Formation mechanisum of step-pool systems in steep rivers and guide lines for the design of construction

Hasegawa, Kazuyoshi; Kanbayashi, Satoru

doi:10.2208/prohe.40.893

Cited by 7 publications

(17 citation statements)

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“…In addition, Whittaker and Jaeggi (1982) and Ashida et al (1984) argued that ribs are formed by antidunes and sorting effects. Grant and Mizuyama (1991), Grant (1994), Hasegawa and Kanbayashi (1996) support this model. Chin (1999) showed that such field data fall into the theoretical domain of antidune formation.…”

Section: Antidunesmentioning

confidence: 81%

“…The flume data of Curran and Wilcock (2005) additionally plot outside the theoretical antidune existence field (see also the review of Chin and Whole, 2005). Hasegawa and Kanbayashi (1996) explained transverse ribs in terms of the antidune model. Moreover, they showed that the circular arrangement of gravel, i.e.…”

Section: Antidunesmentioning

confidence: 87%

“…When the wavelengths of the antidunes and water surface waves coincide, the 2D undulations of antidunes gradually becomes 3D, at which point the surface waves begin to be amplified. Hasegawa and Kanbayashi (1996) and Hasegawa (1997) developed equations that represent the formative conditions for step-pool morphologies, and verified them experimentally.…”

Section: Antidunesmentioning

confidence: 95%

“…There are two patterns of gravel arrangement in such steps. Hasegawa et al (1990) and Hasegawa and Kanbayashi (1996) clearly distinguished them as 'transverse ribs' and 'step-pools'. A transverse rib is a step-like topography in which gravel, cobbles and boulders form ridges transverse to the flow.…”

Section: Antidunesmentioning

confidence: 99%

“…In this study, we have applied the formative conditions for 3D step-pools proposed by Hasegawa and Kanbayashi (1996) and Hasegawa (1997) to fine sand beds, and examined the resultant bedforms formed in a flume. We used this 'step-pool model' because it can express the formative conditions of 3D antidunes in fine sands in terms of a relationship between water discharge per unit width and the bed slope.…”

Section: Antidunesmentioning

confidence: 99%

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Formative conditions and sedimentary structures of sandy 3D antidunes: an application of the gravel step‐pool model to fine‐grained sand in an experimental flume

Yokokawa

Hasegawa

Kanbayashi

et al. 2010

Earth Surf Processes Landf

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Antidunes and their sedimentary structures can be useful in reconstructing paleo-hydraulic conditions, especially for large discharge events. However, three-dimensional (3D) antidunes in sand-sized sediments have not yet been studied extensively, as compared to either two-dimensional (2D) antidunes or antidunes in gravel-sized sediments. In this study, we estimated formative conditions of gravel step-pool morphologies and applied them to the formation of 3D antidunes over a sand bed. Formative conditions are expressed in terms of a relationship between the water discharge per unit width and the bed slope. Flume experiments demonstrated that 3D mound-like antidune configurations and their associated internal sedimentary structures could be preserved. Internal sedimentary structures were characterized by shallow lens-like structures whose bases were erosional. Although gently-dipping concave-upward lamination was dominant, convex-upward lamination was occasionally observed. The dimensions of lenticular lamina-sets can be used to estimate antidune geometry. Thus if 3D antidunes can be interpreted in the stratigraphic record, it is possible to estimate the paleo-hydraulic parameters such as water discharge and bed slope more precisely than previously.

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Section: Antidunesmentioning

confidence: 81%

Section: Antidunesmentioning

confidence: 87%

Section: Antidunesmentioning

confidence: 95%

Section: Antidunesmentioning

confidence: 99%

Section: Antidunesmentioning

confidence: 99%

See 3 more Smart Citations

Formative conditions and sedimentary structures of sandy 3D antidunes: an application of the gravel step‐pool model to fine‐grained sand in an experimental flume

Yokokawa

Hasegawa

Kanbayashi

et al. 2010

Earth Surf Processes Landf

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Three‐dimensional antidunes coexisting with alternate bars

Inoue

Watanabe

Iwasaki

et al. 2020

Earth Surf Processes Landf

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Antidunes are fluvial bedforms that form in rivers with supercritical flows. The water surface over antidunes is strongly in phase with the bed surface, and the water surface is amplified to produce large surface waves. Many experimental studies have addressed antidunes; however, the shapes of three‐dimensional antidunes in a wide channel with alternate bars have not yet been appropriately understood. In this study, we experimentally investigated the streamwise and transverse length scales of antidunes under conditions with a large width–depth ratio. Our experimental results provide evidence for the coevolution of antidunes and free alternate bars, and show for the first time that the development of free bars greatly alters the three‐dimensional shape of water surface waves over antidunes. In the absence of free bars in a wide channel, multiple longitudinal wave trains form, and the number of wave trains counted in the transverse direction increases with increases in the width–depth ratio. However, the presence of free bars affects the local flow characteristics, resulting in a decrease of the number of wave trains in the transverse direction. Therefore, we propose a simple model for predicting the reduction in the number of wave trains by combining two previous theories for antidunes and free bars. Results obtained by the model were found to largely agree with experimental observations. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd

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Fundamental study on the effects of the keystone height and structure on sediment deposition in a high‐gradient channel

Itsukushima

Masago

2019

River Research & Apps

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Step-pool structures are among the most important structures in riverbed morphology that can contribute to the stabilization of riverbeds and riverbanks, energy dissipation during floods, and head reduction function. Two concepts have been suggested regarding step-pool formation: the development of antidunes (antidune concept) and keystone concept. The latter suggests that a large boulder (keystone) incidentally left in a river channel can trap pebbles and build a step-pool structure.The ultimate goal of this study is to reveal the step-pool formation process and establish a design method based on the keystone concept. This paper describes the experimental results of the effects of the keystone arrangement on sediment deposition.Step-pool formation based on the keystone concept has previously been focused on the process of sediment deposition a short distance from a keystone.However, this study reveals that the obstruction of sediment supply due to the decreased flow velocity in the main river course is an important factor. When the arrangement interval of keystones is small, the amount of sediment supply downstream decreases because the flow velocity at the main flow channel between the keystones does not increase. In contrast, the flow velocity at the main river course increases between the keystones, and supplied sediment is transported to the most downstream section if the keystone arrangement interval is large enough to join the flow from the bank side of the keystones.

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Formation mechanisum of step-pool systems in steep rivers and guide lines for the design of construction

Cited by 7 publications

References 0 publications

Formative conditions and sedimentary structures of sandy 3D antidunes: an application of the gravel step‐pool model to fine‐grained sand in an experimental flume

Formative conditions and sedimentary structures of sandy 3D antidunes: an application of the gravel step‐pool model to fine‐grained sand in an experimental flume

Three‐dimensional antidunes coexisting with alternate bars

Fundamental study on the effects of the keystone height and structure on sediment deposition in a high‐gradient channel

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