Testing seismic noise caused by highly concentrated sediment flows in laboratory experiments

2020 ◽  
Author(s):  
Marco Piantini ◽  
Florent Gimbert ◽  
Alain Recking ◽  
Hervé Bellot
Keyword(s):  
Sediment Transport ◽  
Seismic Noise ◽  
Laboratory Experiments ◽  
River Flow ◽  
Mechanistic Model ◽  
Transport Processes ◽  
Sediment Flux ◽  
Extreme Floods ◽  
Starting Point ◽  
Grain Sorting

<p>Sediment transport processes and fluxes play a key role in fluvial geomorphology and hazard triggering. In particular, extreme floods characterized by highly concentrated flows set the pace of mountain landscape evolution, where the linkage between streams and sediment sources leads to strong solid inputs characterized by significant grain sorting processes. The main observation that river processes generate ground vibrations has led to the application of seismic methods for monitoring purposes, which provides an innovative system that overcomes traditional monitoring difficulties especially during floods. Mechanistic models have been proposed in the attempt to invert river flow properties such as sediment fluxes from seismic measurements. Although those models have recently been validated in the laboratory and in the field for low transport rates, it remains unknown whether they are applicable to extreme floods.</p><p>Here we carry a set of laboratory experiments in a steep (18% slope) channel in order to investigate the link between seismic noise and sediment transport under extreme flow conditions with highly concentrated sediment flows. The originality of this set-up is that instead of feeding the flume section directly as usually done, we feed with liquid and solid discharge a low slope storage zone connected to the upstream part of the steep channel. This allows us to produce sediment pulses of varying magnitude (up to the transport capacity) and granulometric composition, traveling downstream as a result of alternate phases of deposition and erosion occurring in the storage area. We measure flow stage, seismic noise, sediment flux and grain size distribution. We find that the previously proposed relationships between seismic power, sediment flux and grain diameter often do not hold in such sediment transport situations. We support that this is due to granular interactions occurring between grains of different sizes within the sediment mixture and leading to complex grain sorting processes. In particular, we observe that bigger grains do not directly impact the bed but rather roll over fines or smaller grains, such that observed seismic power is much lower than expected. These results constitute a starting point for the development of a new mechanistic model for seismic power generated by highly concentrated bedload sediment flows.</p>

Understanding the impacts of hydrograph transience on sediment transport

2020 ◽  
Author(s):  
Colin Phillips ◽  
Eric Lajeunesse ◽  
Kimberly Hill ◽  
Chris Paola
Keyword(s):  
Sediment Transport ◽  
Laboratory Experiments ◽  
Scale Up ◽  
Sediment Flux ◽  
Bed Load ◽  
Length Scale ◽  
Transport Capacity ◽  
Natural Systems ◽  
Intermittency Factor

<p>Sediment transport is an inherently challenging process to predict due to a variety of granular and hydrodynamic phenomena. These challenges are only enhanced in natural systems where the forcing of the hydrograph and the availability of sediment is decidedly unsteady. Here we show through several field and laboratory experiments comprised of sediment flux and tracer displacement under unsteady hydrographs that their dynamics can be understood through the application of an integrated forcing metric (impulse), where the impulse represents the integrated excess transport capacity of a flood or a sequence of floods. When viewed through this framework we show that the cumulative bed load flux and tracer displacement from the particle flight length scale up to multi annual timescales are linearly related with the impulse parameter despite highly unsteady forcing. By considering the integrated forcing and sediment flux the transience of the hydrograph can be recast into a simple linear relation with parallels to long term landscape evolution models, where the details of the hydrograph are approximated as a characteristic flood stress times an intermittency factor. Through the use of an impulse metric we gain new insights that are obscured when only considering the instantaneous fluxes.</p>

Influence of wave and current flow on sediment-carrying capacity and sediment flux at the water–sediment interface

2014 ◽  
Vol 70 (6) ◽  
pp. 1090-1098 ◽  
Author(s):  
Jun Zheng ◽  
Ruijie Li ◽  
Yonghai Yu ◽  
Anning Suo
Keyword(s):  
Sediment Transport ◽  
Carrying Capacity ◽  
Superposition Principle ◽  
Transport Processes ◽  
Sediment Flux ◽  
Spatial And Temporal Scales ◽  
Significant Wave ◽  
New Formula ◽  
Sediment Interface ◽  
Sediment Carrying Capacity

