Morphological changes and grain sorting in mountain gravel-bed streams

The paper shows a mathematical model for the evaluation of the morphological changes in the transitional-aggraded reaches of gravel-bed streams, characterized by a high variability of water discharges abd a braided configuration. The model is based on the continuity and transport equations per fractio. These equations are obtained by using the hypothesis that the actual transport rate is equal to the transport capacity under geomorphoclimatic equilibrium conditions, by averaging over the year the variables involved in the phenomenon. The intra-annual distribution of water discharges is represented by using the flow-duration curve of the stream. The transport capacity is evaluated per each fraction of sediment, hypothesizing that, for each duration, locally steady and quasu-uniformo flow conditions occur. In addition, the model takes into account the presence of the "pavement" controlling the mobility of the mixed-size fractions of the sediment.