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  • 1
    Online Resource
    Online Resource
    Turning the tide: comparison of tidal flow by periodic sea level fluctuation and by periodic bed tilting in scaled landscape experiments of estuaries
    Copernicus GmbH ; 2017
    In:  Earth Surface Dynamics Vol. 5, No. 4 ( 2017-11-28), p. 731-756
    Details
    In: Earth Surface Dynamics, Copernicus GmbH, Vol. 5, No. 4 ( 2017-11-28), p. 731-756
    Abstract: Abstract. Analogue models or scale experiments of estuaries and short tidal basins are notoriously difficult to create in the laboratory because of the difficulty to obtain currents strong enough to transport sand. Our recently discovered method to drive tidal currents by periodically tilting the entire flume leads to intense sediment transport in both the ebb and flood phase, causing dynamic channel and shoal patterns. However, it remains unclear whether tilting produces periodic flows with characteristic tidal properties that are sufficiently similar to those in nature for the purpose of landscape experiments. Moreover, it is not well understood why the flows driven by periodic sea level fluctuation, as in nature, are not sufficient for morphodynamic experiments. Here we compare for the first time the tidal currents driven by sea level fluctuations and by tilting. Experiments were run in a 20  ×  3 m straight flume, the Metronome, for a range of tilting periods and with one or two boundaries open at constant head with free inflow and outflow. Also, experiments were run with flow driven by periodic sea level fluctuations. We recorded surface flow velocity along the flume with particle imaging velocimetry and measured water levels along the flume. We compared the results to a one-dimensional model with shallow flow equations for a rough bed, which was tested on the experiments and applied to a range of length scales bridging small experiments and large estuaries. We found that the Reynolds method results in negligible flows along the flume except for the first few metres, whereas flume tilting results in nearly uniform reversing flow velocities along the entire flume that are strong enough to move sand. Furthermore, tidal excursion length relative to basin length and the dominance of friction over inertia is similar in tidal experiments and reality. The sediment mobility converges between the Reynolds method and tilting for flumes hundreds of metres long, which is impractical. Smaller flumes of a few metres in length, on the other hand, are much more dominated by friction than natural systems, meaning that sediment suspension would be impossible in the resulting laminar flow on tidal flats. Where the Reynolds method is limited by small sediment mobility and high tidal range relative to water depth, the tilting method allows for independent control over the variables flow depth, velocity, sediment mobility, tidal period and excursion length, and tidal asymmetry. A periodically tilting flume thus opens up the possibility of systematic biogeomorphological experimentation with self-formed estuaries.
    Type of Medium: Online Resource
    ISSN: 2196-632X
    URL: Article
    URL: Article
    DOI: 10.5194/esurf-5-731-2017
    DOI: 10.5194/esurf-5-731-2017-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2017
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  • 2
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    Online Resource
    Morphological evolution of bifurcations in tide-influenced deltas
    Copernicus GmbH ; 2020
    In:  Earth Surface Dynamics Vol. 8, No. 2 ( 2020-06-02), p. 413-429
    Details
    In: Earth Surface Dynamics, Copernicus GmbH, Vol. 8, No. 2 ( 2020-06-02), p. 413-429
    Abstract: Abstract. In river-dominated deltas, bifurcations often develop an asymmetrical morphology; i.e. one of the downstream channels silts up, while the other becomes the dominant one. In tide-influenced systems, bifurcations are thought to be less asymmetric and both downstream channels of the bifurcation remain open. The main aim of this study is to understand how tides influence the morphological development of bifurcations. By using a depth-averaged (2DH, two-dimensional horizontal) morphodynamic model (Delft3D), we simulated the morphological development of tide-influenced bifurcations on millennial timescales. The schematized bifurcation consists of an upstream channel forced by river discharge and two downstream channels forced by tides. Two different cases were examined. In the first case, the downstream channels started with unequal depth or length but had equal tidal forcing, while in the second case the morphology was initially symmetric but the downstream channels were forced with unequal tides. Furthermore, we studied the sensitivity of results to the relative role of river flow and tides. We find that with increasing influence of tides over river, the morphology of the downstream channels becomes less asymmetric. Increasing tidal influence can be achieved by either reduced river flow with respect to the tidal flow or by asymmetrical tidal forcing of the downstream channels. The main reason for this behaviour is that tidal flows tend to be less unequal than river flows when geometry is asymmetric. For increasing tidal influence, this causes less asymmetric sediment mobility and therefore transport in both downstream channels. Furthermore, our results show that bedload tends to divide less asymmetrically compared to suspended load and confirm the stabilizing effect of lateral bed slopes on morphological evolution as was also found in previous studies. We show that the more tide-dominated systems tend to have a larger ratio of bedload-to-suspended-load transport due to periodic low sediment mobility conditions during a transition between ebb and flood. Our results explain why distributary channel networks on deltas with strong tidal influence are more stable than river-dominated ones.
