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>

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>

Sources and Distribution of Sediments

2006 ◽  
Author(s):  
Thomas S. Bianchi
Keyword(s):  
Sea Level ◽  
River Estuary ◽  
Deep Ocean ◽  
Sediment Flux ◽  
Turbidity Currents ◽  
Geological Time ◽  
Physical Weathering ◽  
Coastal Margin ◽  
River Estuarine

The uplift of rocks above sea level on the Earth’s surface over geological time, produces rock material that can be altered into soils and sediments by weathering processes. Over geological time, a fraction of sediments can be sequestered for storage in the ocean basins—with most of it stored in the coastal margin. However, much of this material is modified via processing in large river estuarine systems which can ultimately affect the long-term fate of these terrigenous materials. Sediments produced from weathering of igneous, metamorphic, and sedimentary rocks are principally transported to the oceans through river systems of the world. The major routes of sediment transport from land to the open ocean can simply be illustrated through the following sequence: streams, rivers, estuaries, shallow coastal waters, canyons, and the abyssal ocean. It should be noted that significant and long-term storage occurs in river valleys and floodplains (Meade, 1996). Submarine canyons are also thought to be temporary storage sites for land-derived sediments; however, episodic events such as turbidity currents and mud slides can move these sediments from canyons to the abyssal ocean (more details on coastal margin transport to the deep ocean are provided in chapter 16). The annual sediment flux from rivers to the global ocean is estimated to range from 18 to 24 × 109 metric tonnes (Milliman and Syvitski, 1992). Conversely, estuaries will eventually fill-in with fluvial inputs of sediments over time, and ultimately reach an equilibrium whereby export and import of sediment supply are balanced (Meade, 1969). For example, recent studies have shown that sediment accumulation in the Hudson River estuary, both short (Olsen et al., 1978) and long term (Peteet and Wong, 2000), is in equilibrium with sea level rise. More specifically, it is believed that river flow controls the direction of sediment flux in the Hudson, while variations in spring-neap tidal amplitude control the magnitude (Geyer et al., 2001). Weathering is typically separated into two categories: physical and chemical. Physical weathering involves the fragmentation of parent rock materials and minerals through processes such as freezing, thawing, heating, cooling, and bioturbation (e.g., endolithic algae, fungi, plant roots, and earthworms).

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 Response of tidal flow regime and sediment transport in North Malé Atoll, Maldives, to coastal modification and sea level rise

Ocean Science ◽  
2021 ◽  
Vol 17 (1) ◽  
pp. 319-334
Author(s):  
Shuaib Rasheed ◽  
Simon C. Warder ◽  
Yves Plancherel ◽  
Matthew D. Piggott
Keyword(s):  
Grain Size ◽  
Sediment Transport ◽  
Sea Level Rise ◽  
Sea Level ◽  
Land Reclamation ◽  
Transport Processes ◽  
Sediment Grain Size ◽  
Sediment Distribution ◽  
Time Periods ◽  
The Impact

Abstract. Changes to coastlines and bathymetry alter tidal dynamics and associated sediment transport processes, impacting upon a number of threats facing coastal regions, including flood risk and erosion. Especially vulnerable are coral atolls such as those that make up the Maldives archipelago, which has undergone significant land reclamation in recent years and decades and is also particularly exposed to sea level rise. Here we develop a tidal model of Malé Atoll, Maldives, the first atoll-scale and multi-atoll-scale high-resolution numerical model of the atolls of the Maldives and use it to assess potential changes to sediment grain size distributions in the deeper atoll basin, under sea level rise and coastline alteration scenarios. The results indicate that the impact of coastline modification over the last two decades at the island scale is not limited to the immediate vicinity of the modified island but can also significantly impact the sediment grain size distribution across the wider atoll basin. Additionally, the degree of change in sediment distribution which can be associated with sea level rise that is projected to occur over relatively long time periods is predicted to occur over far shorter time periods with coastline changes, highlighting the need to better understand, predict and mitigate the impact of land reclamation and other coastal modifications before conducting such activities.

scholarly journals Emergent behavior in a coupled economic and coastline model for beach nourishment

2011 ◽  
Vol 18 (6) ◽  
pp. 989-999 ◽  
Author(s):  
E. D. Lazarus ◽  
D. E. McNamara ◽  
M. D. Smith ◽  
S. Gopalakrishnan ◽  
A. B. Murray
Keyword(s):  
Sediment Transport ◽  
Sea Level Rise ◽  
Sea Level ◽  
Coupled System ◽  
Beach Nourishment ◽  
Transport Processes ◽  
Emergent Behavior ◽  
Optimization Strategy ◽  
Natural Sediment ◽  
Alongshore Sediment Transport

