From perched high elevation surfaces to sediment entering the foreland: the dynamics of erosion, deformation and landscape evolution in the Argentine Precordillera

2020 ◽  
Author(s):  
Gregory Hoke ◽  
Pedro Val ◽  
Gregory Ruetenik ◽  
Robert Moucha
Keyword(s):  
Numerical Modeling ◽  
Landscape Evolution ◽  
Numerical Models ◽  
Foreland Basin ◽  
Detrital Zircons ◽  
Mountain Range ◽  
Time Lags ◽  
Cosmogenic Nuclide ◽  
Stratigraphic Record ◽  
Argentine Precordillera

<p>The geomorphic processes that control temporal and spatial patterns of erosion, sediment storage and evacuation in an active mountain range (source) have a direct impact on how the signal of tectonics and climate, are recorded in the adjacent sedimentary basins (sinks). Stream power based numerical models of landscape evolution predict strong time lags between rock uplift and waves of erosion in the foreland, but this is difficult to test without proper resolution between source and sink signals..  Confirmation of model results is typically gleaned through observations that are either snapshots of processes in modern systems, or inversion of the stratigraphic record to decipher what occurred in the uplands. While cosmogenic nuclide derived, catchment wide erosion rates in the modern rivers provide a snapshot of processes happening in the last thousands of years, thermochronmeters average over the ≥ millions of years it takes a rock to ascend from the closure isotherm to the Earth’s surface,making it difficult, if not impossible to capture a minimally time averaged signal of the geomorphic system in the stratigraphic record. Paleoerosion rates from the residual cosmogenic nuclide concentration of buried sediments offer a means to bridge the gap in resolution. </p><p> </p><p>This study combines numerical modeling and cosmogenic nuclide paleoerosion rates in the Argentine Precordillera to build a rich picture of how this foreland basin system, from the hinterland through the foreland basin evolves in time and space. Our modeling shows that the dynamics of wedge-top basin formation behind a rising, and then subsequently inactive range have profound and systematic effects on the geomorphic signals both upstream and downstream of the wedge-top basin. Downstream, it is clear that there are strong, million year time lags in the uplift-triggered erosive pulse and spatial controls on where the sediment delivered to the foreland is sourced. Upstream, aggradation in the wedge top leads to the development of a wave of low erosion into the hinterland that results in the creation of perched surfaces coeval to erosive pulses downstream. In the Argentine Precordillera at 30°S an 8 Ma record of paleoerosion rates from the wedge top and foreland basin deposits along with detrital zircons provenance in the foreland largely verifies the predictions of the numerical modeling. Similarly, upstream of the wedge-top basin, there are concordant knickpoints and large, broad planation surfaces perched some 1500 m above the floor of wedge top as predicted by the low erosion wave pulse. Our combination of numerical modeling and paleoerosion rates capture the dynamic evolution of mountain range at million to thousand year timescales. </p>

scholarly journals The push and pull of abandoned channels: How floodplain processes and healing affect avulsion dynamics and alluvial landscape evolution in foreland basins

2021 ◽  
Author(s):  
Harrison K. Martin ◽  
Douglas A. Edmonds
Keyword(s):  
Dynamic Equilibrium ◽  
Landscape Evolution ◽  
Numerical Models ◽  
Foreland Basin ◽  
Field Work ◽  
Foreland Basins ◽  
Abandoned Channel ◽  
Mountain Front ◽  
Set Up ◽  
Abandoned Channels

Abstract. River avulsions are an important mechanism by which sediment is routed and emplaced in foreland basins. However, because avulsions occur infrequently, we lack observational data that might inform where, when, and why avulsions occur and these questions are instead often investigated by rule-based numerical models. These models have historically simplified or neglected the effects of abandoned channels on avulsion dynamics, even though fluvial megafans in foreland basins are characteristically covered in abandoned channels. Here, we investigate the pervasiveness of abandoned channels on modern fluvial megafan surfaces. Then, we present a physically based cellular model that parameterizes interactions between a single avulsing river and abandoned channels in a foreland basin setting. We investigate how abandoned channels affect avulsion set-up, pathfinding, and landscape evolution. We demonstrate and discuss how the processes of abandoned channel inheritance and transient knickpoint propagation post-avulsion serve to shortcut the time necessary to set-up successive avulsions. Then, we address the idea that abandoned channels can both repel and attract future pathfinding flows under different conditions. By measuring the distance between the mountain-front and each avulsion over long (106 to 107 years) timescales, we show that increasing abandoned channel repulsion serves to push avulsions farther from the mountain-front, while increasing attraction pulls avulsions proximally. Abandoned channels do not persist forever, and we test possible channel healing scenarios (deposition-only, erosion-only, and far-field directed) and show that only the final scenario achieves dynamic equilibrium without completely filling accommodation space. We also observe megafan growth occurring via ~O:105 year lobe switching, but only in our runs that employ deposition-only or erosion-only healing modes. Finally, we highlight opportunities for future field work and remote sensing efforts to inform our understanding of the role that floodplain topography, including abandoned channels, plays on avulsion dynamics.

