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1
Gilja, Gordon, and Neven Kuspilić. "Dune geometry estimation using apparent bedload velocity as predictor variable." E3S Web of Conferences 40 (2018): 02054. http://dx.doi.org/10.1051/e3sconf/20184002054.
Повний текст джерелаАнотація:
Dune formation in river systems influences sediment transport, flow characteristics, bank erosion, flood control, navigation and the protection of land and infrastructure. Research on dunes is mainly flume-based, and conclusions from such research are rarely, if at all, verified with field measurements. Dune formation and geometry in terms of height, length and steepness is most commonly correlated with averaged flow parameters as flow depth. Application of relations defined in flume conditions is limited due to stationary flow conditions and extrapolation issues for natural watercourses. It is reasonable to assume that apparent bedload velocity has significant influence on dune field formation due to nature of movement of sand particles across sandy riverbed. This research investigates applicability of apparent bedload velocity as argument in empirical relations for dune geometric characteristics.
2
Badoux, A., J. M. Turowski, L. Mao, N. Mathys, and D. Rickenmann. "Rainfall intensity–duration thresholds for bedload transport initiation in small Alpine watersheds." Natural Hazards and Earth System Sciences 12, no. 10 (October 18, 2012): 3091–108. http://dx.doi.org/10.5194/nhess-12-3091-2012.
Повний текст джерелаАнотація:
Abstract. Although channel discharge represents one of the primary controls of bedload transport rates in mountain streams, it is rarely measured in small, steep catchments. Thus, it is often impossible to use it as a predictor of hazardous bedload events. In this study, the characteristics of rainfall events leading to bedload transport were investigated in five small Alpine catchments located in different geographical and morphological regions of Switzerland, Italy and France. Using rainfall data at high temporal resolution, a total of 370 rainfall events were identified that led to abundant sediment transport in the different catchments, and corresponding threshold lines were defined using a power law in intensity–duration space. Even though considerable differences in the distribution of the rainfall data were identified between catchments located in various regions, the determined threshold lines show rather similar characteristics. Such threshold lines indicate critical conditions for bedload transport initiation, but rainfall events that do not cause transport activity (so called no-bedload events) can still plot above them. With 0.67 overall in the Erlenbach (Swiss Prealps) and 0.90 for long-duration, low-intensity rainfall, the false alarm rate is considerable. However, for short-duration, high-intensity events, it is substantially smaller (0.33) and comparable to values determined in previous studies on the triggering of Alpine debris flows. Our results support the applicability of a traditional, generalized threshold for prediction or warning purposes during high-intensity rainfall. Such (often convective) rainfall events are unfortunately (i) difficult to measure, even by dense rain gauge networks, and (ii) difficult to accurately predict, both due to their small spatial and temporal scales. Still, for the protection of human life (e.g. along transportation infrastructure such as roads and railway) automated alerts based on power law threshold lines may be useful.
3
Kleinhans, M. G., A. W. E. Wilbers, and W. B. M. ten Brinke. "Opposite hysteresis of sand and gravel transport upstream and downstream of a bifurcation during a flood in the River Rhine, the Netherlands." Netherlands Journal of Geosciences 86, no. 3 (September 2007): 273–85. http://dx.doi.org/10.1017/s0016774600077854.
Повний текст джерелаАнотація:
AbstractAt river bifurcations water and sediment is divided among the downstream branches. Prediction of the sediment transport rate and division thereof at bifurcations is of utmost importance for understanding the evolution of the bifurcates for short-term management purposes and for long-term fluvial plain development. However, measured sediment transports in rivers rarely show a uniquely determined relation with hydrodynamic parameters. Commonly a hysteresis is observed of transport rate as a function of discharge or shear stress which cannot be explained with the standard sediment transport predictor approach. The aim of this paper is to investigate the causes of hysteresis at a bifurcation of the lower Rhine river, a meandering river with stable banks, large dunes during flood, and poorly sorted bed sediment. The hydrodynamics and bed sediment transport were measured in detail during a discharge wave with a recurrence interval larger than 10 years. Surprisingly, the hysteresis in bedload against discharge was in the opposite direction upstream and downstream of the bifurcation. The upstream clockwise hysteresis is caused by the lagging development of dunes during the flood. The counter-clockwise hysteresis downstream of the bifurcation is caused by a combination of processes in addition to dune lagging, namely 1) formation of a scour zone upstream of the bifurcation, causing a migrating fine sediment wave, and 2) vertical bed sorting of the bed sediment by dunes with avalanching lee-sides, together leading to surface-sediment fining and increased transport during and after the flood. These findings lead to challenges for future morphological models, particularly for bifurcations, which will have to deal with varying discharge, sediment sorting in the channel bed, lagging dunes and related hydraulic roughness.
