scholarly journals The influence of sediment size, relative grain size and channel slope on initiation of sediment motion in boulder bed rivers. A lichenometric study

2010 ◽  
Vol 35 (13) ◽  
pp. 1535-1547 ◽  
Author(s):  
Frederic Gob ◽  
Jean-Paul Bravard ◽  
François Petit
Keyword(s):  
Grain Size ◽  
Sediment Size ◽  
Channel Slope

scholarly journals Universal relation with regime transition for sediment transport in fine-grained rivers

2019 ◽  
Vol 117 (1) ◽  
pp. 171-176 ◽  
Author(s):  
Hongbo Ma ◽  
Jeffrey A. Nittrouer ◽  
Baosheng Wu ◽  
Michael P. Lamb ◽  
Yuanfeng Zhang ◽  
...  
Keyword(s):  
Grain Size ◽  
Sediment Load ◽  
Yellow River ◽  
Fine Sand ◽  
Sediment Flux ◽  
Universal Relation ◽  
Sediment Grain Size ◽  
Fine Grained ◽  
Predictive Algorithm ◽  
Sediment Size

Fine-grained sediment (grain size under 2,000 μm) builds floodplains and deltas, and shapes the coastlines where much of humanity lives. However, a universal, physically based predictor of sediment flux for fine-grained rivers remains to be developed. Herein, a comprehensive sediment load database for fine-grained channels, ranging from small experimental flumes to megarivers, is used to find a predictive algorithm. Two distinct transport regimes emerge, separated by a discontinuous transition for median bed grain size within the very fine sand range (81 to 154 μm), whereby sediment flux decreases by up to 100-fold for coarser sand-bedded rivers compared to river with silt and very fine sand beds. Evidence suggests that the discontinuous change in sediment load originates from a transition of transport mode between mixed suspended bed load transport and suspension-dominated transport. Events that alter bed sediment size near the transition may significantly affect fluviocoastal morphology by drastically changing sediment flux, as shown by data from the Yellow River, China, which, over time, transitioned back and forth 3 times between states of high and low transport efficiency in response to anthropic activities.

scholarly journals Effect of Roughness on Discharge

2013 ◽  
Vol 4 (3) ◽  
pp. 29-33 ◽  
Author(s):  
T.W. Lau ◽  
N.R. Afshar
Keyword(s):  
Grain Size ◽  
Flow Rate ◽  
Roughness Coefficient ◽  
Coefficient Increase ◽  
Different Types ◽  
Channel Slope ◽  
Experimental Works ◽  
Bed Roughness ◽  
Material Grain Size ◽  
Effect Of Surface

These Water resource projects and hydraulic engineering works have been developing rapidly throughout the world, thus prediction of water roughness coefficient is becoming an importance criteria for the designs of hydraulic related structure like open channel, and dam structure. The purposes of this research are to determine the effect of roughness on discharge and study on the factors that affect roughness coefficient. The roughness coefficient for this study is expressed in terms of Manning’s n. Experimental works were carried out to study the effect of roughness by using flumes (8m x 0.3m x 0.4m) with different types of roughened bed such as 2mm grain size plate and 5mm grain size plate. The experiments were being tested with various flow rates for slope equal to 1:300, 1:600 and 1:900 to determine the effect of slope on roughness coefficient. The results of the experimental study were presented and shown that the effect of surface roughness, material grain size, channel slope, and Manning’s roughness coefficient on flow rate. For the range of conditions tested, the discharge was found to be decreased as roughness coefficient increase. From the experiments, it shows smoother surface is having lower roughness coefficient and less retarding effect on the water flow, higher flow rate is produced. As conclusion, flow rate and roughness coefficient were influenced by bed roughness and slope.

