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Abstract: This paper investigates wood recruitment and deposition dynamics in a large gravel-bed, braided river (Tagliamento River, Italy). We used a combination of field measurements, automatically repeated ground images, and remotely sensed surveys to quantify wood input through bank erosion and associated downstream deposition. Two sites were investigated where floods caused the erosion of vegetated island edges. A lidar survey preceding the erosion events provided data on the morphology and vegetation structure of the eroded areas, allowing estimation of the number of trees that were uprooted. Sequences of ground-based images acquired automatically (and supported by field measurements) showed the time, number, and location of deposited trees. Results show that the complex morphology of braided rivers induces specific deposition patterns. We observed wide dispersal of wood on gravel bars, with jams characterised by a small number of logs (on average 2–3) and, in many cases, only a single log. A large proportion of the eroded trees (up to 40%) were deposited on the nearest downstream bar. This illustrates significant wood retention close to the recruitment site, with the remaining wood dispersed widely downstream. Differences in the observed level of local wood retention were associated with the proximity of the erosion site to the main channel and differences were also observed in retention between the peak and the falling limb of flood events, confirming that water depth and probably flow velocity are the crucial parameters controlling wood deposition. [Copyright &y& Elsevier]

Abstract: Studies on denudation rates can provide insight into the influence of climate change, tectonics, and human activities on landscape evolution. Research performed in Central Italy has shown considerable spatial variability of denudation rates in the major river basins. These studies have focused mainly on the Tyrrhenian side of the Italian peninsula, where Plio-Pleistocene marine deposits filling NW–SE elongated sedimentary basins have been uplifted during the Quaternary up to several hundreds of meters above present sea level. Small sub-catchments developed on clays are affected by sharp- and/or rounded-edged badlands (i.e. calanchi and biancane), representing denudation “hot spots” in the present-day morphoclimatic framework. In this paper, we analyze the relationships between indirectly estimated denudation rates at the catchment scale and field monitoring data at the hillslope scale. We attempt to better understand and quantify all hillslope processes that contribute to seasonal variability of denudation, to help with predicting the net input from “hot spots” to the overall estimated sediment yield at the basin outlets. At the hillslope scale, we discuss, in particular, the variability of denudation rates at calanchi and biancane badlands as a function of their different morphoevolution. [Copyright &y& Elsevier]

Debris flows are natural hazards causing fatalities and damages to infrastructures every year. One of the current challenges is to improve the predictability of such events using simulation tools. In this direction, the paper aims to model debris-flow generation starting from the water component and then simulating the motion of the bulked solid-fluid mixture mass flow. The debris component is progressively increased through entrainment of the channel bed material. The simulation has been performed exploiting the tool r.avaflow, which implements a physically-based model (Pudasaini and Mergili, 2019) for the flow propagation and an empirical multi-phase model for the entrainment processes. The investigated study case occurred in the Northeastern Alps of Italy, near the town of Cortina d'Ampezzo (Veneto Region), during the summer of 2017. The debris flow was triggered by a heavy rainstorm that caused extreme surface runoff, leading to entrainment of sediment from the channel bed. The debris flow obstructed the bridge of a regional road and consequently flooded the adjacent areas. Different types of debris flow simulations are performed, testing four specific functions to compute the entrainment rate. The simulated results are then compared against field observations. The analysis considers the differences in volume and depth of entrainment and in the output hydrograph. We conclude that entrainment is correlated with the terrain slope, particularly if it is calculated on a smoothed digital elevation model, which dilutes a less significant local steepness. We calibrate a spatially distributed slope-dependent erosion coefficient that successfully reproduced the observed entrainment volumes. The outcomes highlight the great importance of simulating debris flow entrainment processes adopting a multiphase model, which resulted particularly suitable for an accurate reproduction of the investigated event. The results, corroborated by further verifications, can improve the reliability of challenging predictive simulations on debris flow erosion. • Sediment entrainment is a fundamental process in debris-flow simulation. • A slope dependent empirical method to model sediment recruitment in debris flow simulation is proposed. • Debris flow erosion is correlated with the smoothed channel slope. [ABSTRACT FROM AUTHOR]