4
Zhang, Bin, Xing Nian Liu, and Feng Guang Yang. "Two Stochastic Fraction Bedload Transport Rate Models for Nonuniform Sediment." Applied Mechanics and Materials 295-298 (February 2013): 1894–97. http://dx.doi.org/10.4028/www.scientific.net/amm.295-298.1894.
Повний текст джерелаАнотація:
Based on a method stochastic processes, two new bedload transport models for the ith size fraction nonuniform sediment are theoretically developed by using a stochastic model of sediment exchange and the probabilistic distribution of fractional bedload transport rates. The relations, proposed recently by Yang, for the probability of fractional incipient motion and for the average velocity of particle motion are introduced to bedload formulas. Plenty of experimental data for the bedload transport rate of uniform sediment are used to determine parameters. Finally, the two models are verified with natural data expressing the transport of nonuniform sediment under full motion in laboratory flume. The result shows that the experimental observations agree well with the predicted fractional bedload transport rates. Comparison of the theory with field data shows that the proposed formula still applies to uniform sediment transportation condition as long as the relevant parameters for uniform sediment are taken into account.
5
Roushangar, Kiyoumars, and Roghayeh Ghasempour. "Prediction of non-cohesive sediment transport in circular channels in deposition and limit of deposition states using SVM." Water Supply 17, no. 2 (September 23, 2016): 537–51. http://dx.doi.org/10.2166/ws.2016.153.
Повний текст джерелаАнотація:
Sedimentation in sewer pipes has a negative impact on the performance of sewerage systems. However, due to the complex nature of sedimentation, determining the governing equations is difficult and the results of the available classic models for computing bedload transport rate often differ from each other. This paper focuses on the capability of a support vector machine (SVM) as a meta-model approach for predicting bedload transport in pipes. The method was applied for the deposition and limit of deposition states of sediment transport. Two different scenarios were proposed: in Scenario 1, the input combinations were prepared using only hydraulic characteristics, on the other hand, Scenario 2 was built using both hydraulic and sediment characteristics as model inputs of bedload transport. A comparison between the SVM and the employed classic approaches in predicting sediment transport indicated the supreme performance of the SVM, in which more accurate results were obtained. Also it was found that for estimation of bedload transport in pipes, Scenario 2 led to a more valid outcome than Scenario 1. Based on the sensitivity analysis, parameters Frm and d50/y in the limit of deposition state and Frm in the deposition state had the more dominant role in prediction of bedload discharge in pipes than other parameters.
6
Bayram, Atilla, Sean O'Neil, and Yang Zhang. "SEDIMENT TRANSPORT FIELD DATA AND NUMERICAL MODELING STUDY TO SUPPORT DREDGE PIT INFILL RATE ESTIMATES." Coastal Engineering Proceedings, no. 36v (December 31, 2020): 57. http://dx.doi.org/10.9753/icce.v36v.papers.57.
Повний текст джерелаАнотація:
Site specific bedload and suspended sediment transport data collected at two test pit locations over a four-day period during April 2015 were analyzed to calibrate a numerical sediment transport model of Cook Inlet, AK. The field data campaign was designed to collect suspended load and bedload field measurements and was carried out in two phases. During Phase 1, both suspended load and bedload measurements were taken at approximately 55 ft water depth. The suspended sediment concentration was observed to be nearly uniform over the water column. Laboratory analysis showed the suspended sediment had an effective grain size of approximately 0.03 mm with 0.005 mm within a 95percent confidence interval. During Phase 2, hydrodynamic, suspended load and bedload measurements were collected over four tidal cycles in the surfzone. A two-dimensional sediment transport model was developed to simulate sediment transport infill rates at the dredged areas of the Project site. The model was calibrated by comparing measured suspended load measurements made at two offshore locations. Calibration results showed that the suspended load transport rate, which is the dominant sediment transport regime in the area, can be predicted accurately at the project site. Based on the calibrated sediment transport model, preliminary annual sediment infill rates were estimated to lie between 1.1 to 1.6 ft/yr at offshore and nearshore locations, respectively, for the presently observed and measured conditions.
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Bonilla-Porras, José A., Aronne Armanini, and Alessandra Crosato. "Extended Einstein's parameters to include vegetation in existing bedload predictors." Advances in Water Resources 152 (June 2021): 103928. http://dx.doi.org/10.1016/j.advwatres.2021.103928.
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Giberson, Donna J., and Daniel Caissie. "Stream habitat hydraulics: interannual variability in three reaches of Catamaran Brook, New Brunswick." Canadian Journal of Fisheries and Aquatic Sciences 55, no. 2 (February 1, 1998): 485–94. http://dx.doi.org/10.1139/f97-247.
