Alluvial Steep Channels: Flow Resistance, Bedload Transport Prediction, and Transition to Debris Flows

When water flows over a stationary bed the fluid motion is retarded by both skin the friction and local pressure gradient forces related to the roughness of the bed. If the bed itself is composed of discreet movable grains, the boundary is less clearly defined and the dynamics poorly understood (see Gust and Southard, 1983). Owen (1964) proposed that saltating grains (grains which lift off the bed, move through the fluid, and fall back to the bed without colliding with other grains) have the effect of increasing the frictional resistance of the bottom. At higher flow stages, Hanes and Bowen (1984) have suggested a model for bedload transport which is based upon the dynamics of collisional grain flows following Bagnold (1954, 1956). In such a collision dominated flow, it appears that the resistance of the bed to the overlying flow can be less than the resistance of a fixed bed to the same overlying flow. This result is consistent with the dynamics of rapid granular-fluid flows, as will be discussed below.

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The Importance of Hail Events for Landslides and Bedload Transport in Austrian Alpine Torrents

10.21203/rs.3.rs-1119659/v1 ◽

2021 ◽

Author(s):

Mario Schritter ◽

Thomas Glade

Keyword(s):

Debris Flow ◽

Debris Flows ◽

Control Unit ◽

Bedload Transport ◽

Weather Data ◽

Process Dynamics ◽

Triggering Conditions ◽

Thiessen Polygons ◽

Trigger Mechanisms ◽

Local Weather

Abstract Landslides and bedload transport can be a threat to people, infrastructure, and vegetation. Many detailed hydrometeorological trigger mechanisms of such natural hazards are still poorly understood. This is in particular valid concerning hail as a trigger of these processes. Therefore, this study aims to determine the influence of hail on landslides and bedload transport in alpine torrents. Based on a generated table from an event register of mountain processes maintained by the Avalanche and Torrent Control Unit (WLV) and weather data provided by the Centre for Meteorology and Geodynamics (ZAMG), 1,573 observed events between 1980 and 2019 in 79 Austrian alpine sites are analysed. Thiessen polygons are used to regionalise local weather data to adjacent regions. The spatial extend of these regions are merged with the registered torrential events. As a result of a stepwise filtering of the used data, the final inventory was created.The results show that 95.1% of the investigated torrential processes triggered by hailstorms are debris flows or debris flow-like transports. Within the study period, a peak of hail-triggered landslides and bedload transport can be recognised in the first 10 days of August in all 39 years. Furthermore, the results suggest that hail is rather a direct than an indirect trigger for landslides and bedload transport.Overall, we conclude that the influence of hail on landslides and bedload transport is significant. Respective hydrometeorological triggering conditions should be included in any regions. Further research for this topic is required to explore the process dynamics in greater detail.

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Short communication: Multiscalar roughness length decomposition in fluvial systems using a transform-roughness correlation (TRC) approach

Earth Surface Dynamics ◽

10.5194/esurf-8-1039-2020 ◽

2020 ◽

Vol 8 (4) ◽

pp. 1039-1051

Author(s):

David L. Adams ◽

Andrea Zampiron

Keyword(s):

Flow Resistance ◽

Roughness Length ◽

Short Communication ◽

Bedload Transport ◽

Fluvial Systems ◽

Relative Contribution ◽

Roughness Elements ◽

Wide Range ◽

Novel Method ◽

Individual Grains

Abstract. In natural open-channel flows over complex surfaces, a wide range of superimposed roughness elements may contribute to flow resistance. Gravel-bed rivers present a particularly interesting example of this kind of multiscalar flow resistance problem, as both individual grains and bedforms may contribute to the roughness length. In this paper, we propose a novel method of estimating the relative contribution of different physical scales of in-channel topography to the total roughness length, using a transform-roughness correlation (TRC) approach. The technique, which uses a longitudinal profile, consists of (1) a wavelet transform which decomposes the surface into roughness elements occurring at different wavelengths and (2) a “roughness correlation” that estimates the roughness length (ks) associated with each wavelength based on its geometry alone. When applied to original and published laboratory experiments with a range of channel morphologies, the roughness correlation estimates the total ks to approximately a factor of 2 of measured values but may perform poorly in very steep channels with low relative submergence. The TRC approach provides novel and detailed information regarding the interaction between surface topography and fluid dynamics that may contribute to advances in hydraulics, bedload transport, and channel morphodynamics.