scholarly journals Two-Dimensional Numerical Modeling of Flow in Physical Models of Rock Vane and Bendway Weir Configurations

Water ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 458
Author(s):  
Drew C. Baird ◽  
Benjamin Abban ◽  
S. Michael Scurlock ◽  
Steven B. Abt ◽  
Christopher I. Thornton
Keyword(s):  
Numerical Modeling ◽  
Physical Model ◽  
Numerical Models ◽  
Hydraulic Performance ◽  
Physical Models ◽  
Protection Measures ◽  
Design Engineers ◽  
Model Study ◽  
Study Results ◽  
Wide Range

While there are a wide range of design recommendations for using rock vanes and bendway weirs as streambank protection measures, no comprehensive, standard approach is currently available for design engineers to evaluate their hydraulic performance before construction. This study investigates using 2D numerical modeling as an option for predicting the hydraulic performance of rock vane and bendway weir structure designs for streambank protection. We used the Sedimentation and River Hydraulics (SRH)-2D depth-averaged numerical model to simulate flows around rock vane and bendway weir installations that were previously examined as part of a physical model study and that had water surface elevation and velocity observations. Overall, SRH-2D predicted the same general flow patterns as the physical model, but over- and underpredicted the flow velocity in some areas. These over- and underpredictions could be primarily attributed to the assumption of negligible vertical velocities. Nonetheless, the point differences between the predicted and observed velocities generally ranged from 15 to 25%, with some exceptions. The results showed that 2D numerical models could provide adequate insight into the hydraulic performance of rock vanes and bendway weirs. Accordingly, design guidance and implications of the study results are presented for design engineers.

scholarly journals Numerical modeling of the hydraulic impact of riparian vegetation

2018 ◽  
Vol 44 ◽  
pp. 00194
Author(s):  
Krzysztof Wolski ◽  
Tomasz Tymiński ◽  
Grzegorz Chrobak
Keyword(s):  
Numerical Modeling ◽  
Riparian Vegetation ◽  
Water Surface ◽  
Numerical Models ◽  
Three Dimensional ◽  
Careful Examination ◽  
Impact Structure ◽  
Hydraulic Impact ◽  
Vegetation Zones ◽  
Maximal Shear Stress

This paper presents results of numerical modelling of riverbed segment with riparian vegetation performed with use of CCHE2 software. Vegetation zones are places where dynamic of water flow increases. Therefore, there is a need of careful examination of hydraulic impact structure of such zones. Accurate research is necessary and should be performed with use of physical or numerical models, two or three dimensional. Paper presents distribution of velocity and area of water surface for two variants of vegetation deposition acquired in CCHE2D software and modelled for riverbed with distinctive riparian vegetation. Results point to significant (30–40%) increase of maximal velocities in riverbed with riparian vegetation, while directly near the vegetation there were zones with very low velocities. Local damming occurs before vegetal zone. Maximal shear stress in zones with increased velocity is significantly augmented compared to conditions with no vegetation, which can cause more intensive erosion in those zones

scholarly journals Numerical Modeling of a Punch Penetration Test Using the Discrete Element Method

2020 ◽  
Vol 28 (2) ◽  
pp. 1-7
Author(s):  
Rouhollah Basirat ◽  
Jafar Khademi Hamidi
Keyword(s):  
Numerical Modeling ◽  
Discrete Element Method ◽  
Numerical Models ◽  
Confining Pressure ◽  
Discrete Element ◽  
Numerical Results ◽  
Strength Parameter ◽  
Penetration Test ◽  
Strength Parameters ◽  
Element Method

AbstractUnderstanding the brittleness of rock has a crucial importance in rock engineering applications such as the mechanical excavation of rock. In this study, numerical modeling of a punch penetration test is performed using the Discrete Element Method (DEM). The Peak Strength Index (PSI) as a function of the brittleness index was calculated using the axial load and a penetration graph obtained from numerical models. In the first step, the numerical model was verified by experimental results. The results obtained from the numerical modeling showed a good agreement with those obtained from the experimental tests. The propagation path was also simulated using Voronoi meshing. The fracture was created under the indenter in the first step, and then radial fractures were propagated. The effects of confining pressure and strength parameters on the PSI were subsequently investigated. The numerical results showed that the PSI increases with enhancing the confining pressure and the strength parameter of the rock, including cohesion and the friction angle. A new relationship between the strength parameters and PSI was also introduced based on two variable regressions of the numerical results.