Повний текст джерелаАнотація:
The hydraulic habitat of 12 sites in a small salmon stream in central New Brunswick was investigated between 1992 and 1995 to determine patterns of habitat (substrate) stability between and within reaches. Stability was evaluated by measuring particle size distribution in replicated erosional and depositional sites in each reach and calculating the proportion of the bed predicted to be in motion at given flood flows. Erosional (riffle) sites in all reaches showed significant differences (ANOVA, p < 0.05) in substrate particle sizes from year to year, movement of embedded sediment samplers, and high predicted bedload mevement, even in small spates. In contrast, depositional sites (flats, some runs) appeared stable, showing no significant year-to-year differences in particle sizes, no movement of embedded samplers, and no increase in predicted bedload movement until high flow. The impact of the flood on the streambed depends heavily on the particle size distribution present during the flood, resulting in different levels of substrate disturbance during equal-magnitude floods in different years. Certain sites (e.g., flats) may be able to serve as hydraulic refugia to stream fauna during some floods. It is clear that year-to-year variations in substrate stability must be considered when evaluating habitat stability for stream fauna.
9
Hosseini, Seyed Abbas, Abbas Abbaszadeh Shahri, and Reza Asheghi. "Prediction of bedload transport rate using a block combined network structure." Hydrological Sciences Journal 67, no. 1 (January 2, 2022): 117–28. http://dx.doi.org/10.1080/02626667.2021.2003367.
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10
Khosravi, Khabat, James R. Cooper, Prasad Daggupati, Binh Thai Pham, and Dieu Tien Bui. "Bedload transport rate prediction: Application of novel hybrid data mining techniques." Journal of Hydrology 585 (June 2020): 124774. http://dx.doi.org/10.1016/j.jhydrol.2020.124774.
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11
Pruszak, Zbigniew, and Ryszard B. Zeidler. "ESTIMATES OP GROSS-SHORE BEDLOAD AND BED CHANGES." Coastal Engineering Proceedings 1, no. 21 (January 29, 1988): 131. http://dx.doi.org/10.9753/icce.v21.131.
Повний текст джерелаАнотація:
Four series of tracer studies employing radioisotopic sand, tracked remotely from land, were carried out at the IBW PAN's coastal research station at Lubiatowo. Incipient motion of single grains with velocity Vcr1 has agreed with Komar and Miller's (1974) formula, and has been 5...8 times smaller than voro, the threshold velocity of water inducing bulk motion_of sediment. The ratio of average nearbed water velocity, v, to_the effective speed of tracer sand, in the inshore zone, va, is estimated about 100...1,000. The cross-shore sediment transport rates measured are ten times smaller than those predicted by Pruszak's (1987) energetics formula, the discrepancy being due to the real field phenomena of mixing and overburdening in a thick bed layer. Our wave flume and wave tank studies with movable bed point to the importance of initial slope in shore evolution. The laboratory findings on bed variability are extended by our 1987 field data obtained with an ultrasonic setup. Intensive cyclic depth changes are acoorapanied by varying transport rates computed from continuity equation.
12
Wyssmann, Micah A., and A. N. (Thanos) Papanicolaou. "Lagrangian modeling of bedload movement via the impulse entrainment method." E3S Web of Conferences 40 (2018): 05041. http://dx.doi.org/10.1051/e3sconf/20184005041.
Повний текст джерелаАнотація:
At low shear stresses merely above incipient conditions, the characteristic travel patterns of bedload particles remain difficult to predict due to intermittent movement. At these conditions, particles rest, are entrained into the flow when sufficient momentum transfer from near-bed turbulence occurs, and then come to rest again. The overarching goal of this research is to close the critical gaps related to intermittent movement in order to allow for Lagrangian modeling of bedload at near incipient conditions. Thereby, the specific objectives of the present work are to predict the statistics of (1) the particle resting time, tR, and (2) the magnitude of hydrodynamic momentum transfer (or impulse) during entrainment, Ient. To predict these statistics, we employed the conceptual framework of the impulse entrainment method and predicted impulse statistics by simulating turbulent time series realizations with a generic, regime-based streamwise velocity spectrum. Model validation was carried out by directly comparing simulation results with published experimental impulse and particle entrainment statistics. Model predictions showed that an increase in stress was correlated with a sharp decrease in the average tR and an increase in Ient.
13
Seminara, Giovanni, Marco Colombini, and Gary Parker. "Nearly pure sorting waves and formation of bedload sheets." Journal of Fluid Mechanics 312 (April 10, 1996): 253–78. http://dx.doi.org/10.1017/s0022112096001991.
