CHARACTERISTICS OF SEDIMENT TRANSPORT IN THE SWASH ZONE UNDER MIXED GRAIN SIZE

The paper examines the dependency between sediment transport rate, q, and grain size, D, (i.e. q∝Dp) in the swash zone. Experiments were performed using a dam break flow as a proxy for swash overtopping on a mobile sediment beach. The magnitude and nature of the dependency (i.e. p value) is inferred for different flow parameters; the initial dam depth (or initial bore height), do, the integrated depth averaged velocity, ∫u3 dt, and against the predicted transport, qp using the Meyer-Peter Muller (MPM) transport model. Experiments were performed over both upward sloping beds and a horizontal bed. The data show that negative dependencies (p0) are obtained for ∫u3 dt. This indicates that a given do and qp transport less sediment as grain size increases, whereas transport increases with grain size for a given ∫u3 dt. The p value is expected to be narrow ranged, 0.5≤ p≤-0.5. A discernible difference observed between the measured and predicted transport on horizontal and sloping beds suggests different modes of transport. The incorporation of a pressure gradient correction, dp/dx, using the surface water slope (i.e. piezometric head), in the transport calculation greatly improved the transport predictions on the horizontal bed, where dp/dx is positive. On average, the incorporation of a pressure gradient term into the MPM formulation reduces qp in the uprush by 4% (fine sand) to 18% (coarse sand) and increases qp over a horizontal bed by 1% (fine sand) to two orders of magnitude (coarse sand). The measured transport for fine and coarse sand are better predicted using MPM and MPM+dp/dx respectively. Poor predictions are obtained using Nielsen (2002) because the pressure gradient in the uprush is of opposite sign to that inferred from velocity data in that paper. It is suggested that future swash sediment transport models should incorporate the grain size effect, partly through the pressure gradient, although the dp/dx influence is small for fine sands because of the grain size scaling contained in the stress term.

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Sediment transport patterns on the Estremadura Spur continental shelf: Insights from grain-size trend analysis

Journal of Sea Research ◽

10.1016/j.seares.2014.04.001 ◽

2014 ◽

Vol 93 ◽

pp. 28-32 ◽

Cited By ~ 5

Author(s):

Maria Balsinha ◽

Carlos Fernandes ◽

Anabela Oliveira ◽

Aurora Rodrigues ◽

Rui Taborda

Keyword(s):

Grain Size ◽

Sediment Transport ◽

Continental Shelf ◽

Trend Analysis ◽

Transport Patterns ◽

Grain Size Trend Analysis

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Sediment transport processes across the Tibetan Plateau inferred from robust grain-size end members in lake sediments

Climate of the Past ◽

10.5194/cp-10-91-2014 ◽

2014 ◽

Vol 10 (1) ◽

pp. 91-106 ◽

Cited By ~ 61

Author(s):

E. Dietze ◽

F. Maussion ◽

M. Ahlborn ◽

B. Diekmann ◽

K. Hartmann ◽

...

Keyword(s):

Grain Size ◽

Sediment Transport ◽

Tibetan Plateau ◽

Transport Processes ◽

The Tibetan Plateau ◽

Dust Deposition ◽

Northerly Wind ◽

Near Surface ◽

Depositional Processes ◽

End Members

Abstract. Grain-size distributions offer powerful proxies of past environmental conditions that are related to sediment sorting processes. However, they are often of multimodal character because sediments can get mixed during deposition. To facilitate the use of grain size as palaeoenvironmental proxy, this study aims to distinguish the main detrital processes that contribute to lacustrine sedimentation across the Tibetan Plateau using grain-size end-member modelling analysis. Between three and five robust grain-size end-member subpopulations were distinguished at different sites from similarly–likely end-member model runs. Their main modes were grouped and linked to common sediment transport and depositional processes that can be associated with contemporary Tibetan climate (precipitation patterns and lake ice phenology, gridded wind and shear stress data from the High Asia Reanalysis) and local catchment configurations. The coarse sands and clays with grain-size modes >250 μm and <2 μm were probably transported by fluvial processes. Aeolian sands (~200 μm) and coarse local dust (~60 μm), transported by saltation and in near-surface suspension clouds, are probably related to occasional westerly storms in winter and spring. Coarse regional dust with modes ~25 μm may derive from near-by sources that keep in longer term suspension. The continuous background dust is differentiated into two robust end members (modes: 5–10 and 2–5 μm) that may represent different sources, wind directions and/or sediment trapping dynamics from long-range, upper-level westerly and episodic northerly wind transport. According to this study grain-size end members of only fluvial origin contribute small amounts to mean Tibetan lake sedimentation (19± 5%), whereas local to regional aeolian transport and background dust deposition dominate the clastic sedimentation in Tibetan lakes (contributions: 42 ± 14% and 51 ± 11%). However, fluvial and alluvial reworking of aeolian material from nearby slopes during summer seems to limit end-member interpretation and should be crosschecked with other proxy information. If not considered as a stand-alone proxy, a high transferability to other regions and sediment archives allows helpful reconstructions of past sedimentation history.