scholarly journals Numerical modeling of hiding properties of underwater acoUStic communication signals with linear sweep of the carrier

2020 ◽  
Author(s):  
К.Г. Кебкал
Keyword(s):  
Numerical Modeling ◽  
Continuous Spectrum ◽  
Gaussian Noise ◽  
Data Exchange ◽  
Numerical Models ◽  
Underwater Acoustic Communication ◽  
Underwater Acoustic ◽  
Communication Signals ◽  
Communication Signal ◽  
Spectrum Spread

На результатах численного моделирования продемонстрировано, что распределения вероятностей огибающей и фазы смеси гауссова шума и (слабого) гидроакустического сигнала связи, характеризуемого линейной разверткой несущей, могут иметь исчезающе малые отличия от аналогичных распределений, характерных для просто гауссова шума. Использование непрерывного расширения спектра сигнала связи может представлять интерес для задач скрытого обмена данными, в которых обнаружение сеанса связи устройствами перехвата должно быть затруднительным или невозможным. С применением численных моделей проанализированы возможности использования сигналов с непрерывным расширением спектра для скрытой цифровой гидроакустической связи посредством штатных приемоизлучающих гидроакустических систем, находящихся на вооружении действующих кораблей. Based on the results of the numerical modeling, the vanishingly small differences between the probability distributions of the envelope and phase of the sum of Gaussian noise and (weak) underwater acoustic signal with linear carrier sweep, and the same distributions for the Gaussian noise all alone are demonstrated. Utilization of the continuous spectrum spread of the communication signal may be applied to the task of covert data exchange, where detection of the communication session by the intercepting equipment must be complicated or impossible. Using numerical models, we analyzed the capabilities of implementation of the signals with continuous spectrum spread for covert digital underwater acoustic communications through the standard underwater acoustic transducers, which are in service on the operational ready vessels.

Chemical weathering response to extreme global warming during Paleocene-Eocene Hyperthermals, Southern Pyrenees, Spain

2021 ◽  
Author(s):  
Rocio Jaimes-Gutierrez ◽  
Thierry Adatte ◽  
Emmanuelle Puceat ◽  
Jean Braun ◽  
Sebastien Castelltort
Keyword(s):  
Climatic Change ◽  
Chemical Weathering ◽  
Numerical Models ◽  
Clay Fraction ◽  
Clay Mineralogy ◽  
Foreland Basin ◽  
Isotopic Analysis ◽  
Feedback Mechanism ◽  
Horizon 2020 ◽  
Sediment Routing

<p>The Paleocene and early Eocene were periods yielding multiple hyperthermal events. The most pronounced of them was the Paleocene-Eocene Thermal Maximum (PETM), which was characterized by an abrupt increase in global temperature (5–8 °C) over a short time (20 ka). A negative carbon isotope excursion marks the onset of the PETM, which resulted in the fast injection of CO<sub>2</sub> into the ocean-atmosphere system, triggering global climatic changes. Geochemical, mineralogical, and sedimentological markers record the resulting increase in continental weathering. This is important, as enhanced chemical erosion influences both the CO<sub>2</sub> concentration in the atmosphere and ocean acidity, generating a feedback mechanism. Hence, constraining the rates and intensity of weathering response can further clarify the causes for the PETM and Eocene hyperthermals. This study focuses on the well-preserved Pyrenean foreland basin and intends to assess the continental chemical weathering response of the sediment routing system during the PETM. Clay mineralogy is a climate-sensitive proxy, which records changes in continental erosion. Therefore, clay mineral proportions will be analyzed using X-ray diffraction and major element chemistry on clay-rich samples from the entire source-to-sink system (continental to deep marine deposits). Kaolinite and smectite will be separated from the detrital clay fraction and further subjected to δ<sup>18</sup>O and δD isotopic analysis for paleoclimatic reconstruction. The combined Lu-Hf and Sm-Nd isotope systems in the clay fraction of the sediments will be used to track the evolution of chemical weathering intensity. The outcome of this project will serve to validate numerical models to understand erosion as a function of rapid climatic change. This topic is of keen interest, as the PETM and its sedimentological signal work as a natural analog for anthropogenically-induced climatic change. The project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie Grant Agreement No 860383.</p>

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