Повний текст джерелаАнотація:
Bedload sheets are coherent migrating patterns of bed material recently observed both in flume studies and in field streams with beds of coarse sand and fine gravel. This newly recognized feature is inherently associated with the heterogeneous character of the sediment and consists of sorting waves with distinct coarse fronts only one or two coarse grains high.The question of the formation of bedload sheets poses an interesting and peculiar stability problem for the grain size distribution. Sorting waves are essentially two-dimensional migrating perturbations associated with variations of this distribution. We show that their growth is strictly associated with grain sorting. In fact the latter gives rise to perturbations of bedload transport which drive small perturbations of bottom elevation the amplitude of which scales with grain size. The sorting wave also induces spatial variations of bottom roughness, and consequently alters the fluid motion, which conversely exerts a spatially varying stress on the bed. The feature of bedload sheets which allows them to be distinguished from dunes over beds with coarse sand or fine gravel is then the fact that sorting is the dominant effect controlling their growth, rather than being a relatively small perturbation of the mechanism which gives rise to dunes in the case of uniform sediment.The requirement that perturbations should not alter the sediment budget leads to an integral condition which gives rise to an integro-differential mathematical problem. With the help of recently developed bedload relationships suitable for mixtures, as well as appropriate modelling of turbulent channel flow over a bed with spatially periodic perturbations of bottom elevation and roughness we are able to derive a general dispersion relation which can be readily solved in terms of undisturbed size densities in the form of sums of Dirac distributions.Perturbations are found to be unstable within a range of wavenumbers depending on the relative roughness and Froude number. We show that when the effects of perturbations of bottom elevation are neglected the unstable region corresponds to the range of conditions where the bottom stress leads bottom roughness, a range distinct from that which characterizes the formation of dunes. This result is given a physical explanation which depends crucially on the deviation from equal mobility of different grain sizes in the surface layer. The effect of perturbations of bottom elevation is however not negligible when the bottom roughness is fairly large compared to depth. In the latter case perturbations of bottom elevation and of bottom roughness are equally important, and gravel sheets are not easily distinguished from small-amplitude dunes.Comparison with the field observations of Whiting et al. (1985, 1988) is satisfactory insofar as the bedload sheet mode is unstable under the conditions of the experiments, and the predicted wavelengths fall within the experimental range. The laboratory observations of Kuhnle & Southard (1988), on the other hand, appear to fall within a range of bottom roughness where the observed bedforms do not exhibit features unambiguously distinct from those of small-amplitude dunes.
14
Kovacs, Agnes, and Gary Parker. "A new vectorial bedload formulation and its application to the time evolution of straight river channels." Journal of Fluid Mechanics 267 (May 25, 1994): 153–83. http://dx.doi.org/10.1017/s002211209400114x.
Повний текст джерелаАнотація:
The derivation of a new vectorial bedload formulation for the transport of coarse sediment by fluid flow is presented in the first part of the paper. This relation has been developed for slopes up to the angle of repose both in the streamwise and transverse directions. The pressure distribution is assumed to be hydrostatic. The bed shear stress for the onset of particle motion and mean particle velocity are obtained from the mean force balance on a particle. A new generalized Bagnold hypothesis is introduced to calculate the sediment content of the bedload layer. The new formulation possesses two innovative features. It is fully nonlinear and vectorial in nature, in addition, it behaves smoothly up to the angle of repose.A mathematical model of the time evolution of straight river channels is presented in the second half of the paper. This study focuses on the evolution process due to bank erosion in the presence of bedload only. The bed and bank material is taken to be coarse, non-cohesive and uniform in size. The sediment continuity and the fluid momentum conservation equations describe the time evolution of the bed topography and flow field. These equations are coupled through the fluid shear stress acting on the bed. This bed shear stress distribution is predicted with the aid of a simple algebraic turbulent closure model. As regards the computation of the sediment flux, the new fully nonlinear vectorial formulation is found to perform well and renders the evolution model fully mechanistic.The formation of an erosional front in the time development of straight river channels has been so far obscured in physical experiments. Herein, with the help of the new bedload formulation, the existence and migration speed of the front of erosion are inferred from the analysis of the sediment continuity equation.The model successfully describes the time relaxation of an initially trapezoidal channel toward an equilibrium cross-sectional shape, as evidenced by comparison with experimental data. This equilibrium is characterized by a constant width, vanishing sediment transport in the transverse direction, and a small but non-vanishing streamwise transport rate of bed sediment.
15
Pournazeri, S., S. S. Li, and F. Haghighat. "Efficient non-hydrostatic modelling of flow and bed shear stress in a pier scour hole." Canadian Journal of Civil Engineering 41, no. 5 (May 2014): 450–60. http://dx.doi.org/10.1139/cjce-2013-0160.
Повний текст джерелаАнотація:
Predicting 3-D flow in a pier scour hole and the associated bed shear stress τb is important for the safe and economical design of bridge piers. This paper combines layered, hydrostatic hydrodynamic computations with non-hydrostatic pressure corrections, exploring a new modelling approach for efficient and reliable predictions of 3-D flow velocity. The law of the wall method is used for estimating τb. Its suitability for incorporation into layered models for bedload transport and pier scour simulations is also discussed. The predicted flow shows realistic features: strong downward flow adjacent to the upstream nose of a circular pier, vortex motions in the vertical and horizontal direction, and meandering flow wakes. The velocity results compare well with available experimental data. In the approach region, τb is uniform. It attains a local maximum immediately before flow enters the scour hole and then drops non-linearly in the scour-hole region toward the pier. In the wake region, τb has very low values. The τb predictions are consistent with the experimental data. In multi-layer models, when applying the law of wall method, one should use near-bed velocities as opposed to bottom-layer velocities to obtain more reliable τb estimates and avoid noisy results, which can cause a numerical instability problem in bedload transport simulations.
