Inorganic sediment is not the only solid‐fraction component of river flows; flows may also carry significant amounts of large organic material (i.e. large wood), but the characteristics of these wood‐laden flows (WLFs) are not well understood yet. With the aim to shed light on these relatively unexamined phenomena, we collected home videos showing natural flows with wood as the main solid component. Analyses of these videos as well as the watersheds and streams where the videos were recorded allowed us to define for the first time WLFs, describe the main characteristics of these flows and broaden the definition of wood transport regimes (adding a new regime called here hypercongested wood transport). According to our results, WLFs may occur repeatedly, in a large range of catchment sizes, generally in steep, highly confined single thread channels in mountain areas. WLFs are typically highly unsteady and the log motion is non‐uniform, as described for other inorganic sediment‐laden flows (e.g. debris flows). The conceptual integration of wood into our understanding of flow phenomena is illustrated by a novel classification defining the transition from clear water to hypercongested, wood and sediment‐laden flows, according to the composition of the mixture (sediment, wood, and water). We define the relevant metrics for the quantification and modelling of WLFs, including an exhaustive discussion of different modelling approaches (i.e. Voellmy, Bingham and Manning) and provide a first attempt to simulate WLFs. We draw attention to WLF phenomena to encourage further field, theoretical, and experimental investigations that may contribute to a better understanding of flows in river basins, leading to more accurate predictions, and better hazard mitigation and management strategies. © 2019 John Wiley & Sons, Ltd.

Large pieces of in-channel wood can exert an important role on the ecological and morphological properties of gravel-bed rivers. On the other side, when transported during flood events, large wood can become a source of risk for sensitive structures such as bridges. However, wood displacement and velocity in river systems are still poorly understood, especially in large gravel-bed rivers. This study focuses on log transport in a valley reach of Tagliamento River (Italy). Log displacement during flood events of different magnitude recorded from June 2010 to October 2011 have been analysed thanks to the installation of 113 radio frequency identification (RFID) tags and 42 GPS tracker devices in logs of different dimensions. Recovery rate of logs equipped with RFID and GPS trackers was about 43% and 42%, respectively. The GPS devices allowed us to analyse in details the log displacement and transport overtime, indicating a higher log entrainment during rising limb of hydrographs. The threshold for the entrainment of logs from low bars is around 40% of bankfull water stage. No clear relationship was found between the peak of flood and log displacement length and velocity. However, log displacement length and velocity appears significantly correlated to the ratio between the peak of flow and the water stage exceeding the flow duration curve for 25% of *Revised manuscript with no changes marked Click here to view linked References

The 2008 eruption of Chaitén volcano in southern Chile severely impacted several densely forested river catch-\ud ments by supplying excess pyroclastic sediment to the channel networks. Our aim is to substantiate whether\ud and how channel geometry and forest stands changed in the Rayas River following the sudden input of pyroclas-\ud tic sediment. We measured the resulting changes to channel geometry and riparian forest stands along 17.6 km of\ud the impacted gravel-bed Rayas River (294 km\ud 2\ud ) from multiple high-resolution satellite images, aerial photo-\ud graphs, and fieldwork to quantify yield volume characteristics of the forest stands. Limited channel changes dur-\ud ing the last 60 years before the eruption reflect a dynamic equilibrium condition of the river corridor, despite the\ud high annual precipitation and the sediment supply from Chaitén and Michinmahuida volcanoes in the headwa-\ud ters. Images taken in 1945, 2004, and 2005 show that total size of the vegetated channel islands nearly doubled\ud between 1945 and 2004 and remained unchanged between 2004 and 2005. Pyroclastic sediment entering the\ud Rayas River after the 2008 eruption caused only minor average channel widening (7%), but killed all island veg-\ud etation in the study reach. Substantial shifts in the size distribution of in-channel vegetation patches reflect losses\ud in total island area of 46% from 2005 to 2009 and an additional 34% from 2009 to 2012. The estimated pulsed re-\ud lease of organic carbon into the channel, mainly in the form of large wood from obliterated island and floodplain\ud forests, was 78–400 tC/km/y and surpasses most documented yields from small mountainous catchments with\ud similar rainfall, forest cover, and disturbance history, while making up between 20% and 60% of the annual carbon\ud burial rate of fluvial sediments in the northern Patagonian fjords. We conclude that the carbon footprint of the\ud 2008 Chaitén eruption on the Rayas River was more significant than the measured geomorphic impacts on chan-\ud nel geometry for the first five years following disturbance. The modest post-eruptive geomorphic response in this\ud river is a poor indicator of its biogeochemical response

Until very recently, rivers have been considered as the result of the interaction between water and sediments, thus simplifying this very complex system. In doing so, one important component was missed. This is vegetation, namely trees growing on banks, floodplains, and bars/islands. The pattern of riparian vegetation in gravel bed rivers depends on the climate, hydrological regime, floods, sediment transport and the morphological settings of the river. Also, the marked spatial variability of density, height, species diversity, age, and rates of growth reflects the very complex nature of bed colonization, the strong influence of sequences and magnitude of floods, and the feedbacks between morphology, vegetation and hydraulics. Furthermore, a wide array of human impacts acting at either the basin or river network scales can influence substantially the morphodynamics and thus the characteristics, types and distribution of vegetation within the river corridor. The aim of the work is to analyze the relationship between the vegetation structure and the morphological characteristics of two sub-reaches of the Piave river which suffered both floods and intense and multiple human impacts especially due to dam building and inchannel gravel mining. Six cross sections were surveyed and vegetation, soil variables and sediment deposited were measured on 214 plots, (4 x 4 m each one and 10 m spaced). Each vegetation plot were recognized on a recent aerial photo (2009) and its ages were calculated performing both a multi-temporal analysis of older photos (1960, 70, 80, 91, 99, 2006 and 2009) analysis. The Piave River shows a complex pattern of vegetation distribution along the cross-sections with no clear relationship between the elevation and the plant communities. However later successional plant communities cover older surfaces and the thickness of the sand layer helps explaining differences in areas dominated by different species (e.g. Salix alba and Salix eleagnos).

Riparian vegetation and large wood play a crucial role in shaping rivers. On the one hand, vegetation tends to increase bank stability, reduce channel width and reduce the braiding index in gravel-bed rivers.Conversely, large wood tends to increase channel dynamics and promote avulsions. The effects of vegetation and large wood have been rarely simulated together in flume experiments. In this paper we present a series of experimental runs conducted in a large flume facility, using cylindrical wooden dowels and alfalfa seedlings to represent logs and vegetation, respectively, in order to investigate their role on determining the topographical nature of braided river systems. A terrestrial laser scanner was used to measure in detail the topography of the channels and bars, and distribution of the elevations and secondorder structure functions were used to explore the topography that large wood and vegetation imposed on the braided pattern in the flumes. Results show that vegetation reduced the braiding index and produced wider and deeper channels. The standard deviation of the bed elevations was higher than in flumes without vegetation. Large wood alone was not effective in changing the braiding index or the standard deviation of the elevations. When vegetation and large wood acted together in the flume, the braiding index reached a minimum value, and the skewness of the distribution of elevation increased, revealing shallower pools if compared with runs conducted with only vegetation.