New Bedform Phase Diagrams and Discriminant Functions for Formative Conditions of Bedforms in Open‐Channel Flows

Ohata, Koji; Naruse, Hajime; Yokokawa, Miwa; Viparelli, E.

doi:10.1002/2017jf004290

Cited by 31 publications

(28 citation statements)

References 46 publications

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“…3B. Finally, we validated the bedform stability diagram using a recent compilation of experimental and field data (46). We reduced this compilation to the range of Re p that span observations in the Torridonian Group, which resulted in 998 experimental data points and 47 field data points.…”

Section: [1]mentioning

confidence: 99%

Low-gradient, single-threaded rivers prior to greening of the continents

Ganti

Whittaker

Lamb

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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The Silurian-age rise of land plants is hypothesized to have caused a global revolution in the mechanics of rivers. In the absence of vegetation-controlled bank stabilization effects, pre-Silurian rivers are thought to be characterized by shallow, multithreaded flows, and steep river gradients. This hypothesis, however, is at odds with the pancontinental scale of early Neoproterozoic river systems that would have necessitated extraordinarily high mountains if such river gradients were commonplace at continental scale, which is inconsistent with constraints on lithospheric thickness. To reconcile these observations, we generated estimates of paleogradients and morphologies of pre-Silurian rivers using a well-developed quantitative framework based on the formation of river bars and dunes. We combined data from previous work with original field measurements of the scale, texture, and structure of fluvial deposits in Proterozoic-age Torridonian Group, Scotland—a type-example of pancontinental, prevegetation fluvial systems. Results showed that these rivers were low sloping (gradients 10−5 to 10−4), relatively deep (4 to 15 m), and had morphology similar to modern, lowland rivers. Our results provide mechanistic evidence for the abundance of low gradient, single-threaded rivers in the Proterozoic eon, at a time well before the evolution and radiation of land plants—despite the absence of muddy and vegetated floodplains. Single-threaded rivers with stable floodplains appear to have been a persistent feature of our planet despite singular changes in its terrestrial biota.

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Section: [1]mentioning

confidence: 99%

Low-gradient, single-threaded rivers prior to greening of the continents

Ganti

Whittaker

Lamb

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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“…First, the hydraulic conditions of plane bed regimes were examined with the sediment diameter and the sediment transport mechanism by which the sediment was moved, i.e., no sediment movement, bed-load, and suspended load. Bedform phases were expressed in the space of dimensionless parameters that reflected the properties of flows and sediment particles (Ohata et al, 2017;van den Berg & van Gelder, 1993). In this study, we employed the following dimensionless parameters to represent hydraulic conditions and sediment properties: the particle Reynolds number Re p , Shields number * , and the suspension index * s ⁄ .…”

Section: Data Sources and Dimensionless Parameters For Morphodynamic mentioning

confidence: 99%

“…Thus, bedform phase diagrams have been proposed based on laboratory and field observations (e.g., van den Berg & van Gelder, 1993). Recently, Ohata et al (2017) proposed bedform phase diagrams in three-dimensional parametric space, and their diagrams successfully reconstructed paleo-flow conditions from sedimentary structures.…”

Section: Introductionmentioning

confidence: 99%

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Upper and lower plane bed revisited

Ohata¹,

Naruse²,

Izumi³

2019

Preprint

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This study proposes a new definition of plane bed regimes. The upper plane bed is defined as a flat bedform that appears under conditions of active suspended load, whereas the lower plane bed forms when sediment particles are moved only by bed-load. Previous studies have recognized that two types of plane bed could be distinguished by shear stress, particle size, or flow regime. However, the compilation of a large amount of existing open-channel flow data indicates that the plane bed regimes cannot be differentiated by existing definitions. Newly produced phase diagrams indicate that plane bed data plot in two separate regions, and the gap between the two regions corresponds to the threshold condition of suspension. Further investigation is needed to understand the physical mechanisms generating lower plane beds and characterizations of parallel laminae from lower and upper plane beds.

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“…For example, (Dorrell et al, 2011) suggested that poorly graded division in turbidites is a product of high-concentration suspension. However, analyses of the sedimentary structures only provide a range of flow conditions (Ohata et al, 2017), not the spatio-temporal development of flows.…”

Section: Introductionmentioning

confidence: 99%

Inverse Analysis to Reconstruct Hydraulic Conditions of Non-steady Turbidity Currents: Application to an Ancient Turbidite of the Kiyosumi Formation of the Awa Group, Boso Peninsula, Central Japan

Nakao¹,

Naruse²,

Tokuhashi³

2020

Preprint

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This study proposes a new method of inverse analysis from ancient turbidites to the non-steady turbidity currents with consideration of multiple grain-size classes. The forward model employed in this study is based on the shallow water equation, and the initial condition of flows are assumed to be the lock-exchange type condition. To obtain a solution of the inverse problem, this study employed the genetic algorithm for finding the optimized initial conditions. The present method successfully estimated the true given initial conditions of the turbidity currents from the artificial data sets of deposits created by the calculation of the forward model. The author also applied the method to the turbidite bed in the Kiyosumi Formation. As a result of inverse analysis, the obtained solution fits well to the observed data of the individual turbidite, providing estimates of the flow velocity, the flow thickness and the sediment concentration of the turbidity current. The flow thickness and velocity when the turbidity current reached at the downstream end of the study area were reconstructed to be 334.6 m, 0.98 m/s respectively at the location of the downstream end. Result of our analysis is the first example of reconstructing a reasonable conditions of the turbidity current from an ancient turbidite observed in the field, and the method is expected to be applied in various regions in the future.

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New Bedform Phase Diagrams and Discriminant Functions for Formative Conditions of Bedforms in Open‐Channel Flows

Cited by 31 publications

References 46 publications

Low-gradient, single-threaded rivers prior to greening of the continents

Low-gradient, single-threaded rivers prior to greening of the continents

Upper and lower plane bed revisited

Inverse Analysis to Reconstruct Hydraulic Conditions of Non-steady Turbidity Currents: Application to an Ancient Turbidite of the Kiyosumi Formation of the Awa Group, Boso Peninsula, Central Japan

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