16
Zang, Zhipeng, Yiping Zhang, Tongqing Chen, Botao Xie, Xing Zou, and Zhichuan Li. "A Numerical Simulation of Internal Wave Propagation on a Continental Slope and Its Influence on Sediment Transport." Journal of Marine Science and Engineering 11, no. 3 (February 27, 2023): 517. http://dx.doi.org/10.3390/jmse11030517.
Повний текст джерелаАнотація:
Significant current velocity near the sea bottom can be induced by internal waves, even for water a few hundred meters in depth. In this study, a nonhydrostatic ocean model was applied to simulate the generation and propagation of internal waves on the continental slope of the northern SCS. Based on the analyses of the vertical profiles of the currents, the propagation of internal waves along the continental slope can be categorized into six modes. The bed shear stress and the bedload transport were calculated to analyze the general characteristics of sediment transport along the continental slope of the northern SCS. Generally, there was no sediment transport on the sea bottom induced by the internal waves when the water depth was deeper than 650 m or shallower than 80 m. The downslope sediment transport dominated the slope at a water depth range of 200~650 m, while the upslope sediment transport dominated the slope at a water depth range of 80~200 m. The predicted directions of the bedload transport are coincident with the field observations of sand wave migration on the continental slope, which further confirms that the main cause of the generation and formation of sand waves on the continental slope of the northern SCS is the strong bottom current induced by the shoaling process of internal waves.
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Mohammed Pirot, Omed, and Sobri Harun. "THE INFLUENCE OF THE CHANNEL BED RECTANGULAR CONFIGURATION ON SEDIMENT TRANSPORTATION." Jurnal Teknologi 85, no. 2 (February 23, 2023): 41–51. http://dx.doi.org/10.11113/jurnalteknologi.v85.18815.
Повний текст джерелаАнотація:
Sediment transport is the movement of organic and inorganic particles caused by gravity, a moving fluid’s force, the wind, and ice motion. Sediment deposition degrades dams’ safety, leading to environmental pollution and channel area reduction. This study describes the effect of the weir height and spacing of used and non-used rectangular configuration structures on sediment transport rates in an open channel. This project was created using a rectangular open channel (30 cm wide and 60 cm deep). A sharp-crested weir was installed in the channel, and the rectangular wooden configurations were fixed in specific locations on each weir to reduce the bedload transportation rate and sediment motion. The weir heights were different (0.25B, 0.35B, 0.45B, and 0.55B, where B is the channel width). Also, the spacing between the baffle blocks (S) was set to 4Y, 8Y, 12Y, and 16Y, where Y was the maximum water depth without installing blocks and weirs. The results showed that the maximum transported bedload for the lowest weir was 1.4 kg/min, but only 4.4 × 10-3 kg/min was transported for the weir 16.5-cm high with baffle blocks. Using long baffle blocks yielded a worse result than using no blocks. The sediment-transport rate increased to 1.66 kg/min for the 7.5-cm weir due to block configurations. In conclusion, the obtained result contradicts the predicted result, as using baffle blocks increased the sediment transportation rate.
18
Khorram, Saeed. "Bedload Sediment Rate Prediction for the Sand Transport Along Coastal Waters in Ocean Management Strategy." China Ocean Engineering 34, no. 6 (December 2020): 840–52. http://dx.doi.org/10.1007/s13344-020-0076-7.
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Khorram, Saeed. "Bedload Sediment Rate Prediction for the Sand Transport Along Coastal Waters in Ocean Management Strategy." China Ocean Engineering 34, no. 6 (December 2020): 840–52. http://dx.doi.org/10.1007/s13344-020-0076-7.
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Hunt, Heather L., David C. Fugate, and Robert J. Chant. "Modeling Bedload Transport of Juvenile Bivalves: Predicted Changes in Distribution and Scale of Postlarval Dispersal." Estuaries and Coasts 32, no. 6 (August 11, 2009): 1090–102. http://dx.doi.org/10.1007/s12237-009-9205-5.
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Latosinski, Francisco Guillermo, Ricardo Nicolás Szupiany, Massimo Guerrero, Mario Luis Amsler, and Carlos Vionnet. "The ADCP's bottom track capability for bedload prediction: Evidence on method reliability from sandy river applications." Flow Measurement and Instrumentation 54 (April 2017): 124–35. http://dx.doi.org/10.1016/j.flowmeasinst.2017.01.005.