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EFFECTS OF SEASONAL VARIATIONS ON SANDY BEACH GROUNDWATER TABLE AND SWASH ZONE SEDIMENT TRANSPORT

Coastal Engineering Proceedings ◽

10.9753/icce.v34.sediment.59 ◽

2014 ◽

Vol 1 (34) ◽

pp. 59

Author(s):

Norasman Othman ◽

Ahmad Khairi Abd Wahab ◽

Mohamad Hidayat Jamal

Keyword(s):

Sediment Transport ◽

Seasonal Variations ◽

Sandy Beach ◽

Groundwater Table ◽

Swash Zone

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RANS MODELLING OF CROSS-SHORE SEDIMENT TRANSPORT AND MORPHODYNAMICS IN THE SWASH-ZONE

Coastal Engineering Proceedings ◽

10.9753/icce.v36v.sediment.14 ◽

2020 ◽

pp. 14

Author(s):

Joost Kranenborg ◽

Geert Campmans ◽

Niels Jacobsen ◽

Jebbe van der Werf ◽

Robert McCall ◽

...

Keyword(s):

Sediment Transport ◽

Numerical Model ◽

Navier Stokes ◽

Swash Zone ◽

Rans Equations ◽

Model Based ◽

Numerical Studies ◽

Reynolds Averaged Navier Stokes ◽

Averaged Models

Most numerical studies of sediment transport in the swash zone use depth-averaged models. However, such models still have difficulty predicting transport rates and morphodynamics. Depth-resolving models could give detailed insight in swash processes but have mostly been limited to hydrodynamic predictions. We present a depth-resolving numerical model, based on the Reynolds Averaged Navier-Stokes (RANS) equations, capable of modelling sediment transport and morphodynamics in the swash zone.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/PB8Vs0LJq88

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Effects of Cascade Reservoir Systems on the Longitudinal Distribution of Sediment Characteristics: A Case Study of the Heihe River Basin

10.21203/rs.3.rs-189115/v1 ◽

2021 ◽

Author(s):

Yu Wang ◽

Bao-long Li ◽

Juan-juan Liu ◽

Qi Feng ◽

Wei Liu ◽

...

Keyword(s):

Grain Size ◽

Sediment Transport ◽

Longitudinal Distribution ◽

Heihe River ◽

Hydrodynamic Conditions ◽

Sediment Grain Size ◽

Cascade Reservoirs ◽

Grain Size Distributions ◽

Transport Patterns ◽

The Impact

Abstract Spatial variations in grain-size parameters can reflect river sediment transport patterns and depositional dynamics. Therefore, 22 surficial sediment samples taken from the Heihe River and its cascade reservoirs were analyzed to better understand the impact of cascade reservoir construction on sediment transport patterns in inland rivers in China. The results showed that the longitudinal distribution of sediment grain size in the Heihe River was significantly affected by the influence of the cascade reservoirs. The grain size of the reservoir sediments within the cascade reservoir system was much lower than that of sediments in the natural river section, and the sediments in the natural river were well sorted, exhibiting leptokurtosis and positive or very positive skew. The lower reaches of the dammed river experienced strong erosion, and the grains of the bed sediments were coarse and poorly sorted; the grain-size distributions were more positively skewed and exhibited leptokurtosis. The backwater zone of the reservoir was influenced by both backwater and released water, and the sediment grain size was between the grain size of the natural river and that of the lower reaches of the dam; these sediments were moderately well sorted and had a positively skewed, leptokurtic grain-size distribution. Sedimentary environmental analysis revealed that the characteristics of the sediment grain size in an upstream tributary of the Heihe River were more influenced by source material than by hydrodynamic conditions, while the grain-size characteristics of the mainstream sediments were controlled mainly by hydrodynamic conditions.