In nearshore waters, spatial and temporal scales of waves, tidal currents, and circulation patterns vary greatly. It is, therefore, difficult to combine these factors’ effects when trying to predict sediment transport processes. This paper proposes the concept of significant wave velocity, which combines the effects of waves, tides, and ocean currents using the horizontal kinetic energy superposition principle. Through a comparison of the relationship between shear stress at the water–sediment interface and sediment-carrying capacity, assuming equilibrium sediment flux, a new formula for sediment-carrying capacity, which incorporates the concept of significant wave velocities, is derived. Sediment-carrying capacity is a function of the critical velocity, which increases with water depth and decreases with increasing relative roughness of the seabed. Finally, data from field observation stations and simulations are used to test the proposed formula. The results show that the new formula is in good agreement with both field and simulation data. This new formula for sediment-carrying capacity can be used to simulate nearshore sediment transport.

scholarly journals CFD-DEM modelling of sediment transport in sewer systems under steady and unsteady flow conditions

2019 ◽  
Vol 80 (11) ◽  
pp. 2141-2147 ◽  
Author(s):  
Maryam Alihosseini ◽  
Sveinung Sægrov ◽  
Paul Uwe Thamsen
Keyword(s):  
Sediment Transport ◽  
Laboratory Experiments ◽  
Transport Processes ◽  
Experimental Investigations ◽  
Flow Conditions ◽  
Ansys Fluent ◽  
Sewer Pipes ◽  
Rough Bed ◽  
New Methodologies ◽  
Sand And Gravel

Abstract Numerical and experimental investigations were undertaken to study sediment transport under steady flow conditions and under flush waves in sewer pipes. Experiments were carried out with sand and gravel of different size distributions under smooth and rough bed conditions. Moreover, different hydraulic boundary conditions were investigated for flush waves. The numerical part of this study was carried out in the computational fluid dynamics (CFD) software ANSYS Fluent, which is two-way coupled to the Discrete Element Method (DEM) software EDEM. The main focus of this study is to determine if the CFD-DEM coupled method could reasonably predict the behaviour of sediments in sewers and thus be used for studying various features of sediment transport that are not easy to determine in laboratory experiments or in-situ measurements. Furthermore, it is important to replace the traditional empirical approaches developed for fluvial conditions with new methodologies, which are able to consider the high number of variables involved in sediment transport in sewers. The numerical model was validated with laboratory experiments and used to study details of sediment transport processes in sewers.

scholarly journals Forest harvesting impacts on micrometeorological conditions and sediment transport activities in a humid periglacial environment

2018 ◽  
Author(s):  
Fumitoshi Imaizumi ◽  
Ryoko Nishii ◽  
Kenichi Ueno ◽  
Kousei Kurobe
Keyword(s):  
Sediment Transport ◽  
Vegetation Cover ◽  
Forest Canopy ◽  
Forest Harvesting ◽  
Transport Processes ◽  
Sediment Flux ◽  
Surface Erosion ◽  
Soil Creep ◽  
Dry Ravel ◽  
Micrometeorological Conditions

Abstract. Sediment transport activities in the periglacial environment are controlled by hillslopes micrometeorological conditions (i.e., air and ground temperatures, ground water content), which are highly affected by vegetation cover. Thus, there is a possibility that forest harvesting, which is the most dramatic change to vegetation cover in mountain areas, may severely impact sediment transport activities in periglacial areas (i.e., soil creep, dry ravel). Knowledge of the effects of forest harvesting on sediment transport are needed to protect aquatic ecosystems as well as to develop better mitigation measures for preventing sediment disasters. In this study, we investigated changes in sediment transport activities following forest harvesting in steep artificial forests located in a humid periglacial area of the Southern Japanese Alps. In the Southern Japanese Alps, rainfall is abundant in summer and autumn, and air temperatures frequently rise above and fall below 0 degrees in the winter. Our monitoring by time laps cameras revealed that gravitational transport processes (e.g., frost creep and dry ravel) dominate during the freeze-thaw season, while rainfall-induced processes (surface erosion and soil creep) occur during heavy rainfall seasons. Removal of the forest canopy by forest harvesting alters the type of winter soil creep from deeper frost creep to diurnal needle-ice creep. Winter creep velocity of the ground surface sediment in the harvested site was significantly higher than that in the non-harvested site. Meanwhile, sediment flux on the hillslopes observed by sediment traps decreased in the harvested site. Branches of harvested trees left on the hillslopes captured sediment coming from upslope. In addition, the growth of understories after harvesting possibly reduced surface erosion. Consequently, removal of the forest canopy by forest harvesting directly impacts micrometeorological conditions and periglacial sediment transport activity, while sediment flux on hillslopes is also affected by branches left on the hillslopes and recovery of understories.

