Understanding river dune splitting through flume experiments and analysis of a dune evolution model

Warmink, Jord Jurriaan; Dohmen-Janssen, Catarine M.; Lansink, Joost; Naqshband, Suleyman; Duin, Olav J. M. van; Paarlberg, Andries; Termes, A.P.P.; Hulscher, Suzanne J.M.H.

doi:10.1002/esp.3529

Cited by 20 publications

(31 citation statements)

References 51 publications

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“…In this simulation, the superimposed bed form has a height of H = 0.009 m at t = 2640 s while it is merging with the dune crest, which represents ∼28% of the dune height (0.032 m). This result is consistent with the results of Warmink et al [] and Reesink and Bridge [] who obtained 21% and 25% ratios, respectively, in their experiment with dunes of comparable dimensions. Warmink et al [] describe the sequence as being a dune splitting but during the process the dune crest merges with the superimposed bed form and does not survive in the form of a smaller bed form.…”

Section: Resultssupporting

confidence: 93%

Numerical modeling of subaqueous sand dune morphodynamics

et al. 2016

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The morphodynamic evolution of subaqueous sand dunes is investigated, using a 2‐D Reynolds‐averaged Navier‐Stokes numerical model. A laboratory experiment where dunes are generated under stationary unidirectional flow conditions is used as a reference case. The model reproduces the evolution of the erodible bed until a state of equilibrium is reached. In particular, the simulation exhibits the different stages of the bed evolution, e.g., the incipient ripple generation, the nonlinear bed form growing phase, and the dune field equilibrium phase. The results show good agreement in terms of dune geometrical dimensions and time to equilibrium. After the emergence of the first ripple field, the bed growth is driven by cascading merging sequences between bed forms of different heights. A sequence extracted from the simulation shows how the downstream bed form is first eroded before merging with the upstream bed form. Superimposed bed forms emerge on the dune stoss sides during the simulation. An analysis of the results shows that they emerge downstream of a slight deflection on the dune profile. The deflection arises due to a modification of the sediment flux gradient consecutive to a reduction in the turbulence relaxation length while the upstream bed form height decreases. As they migrate, superimposed bed forms grow on the dune stoss side and eventually provoke the degeneration of the dune crest. Cascading merging sequences and superimposed bed forms dynamics both influence the dune field evolution and size and therefore play a fundamental role in the dune field self‐organization process.

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Section: Resultssupporting

confidence: 93%

Numerical modeling of subaqueous sand dune morphodynamics

et al. 2016

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“…Furthermore, the flow fields of the host and superimposed forms are known to interact (Fernandez et al, 2006;Reesink et al, 2014b), and these hydrodynamic interactions affect the relation between the heights and scour depths of the superimposed bedforms (e.g. McCabe and Jones, 1977;Bridge, 2007, 2009;Warmink et al, 2014). The sediment transport processes on the leeside of the host bedform will also alter in association with the evolving flow field, causing a spatio-temporal variation in both deposition rate and local sediment bypassing (Jopling, 1961;Allen, 1982;Kostaschuk et al, 2009).…”

