Large wood recruitment processes and transported volumes in Swiss mountain streams during the extreme flood of August 2005

Earth Surf Processes Landf

Castellet

et al. 2019

Self Cite

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.

Section: Implications For Hazards and River Managementmentioning

confidence: 99%

Characterization of wood‐laden flows in rivers

Ruíz-Villanueva

Earth Surf Processes Landf

Castellet

et al. 2019

Self Cite

“…Current debris-flow models consider sediment the only component of the solid fraction, but logs can definitely play a major role in determining the rheology of these phenomena. Because the contribution of debris-flows to the wood budget of extreme events can be very relevant (see Lucia et al, 2015;Steeb et al, 2017), there is an urgent need to develop better models for large-wood-congested transport and even more of a need to consider mass transport of large wood in the models.…”

Section: Resultsmentioning

confidence: 99%

“…Especially in mountain rivers, floods tend to be short and intense, and are thus poorly investigated and rarely observed directly. During these types of events, large quantities of both sediments and large wood (commonly defined as logs ≥ 1.0 m in length and ≥ 0.1 m in diameter) are supplied into the channels and can cause serious harm to buildings and infrastructure within the river corridor (Lucia et al, 2015;Steeb et al, 2017). In order to assess and mitigate risks associated to large-wood transport in rivers, it is crucial to properly understand the dynamics of wood during floods (RuizVillanueva et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Brief communication: The curious case of the large wood-laden flow event in the Pocuro stream (Chile)

Ravazzolo

Mao

Nat. Hazards Earth Syst. Sci.

et al. 2017

Abstract. Large wood transported during extreme flood events can represent a relevant additional source of hazards that should be taken into account in mountain environments. However, direct observations and monitoring of large-wood transport during floods are difficult and scarce. Here we present a video of a flood characterised by multiple phases of large-wood transport, including an initial phase of wood-laden flow rarely described in the literature. Estimations of flow velocity and transported wood volume provide a good opportunity to develop models of large-woodcongested transport.

“…a; Comiti et al . a; Steeb et al ., ). The data collected after flood events are useful to develop relationships between the exported wood volume and the maximum discharge of the flood, or other parameters (Rickenmann, ; Steeb et al ., ), although a reliable prediction of potential wood volumes and transport rates remains to be developed.…”

Section: Introductionmentioning

confidence: 97%

“…a; Steeb et al ., ). The data collected after flood events are useful to develop relationships between the exported wood volume and the maximum discharge of the flood, or other parameters (Rickenmann, ; Steeb et al ., ), although a reliable prediction of potential wood volumes and transport rates remains to be developed. In addition, post‐event data are helpful to calibrate existing LW transport models (Mazzorana et al ., , 2011; Rigon et al ., ; Ruiz‐Villanueva et al ., ; Gems et al ., ; Gems et al ., ).…”

Section: Introductionmentioning

confidence: 97%

Assessing and mitigating large wood‐related hazards in mountain streams: recent approaches

J Flood Risk Management

Ruíz-Villanueva

Marchi

et al. 2017

The assessment and mitigation of floods in mountain streams, when large wood (LW) is transported, pose several challenges. The process chain consisting of flood propagation, LW recruitment, entrainment, transport, and entrapment triggers, at critical sections such as bridges, unexpected and exacerbated impacts to the exposed built environment. We provide a review on the recent advances in modelling LW dynamics during extreme river floods through computational approaches. Moreover, we describe how scaled flume experiments can enhance process understanding at critical flow sections such as bridges to address risk mitigation problems. Additionally, we present a framework based on Formative Scenario Analysis (FSA) to allow for expert knowledge integration and to subsequently derive consistent hazard process scenarios in steep mountain streams where the application of computational approaches is less reliable. Finally, we discuss how the application of the presented set of assessment methods can support integral flood risk management by explicitly considering LW dynamics since the effectiveness of mitigation critically depends on the acquired process understanding.