scholarly journals Mud in sandy riverbed deposits as a proxy for ancient fine-sediment supply

Geology ◽  
2021 ◽  
Author(s):  
N. Wysocki ◽  
E. Hajek
Keyword(s):  
Fine Sediment ◽  
Sediment Supply ◽  
Primary Control ◽  
Flow Conditions ◽  
Sediment Retention ◽  
Channel Networks ◽  
High Discharge ◽  
River Deposits ◽  
Series Of Experiments ◽  
Bed Material

The amount of silt and clay available to rivers reflects source-terrain composition and weathering and can be a primary control on the form and dynamics of channel networks. Fine sediment also affects the permeability of buried fluvial reservoirs. Despite this significance, there is currently a lack of methods for reconstructing how much fine sediment was transported by ancient rivers. Mud accumulations in sandy river deposits are often interpreted as indicators of variable flow conditions; however, these deposits may present an opportunity to constrain how much fine sediment was transported through ancient rivers. We report results from a series of experiments designed to evaluate how much clay and silt are preserved in sandy riverbed deposits under constant and variable discharge conditions. Our results demonstrate that (1) mud deposits, including drapes and lenses, form readily under constant, high-discharge conditions, (2) the amount of fine sediment recovered from bed-material deposits increases as fine-sediment supply increases, and (3) fine-sediment retention is higher during bed aggradation than during bypass conditions. These results indicate that the net retention of clay and silt in sandy riverbed deposits may be a simple but powerful proxy for comparing the overall amount of fine sediment supplied to ancient rivers.

Fine sediment retention in storage chambers: an assessment of time-dependent effects

2002 ◽  
Vol 45 (7) ◽  
pp. 123-131 ◽  
Author(s):  
V.R. Stovin ◽  
J.P. Grimm ◽  
A.J. Saul
Keyword(s):  
Fine Sediment ◽  
Multiphase Model ◽  
Storm Events ◽  
Dimensional Model ◽  
Flow Conditions ◽  
Sediment Retention ◽  
Fine Sediments ◽  
Storage Chamber ◽  
Flow Hydraulics ◽  
The Uk

The optimisation of the design of a storage chamber is generally based upon some measure of the chamber's sedimentation efficiency. In the UK, chambers that minimise the deposition of fine sediments are preferred. Previous laboratory and CFD-based studies to measure efficiency have focused on steady flow conditions. However, both the flow hydraulics within a storage chamber and the pollutant loading in the incoming sewage vary markedly during storm events. This paper outlines a CFD-based approach for determining “overall” chamber efficiency. The approach employs an unsteady volume-of-fluid multiphase model and stochastic particle tracking. Preliminary results from a simplified two-dimensional model are presented.

scholarly journals Sediment supply and relative size distribution effects on fine sediment infiltration into immobile gravels

2008 ◽  
Vol 44 (3) ◽  
Author(s):  
John K. Wooster ◽  
Scott R. Dusterhoff ◽  
Yantao Cui ◽  
Leonard S. Sklar ◽  
William E. Dietrich ◽  
...  
Keyword(s):  
Size Distribution ◽  
Relative Size ◽  
Fine Sediment ◽  
Sediment Supply

Relating sediment supply to the morphological and hydro-meteorological characteristics of torrent catchments

2021 ◽  
Author(s):  
Maxime Morel ◽  
Guillaume Piton ◽  
Caroline Le Bouteiller ◽  
Alexandre Mas ◽  
Guillaume Evin
Keyword(s):  
Sediment Yield ◽  
Prediction Method ◽  
Original Data ◽  
Sediment Supply ◽  
Set Covering ◽  
Sediment Retention ◽  
Multivariate Statistical ◽  
Catchment Basin ◽  
Mountain Areas ◽  
Data Set

<p>In mountain areas, the quantification of sediment yield is essential in the diagnosis of a torrential watershed. The objective of this study is to present a prediction method based on multivariate statistical models calibrated from an original data set covering nearly 130 torrential basins in the Northern French Alps. Data on sediment yield and occurrence of torrential events were collected on these catchments thanks to registries from sediment retention basins (average monitoring period of 20 years) and historical archives of the catchment basin managers. On these catchments, several morphological and hydro-meteorological characteristics were calculated (e.g. geological and sediment connectivity indices, the rate of connected eroding areas in the catchment, the Melton index, the slope of the fan, etc.) in order to relate them to sediment production and the frequency of occurrence of torrential events. These models allow the estimation of quantiles of the sediment yield in small torrent catchments. These models could be useful to evaluate sediment yield and the occurrence of torrential events on catchment not equipped with sedimentation structures.</p>

Effects of episodic sediment supply on experimental step-pool channel morphology, bedload transport and channel stability

