scholarly journals Two-dimensional numerical simulation of sediment transport using improved critical shear stress methods

2020 ◽  
Vol 35 (1) ◽  
pp. 15-26 ◽  
Author(s):  
Zhiyong Feng ◽  
Guangming Tan ◽  
Junqiang Xia ◽  
Caiwen Shu ◽  
Peng Chen ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Shear Stress ◽  
Sediment Transport ◽  
Critical Shear Stress ◽  
Two Dimensional

scholarly journals BEACH PROFILES AND ON-OFFSHORE SEDIMENT TRANSPORT

1980 ◽  
Vol 1 (17) ◽  
pp. 67 ◽  
Author(s):  
Akira Watanabe ◽  
Yoshihiko Riho ◽  
Kiyoshi Horikawa
Keyword(s):  
Shear Stress ◽  
Sediment Transport ◽  
Laboratory Test ◽  
Test Data ◽  
Critical Shear Stress ◽  
Two Dimensional ◽  
Bottom Shear Stress ◽  
Beach Profile ◽  
Profile Changes ◽  
Sloping Beach

The on-offshore sediment transport due to waves on a sloping beach is studied by analyzing the laboratory test data on two-dimensional beach deformation. The net rates of sediment transport both inside and outside the breaker zone are evaluated from beach profile changes and are related to the nondimensional bottom shear stress or the Shields parameter. The importance of the critical shear stress and of asymmetrical to-and-fro water partical motion near the bottom is pointed out.

scholarly journals Bed Shear Stress Influence on Local Scour Geometry Properties in Various Flume Development Conditions

Water ◽  
2019 ◽  
Vol 11 (11) ◽  
pp. 2346 ◽  
Author(s):  
Kiraga ◽  
Popek
Keyword(s):  
Shear Stress ◽  
Sediment Transport ◽  
Mutual Influence ◽  
Three Dimensional ◽  
Critical Shear Stress ◽  
Water Structure ◽  
Correlation Coefficients ◽  
Bed Shear Stress ◽  
Hole Dimensions ◽  
Bed Material

Numerous approaches in sediment mobility studies highlighted the key meaning of channel roughness, which results not only from bed material granulation but also from various bed forms presence, caused by continuous sediment transport. Those forms are strictly connected with the intensity of particle transport, and they eventuate from bed shear stress. The present paper comprised of local scours geometric dimensions research in three variants of lengthwise development of laboratory flume in various hydraulic properties, both in “clear-water” and “live-bed” conditions of sediment movement. Lots of measurements of the bed conformation were executed using the LiDAR device, marked by a very precise three-dimensional shape description. The influence of the bed shear stress downstream model on scours hole dimensions of water structure was investigated as one of the key factors that impact the sediment transport intensity. A significant database of 39 experimental series, lasting averagely 8 hours, was a foundation for delineating functional correlations between bed shear stress-and-critical shear stress ratio and geometry properties of local scours in various flume development cases. In the scope of mutual influence of bed shear stress and water depth, high correlation coefficients were attained, indicating very good and good functional correlations. Also, the influence of bed shear stress and the total length of the scour demonstrated a high correlation coefficient.

scholarly journals THREE DIMENSIONAL TESTS ON DYNAMIC EQUILIBRIUM AND ARTIFICIAL NOURISHMENT

1976 ◽  
Vol 1 (15) ◽  
pp. 89 ◽  
Author(s):  
J.W. Kamphuis ◽  
R.M. Myers
Keyword(s):  
Shear Stress ◽  
Dynamic Equilibrium ◽  
Three Dimensional ◽  
Critical Shear Stress ◽  
Two Dimensional ◽  
Dimensional Facility ◽  
Trap Location ◽  
Artificial Nourishment ◽  
Reflection Of Waves

A three dimensional facility for testing dynamic equilibrium and artificial nourishment of beaches was developed. Specific conclusions are drawn with respect to trap location and re-reflection of waves. It was found that dynamic equilibrium is achieved faster in three dimensional tests than in previous two dimensional work and that the profiles are eroding profiles rather than potential (limit) profiles. It was seen that profiles develop around the offshore bar which is shaped early in the experiments. Also the depth of the summer step was found predictable from critical shear stress considerations. Finally, onshore nourishment of eroding beaches was found to be successful.

