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Conceptual models of first-order controls governing river channel dynamics in mountain streams have been rarely tested in the field. In this Ph.D. thesis we examine the effects of hydro-meteorological forcing and sediment supply on the bedload transport dynamics of mountain streams. To this purpose we select three step-pool mountain streams that share identical granitic lithology, but exhibit contrasting sediment supply and hydro-climatic conditions. The three study sites, which are located in Trentino, Eastern Italian Alps, include the Ussaia Creek (2.3 km2) in Val di Sole, and the Grigno and Tolvà Creeks (7 km2) in Valsugana. The former is characterized by high, sand-rich sediment supply delivered by some 20 m-thick glacigenic deposits. The latter two, which flow through glacially carved bedrock terrain, are disconnected from colluvial sediment inputs so that sediment sources are limited to channel banks and bars during high flows. Mean annual precipitation is respectively 844 mm in Ussaia Creek and 1511 mm in Grigno and Tolvà Creeks. All study streams experience, to variable extents, snowmelt and rainfall-induced bedload transporting flows. To estimate quantitatively the effects and the interactions associated with sediment supply and hydro-meteorological forcing, we monitor precipitation and atmospheric temperature. Hydrological levels at instrumented sections are recorded via pressure transducers. Bedload transport is monitored by tagging and tracking 632 stones (b-axis: 30 to 131 mm; weight 88-4004 g). The tracking of these PIT-tagged tracers was conducted from December 2013 to December 2015 by means of an RFID portable pole antenna. Cumulatively, a total of 16, 11 and 19 bedload events were monitored respectively at Grigno, Tolvà and Ussaia Creek. We measured displacement lengths occurred during inter-survey periods, induced by peak flows associated to snowmelt, rainfall or a combination of the two (mixed-type). Active channel depth was evaluated via direct d

Coarse bed load transport is a crucial process in river morphodynamics but is difficult to monitor in mountain streams. Here we present a new sediment transport dataset obtained from two years of field‐based monitoring (2014‐2015) at the Estero Morales, a high‐gradient stream in the central Chilean Andes. This stream features step‐pool bed geometry and a glacier‐fed hydrologic regime characterized by abrupt daily fluctuations in discharge. Bed load was monitored directly using Bunte samplers and by surveying the mobility of PIT (passive integrated transponder) tags. We used the competence method to quantify the effective slope, which is the fraction of the topographical slope responsible for bed load transport. This accounts for only 10% of the topographical slope, confirming that most of the energy is dissipated on macroroughness elements. We used the displacement lengths of PIT tags to analyze displacement lengths and virtual velocity of a wide range of tracer sizes (38‐415 mm). Bed load transport in the Estero Morales show to be size‐selective and the distance between steps influences the displacement lengths of PIT tags. Displacement lengths were also used to derive the statistics of flight distances and resting times. Our results show that the average length of flight scales inversely to grain size. This contradicts Einstein's conjecture about the linear relationship between grain size and intervals between resting periods in a steep step‐pool stream in ordinary flood conditions.