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Métivier, François, Olivier Devauchelle, Hugo Chauvet, Eric Lajeunesse, Patrick Meunier, Koen Blanckaert, Peter Ashmore, et al. "Geometry of meandering and braided gravel-bed threads from the Bayanbulak Grassland, Tianshan, P. R. China." Earth Surface Dynamics 4, no. 1 (March 22, 2016): 273–83. http://dx.doi.org/10.5194/esurf-4-273-2016.
Повний текст джерелаАнотація:
Abstract. The Bayanbulak Grassland, Tianshan, P. R. China, is located in an intramontane sedimentary basin where meandering and braided gravel-bed rivers coexist under the same climatic and geological settings. We report and compare measurements of the discharge, width, depth, slope and grain size of individual threads from these braided and meandering rivers. Both types of threads share statistically indistinguishable regime relations. Their depths and slopes compare well with the threshold theory, but they are wider than predicted by this theory. These findings are reminiscent of previous observations from similar gravel-bed rivers. Using the scaling laws of the threshold theory, we detrend our data with respect to discharge to produce a homogeneous statistical ensemble of width, depth and slope measurements. The statistical distributions of these dimensionless quantities are similar for braided and meandering threads. This suggests that a braided river is a collection of intertwined threads, which individually resemble those of meandering rivers. Given the environmental conditions in Bayanbulak, we furthermore hypothesize that bedload transport causes the threads to be wider than predicted by the threshold theory.
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Métivier, F., O. Devauchelle, H. Chauvet, E. Lajeunesse, P. Meunier, K. Blanckaert, Z. Zhang, et al. "Morphology of meandering and braided gravel-bed streams from the Bayanbulak Grassland, Tianshan, China." Earth Surface Dynamics Discussions 3, no. 4 (November 13, 2015): 1289–316. http://dx.doi.org/10.5194/esurfd-3-1289-2015.
Повний текст джерелаАнотація:
Abstract. The Bayanbulak Grassland, Tianshan, China is located in an intramountane sedimentary basin where meandering and braided gravel-bed streams coexist under the same climatic and geological settings. We report on measurements of their discharge, width, depth, slope and grain size. Based on this data set, we compare the morphology of individual threads from braided and meandering streams. Both types of threads share statistically indistinguishable regime relations. Their depths and slopes compare well with the threshold theory, but they are wider than predicted by this theory. These findings are reminiscent of previous observations from similar gravel-bed streams. Using the scaling laws of the threshold theory, we detrend our data with respect to discharge to produce a homogeneous statistical ensemble of width, depth and slope measurements. The statistical distributions of these dimensionless quantities are similar for braided and meandering streams. This suggests that a braided river is a collection of intertwined channels, which individually resemble isolated streams. Given the environmental conditions in Bayanbulak, we furthermore hypothesize that bedload transport causes the channels to be wider than predicted by the threshold theory.
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Lotsari, Eliisa S., Mikel Calle, Gerardo Benito, Antero Kukko, Harri Kaartinen, Juha Hyyppä, Hannu Hyyppä, and Petteri Alho. "Topographical change caused by moderate and small floods in a gravel bed ephemeral river – a depth-averaged morphodynamic simulation approach." Earth Surface Dynamics 6, no. 1 (March 5, 2018): 163–85. http://dx.doi.org/10.5194/esurf-6-163-2018.
Повний текст джерелаАнотація:
Abstract. In ephemeral rivers, channel morphology represents a snapshot at the end of a succession of geomorphic changes caused by floods. In most cases, the channel shape and bedform migration during different phases of a flood hydrograph cannot be identified from field evidence. This paper analyses the timing of riverbed erosion and deposition of a gravel bed ephemeral river channel (Rambla de la Viuda, Spain) during consecutive and moderate- (March 2013) and low-magnitude (May 2013) discharge events, by applying a morphodynamic model (Delft3D) calibrated with pre- and post-event surveys by RTK-GPS points and mobile laser scanning. The study reach is mainly depositional and all bedload sediment supplied from adjacent upstream areas is trapped in the study segment forming gravel lobes. Therefore, estimates of total bedload sediment mass balance can be obtained from pre- and post-field survey for each flood event. The spatially varying grain size data and transport equations were the most important factors for model calibration, in addition to flow discharge. The channel acted as a braided channel during the lower flows of the two discharge events, but when bars were submerged in the high discharges of May 2013, the high fluid forces followed a meandering river planform. The model results showed that erosion and deposition were in total greater during the long-lasting receding phase than during the rising phase of the flood hydrographs. In the case of the moderate-magnitude discharge event, deposition and erosion peaks were predicted to occur at the beginning of the hydrograph, whereas deposition dominated throughout the event. Conversely, the low-magnitude discharge event only experienced the peak of channel changes after the discharge peak. Thus, both type of discharge events highlight the importance of receding phase for this type of gravel bed ephemeral river channel.