Controls on sediment transport in semi-alluvial boulder-bed streams—implications for restoration of spawning gravel

2020 ◽  
Author(s):  
Lina Polvi
Keyword(s):  
Shear Stress ◽  
Sediment Transport ◽  
Critical Shear Stress ◽  
Field Research ◽  
Tracer Experiment ◽  
Transport Processes ◽  
Mountain Streams ◽  
Northern Fennoscandia ◽  
Transport Distance ◽  
Individual Grains

<p>Many streams in northern Fennoscandia are considered semi-alluvial in that they contain abundant coarse sediment (cobbles and boulders) deposited during continental glaciation in the form of moraines, eskers, and erratics. These streams contain sensitive trout and salmon populations, and restoration efforts (after channelization from over a century of timber-floating) strive to re-create essential habitat and spawning beds. However, little is known about controls on sediment transport processes in boulder-bed streams that can affect both channel evolution and restoration of spawning gravel. Prior flume and field research of boulder-bed channels in mountainous areas show that boulder protrusion and proximity can alter critical shear stress; however, in contrast to mountain streams, boulder-bed channels in northern Fennoscandia have relatively low bed slopes (S<sub>0</sub>: 0.5-6%) and low-magnitude flow regimes (buffered by upstream lakes).</p><p>In order to determine controls on gravel and cobble sediment transport in semi-alluvial boulder-bed streams, a sediment tracer experiment was conducted in the Vindel River catchment in northern Sweden. Approximately 1500 tracer clasts (b-axis: 2.5-15 cm), with imbedded RFID tags, were placed in five stream reaches (121-556 per reach) with a range of channel slopes (S<sub>0</sub>: ~2-6%), boulder densities, and degrees of protrusion. The geometry of each tracer clast (a-, b-, and c-axes) was quantified, and the location of each tracer clast was surveyed with a total station in the summers of 2017, 2018, and 2019. Both the morphologic setting (e.g., step, pool, riffle, backwater, directly above/below boulder) and constrainment class (e.g., unconstrained, shielded, imbricated, buried) were classified for each tracer at each survey occasion. There was a 80-90% recovery rate of tracer clasts; despite several reaches experiencing >Q<sub>50</sub> snowmelt flood, the median transport distance for D<sub>10</sub>- to D<sub>50 </sub>clasts was ~0.1 m. Preliminary analyses showed large variation in particle-size thresholds for entrainment and relationships with transport distance within and among reaches. There was no clear relationship between local bed slope or calculated bankfull shear stress and transport distance. Differences in entrainment and transport distances among reaches was controlled by boulder density and protrusion, which likely increase grain resistance and thus critical shear stress, reducing sediment transport (as shown by previous studies in boulder-bed mountain streams). Factors negatively affecting sediment transport include shielding, proximity to boulders, and certain morphologic settings (e.g., backwaters and pools). Variability was too high to allow confident prediction of entrainment of individual grains; however, based on these results and observations, some general guidelines for stream restoration of spawning gravel in semi-alluvial boulder-bed channels are presented.      </p>

scholarly journals ANALISIS ANGKUTAN SEDIMEN DASAR (BED LOAD) PADA SALURAN IRIGASI MATARAM YOGYAKARTA

Teknisia ◽  
2021 ◽  
Vol XXVI (1) ◽  
Author(s):  
Anggi Hermawan ◽  
◽  
Erwin Afiato ◽  
Keyword(s):  
Shear Stress ◽  
Sediment Transport ◽  
Froude Number ◽  
Critical Shear Stress ◽  
Bed Load ◽  
Cross Sectional ◽  
Logarithmic Curve ◽  
Agricultural Areas ◽  
The Relationship ◽  
Downstream Area