AGGREGATE SIZE DISTRIBUTION OF SELECTED TERENGGANU BEACH AREA

2015 ◽  
Vol 77 (32) ◽  
Author(s):  
Noraisyah Sapon ◽  
Rosnan Yaacob ◽  
Mohd-Lokman Husain ◽  
Mohd-Zaini Mustapa ◽  
Rokiah Suriadi
Keyword(s):  
Grain Size ◽  
High Tide ◽  
Size Fraction ◽  
River Mouth ◽  
Aggregate Size ◽  
Coarse Grained ◽  
Northeast Monsoon ◽  
Sediment Size ◽  
Mean Size ◽  
One Year

In general, the Terengganu beaches consist mainly of medium- to coarse-grained sand. Grain sizes were determined by dry sieving sediments; samples represent the upper 15 cm of surficial sediment, collected from the three main geomorphological tidal units during one year observation periods, covering the southwest and northeast monsoon seasons. The result demonstrates a good relationship between the monsoonal processes and the corresponding geomorphological elements. There are some differences between the various geomorphological tidal units, with a subtle trend from the low tide to high tide zone. Grain size decreases slightly from the low tide to the high tide. The sediment size fraction averaging from -0.48phi to 1.87phi. The most fine material was found at Kuala Besut (northernmost Terengganu) while the coarsest particle was found at Seberang Takir. However, the grain size parameters at different beach locations do not suggest a general trend of long-shore variations, except on the beach close to the river mouth. The differences between the seasons were larger than those between the geomorphological tidal units. During the northeast monsoon the mean size was coarser, sorting was worse and the distribution was more positively skewed.

scholarly journals Characteristics of Point-Bar Development under the Influence of a Dam: Case Study on the Dráva River at Sigetec, Croatia

2015 ◽  
Vol 8 (1-2) ◽  
pp. 23-30 ◽  
Author(s):  
Tímea Kiss ◽  
Márton Balogh
Keyword(s):  
Grain Size ◽  
Power Plants ◽  
Human Impacts ◽  
Bank Erosion ◽  
Sediment Supply ◽  
Grain Size Analysis ◽  
Size Analysis ◽  
Point Bar ◽  
Sediment Size ◽  
Drava River

Abstract Before the extensive engineering works the Dráva River had braided pattern. However in the 19-20th centuries river regulation works became widespread, thus meanders were cut off, side-channels were blocked and hydroelectric power plants were completed. These human impacts significantly changed the hydro-morphology of the river. The aim of the present research is to analyse meander development and the formation of a point-bar from the point of view of indirect human impact. Series of maps and ortho-photos representing the period of 1870-2011 were used to quantify the longterm meander development, rate of bank erosion and point-bar aggradation. Besides, at-a-site erosion measurements and grain-size analysis were also carried out. As the result of reservoir constructions during the last 145 years floods almost totally disappeared, as their return period increased to 5-15 years and their duration decreased to 1-2 days. The channel pattern had changed from braided to sinuous and to meandering, thus the rate of bank erosion increased from 3.7 m/y to 32 m/y. On the upstream part of the point-bar the maximum grain size is 49.7-83.4 mm and the mean particle size is 7.6 mm, whilst on the downstream part the maximum grain size was only 39.7-39.9 mm and mean sediment size decreased to 6.1 mm. Due to the coarse sediment supply and the decreasing stream energy the point-bars develop quickly upstream and laterally too.

The role of sedimentology in the mobility of debris avalanches: Evidence from their deposits and granular flow experiments

2021 ◽  
Author(s):  
Symeon Makris ◽  
Irene Manzella ◽  
Paul Cole ◽  
Matteo Roverato
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Granular Flows ◽  
High Water ◽  
Debris Avalanche ◽  
High Water Content ◽  
Sediment Size ◽  
Debris Avalanches ◽  
Volcanic Debris