    Type of Medium: Online Resource
    ISSN: 2196-632X
    URL: Article
    URL: Article
    DOI: 10.5194/esurf-8-413-2020
    DOI: 10.5194/esurf-8-413-2020-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2020
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  • 3
    Online Resource
    Online Resource
    Turning the tide: Growth and dynamics of a tidal basin and inlet in experiments
    American Geophysical Union (AGU) ; 2015
    In:  Journal of Geophysical Research: Earth Surface Vol. 120, No. 1 ( 2015-01), p. 95-119
    Details
    In: Journal of Geophysical Research: Earth Surface, American Geophysical Union (AGU), Vol. 120, No. 1 ( 2015-01), p. 95-119
    Type of Medium: Online Resource
    ISSN: 2169-9003
    URL: Article
    DOI: 10.1002/2014JF003127
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2015
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  • 4
    Online Resource
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    Effects of sediment grain size and channel slope on the stability of river bifurcations
    Wiley ; 2021
    In:  Earth Surface Processes and Landforms Vol. 46, No. 10 ( 2021-08), p. 2004-2018
    Details
    In: Earth Surface Processes and Landforms, Wiley, Vol. 46, No. 10 ( 2021-08), p. 2004-2018
    Abstract: Channel bifurcations can be found in river network systems from high gradient gravel‐bed rivers to fine‐grained low gradient deltas. In these systems, bifurcations often evolve asymmetrically such that one downstream channel silts up and the other deepens and, in most cases, they eventually avulse. Past analytical and numerical studies showed that symmetric bifurcations are unstable in high and low Shields stress conditions resulting in asymmetric bifurcations and avulsion, while they can be stable in the mid‐Shields range, but this range is smaller for larger width‐to‐depth ratio. Here, using a one‐dimensional (1D) numerical model, we show that effects of sediment grain size and of channel slope are much larger than expected for low‐gradient systems when a sediment transport relation is used that separates between bedload and suspended load transport. We found that the range of Shields stress conditions with unstable symmetric bifurcations expanded for lower channel slopes and for finer sediment. In high sediment mobility, suspended load increasingly dominates the sediment transport, which increases the sediment transport nonlinearity and lowers the relative influence of the stabilizing transverse bedslope‐driven flux. Contrary to previous works, we found another stable symmetric solution in high Shields stress, but this only occurs in the systems with small width‐to‐depth ratio. This indicates that suspended load‐dominated bifurcations of lowland rivers are more likely to develop into highly asymmetric channels than previously thought. This explains the tendency of channel avulsion observed in many systems.
    Type of Medium: Online Resource
    ISSN: 0197-9337 , 1096-9837
    URL: Issue
    URL: Article
    DOI: 10.1002/esp.v46.10
    DOI: 10.1002/esp.5141
    Language: English
    Publisher: Wiley
    Publication Date: 2021
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  • 5
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    Online Resource
    Sea-level-rise-induced threats depend on the size of tide-influenced estuaries worldwide
    Springer Science and Business Media LLC ; 2019
    In:  Nature Climate Change Vol. 9, No. 12 ( 2019-12), p. 986-992
    Details
    In: Nature Climate Change, Springer Science and Business Media LLC, Vol. 9, No. 12 ( 2019-12), p. 986-992
    Type of Medium: Online Resource
    ISSN: 1758-678X , 1758-6798
    URL: Article
    DOI: 10.1038/s41558-019-0608-4
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2019
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  • 6
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    Online Resource
    Processes controlling the dynamics of compound sand waves in the North Sea, Netherlands : PROCESSES FOR SAND WAVE DYNAMICS
    American Geophysical Union (AGU) ; 2005
    In:  Journal of Geophysical Research: Earth Surface Vol. 110, No. F4 ( 2005-12), p. n/a-n/a
    Details
    In: Journal of Geophysical Research: Earth Surface, American Geophysical Union (AGU), Vol. 110, No. F4 ( 2005-12), p. n/a-n/a
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/2004JF000173
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2005
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    detail.hit.zdb_id: 2016813-5
    detail.hit.zdb_id: 2016810-X
    detail.hit.zdb_id: 2403298-0
    detail.hit.zdb_id: 2016800-7
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    detail.hit.zdb_id: 2969341-X
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    detail.hit.zdb_id: 3094268-8
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    detail.hit.zdb_id: 2016804-4
    detail.hit.zdb_id: 3094181-7
    detail.hit.zdb_id: 3094219-6
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    detail.hit.zdb_id: 2220777-6
    detail.hit.zdb_id: 3094197-0
    SSG: 16,13
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  • 7
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    Ediacaran life close to land: Coastal and shoreface habitats of the Ediacaran macrobiota, the Central Flinders Ranges, South Australia
    Society for Sedimentary Geology ; 2020
    In:  Journal of Sedimentary Research Vol. 90, No. 11 ( 2020-11-30), p. 1463-1499