Abstract. Developed coastal areas often exhibit a strong systemic coupling between shoreline dynamics and economic dynamics. "Beach nourishment", a common erosion-control practice, involves mechanically depositing sediment from outside the local littoral system onto an actively eroding shoreline to alter shoreline morphology. Natural sediment-transport processes quickly rework the newly engineered beach, causing further changes to the shoreline that in turn affect subsequent beach-nourishment decisions. To the limited extent that this landscape/economic coupling has been considered, evidence suggests that towns tend to employ spatially myopic economic strategies under which individual towns make isolated decisions that do not account for their neighbors. What happens when an optimization strategy that explicitly ignores spatial interactions is incorporated into a physical model that is spatially dynamic? The long-term attractor that develops for the coupled system (the state and behavior to which the system evolves over time) is unclear. We link an economic model, in which town-manager agents choose economically optimal beach-nourishment intervals according to past observations of their immediate shoreline, to a simplified coastal-dynamics model that includes alongshore sediment transport and background erosion (e.g. from sea-level rise). Simulations suggest that feedbacks between these human and natural coastal processes can generate emergent behaviors. When alongshore sediment transport and spatially myopic nourishment decisions are coupled, increases in the rate of sea-level rise can destabilize economically optimal nourishment practices into a regime characterized by the emergence of chaotic shoreline evolution.

scholarly journals Modelling braided river morphodynamics using a particle travel length framework

2019 ◽  
Vol 7 (1) ◽  
pp. 247-274 ◽  
Author(s):  
Alan Kasprak ◽  
James Brasington ◽  
Konrad Hafen ◽  
Richard D. Williams ◽  
Joseph M. Wheaton
Keyword(s):  
Sediment Transport ◽  
Path Length ◽  
Numerical Models ◽  
Hybrid Approach ◽  
Length Distribution ◽  
Transport Processes ◽  
Model Verification ◽  
Event Scale ◽  
Volumetric Assessment ◽  
Decadal Scale

Abstract. Numerical models that predict channel evolution are an essential tool for investigating processes that occur over timescales which render field observation intractable. The current generation of morphodynamic models, however, either oversimplify the relevant physical processes or, in the case of more physically complete codes based on computational fluid dynamics (CFD), have computational overheads that severely restrict the space–time scope of their application. Here we present a new, open-source, hybrid approach that seeks to reconcile these modelling philosophies. This framework combines steady-state, two-dimensional CFD hydraulics with a rule-based sediment transport algorithm to predict particle mobility and transport paths which are used to route sediment and evolve the bed topography. Data from two contrasting natural braided rivers (Rees, New Zealand, and Feshie, United Kingdom) were used for model verification, incorporating reach-scale quantitative morphological change budgets and volumetric assessment of different braiding mechanisms. The model was able to simulate 8 of the 10 empirically observed braiding mechanisms from the parameterized bed erosion, sediment transport, and deposition. Representation of bank erosion and bar edge trimming necessitated the inclusion of a lateral channel migration algorithm. Comparisons between simulations based on steady effective discharge versus event hydrographs discretized into a series of model runs were found to only marginally increase the predicted volumetric change, with greater deposition offsetting erosion. A decadal-scale simulation indicates that accurate prediction of event-scale scour depth and subsequent deposition present a methodological challenge because the predicted pattern of deposition may never “catch up” to erosion if a simple path-length distribution is employed, thus resulting in channel over-scouring. It may thus be necessary to augment path-length distributions to preferentially deposit material in certain geomorphic units. We anticipate that the model presented here will be used as a modular framework to explore the effect of different process representations, and as a learning tool designed to reveal the relative importance of geomorphic transport processes in rivers at multiple timescales.

Autogenic progradation of Bayhead deltas during sea-level rise wIthin incised valleys : theory, experiment and field examples    

2021 ◽  
Author(s):  
Laure Guerit ◽  
Brady Foreman ◽  
Chen Chen ◽  
Chris Paola ◽  
Sébastien Castelltort
Keyword(s):  
Sediment Transport ◽  
Sea Level Rise ◽  
Sea Level ◽  
Large Scale ◽  
Sediment Supply ◽  
Sediment Flux ◽  
Surface Evolution ◽  
Sequence Stratigraphic ◽  
Incised Valleys ◽  
The Trinity

<p>The evolution of sedimentary landscapes is primary driven by the interplay between the rate of accommodation creation A, controlled by sea-level and subsidence, and the rate of sediment supply S, controlled by erosion and sediment transport. In simple terms, the balance between A and S can be used to predict periods of progradation (when sediment supply exceeds accommodation) and periods of retrogradation (when accommodation exceeds sediment supply). However, a growing list of observations show that internal feedbacks within the sediment transport system can generate large-scale, autogenic stratigraphic patterns that are not anticipated by the A/S theory. These observations call for a reanalysis of several sequence stratigraphic precepts that assume a deterministic relationship between external forcings and stratigraphic products. Here, we focus on the filling of incised valleys during constant sea-level rise, and by a constant sediment flux. We develop a simple conceptual model of valley filling and we show that the classic sequence stratigraphic phenomenon of bayhead deltaic systems can be generated by purely autogenic progradation during the late stage of valley flooding. This transient “auto-advance” event results from a strong decrease of in-valley accommodation as base-level rises towards the valley apex. To test this model, we build a laboratory experiment that successfully reproduces the dynamics predicted by the model. Finally, we apply our model to two similar field examples, the Trinity and Brazos rivers incised valleys (Texas, USA). There systems are broadly similar in dimension and sea-level history but were filled at different sediment rates. We propose that this led to auto-advance event in the Trinity River valley while no advance is observed in the Brazos system. We thus show by conceptual, experimental and natural examples that auto-advance can produce out-of-sequence regressive bayhead diastems during highstands similar to a transient change in allogenic forcing. Combined with other recent studies, our findings support the idea that meso-scale autogenic patterns are ubiquitous in the fluvio-deltaic record, and need to be more extensively incorporated into reconstructions of Earth surface evolution and reservoir models.</p>

