Subaerial sediment-water flows on hillslopes

Germain, Daniel; Ouellet, Marie‐Audray

doi:10.1177/0309133313507943

Cited by 20 publications

(2 citation statements)

References 110 publications

(195 reference statements)

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“…Recent North American usage, following influential reviews by Costa (1984, his Table 4;1988, his Germain & Ouellet, 2013), has generally defined severe sediment transporting events in steep channels as "water floods," "hyperconcentrated flows" (also called "mud floods"), and "debris flows." Water floods (also called "clearwater floods") have low sediment transport.…”

Section: Contextmentioning

confidence: 99%

What Is a Debris Flood?

Church

Jakob

2020

Water Resources Research

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Debris floods have been defined descriptively as mineral and organic sediment‐rich floods, occurring in a steep channel and potentially destabilizing the streambed and banks. While this definition allows one to visualize the process, it does not inform on the mechanics, nor does it recognize different types. We propose to define debris floods as “floods during which the entire bed, possibly barring the very largest clasts, becomes mobile for at least a few minutes and over a length scale of at least 10 times the channel width.” We define the onset of a debris flood by the exceedance of a critical shear stress threshold required to mobilize at least the D84 of bed material. A threefold classification is proposed in which the first type is triggered by the shear stress exceedance. The second is initiated by transition from a debris flow either in the channel or by oblique impact of a debris‐flow‐prone tributary. In this context we highlight the importance of effective fluid density. The third type is associated with outbreak floods from artificial or natural dams. A further subdivision of debris floods is made by using the ratio of the actual shear stress to the critical shear stress, with higher values indicating damaging and finally catastrophic debris floods in which even preexisting channel bank and bed protection is mobilized. This contribution aims to provide a more succinct mechanistic definition of debris floods that can be implemented in hazard and risk assessments for steep streams and rivers.

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Section: Contextmentioning

confidence: 99%

What Is a Debris Flood?

Church

Jakob

2020

Water Resources Research

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“…Poorly sorted laminae with inversed graded end members are identified as bipartite flow (Lowe, 1982; Postma et al ., 1988; Sohn, 1997; Dasgupta, 2003) and denominated high to low transitional density flows, whereby layers ‘a’ and ‘b’ of the laminae are interpreted as traction carpet (Hanes & Bowen, 1985; Postma et al ., 1988; Cartigny et al ., 2013) and layer ‘c’ as floating outsized clasts of a hyperconcentrated flow end member described by Sohn (1997) (Figs 4 and 5). In a subaerial environment, end members containing a traction carpet are associated with hyperconcentrated flow (or high to low transitional density flows) with volumetric concentrations above 9% (Sohn, 1997), which is a transitional category between low concentration (Newtonian flows) and mud/debris flow (non‐Newtonian plastic flows) (Postma et al ., 1988; Dasgupta, 2003; Pierson, 2005; Germain & Oullet, 2013).…”

Section: Discussionmentioning

confidence: 99%

Modern soil aggregates–colluvium generated by overland flow – stratigraphy and physical experiments

et al. 2023

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In tropical and subtropical zones, sandy colluviums composed of soil aggregates are highly significant for the understanding of depositional processes in the natural realm. The formation processes of soil aggregates–colluviums (pedosediments in other climate zones) are poorly defined. Deeper knowledge on the origin of soil aggregates–colluviums from low‐density or high‐density overland flows is essential for improved understanding of colluviums found in modern, Quaternary and ancient stratigraphic records. The understanding of depositional processes of soil aggregates–colluviums has been integrated into this study by combining macrostratigraphy and microstratigraphy and laboratory experimental techniques. The actualism principle was applied using a sedimentological description of a modern soil aggregates–colluvium deposit generated by overland flows. In addition, physical experiments were performed to simulate the natural sedimentation processes of overland flows composed of various sediment concentrations. The results indicate the maximum grain size (granules and pebbles) of the soil aggregates–colluvium beds originating from high competence overland flows involving large volumes of local rainfall (storms). Overland flows are responsible for laminated beds of soil aggregates–colluviums; however, the laminations are heterogeneous sequences compared to those of low‐density flows, which have homogeneous sequences. The microstratigraphy of the natural, modern soil aggregates–colluviums shows varied structures in overland flow laminations, implying several types of flow density. The internal organization of the laminae suggests that the accretion of the colluvium deposit occurred through high‐density flows and high to low‐transitional density flows. Low‐density flows were less frequent and may constitute either single or more diluted tail flows. Finally, overland flow can generate facies with similar end members to mass movements, being distinguished only by bed thickness. Linking field observations with experimental results, as in the present study, leads to deeper understanding of overland flow sedimentation processes, especially in tropical and subtropical zones.

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Hyperconcentrated flows on a forested alluvial fan of eastern Canada: geomorphic characteristics, return period, and triggering scenarios

Ouellet

Germain

2014

Earth Surf Processes Landf

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The assessment of the dominant flow type on alluvial fans usually refers to two categories: debris-flow fans (i.e. sediment gravity flows) and fluvial fans (i.e. fluid gravity flows). Here we report the results of combined morphometric, stratigraphic and sedimentological approaches which suggest that hyperconcentrated flows, a transitional process rheologically distinct from debris flows and floods and sometimes referred to as debris floods, mud floods, or transitional debris flows, are the dominant fan building process in eastern Canada. These flows produce transitional facies between those of debris flows which consist of a cohesive matrix-supported diamicton, and those of river flows which display more distinct stratification. The size of the blocks in the channels and the abrasion scars at the base of several trees attest to the high transport capacity of these flows. The fan channels are routed according to various obstacles comprised primarily of woody debris that impede sediment transit. However, these conditions of sediment storage are combined with readily available sediment due to the friable nature of the local lithology. Tree-ring analysis allowed the reconstruction of eight hydrogeomorphic events which are characterized by a return period of 9.25 years for the period 1934-2008, although most of the analyzed events occurred after 1970. Historical weather data analysis indicates that they were related to rare hydrometeorological events at regional and local scales. This evidence led to the elaboration of weather scenarios likely responsible for triggering flows on the fan. According to these scenarios, two distinct hydrologic regimes emerge: the torrential rainfall regime and the nival regime related to snowmelt processes. Hydrogeomorphic processes occurring in a cold-temperate climate, and particularly on small forested alluvial fans of north-eastern North America, should receive more attention from land managers given the hazard they represent, as well as because of their sensitivity to various meteorological parameters.

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Subaerial sediment-water flows on hillslopes

Cited by 20 publications

References 110 publications

What Is a Debris Flood?

What Is a Debris Flood?

Modern soil aggregates–colluvium generated by overland flow – stratigraphy and physical experiments

Hyperconcentrated flows on a forested alluvial fan of eastern Canada: geomorphic characteristics, return period, and triggering scenarios

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