    Details
    In: Journal of Sedimentary Research, Society for Sedimentary Geology, Vol. 90, No. 11 ( 2020-11-30), p. 1463-1499
    Abstract: The Rawnsley Quartzite of South Australia hosts some of the world's most diverse Ediacaran macrofossil assemblages, with many of the constituent taxa interpreted as early representatives of metazoan clades. Globally, a link has been recognized between the taxonomic composition of individual Ediacaran bedding-plane assemblages and specific sedimentary facies. Thorough characterization of fossil-bearing facies is thus of fundamental importance for reconstructing the precise environments and ecosystems in which early animals thrived and radiated, and distinguishing between environmental and evolutionary controls on taxon distribution. This study refines the paleoenvironmental interpretations of the Rawnsley Quartzite (Ediacara Member and upper Rawnsley Quartzite). Our analysis suggests that previously inferred water depths for fossil-bearing facies are overestimations. In the central regions of the outcrop belt, rather than shelf and submarine canyon environments below maximum (storm-weather) wave base, and offshore environments between effective (fair-weather) and maximum wave base, the succession is interpreted to reflect the vertical superposition and lateral juxtaposition of unfossiliferous non-marine environments with fossil-bearing coastal and shoreface settings. Facies comprise: 1, 2) amalgamated channelized and cross-bedded sandstone (major and minor tidally influenced river and estuarine channels, respectively), 3) ripple cross-laminated heterolithic sandstone (intertidal mixed-flat), 4) silty-sandstone (possible lagoon), 5) planar-stratified sandstone (lower shoreface), 6) oscillation-ripple facies (middle shoreface), 7) multi-directed trough- and planar-cross-stratified sandstone (upper shoreface), 8) ripple cross-laminated, planar-stratified rippled sandstone (foreshore), 9) adhered sandstone (backshore), and 10) planar-stratified and cross-stratified sandstone with ripple cross-lamination (distributary channels). Surface trace fossils in the foreshore facies represent the earliest known evidence of mobile organisms in intermittently emergent environments. All facies containing fossils of the Ediacaran macrobiota remain definitively marine. Our revised shoreface and coastal framework creates greater overlap between this classic “White Sea” biotic assemblage and those of younger, relatively depauperate “Nama”-type biotic assemblages located in Namibia. Such overlap lends support to the possibility that the apparent biotic turnover between these assemblages may reflect a genuine evolutionary signal, rather than the environmental exclusion of particular taxa.
    Type of Medium: Online Resource
    ISSN: 1527-1404
    URL: Article
    DOI: 10.2110/jsr.2020.029
    Language: English
    Publisher: Society for Sedimentary Geology
    Publication Date: 2020
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  • 8
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    Distinct patterns of bank erosion in a navigable regulated river
    Wiley ; 2020
    In:  Earth Surface Processes and Landforms Vol. 45, No. 2 ( 2020-02), p. 361-374
    Details
    In: Earth Surface Processes and Landforms, Wiley, Vol. 45, No. 2 ( 2020-02), p. 361-374
    Abstract: Distinct bankline patterns appeared after the removal of protection works along a navigable reach of the Meuse River. A series of oblique embayments now dominate the riverine landscape after ten years of bank erosion, but their location and asymmetry cannot be explained yet. This work analyses and integrates field measurements of flow, ship waves, bank composition, bed topography and historical maps to explain the observed patterns along two reaches of the river. An extraordinary low‐water‐level event generated by a ship accident provided the unique opportunity to also analyse the subaqueous bank topography. The results indicate that the formation of oblique embayments arises from the combination of floodplain heterogeneity, structured by scroll‐bar deposits, and the regulation of water levels, resulting in ship‐wave attack at a narrow range of bank elevation for 70% of the time. Substrate erodibility acts on the effectiveness of trees to slow down local bank erosion rates, which is possibly enhanced by a positive feedback between woody roots and cohesive soil. The strong regulation of water levels and the waves generated by the intense ship traffic produce an increasingly long mildly‐sloping terrace at the bank toe and progressively dominate the bank erosion process. This study demonstrates the important role of floodplain and scroll bar formation in shaping later bank erosion, which has implications for predictive numerical models, restoration strategies, and understanding the role of vegetation in bank erosion processes. © 2019 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd
    Type of Medium: Online Resource
    ISSN: 0197-9337 , 1096-9837
    URL: Issue
    URL: Article
    DOI: 10.1002/esp.v45.2
    DOI: 10.1002/esp.4736
    Language: English
    Publisher: Wiley
    Publication Date: 2020
    detail.hit.zdb_id: 1479188-2
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  • 9
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    Modelling the effects of normal faulting on alluvial river meandering
    Wiley ; 2022