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SEDIMENT DISTRIBUTION BASED ON GRAIN SIZE ANALYSES IN WEDA BAY, NORTHERN MALUKU

Jurnal Ilmu dan Teknologi Kelautan Tropis ◽

10.28930/jitkt.v6i1.8644 ◽

2014 ◽

Vol 6 (1) ◽

Author(s):

Septriono Hari Nugroho ◽

Abdul Basit

Keyword(s):

Grain Size ◽

Sediment Transport ◽

Size Distribution ◽

Deposition Process ◽

General Information ◽

Current Speed ◽

Sediment Grain Size ◽

Sediment Distribution ◽

Sea Floor ◽

Integrated Study

An integrated study of sediment distribution was conducted in Weda Bay, Northern Maluku to provide general information on transportation and deposition process based on sediment grain size distribution. The study was conducted during the Weda Bay Expedition using the “Baruna Jaya VII” research vessel in March 13th –22th 2013. Sieving method (granulometric) was used to analyze the grain size. The results indicated that in general the pattern of sea floor sediment distribution was dominated by clay – sand grain-sized. The current speed influenced the sediment transport, deposition, and distribution. Larger fractions of sediment were quickly settled on the sea floor due to stronger currents around Southern area (Widi islands), meanwhile the lesser fractions of the transported away into other places with weaker currents conditions. Keywords: current, the Weda Bay expedition, granulometric, grain size, sediment distribution

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Mineralogy, chemistry, and grain size composition of recent sediments in the northern Tyrrhenian Sea: Contribution to the study of sediment transport and distribution

Environmental Geology ◽

10.1007/bf01716072 ◽

1991 ◽

Vol 17 (1) ◽

pp. 23-46 ◽

Cited By ~ 6

Author(s):

Leonardo Leoni ◽

Franco Sartori ◽

Maurizio Saitta ◽

Vincenzo Damiani ◽

Ornella Ferretti ◽

...

Keyword(s):

Grain Size ◽

Sediment Transport ◽

Size Composition ◽

Tyrrhenian Sea ◽

Grain Size Composition ◽

Recent Sediments

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Bedforms in a turbulent stream: formation of ripples by primary linear instability and of dunes by nonlinear pattern coarsening

Journal of Fluid Mechanics ◽

10.1017/s0022112009993466 ◽

2010 ◽

Vol 649 ◽

pp. 287-328 ◽

Cited By ~ 85

Author(s):

ANTOINE FOURRIÈRE ◽

PHILIPPE CLAUDIN ◽

BRUNO ANDREOTTI

Keyword(s):

Grain Size ◽

Shear Stress ◽

Free Surface ◽

Stability Analysis ◽

Sediment Transport ◽

Phase Shift ◽

Linear Instability ◽

Basal Shear ◽

Flat Sand ◽

Nonlinear Pattern

It is widely accepted that both ripples and dunes form in rivers by primary linear instability; the wavelength of the former scaling on the grain size and that of the latter being controlled by the water depth. We revisit here this problem in a theoretical framework that allows to give a clear picture of the instability in terms of dynamical mechanisms. A multi-scale description of the problem is proposed, in which the details of the different mechanisms controlling sediment transport are encoded into three quantities: the saturated flux, the saturation length and the threshold shear stress. Hydrodynamics is linearized with respect to the bedform aspect ratio. We show that the phase shift of the basal shear stress with respect to the topography, responsible for the formation of bedforms, appears in an inner boundary layer where shear stress and pressure gradients balance. This phase shift is sensitive to the presence of the free surface, and the related effects can be interpreted in terms of standing gravity waves excited by topography. The basal shear stress is dominated by this finite depth effect in two ranges of wavelength: when the wavelength is large compared to the flow depth, so that the inner layer extends throughout the flow, and in the resonant conditions, when the downstream material velocity balances the upstream wave propagation. Performing the linear stability analysis of a flat sand bed, the relation between the wavelength at which ripples form and the flux saturation length is quantitatively derived. It explains the discrepancy between measured initial wavelengths and predictions that do not take this lag between flow velocity and sediment transport into account. Experimental data are used to determine the saturation length as a function of grain size and shear velocity. Taking the free surface into account, we show that the excitation of standing waves has a stabilizing effect, independent of the details of the flow and sediment transport models. Consequently, the shape of the dispersion relation obtained from the linear stability analysis of a flat sand bed is such that dunes cannot result from a primary linear instability. We present the results of field experiments performed in the natural sandy Leyre river, which show the formation of ripples by a linear instability and the formation of dunes by a nonlinear pattern coarsening limited by the free surface. Finally, we show that mega-dunes form when the sand bed presents heterogeneities such as a wide distribution of grain sizes.

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