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An improved landslide mobility model

Canadian Geotechnical Journal ◽

10.1139/t06-010 ◽

2006 ◽

Vol 43 (5) ◽

pp. 531-539 ◽

Cited By ~ 30

Author(s):

Julian SH Kwan ◽

H W Sun

Keyword(s):

Debris Flows ◽

Flow Resistance ◽

Dynamic Modelling ◽

Mobility Model ◽

Technical Note ◽

Flow Channel ◽

Cross Sectional ◽

Deposition Area ◽

Landslide Mobility ◽

Landslide Data

A relatively simple and versatile numerical model known as DAN, developed by Oldrich Hungr for the assessment of landslide mobility, has been enhanced to incorporate the consideration of a trapezoidal-shaped flow channel for more realistic modelling purposes. This enhanced debris mobility model (DMM) has been programmed to run on a spreadsheet and has been calibrated against detailed landslide data in Hong Kong. In contrast to previous work, the enhanced DMM eliminates the limitations inherited from the assumption of a rectangular flow channel with frictionless side boundaries. When using DMM, no predefined width of landslide is needed. The DMM simulates landslide mobility with the flow resistance on the whole wetted perimeter of the channel, calculates the surface width of the landslide based on the cross-sectional geometry of the channel, and is capable of predicting a lobe-shaped debris deposition area. This technical note presents details of the enhancement to the DAN formulation.Key words: landslides, debris flows, runout analysis, landslide mobility, dynamic modelling, numerical methods.

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Flow Resistance of Inertial Debris Flows

Journal of Hydraulic Engineering ◽

10.1061/(asce)hy.1943-7900.0000664 ◽

2013 ◽

Vol 139 (2) ◽

pp. 187-194 ◽

Cited By ~ 8

Author(s):

Diego Berzi ◽

Enrico Larcan

Keyword(s):

Debris Flows ◽

Flow Resistance

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Riverbed dune morphology of the Lowermost Mississippi River – Implications of leeside slope, flow resistance and bedload transport in a large alluvial river

Geomorphology ◽

10.1016/j.geomorph.2021.107733 ◽

2021 ◽

pp. 107733

Author(s):

Shuaihu Wu ◽

Y. Jun Xu ◽

Bo Wang ◽

Heqin Cheng

Keyword(s):

Mississippi River ◽

Flow Resistance ◽

Bedload Transport ◽

Alluvial River ◽

Dune Morphology ◽

Slope Flow

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Bedload transport and flow resistance in steep channels – introduction to the issues in the context of mountain basins of the Central European region

AUC GEOGRAPHICA ◽

10.14712/23361980.2015.21 ◽

2017 ◽

Vol 47 (1) ◽

pp. 23-33

Author(s):

Tomáš Galia ◽

Jan Hradecký

Keyword(s):

Flow Resistance ◽

Bedload Transport ◽

European Region ◽

Central European ◽

Central European Region ◽

Mountain Basins

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Sediment budget monitoring of debris-flow and bedload transport in the Manival Torrent, SE France

Natural Hazards and Earth System Science ◽

10.5194/nhess-12-731-2012 ◽

2012 ◽

Vol 12 (3) ◽

pp. 731-749 ◽

Cited By ~ 70

Author(s):

J. I. Theule ◽

F. Liébault ◽

A. Loye ◽

D. Laigle ◽

M. Jaboyedoff

Keyword(s):

Debris Flow ◽

Debris Flows ◽

Laser Scanning ◽

Sediment Budget ◽

Bedload Transport ◽

High Order ◽

Time Shift ◽

Catchment Scale ◽

Sediment Routing ◽

Budget Analysis

Abstract. Steep mountain catchments typically experience large sediment pulses from hillslopes which are stored in headwater channels and remobilized by debris-flows or bedload transport. Event-based sediment budget monitoring in the active Manival debris-flow torrent in the French Alps during a two-year period gave insights into the catchment-scale sediment routing during moderate rainfall intensities which occur several times each year. The monitoring was based on intensive topographic resurveys of low- and high-order channels using different techniques (cross-section surveys with total station and high-resolution channel surveys with terrestrial and airborne laser scanning). Data on sediment output volumes from the main channel were obtained by a sediment trap. Two debris-flows were observed, as well as several bedload transport flow events. Sediment budget analysis of the two debris-flows revealed that most of the debris-flow volumes were supplied by channel scouring (more than 92%). Bedload transport during autumn contributed to the sediment recharge of high-order channels by the deposition of large gravel wedges. This process is recognized as being fundamental for debris-flow occurrence during the subsequent spring and summer. A time shift of scour-and-fill sequences was observed between low- and high-order channels, revealing the discontinuous sediment transfer in the catchment during common flow events. A conceptual model of sediment routing for different event magnitude is proposed.

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