Can the discharge of a hyperconcentrated flow be estimated from paleoflood evidence?

Many flood events involving water and sediments have been characterized using classic hydraulics principles, assuming the existence of critical flow and many other simplifications. In this paper, hyperconcentrated flow discharge was evaluated by using paleoflood reconstructions (based on paleostage indicators [PSI]) combined with a detailed hydraulic analysis of the critical flow assumption. The exact location where this condition occurred was established by iteratively determining the corresponding cross section, so that specific energy is at a minimum. In addition, all of the factors and parameters involved in the process were assessed, especially those related to the momentum equation, existing shear stresses in the wetted perimeter, and nonhydrostatic and hydrostatic pressure distributions. The superelevation of the hyperconcentrated flow, due to the flow elevation curvature, was also estimated and calibrated with the PSI. The estimated peak discharge was established once the iterative process was unable to improve the fit between the simulated depth and the depth observed from the PSI. The methodological approach proposed here can be applied to other higher-gradient mountainous torrents with a similar geomorphic configuration to the one studied in this paper. Likewise, results have been derived with fewer uncertainties than those obtained from standard hydraulic approaches, whose simplifying assumptions have not been considered. © 2011 by the American Geophysical Union.This work was funded by the Spanish Ministry of Science and Innovation within the framework of the CICYT Dendro-Avenidas project (CGL2007-62063) and the MAS Dendro-Avenidas project (CGL2010-19274). We are especially grateful to Robert D. 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Strategies in the 2D numerical modelling of wood transport in rivers

In recent years the improvements in computational capacity and the advances in numerical modelling techniques have produced a significant increase in the type of river processes that can be studied with the support of numerical models. Water quality and sediment transport are some of these processes, and it also applies to the case of wood transport. In the last five years several publications have proven the utility of numerical modelling of wood transport for predicting and better understanding wood dynamics, analyzing the influence of wood on flow conditions, and the interactions with infrastructures, and for including this phenomenon in the flood risk assessment. Besides these studies, numerical modelling of wood in rivers is still challenging, and different strategies can be used. We present and discuss some details of numerical strategies used in the simulation of wood transport within a 2D hydrodynamic model based on the finite volume method.Peer Reviewe

Characterization of wood-laden flows in rivers

This is the accepted version of the following article: [Ruiz‐Villanueva, V., Mazzorana, B., Bladé, E., Bürkli, L., Iribarren‐Anacona, P., Mao, L., Nakamura, F., Ravazzolo, D., Rickenmann, D., Sanz‐Ramos, M., Stoffel, M., and Wohl, E. ( 2019) Characterization of wood‐laden flows in rivers. Earth Surf. Process. Landforms, https://doi.org/10.1002/esp.4603.], which has been published in final form at https://onlinelibrary.wiley.com/doi/abs/10.1002/esp.4603Inorganic 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 (WLF) 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 WLF, 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, WLF may occur repeatedly, in a large range of catchment sizes, generally in steep, highly confined single thread channels in mountain areas. WLF 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 WLF, including an exhaustive discussion of different modelling approaches (i.e., Voellmy, Bingham and Manning) and provide a first attempt to simulate WLF. We draw attention to WLF phenomena to encourage further field, theoretical, and experimental investigations that may contribute to a better understanding of flows river basins, leading to more accurate predictions, and better hazard mitigation and management strategies.Peer Reviewe