Characterization of wood‐laden flows in rivers

Abstract

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.

Las ecuaciones de Saint Venant para la modelización de avalanchas de nieve densa

“…), y por los que, además, los supuestos de fluido barotrópico e isotrópico pueden no ser adecuados. Incluso, en función de su naturaleza, podría ser necesario distinguir dos o tres fases fluidos-sólido para capturar adecuadamente su comportamiento (Ruiz-Villanueva et al, 2019).…”

“…El presente documento tiene por objeto mostrar las posibilidades de las ecuaciones de Saint Venant para simular flujos de agua en estado sólido (avalanchas de nieve), empleando para ello un tratamiento numérico específico para resolver las ecuaciones que permite detener el fluido aun en ausencia de terreno plano. Para ello se ha empleado el modelo Iber (Bladé et al, 2014), un modelo hidráulico bidimensional que recientemente ha incorporado un módulo para la simulación de fluidos no-Newtonianos (Ruiz-Villanueva et al, 2019), y concretamente para avalanchas de nieve de placa-densa . La herramienta se ha probado en dos casos de estudio para analizar el comportamiento del fluido en función de los parámetros de los modelos reológicos.…”

Role of friction terms in two-dimensional modelling of dense snow avalanches

“…where ℎ is the flow depth, and are the two velocity components, is the gravitational acceleration, , and , are the two bottom slope components, and ℎ, and ℎ, are the two components of the rheological model. For water flows, the factor is equal to 1 (hydrostatic pressure), and is the a variation rate of the fluid column at a specific point, for example, a source or a sink (Bladé et al, 2019b), or during rainfall/infiltration processes in hydrological modelling (Cea and Bladé, 2015).…”

“…In the numerical modelling of flows it is necessary to establish a wet-dry limit depth, which is a threshold to consider whether there is flow in a mesh element or not. This is a relevant parameter for water flow, especially in flat areas (Cea et al, 2007;Ramos-Fuertes et al, 2013;Sanz-Ramos et al, 2019b) and for hydrological modelling (Cea and Bladé, 2015;Sanz-Ramos et al, 2018b), but it also applies to non-Newtonian-fluid flows such as snow avalanches. Very large wet-dry limits, https://doi.org/10.5194/nhess-2019-423 Preprint.…”

A New Framework to Model Hydraulic Bank Erosion Considering the Effects of Roots

“…Further, streambank retreat can cause large wood (LW) recruitment, subsequent entrainment and mobilization of LW. This ultimately adds to the severity of floods, exacerbating damage near civil structures and in urbanized areas [10][11][12][13][14][15].…”