In the last decade, the problem that has occurred in the Yogyakarta Mataram irrigation channel is the occurrence of sedimentation in the channel. This has an impact on reducing the cross-sectional discharge capacity of the canal and resulting in the supply of irrigation discharge to agricultural areas to be not optimal, so that agricultural productivity in the Mataram Irrigation Area will also not be optimal. The sediment transport (bed load) that occurs in an open channel can be approached using the empirical equation, including the Einstein, Meyer - Peter Muller and Frijlink equations. Sediment transport events that occur in the channel are stated based on the magnitude of the flow shear stress which exceeds the critical shear stress of the sediment particles. The quantity of sediment transport in the channel is stated on the logarithmic curve of the relationship between the froude number (fr) to the sediment transports (qb). The Curve explains that the increase in the froude number (fr) that occurs on each section of the channel will be directly proportional to the increase in the quantity of transport sediment (qb). The largest sediment transport occurred at the site of the Gambang and Nambongan channel section with a prediction of sediment transport of 3.57 m3/day and 3.67 m3/day, respectively. Thus, the potential for sediment transport that will settle in the downstream area is 3.67 m3/day.

scholarly journals Formulae of Sediment Transport in Steady Flows (Part 1)

2021 ◽  
Author(s):  
Shu-Qing Yang ◽  
Ishraq AL-Fadhly
Keyword(s):  
Shear Stress ◽  
Sediment Transport ◽  
Vertical Velocity ◽  
Critical Shear Stress ◽  
Vertical Motion ◽  
Steady Flows ◽  
Leading Role ◽  
Natural Streams ◽  
Accelerating Flows ◽  
Shields Curve

This paper makes an attempt to answer why the observed critical shear stress for incipient sediment motion sometimes deviates from the Shields curve largely, and the influence of vertical velocity is analyzed as one of the reasons. The data with d50 = 0.016 ∼ 29.1 mm from natural streams and laboratory channels were analyzed. These measured data do not always agree with the Shields diagram’s prediction. The reasons responsible for the deviation have been re-examined and it is found that, among many factors, the vertical motion of sediment particles plays a leading role for the invalidity of Shield’s prediction. The positive/negative deviations are associated with the up/downward vertical velocity in decelerating/accelerating flows, and the Shields diagram is valid only when flow is uniform. A new theory for critical shear stress has been developed, a unified critical Shields stress for sediment transport has been established, which is valid to predict the critical shear stress of sediment with/without vertical motion.

scholarly journals Review of a Semi-Empirical Modelling Approach for Cohesive Sediment Transport in River Systems

Water ◽  
2022 ◽  
Vol 14 (2) ◽  
pp. 256
Author(s):  
Bommanna G. Krishnappan
Keyword(s):  
Shear Stress ◽  
Sediment Transport ◽  
Critical Shear Stress ◽  
Cohesive Sediment ◽  
River Systems ◽  
Empirical Modelling ◽  
Cohesive Sediment Transport ◽  
Definition Of ◽  
Semi Empirical ◽  
Modelling Approach

In this paper, a review of a semi-empirical modelling approach for cohesive sediment transport in river systems is presented. The mathematical modelling of cohesive sediment transport is a challenge because of the number of governing parameters controlling the various transport processes involved in cohesive sediment, and hence a semi-empirical approach is a viable option. A semi-empirical model of cohesive sediment called the RIVFLOC model developed by Krishnappan is reviewed and the model parameters that need to be determined using a rotating circular flume are highlighted. The parameters that were determined using a rotating circular flume during the application of the RIVFLOC model to different river systems include the critical shear stress for erosion of the cohesive sediment, critical shear stress for deposition according to the definition of Partheniades, critical shear stress for deposition according to the definition of Krone, the cohesion parameter governing the flocculation of cohesive sediment and a set of empirical parameters that define the density of the floc in terms of the size of the flocs. An examination of the variability of these parameters shows the need for testing site-specific sediments using a rotating circular flume to achieve a reliable prediction of the RIVFLOC model. Application of the model to various river systems has highlighted the need for including the entrapment process in a cohesive sediment transport model.

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