    In:  Earth Surface Processes and Landforms Vol. 47, No. 5 ( 2022-04), p. 1252-1270
    Details
    In: Earth Surface Processes and Landforms, Wiley, Vol. 47, No. 5 ( 2022-04), p. 1252-1270
    Abstract: The meandering of alluvial rivers may be forced by normal faulting due to tectonically altered topographic gradients of the river valley and channel at and near the fault zone. Normal faulting can affect river meandering by either instantaneous (e.g. surface‐rupturing earthquakes) or gradual displacement. To enhance our understanding of river channel response to tectonic faulting at the fault zone scale we used the physics‐based, two‐dimensional morphodynamic model Nays2D to simulate the responses of a laboratory‐scale alluvial river with vegetated floodplain to various faulting and offset scenarios. The results of a model with normal fault downstepping in the downstream direction show that channel sinuosity and bend radius increase up to a maximum as a result of the faulting‐enhanced valley gradient. Hereafter, a chute cutoff reduces channel sinuosity to a new dynamic equilibrium value that is generally higher than the pre‐faulting sinuosity. A scenario where a normal fault downsteps in the upstream direction leads to reduced morphological change upstream of the fault due to a backwater effect induced by the faulting. The position within a meander bend at which faulting occurs has a profound influence on the evolution of sinuosity; fault locations that enhance flow velocities over the point bar during floods result in a faster sinuosity increase and subsequent chute cutoff than locations that enhance flow velocity directed towards the floodplain. This upward causation from the bend scale to the reach and floodplain scale arises from the complex interactions between meandering and floodplain and the nonlinearities of the sediment transport and chute cutoff processes. Our model results provide a guideline to include process‐based reasoning in the interpretation of geomorphological and sedimentological observations of fluvial response to faulting. The combination of these approaches leads to better predictions of possible effects of faulting on alluvial river meandering.
    Type of Medium: Online Resource
    ISSN: 0197-9337 , 1096-9837
    URL: Issue
    URL: Article
    DOI: 10.1002/esp.v47.5
    DOI: 10.1002/esp.5315
    Language: English
    Publisher: Wiley
    Publication Date: 2022
    detail.hit.zdb_id: 1479188-2
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  • 10
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    Upstream control of river anastomosis by sediment overloading, upper Columbia River, British Columbia, Canada
    Wiley ; 2017
    In:  Sedimentology Vol. 64, No. 6 ( 2017-10), p. 1488-1510
    Details
    In: Sedimentology, Wiley, Vol. 64, No. 6 ( 2017-10), p. 1488-1510
    Abstract: Anastomosing rivers, systems of multiple interconnected channels that enclose floodbasins, constitute a major category of rivers for which various sedimentary facies models have been developed. While the sedimentary products of anastomosing rivers are relatively well‐known, their genesis is still debated. A rapidly growing number of ancient alluvial successions being interpreted as of anastomosing river origin, including important hydrocarbon reservoirs, urge the development of robust models for the genesis of anastomosis, to facilitate better interpretation of ancient depositional settings and controls. The upper Columbia River, British Columbia, Canada, is the most‐studied anastomosing river and has played a key role in the development of an anastomosing river facies model. Two hypotheses for the origin of upper Columbia River anastomosis include the following: (i) downstream control by aggrading cross‐valley alluvial fans; and (ii) upstream control by excessive bedload input from tributaries. Both upstream and downstream control may force aggradation and avulsions in the upper Columbia River. In order to test both hypotheses, long‐term (millennia‐scale) floodplain sedimentation rates and avulsion frequencies are calculated using 14 C‐dated deeply buried organic floodplain material from cross‐valley borehole transects. The results indicate a downstream decrease in floodplain sedimentation rate and avulsion frequency along the anastomosed reach, which is consistent with dominant upstream control by sediment overloading. The data here link recent avulsion activity to increased sediment supply during the Little Ice Age ( ca 1100 to 1950  ad ). This link is supported by data showing that sediment supply to the upper Columbia study reach fluctuated in response to Holocene glacial advances and retreats in the hinterland. Upstream control of anastomosis has considerable implications for the reconstruction of the setting of interpreted ancient anastomosing systems. The present research underscores that anastomosing systems typically occur in relatively proximal settings with abundant sediment supplied to low‐gradient floodplains, a situation commonly found in intermontane and foreland basins.
    Type of Medium: Online Resource
    ISSN: 0037-0746 , 1365-3091
    URL: Issue
    URL: Article
    DOI: 10.1111/sed.2017.64.issue-6
    DOI: 10.1111/sed.12361
    RVK:
    RB 10121
    Language: English
    Publisher: Wiley
    Publication Date: 2017
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    SSG: 13
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