<p>Debris avalanches and lahars are among the most destructive and hazardous mass flows in volcanic environments making them important to understand from a hazard assessment perspective. Sedimentological characteristics of their deposits are important for assessing their propagation and emplacement mechanisms. Here, we compare the sedimentology of nine volcanic debris avalanches and eight lahars, by the descriptive statistics: median grain size, sand, gravel and finer particle proportion, skewness, and sorting.</p><p>Results suggest that lahars and debris avalanches diverge in their grain size distribution evolution during propagation, even when sourced from the same material. Increasing bimodality, evolution to negative skewness, with decreasing sediment size, accompanied by very poor sorting suggest comminution of particles due to particle-particle interactions in debris avalanches. Instead, preferential deposition of the coarsest particles and improved sorting suggest that the decrease in grain size of lahars is the result of debulking. The divergence is mainly caused by the high water content in lahars, which introduce different processes during propagation. This suggests, in agreement with previous studies, that debris avalanches can be considered as dense granular flows where the effect of inertial collisions of solid fragments are more important than fluid effects.</p><p>Present findings and previous sedimentological studies suggest that both volcanic and non-volcanic debris avalanches exhibit bimodal grain-size distributions, at least locally, in areas of high shear accommodation. Following these results, an experimental campaign has been carried out to test the effect of bimodality on the propagation of granular flows. These experiments are flows of bidisperse granular material on an initial inclined plane, with a horizontal accumulation surface at the bottom.  Findings confirm that the bimodality of the grain size distribution generates a more efficient shearing arrangement, which can increase the mobility of granular flows in the same way recorded in debris avalanche deposits.</p>

Seabed geomorphology of the Prokljan Lake – a Krka River estuary on the eastern Adriatic coast (Dalmatia)

2021 ◽  
Author(s):  
Ozren Hasan ◽  
Slobodan Miko ◽  
Dea Brunović ◽  
Natalia Šenolt ◽  
Martina Šparica Miko ◽  
...  
Keyword(s):  
Grain Size ◽  
Sea Level Rise ◽  
Sea Level ◽  
Late Quaternary ◽  
River Estuary ◽  
Lake Area ◽  
Fine Silt ◽  
The Holocene ◽  
Sediment Size ◽  
Adriatic Coast

<p>Vast areas of the shallow Adriatic shelf were exposed at the time of the Last Glacial Maximum lowstand. This enabled formation of lakes, river valleys and river floodplains that were submerged during the Holocene transgression. Here we present a study of the karst estuary of the Krka River located in central Dalmatia on the eastern Adriatic coast. The Krka River creates a 23 km long estuary extending north from the Šibenik Channel, over the Prokljan Lake, up to the tufa waterfall Skradinski buk. We used high resolution acoustic methods including sub-bottom profiler (SBP) coupled with multibeam echo sounder (MBES) (MBES bathymetry and MBES backscatter) and side-scan sonar (SSS) to investigate the submerged karst river valley and lake system that existed before the Holocene relative sea level rise. A total of 70 km of SBP profiles and a point cloud of 241 991 638 points in the area of 6.2 km<sup>2</sup> were collected during the surveys. Water depth ranges from 5 m b.s.l. in the most northern part of the study area, to 25 m b.s.l. in the southern part of the Prokljan lake.</p><p>To create a better geomorphological and geological classifications of the seabed, we made a network of 36 ground truthing stations where we sampled sediments with Van Veen grab sampler and obtained underwater images. Sediment samples were analyzed for grain size, bulk density, carbon and nitrogen concentrations, as well as mineralogical XRD analysis and magnetic susceptibility. We combined gathered data with GIS classification tools to create accurate seabed maps of the area. Our results also showed that well-defined submerged river canyon in the Prokljan Lake area was filled with three sedimentary units: fluvial, brackish and marine. Quaternary sediment thickness is up to 15 m. Seabed geomorphology of the investigated area is characterized by many submerged tufa barriers. They are similar to present barriers upstream of the Skradinski buk waterfall. These unique karst geomorphological features, that grow as algae and mosses are encrusted by carbonate, enabled formation of lakes, as well as prevented a marine flooding during the Holocene sea-level rise. The depth of each barrier (4.5 to 12 m b.s.l.), in connection to the onset of marine sedimentation within the estuary, can be used as an indicator of sea level. Barriers are emphasized on the MBES backscatter data as strong reflectors. Grain size of sampled sediments ranges from poorly sorted sand and gravel on underwater barriers to fine silt sediments in the deeper parts of Prokljan Lake. Larger sediment size on barriers is caused by tufa debris while fine silt is sedimented in the deeper parts of the basin. Grain size results vary for different geomorphological provinces, allowing for a more precise (GIS) classification and description of the seabed.</p><p>This work was supported by the Croatian Science Foundation Project “Sediments between source and sink during a late Quaternary eustatic cycle: the Krka River and the Mid Adriatic Deep System” (QMAD) (HRZZ IP-04-2019-8505).</p>