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Hinton, Darren, Rollin H. Hotchkiss, and Michael Cope. "Comparison of Calibrated Empirical and Semi-Empirical Methods for Bedload Transport Rate Prediction in Gravel Bed Streams." Journal of Hydraulic Engineering 144, no. 7 (July 2018): 04018038. http://dx.doi.org/10.1061/(asce)hy.1943-7900.0001474.
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Gonzalez-Rodriguez, David, and Ole Secher Madsen. "PREDICTION OF NET BEDLOAD TRANSPORT RATES OBTAINED IN OSCILLATING WATER TUNNELS AND APPLICABILITY TO REAL SURF ZONE WAVES." Coastal Engineering Proceedings 1, no. 32 (January 19, 2011): 21. http://dx.doi.org/10.9753/icce.v32.sediment.21.
Повний текст джерелаАнотація:
Experimental studies of sediment transport rates due to nearshore waves are often conducted in oscillating water tunnels (OWTs). In an OWT, the oscillatory motion produced by the piston propagates almost instantaneously along the entire tunnel. Consequently, unlike the wave motion in the sea or in a wave flume, flow in an OWT is uniform along the tunnel, and second-order wave propagation effects (such as Longuet-Higgins's streaming) are absent. The effect of these hydrodynamic differences between OWT and sea waves on sediment transport rates has generally been neglected. In this paper we present a simple, practical formulation to evaluate bed shear stresses and bedload transport rates due to asymmetric and skewed waves plus a current in an OWT, based on fitting the exact results of a rigorous, analytical model of the OWT wave-current boundary layer. By then accounting for real wave effects we find that wave propagation significantly affects the predicted period-averaged net sediment transport rates. Such real wave effects can therefore not be neglected when comparing nearshore transport models with OWT data.
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COLOMBINI, M., and A. STOCCHINO. "Ripple and dune formation in rivers." Journal of Fluid Mechanics 673 (March 2, 2011): 121–31. http://dx.doi.org/10.1017/s0022112011000048.
Повний текст джерелаАнотація:
A linear stability analysis for dune and ripple formation is presented that implements a rotational two-dimensional flow model valid in the smooth as well as in the transitional and rough flow regimes. Sediment is assumed to be transported as bedload, disregarding the role of suspension. Therefore, the main mechanism driving instability, for both ripples and dunes, is the phase lag between bed shear stress and bed elevation. Ripples are shown to be confined to relatively low values of the Shields parameter and of the particle Reynolds number. For higher values of the Shields parameter and of the particle Reynolds number (and thus of the Froude number and of the roughness Reynolds number), ripples are replaced by dunes. The present analysis ultimately allows for a successful unification of the theories of dune and ripple formation and for a clarification of the debated role of ripples on the formation of dunes. A good agreement between predicted and observed wavelengths for both ripples and dunes is found.
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Carrillo, Veronica, Daniel Mendoza, John Petrie, Pedro Matovelle, Sebastian Torres, Esteban Pacheco, Felipe Cisneros, and Luis Timbe. "Using a statistical efficiency methodology for predictors’ selection in the bedload transport problem: A high gradient experimental channel case." Alexandria Engineering Journal 61, no. 8 (August 2022): 6205–19. http://dx.doi.org/10.1016/j.aej.2021.11.052.
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Terwisscha van Scheltinga, Renske C., Heide Friedrich, and Giovanni Coco. "A PIV-based method to measure spatial gradients in bedload transport over a dune." E3S Web of Conferences 40 (2018): 04012. http://dx.doi.org/10.1051/e3sconf/20184004012.
Повний текст джерелаАнотація:
Traditional sediment transport equations calculate sediment flux from bed shear stress and the equations predict that transport increases nonlinearly with an increase in flow velocity. In a dune field, the dune geometry affects the flow velocity causing accelerating flow over the dune crest and de- and reattachment of the flow downstream of the dune crest. Sediment flux predicted from the reach-averaged bed shear stress gives fairly good results for dune fields, though their simplification is discordant for the complexity of the processes involved. Measurements of the displacement of sand particles over the dune bed were derived from highfrequency image capturing. The two main methods to measure particle velocities from images are particle tracking velocimetry (PTV) and particle image velocimetry (PIV). We compare individual particle tracking with a PIV-based correlation method. The PIV-based method promises to be a more efficient and effective approach to track particle motion. It is more suitable for the conditions of high bedload transport, as present in our experiments. The PIV-based method is based on using images of difference (IoD) and is fully automated and identifies spatial gradients at a support scale in the order of centimetres. Findings align with our general knowledge of accelerating flow over the dune crest. The mean streamwise particle velocity and activity over a dune stoss slope increase. At the scale of 0.026 m the observed particle velocity variability can be explained in the context of general onset and cessation of sediment transport, the effect of the reattachment zone and observed sweep/burst events. By decreasing the streamwise distance between cross-sections, the variations in mean particle velocity induced by superimposed bed defects are distinguished as well. The maximum particle velocity and activity occurred at the same location and consequently the location of the maximum transport over the dune crest was identified. The measurements bridge the gap between individual particle motion studies and (non-local) sediment transport flux measurements.