2021 ◽  
Author(s):  
Jiamei Wang ◽  
Marwan A. Hassan ◽  
Matteo Saletti ◽  
Xingyu Chen ◽  
Xudong Fu ◽  
...  
Keyword(s):  
Grain Size ◽  
Morphological Changes ◽  
Mass Movement ◽  
Channel Morphology ◽  
Bedload Transport ◽  
Sediment Supply ◽  
Primary Control ◽  
Channel Stability ◽  
Flume Experiments ◽  
Small Magnitude

<p>Steep step-pool streams are often coupled to adjacent hillslope, directly receiving episodic sediment supply from mass movement processes such as landslides and debris flows. The response of step-pool channels to the variations in sediment supply remains largely unexplored. We conducted flume experiments with a poorly sorted grain-size distribution in an 8%-steep, 5-m long flume with variable width at the University of British Columbia, to study the effects of episodic sediment supply on channel evolution. After a conditioning phase with no feed, the channel was subjected to sediment pulses of different magnitude and frequency under constant flow discharge. High-resolution data of hydraulics, bedload transport, bed surface grain size, and channel morphology were collected every 10-20 minutes and an additional time at the end of each pulse.</p><p>In response to sediment pulses, we recorded an increase in bedload transport rates, channel aggradation, bed surface fining, and continuous step formation and collapse. In between pulses, bedload rates dropped by several orders of magnitude, net erosion occurred, the bed surface gradually coarsened, and steps became more stable. The small-magnitude high-frequency pulses caused smaller but more frequent spikes in bedload transport, bed surface evolution, and thus step stability. Instead, the large-magnitude low-frequency pulses cause larger changes but provided a longer time for the channel to recover. This suggests that in step-pool channels pulse magnitude is a key control on channel rearrangement, while pulse frequency controls how fast and strong the recovery is.</p><p>The frequency and stability of steps varied as a function of local channel width, showing that channel geometry is a primary control on step formation and stability even under episodic sediment supply conditions. Instead, the effect of sediment pulses is less important because the total number and average survival time of steps were similar among runs with different pulses. The critical Shields stress decreased following sediment pulses, then increased immediately after, and fluctuated until the next pulse. The variations in sediment supply caused cycles in bedload transport rate, surface and bedload texture, thus controlling the variability in the threshold for motion.</p><p>Our results indicate that episodic sediment supply is a primary control on the evolution of step-pool channels, with sediment feed magnitude affecting mostly morphological changes, and sediment feed frequency controlling channel stability.</p>

scholarly journals Armor breakup and reformation in a degradational laboratory experiment: detailed measurements of spatial and temporal changes of the bed surface texture

2016 ◽  
Author(s):  
C. Orru ◽  
A. Blom ◽  
W.S.J. Uijttewaal
Keyword(s):  
Laboratory Experiment ◽  
Sediment Supply ◽  
Sudden Increase ◽  
Normal Flow ◽  
Flow Conditions ◽  
Initial Stage ◽  
The Reformation ◽  
Spatial And Temporal Changes ◽  
Sand And Gravel ◽  
Slope Adjustment

Abstract. Armor breakup and reformation was studied in a laboratory experiment using a trimodal mixture composed of sand and gravel. The armor was formed in the initial stage of the experiment under conditions without sediment supply. Higher flow conditions led to the breakup of the mobile armor and the reformation of a new coarser armor. The breakup initially induced a fining due to the exposure of the finer substrate, which was accompanied by a sudden increase of the local sediment transport rate, followed by the formation of an armor that was coarser than the initial one. The reformation of the armor was due to the supply of coarse material from the upstream degrading reach and the presence of gravel in the original substrate sediment. Provided that the gravel supply from upstream suffices for armor reformation, armor breakup enables slope adjustment such that the new steady state is closer to normal flow conditions.

A Feasibility Study of a High-Speed Combustor for Turbomachine Applications

1970 ◽  
Author(s):  
Irving Fruchtman
Keyword(s):  
Turbulent Mixing ◽  
High Speed ◽  
Pressure Ratio ◽  
Small Mass ◽  
Temperature Profiles ◽  
Flow Conditions ◽  
Finite Rate ◽  
High Pressure Ratio ◽  
Series Of Experiments ◽  
Analysis Design

The theoretical analysis, design, and experimental study of a high-speed combustion chamber are described. Such a burner may be used when the compressor outflow speed is so high that diffusion to the usual burner entrance conditions presents severe loss penalties. The study showed for a small mass flow-high pressure ratio turbomachine, that combined diffusor and combustor losses are minimum for a burner entrance Mach number of about 0.5. To design the burner a finite rate chemistry and turbulent mixing computer program was used; the combustor modeling and flame spread predictions are discussed. A series of experiments are described and burner pressure loss and temperature profiles are shown over a range of burner air-flow conditions.

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