Section: Using Form-set Analysis To Constrain 'Variability-dominated'mentioning

confidence: 99%

Extremes in dune preservation: Controls on the completeness of fluvial deposits

Reesink

Berg

Parsons

et al. 2015

Earth-Science Reviews

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Understanding sedimentary preservation underpins our ability to interpret the ancient sedimentary record and reconstruct paleoenvironments and paleoclimates. Dune sets are ubiquitous in preserved river deposits and are typically interpreted based on a model that describes the recurrence of erosion in a vertical sequence, but without considering spatial variability. However, spatial variability in flow and sediment transport will change the recurrence of erosion, and therefore dune preservation. In order to better understand the limits of these interpretations and outline the causes of potential variability in preservation potential, this paper reviews existing work and presents new observations of an extreme end-member of dune preservation: 'form-sets', formed by dunes in which both stoss-and lee-slopes are preserved intact. These form-sets do not conform to models that are based on the recurrence of erosion, since erosion does not recur in their case, and can therefore be used to evaluate the assumptions that underpin sedimentary preservation. New Ground Penetrating Radar data from the Río Paraná, Argentina, show dune fields that are buried intact within larger scale barforms. These trains of form-sets are up to 300 m in length, are restricted to unit-bar troughs in the upper 5 m of the channel deposits, occur in N 5% of the mid-channel bar deposits, show reactivation surfaces, occur in multiple levels, and match the size of average-flow dunes. A review of published accounts of form-sets highlights a diversity of processes that can be envisaged for their formation: i) abandonment after extreme floods, ii) slow burial of abandoned dune forms by cohesive clay in sheltered bar troughs and meander-neck cut-offs, iii) fast burial by mass-movement processes, and iv) climbing of dune sets due to local dominance of deposition over dune migration. Analysis of these new and published accounts of form-sets and their burial processes highlights that form-sets need not be indicative of extreme floods. Instead, form-sets are closely associated with surrounding geomorphology such as river banks, meander-neck cut-offs, and bars because this larger-scale context controls the local sediment budget and the nature of recurrence of erosion. Locally enhanced preservation by the 'extreme' dominance of deposition is further promoted by finer grain sizes and prolonged changes in flow stage. Such conditions are characteristic, although not exclusive, of large lowland rivers such as the Río Paraná. The spatial control on dune preservation is critical: although at-a-point models adequately describe near-horizontal sets of freely migrating dunes in uniform flows, they are unsuitable for inclined dune co-sets and other cases where multiple scales of bedforms interact. Spatial and temporal variations in flow and sediment transport between the thalweg and different positions on larger bar-forms can change the preservation potential of dunes within river channels. Therefore, dune set thickness distributions are likely grouped in larger-scale un...

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“…They are formed with different sediment sizes, mostly ranging from medium sand to gravel [4], and show rhythmic patterns caused by the interaction of turbulent flow on the riverbed [5]. The geometry of these dunes is a function of flow velocity, flow depth, and other physical parameters describing occurs from May to August [39].…”

Section: Introductionmentioning

confidence: 99%

Riverbed Micromorphology of the Yangtze River Estuary, China

Cheng

et al. 2016

Water

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Dunes are present in nearly all fluvial channels and are vital in understanding sediment transport, deposition, and flow conditions during floods of rivers and estuaries. This information is pertinent for helping developing management practices to reduce risks in river transportation and engineering. Although a few recent studies have investigated the micromorphology of a portion of the Yangtze River estuary in China, our understanding of dune development in this large estuary is incomplete. It is also poorly understood how the development and characteristics of these dunes have been associated with human activities in the upper reach of the Yangtze River and two large-scale engineering projects in the estuarine zone. This study analyzed the feature in micromorphology of the entire Yangtze River estuary bed over the past three years and assessed the morphological response of the dunes to recent human activities. In 2012, 2014, and 2015, multi-beam bathymetric measurements were conducted on the channel surface of the Yangtze River estuary. The images were analyzed to characterize the subaqueous dunes and detect their changes over time. Bottom sediment samples were collected for grain size analysis to assess the physical properties of the dunes. We found that dunes in the Yangtze River estuary can be classified in four major classes: very large dunes, large dunes, medium dunes, and small dunes. Large dunes were predominant, amounting to 51.5%. There was a large area of dunes developed in the middle and upper reaches of the Yangtze River estuary and in the Hengsha Passage. A small area of dunes was observed for the first time in the turbidity maximum zone of the Yangtze River estuary. These dunes varied from 0.12 to 3.12 m in height with a wide range of wavelength from 2.83 to 127.89 m, yielding a range in height to wavelength of 0.003-0.136. Sharp leeside slope angles suggest that the steep slopes of asymmetrical dunes in the middle and upper reaches, and the turbidity maximum zone of the Yangtze River estuary face predominantly towards tides because of the ebb-dominated currents. Sharp windward slope angles in the lower reach of the North Passage show the influence of flood-dominated currents on dunes. It is likely that the scale of dunes will increase in the future in the South Channel because of a sharp decline of sediment discharge caused by recent human activities.

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Understanding river dune splitting through flume experiments and analysis of a dune evolution model

Cited by 20 publications

References 51 publications

Numerical modeling of subaqueous sand dune morphodynamics

Numerical modeling of subaqueous sand dune morphodynamics

Extremes in dune preservation: Controls on the completeness of fluvial deposits

Riverbed Micromorphology of the Yangtze River Estuary, China

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