Grain‐Size, Sediment‐Transport Regime, and Channel Slope in Alluvial Rivers

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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Impact of flow variability and sediment characteristics on channel width evolution

E3S Web of Conferences ◽

10.1051/e3sconf/20184005044 ◽

2018 ◽

Vol 40 ◽

pp. 05044

Author(s):

Andrés Vargas-Luna ◽

Alessandra Crosato ◽

Protogene Byishimo ◽

Wim Uijttewaal

Keyword(s):

Grain Size ◽

Peak Flow ◽

River Channel ◽

Channel Width ◽

River Morphology ◽

Channel Formation ◽

Sediment Characteristics ◽

Alluvial Rivers ◽

Water Flows ◽

Streamflow Variability

Alluvial rivers are shaped by sequences of water flows excavating their channels. Observations show that besides the magnitude, also the frequency and duration of streamflow oscillations might be important for the river channel formation. In addition, the river morphology appears influenced also by both size and degree of uniformity of the sediment. Nevertheless, many morphodynamic studies still represent the flow regime with a single value of the discharge, often corresponding to the bankfull condition, and the sediment with its median grain size. This work investigates the effects of streamflow variability and sediment characteristics on channel width formation, analysing the evolution of experimental streams with different sediments and discharge hydrographs. Results show that the formative condition of the channel width is not the geometric bankfull flow but a rather frequent peak flow. Remarkably different channel configurations arise from different sediment characteristics in the laboratory, where sediment non-uniformity produces more stable banks.

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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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Effect of input-target datasets on sediment transport modelling in alluvial rivers using artificial neural network

Hydrological Sciences Journal ◽

10.1080/02626667.2021.1998508 ◽

2021 ◽

Author(s):

Shehnaz Ara Rahman ◽

Dibakar Chakrabarty

Keyword(s):

Neural Network ◽

Artificial Neural Network ◽

Sediment Transport ◽

Transport Modelling ◽

Alluvial Rivers ◽

Artificial Neural ◽

Sediment Transport Modelling

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Theoretical Interpretation of the Exceptional Sediment Transport of Fine-grained Dispersal Systems Associated with Bedform Categories

10.5194/esurf-2018-64 ◽

2018 ◽

Author(s):

Tian Zhao ◽

Qian Yu ◽

Yunwei Wang ◽

Shu Gao

Keyword(s):

Sediment Transport ◽

Regime Shift ◽

Sedimentary Environment ◽

Sediment Flux ◽

Theoretical Interpretation ◽

Fine Grained ◽

Transport Regime ◽

Source To Sink ◽

Bed Roughness ◽

Set Up

Abstract. Being a widespread source-to-sink sedimentary environment, the fine-grained dispersal system (FGDS) features remarkably high sediment flux, interacting closely with local morphology and ecosystem. Such exceptional transport is believed to be associated with changes in bedform geometry, which further demands theoretical interpretation. Using van Rijn (2007a) bed roughness predictor, we set up a simple numerical model to calculate sediment transport, classify sediment transport behaviors into dune and (mega-)ripple dominant regimes, and discuss the causes of the sediment transport regime shift linked with bedform categories. Both regimes show internally consistent transport behaviors, and the latter, associated with FGDSs, exhibits considerably higher sediment transport rate than the previous. Between lies the coexistence zone, the sediment transport regime shift accompanied by degeneration of dune roughness, which can considerably reinforce sediment transport and is further highlighted under greater water depth. This study can be applied to modeling of sediment transport and morphodynamics.

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