IODP Expedition 379: Late Miocene to Pleistocene shelf to rise processes in the Amundsen Sea, West Antarctica, from seismic correlation

2021 ◽  
Author(s):  
Karsten Gohl ◽  
Johanna Gille-Petzoldt ◽  
Gabriele Uenzelmann-Neben ◽  
Rachel Lamb ◽  
Johann Klages ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Late Miocene ◽  
Climatic Conditions ◽  
Transport Processes ◽  
Turbidity Currents ◽  
The West ◽  
Amundsen Sea ◽  
Climate Conditions ◽  
West Antarctic

<p>The West Antarctic Ice Sheet (WAIS) is thought to be highly sensitive to climatic and oceanographic changes. Modelling infers that the WAIS likely had a very dynamic history throughout the Neogene to the present. A complete collapse of the WAIS would result in a global sea level rise of 3.3 to 4.3 m, yet there is large uncertainty on predicting its future behavior and its contribution to sea level rise. Geological constraints on the past behavior of the WAIS are relatively sparse and mainly based on records from the Ross Sea sector. In particular, records of time intervals with climatic conditions similar to those expected for the near and distant future, such as the Pliocene, are needed. Deglaciation of the WAIS in the Amundsen Sea sector is hypothesized to have triggered WAIS collapses during past warm times. Drill records from the International Ocean Discovery Program (IODP) Expedition 379 provide continuous late Miocene to Pleistocene sediment sequences from a drift on the continental rise, allowing the assessment of sedimentation processes from cold and warm times. In particular Site U1532 recovered an expanded sequence of Pliocene lithofacies with an excellent paleomagnetic record allowing for very high-resolution, sub-orbital scale climate change studies of the previously sparsely sampled eastern Pacific sector of the West Antarctic margin. At both Sites U1532 and U1533, sediments characterized by high microfossil content and high abundance of ice-rafted debris alternate with laminated terrigenous muds and are interpreted to result from cyclic deposition under interglacial and glacial conditions, respectively. Deep-sea channels likely mark the pathways of terrigenous detritus that was transported downslope from the Amundsen Sea shelf via turbidity currents or other gravitational transport processes predominantly during glacial periods. The association of lithological facies predominantly reflects an interplay of these downslope and contouritic sediment transport processes as well as phases of increased pelagic and hemipelagic sediment input. Correlation of the seismic stratigraphy at the drill sites on the rise with that of the continental shelf of the Amundsen Sea Embayment allowed us to identify massive prograding sequences that expanded the outer shelf seaward by about 80 km by frequent advances of grounded ice across the shelf mainly during Pliocene times. The preservation of buried grounding zone wedges visible in seismic profiles from the shelf is explained by (hemi)pelagic sedimentation during prolonged periods of ice retreat. This can be correlated with an extended warm middle Pliocene period chronologically constrained by the drill records. The contrast between sediments deposited under cold and warm climate conditions indicates that this WAIS sector was highly dynamic in the Pliocene.</p>

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.

scholarly journals Aeolian Sediment Transport Integration in General Stratigraphic Forward Modeling

2011 ◽  
Vol 2011 ◽  
pp. 1-12
Author(s):  
T. Salles ◽  
C. Griffiths ◽  
C. Dyt
Keyword(s):  
Sediment Transport ◽  
Numerical Model ◽  
Transport Model ◽  
Numerical Models ◽  
Three Dimensional ◽  
Transport Processes ◽  
Aeolian Deposits ◽  
Geological Processes ◽  
Wide Range ◽  
Mixed Soils

A large number of numerical models have been developed to simulate the physical processes involved in saltation, and, recently to investigate the interaction between soil vegetation cover and aeolian transport. These models are generally constrained to saltation of monodisperse particles while natural saltation occurs over mixed soils. We present a three-dimensional numerical model of steady-state saltation that can simulate aeolian erosion, transport and deposition for unvegetated mixed soils. Our model simulates the motion of saltating particles using a cellular automata algorithm. A simple set of rules is used and takes into account an erosion formula, a transport model, a wind exposition function, and an avalanching process. The model is coupled to the stratigraphic forward model Sedsim that accounts for a larger number of geological processes. The numerical model predicts a wide range of typical dune shapes, which have qualitative correspondence to real systems. The model reproduces the internal structure and composition of the resulting aeolian deposits. It shows the complex formation of dune systems with cross-bedding strata development, bounding surfaces overlaid by fine sediment and inverse grading deposits. We aim to use it to simulate the complex interactions between different sediment transport processes and their resulting geological morphologies.

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