Toward a unified model for sediment transport from terrestrial source to abyssal-plain sink

2020 ◽  
Author(s):  
Charles M. Shobe ◽  
Jean Braun ◽  
Xiaoping Yuan ◽  
Benjamin Campforts ◽  
François Guillocheau ◽  
...  
Keyword(s):  
Sediment Transport ◽  
Sea Level ◽  
Numerical Models ◽  
Transport Processes ◽  
Sediment Flux ◽  
Abyssal Plain ◽  
Marine Debris ◽  
Sensitivity Analyses ◽  
Turbidity Currents ◽  
Local Slope

<p>Marine stratigraphy contains time-resolved information about the erosion of continents and its tectonic and climatic drivers. Quantitatively inverting marine stratigraphy for long-term terrestrial erosion histories requires numerical models that encompass the entire source-to-sink (S2S) system. Because inversion schemes require many model realizations to constrain free parameters against a misfit function, S2S models must be efficient (both in terms of allowing large time steps and scaling well for large problems) and have only a few parameters. Accordingly, most previous S2S models have treated seafloor evolution as a diffusion problem where sediment flux depends linearly on local topographic gradient. Such approaches have shown success in shallow marine settings like the continental shelf. However, they are less likely to apply to deeper marine environments where large deposits are observed and where nonlocal sediment transport processes (e.g., turbidity currents or marine debris flows) dominate sediment fluxes.</p><p>We present a unified modeling approach for coupling terrestrial and marine erosion, sediment transport, and deposition from the continent to the abyssal plain. Our model is based on the erosion-deposition family of models, where sediment flux is tracked across the landscape and seascape. Above sea level, erosion and deposition depend on river discharge, local slope, and sediment flux. Below sea level, local slope and sediment flux drive topographic change. The equations governing the terrestrial and marine domains take the same basic form such that a single semi-implicit numerical solution based on Gauss-Seidel iteration can be used across the whole S2S system. The solution scheme is near O(N) complexity in that the number of iterations required typically does not increase significantly with increasing grid resolution. The S2S model contains only five total parameters. We show preliminary analytical and numerical results and sensitivity analyses, and discuss the applicability of the model for the efficient inversion of deep marine stratigraphic data.</p>

scholarly journals Sediment transport processes across the Tibetan Plateau inferred from robust grain-size end members in lake sediments

2014 ◽  
Vol 10 (1) ◽  
pp. 91-106 ◽  
Author(s):  
E. Dietze ◽  
F. Maussion ◽  
M. Ahlborn ◽  
B. Diekmann ◽  
K. Hartmann ◽  
...  
Keyword(s):  
Grain Size ◽  
Sediment Transport ◽  
Tibetan Plateau ◽  
Transport Processes ◽  
The Tibetan Plateau ◽  
Dust Deposition ◽  
Northerly Wind ◽  
Near Surface ◽  
Depositional Processes ◽  
End Members

Abstract. Grain-size distributions offer powerful proxies of past environmental conditions that are related to sediment sorting processes. However, they are often of multimodal character because sediments can get mixed during deposition. To facilitate the use of grain size as palaeoenvironmental proxy, this study aims to distinguish the main detrital processes that contribute to lacustrine sedimentation across the Tibetan Plateau using grain-size end-member modelling analysis. Between three and five robust grain-size end-member subpopulations were distinguished at different sites from similarly–likely end-member model runs. Their main modes were grouped and linked to common sediment transport and depositional processes that can be associated with contemporary Tibetan climate (precipitation patterns and lake ice phenology, gridded wind and shear stress data from the High Asia Reanalysis) and local catchment configurations. The coarse sands and clays with grain-size modes >250 μm and <2 μm were probably transported by fluvial processes. Aeolian sands (~200 μm) and coarse local dust (~60 μm), transported by saltation and in near-surface suspension clouds, are probably related to occasional westerly storms in winter and spring. Coarse regional dust with modes ~25 μm may derive from near-by sources that keep in longer term suspension. The continuous background dust is differentiated into two robust end members (modes: 5–10 and 2–5 μm) that may represent different sources, wind directions and/or sediment trapping dynamics from long-range, upper-level westerly and episodic northerly wind transport. According to this study grain-size end members of only fluvial origin contribute small amounts to mean Tibetan lake sedimentation (19± 5%), whereas local to regional aeolian transport and background dust deposition dominate the clastic sedimentation in Tibetan lakes (contributions: 42 ± 14% and 51 ± 11%). However, fluvial and alluvial reworking of aeolian material from nearby slopes during summer seems to limit end-member interpretation and should be crosschecked with other proxy information. If not considered as a stand-alone proxy, a high transferability to other regions and sediment archives allows helpful reconstructions of past sedimentation history.

scholarly journals Application of a 3D Layer Integrated Numerical Model of Flow and Sediment Transport Processes to a Reservoir

Water ◽  
2015 ◽  
Vol 7 (10) ◽  
pp. 5239-5257 ◽  
Author(s):  
Shervin Faghihirad ◽  
Binliang Lin ◽  
Roger Falconer
Keyword(s):  
Sediment Transport ◽  
Numerical Model ◽  
Transport Processes ◽  
Flow And Sediment Transport
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