Fator de encobrimento e seletividade no transporte: análise do fenônemo e estudo experimental

Abstract

The degree of size-selectivity in sediment transport of sand mixtures was studied by making experiments using a sediment-feed laboratory channel. Four different mixtures were used, with diameters varying between 0,59 mm and 1,91 mm. The reference-transport method proposed by Parker et al. (1982) was adopted to calculate the critical shear stress for motion. One the development of the studies, M1 and M2 mixtures, with a nearly uniform size distribution, were represented by the median diameters D50 and submitted to a general analysis of transport for the whole mixture. On the other hand, M3 and M4 mixtures, with a logarithm type size distribution, were submitted to a fractional analysis of transport. M2 and M4 have the same diameter. The obtained hiding function parameters show a condition of equality for the transport. The critical shear stress rates obtained for M2 and M4 confirm D50 as a representative parameter of the mixture. The results lead to conclude that critical shear stress for the median size (tc50) based on a general analysis of transport can be used to express the average shear stress of each fraction of the mixture