A late Pleistocene sedimentation in the Indus Fan, Arabian Sea, IODP Site U1457

2019 ◽  
Vol 157 (6) ◽  
pp. 920-928 ◽  
Author(s):  
Anil Kumar ◽  
Som Dutt ◽  
Rajeev Saraswat ◽  
Anil Kumar Gupta ◽  
Peter D Clift ◽  
...  
Keyword(s):  
Grain Size ◽  
Magnetic Susceptibility ◽  
Sea Level ◽  
Arabian Sea ◽  
Large Fraction ◽  
Climatic Variability ◽  
Sediment Delivery ◽  
Magnetic Parameters ◽  
Sediment Size ◽  
Narmada River

AbstractThe intensity of turbidite sedimentation over long timescales is driven by sea-level change, tectonically driven rock uplift and climatically modulated sediment delivery rates. This study focuses on understanding the effect of sea-level fluctuations and climatic variability on grain-size variations. The grain size and environmental magnetic parameters of Arabian Sea sediments have been documented using 203 samples, spanning the last 200 ka, obtained from International Ocean Discovery Program (IODP) Site U1457. Grain-size end-member modelling suggests that between ~200 and 130 ka there was an increase in the coarse silt fraction caused by sediment transport following reworking of the Indus Fan and development of deep-sea canyons. The sediment size and enhanced magnetic susceptibility indicate a dominant flux of terrestrial sediments. Sedimentation in the distal Indus Fan at c. 200–130 ka was driven by a drop in sea level that lowered the base level in the Indus and Narmada river systems. The low sea-stand caused incision in the Indus delta, canyons and fan area, which resulted in the transportation of coarser sediment at the drilling site. Magnetic susceptibility and other associated magnetic parameters suggest a large fraction of the sediment was supplied by the Narmada River during ~200–130 ka. Since ~130 ka, clay-dominated sedimentation is attributed to the rise in sea level due to warm and wet climate.

scholarly journals Patterns of grain-size temporal variation of sediment transported by overland flow associated with moving storms: interpreting soil flume experiments

2011 ◽  
Vol 11 (9) ◽  
pp. 2605-2615 ◽  
Author(s):  
J. L. M. P. de Lima ◽  
P. A. Dinis ◽  
C. S. Souza ◽  
M. I. P. de Lima ◽  
P. P. Cunha ◽  
...  
Keyword(s):  
Grain Size ◽  
Overland Flow ◽  
Strong Relationship ◽  
Flume Experiments ◽  
Sediment Grain Size ◽  
Sediment Yields ◽  
Sediment Size ◽  
Size Evolution ◽  
Mean Grain Size ◽  
Recession Limb

Abstract. This study describes and interprets the evolution of grain-size distribution of sediment yields generated in an experimental soil flume subjected to downstream and upstream moving rain storms. Results of laboratory experiments show that downstream moving storms cause more soil loss than do upstream moving storms. The pattern of sediment grain-size evolution in time during a runoff event exhibits a clear dependence on the direction of storm movement. A strong relationship between overland flow discharge and mean sediment size is found. Nevertheless, the mean grain-size of sediments transported during the rising limb of the hydrograph is coarser than during the recession limb of the hydrograph. This is more marked for downstream moving storms.

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