMENT IN TURBULENT OPEN-CHANNEL FLOWS. A PHENOMENOLOGICAL APPROACH

摘要

The description of bedload transport as an event-driven phenomena constitutes a promising alternative to the current bedload formulas. The impinging jet model proposed by Hogg et al. (1996) allows for the quantification of the discharge as a function of the characteristics of the jet and of the bed particles. The jet simulates the action of a sweep event. In spite of disregarding all other turbulent events as contributors for bed load, it is regarded as a sound framework upon which a more realistic model can be built. The task of ameliorating the impinging jet model is, in this work, limited to the estimation of a number of non-dimensional parameters and its generalisation for poorly sorted sediment mixtures. The methodology followed was of experimental nature. Laboratory experiments were conducted in order to obtain mean flow parameters, turbulent event statistics, bedload composition and individual grain paths and velocities. The impinging jet model was then modified to accommodate the relevant empirical information. Comparison with independent experimental data on fractional bedlod transport rates provided an estimation of the quality of the model.