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Daham, Mariam H. "A Prediction Formula for The Estimation of Sediment Load in The Upper Reach of Al-Gharraf River." Journal of Engineering 27, no. 5 (May 1, 2021): 63–74. http://dx.doi.org/10.31026/j.eng.2021.05.05.
Повний текст джерелаАнотація:
The presence of deposition in the river decreases the river flow capability's efficiency due to the absence of maintenance along the river. In This research, a new formula to evaluate the sediment capacity in the upstream part of Al-Gharraf River will be developed. The current study reach lies in Wasit province with a distance equal to 58 km. The selected reach of the river was divided into thirteen stations. At each station, the suspended load and the bedload were collected from the river during a sampling period extended from February 2019 till July 2019. The samples were examined in the laboratory with a different set of sample tests. The formula was developed using data of ten stations, and the other three stations were used for validation. The determination coefficient, root mean square error and average relative error values were equal to 0.987,0.97 kg/s and 7%, respectively. Also, the values of the sediment load that resulted from the formula close to the results of the HEC-RAS model from a previous study, and the determination coefficient, root mean square error, and average relative error values were equal to 0.988, 0.88 kg/s, and 7 % respectively for the simulated model.
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MIURA, Sawa, Takahiro KOSHIBA, and Tetsuya SUMI. "SEDIMENT VOLUME PREDICTION IN THE DIVERSION POOL OF THE KOSHIBU DAM SEDIMENT BYPASS TUNNEL USING BEDLOAD MONITORING IN UPSTREAM REACHES." Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) 77, no. 2 (2021): I_577—I_582. http://dx.doi.org/10.2208/jscejhe.77.2_i_577.
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Kranenborg, Joost W. M., Geert H. P. Campmans, Niels G. Jacobsen, Jebbe J. van der Werf, Ad J. H. M. Reniers, and Suzanne J. M. H. Hulscher. "Depth-Resolved Modelling of Intra-Swash Morphodynamics Induced by Solitary Waves." Journal of Marine Science and Engineering 10, no. 9 (August 24, 2022): 1175. http://dx.doi.org/10.3390/jmse10091175.
Повний текст джерелаАнотація:
We present a fully coupled 2DV morphodynamic model, implemented in OpenFOAM® that is capable of simulating swash-zone morphodynamics of sandy beaches. The hydrodynamics are described by the Reynolds-averaged Navier–Stokes (RANS) equations with a k−ω turbulence model and the Volume of Fluid (VoF) approach for discriminating between air and water. Sediment transport is described in terms of bedload and suspended load transport. We show that the default divergence scheme in OpenFOAM can become numerically unstable and lead to negative sediment concentrations, and propose a solution to avoid this problem. The model performance is assessed in terms of surface elevation, flow velocities, runup, suspended sediment concentrations, bed profile evolution and sediment transport volumes by comparing with measurements of field-scale (wave height of 0.6 m) solitary waves. The model shows reasonable agreement in terms of hydrodynamics and predicts the correct sediment transport volumes, although the deposition is predicted more onshore compared to the measurements. This is partially attributed to an overprediction of the runup. The model shows that the suspended sediment concentration displays a strong vertical dependence. These results show the potential of depth-resolving models in providing more insight into morphodynamic processes in the swash zone, particularly with respect to vertical structures in the flow and suspended sediment transport.
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Anderson, Noah T., Clinton A. Cowan, and Kristin D. Bergmann. "A case for the growth of ancient ooids within the sediment pile." Journal of Sedimentary Research 90, no. 8 (August 19, 2020): 843–54. http://dx.doi.org/10.2110/jsr.2020.45.
Повний текст джерелаАнотація:
ABSTRACT In modern ooid-forming environments in the Caribbean, aerobic respiration of organic matter below the sediment–water interface drives an increase in pCO2 and a corresponding decrease in carbonate saturation state (Ω) that creates shallow sediment porewater that is neutral or slightly caustic to carbonate. The locus of ooid growth, therefore, is presumed to be in the water column during suspension, where supersaturation with respect to calcium carbonate is the norm. In the past, however, during conditions of low aqueous O2, high Ω, or low organic-matter input, the shallow sub-sediment marine burial environment was conducive to carbonate precipitation. Here we present petrographic and electron probe microanalyzer (EPMA) data from exquisitely preserved oolites through time that suggests that some ancient ooids may have grown within the sediment pile. We propose that each increment of ooid cortical growth originated as incipient isopachous marine cement formed during shallow burial within migrating ooid dunes. After a period of burial (∼ weeks to months), ooids were remobilized and rounded during bedload transport. This “bedform model” for ooid growth explains: 1) why ancient ooids are not limited by the precipitation–abrasion balance that appears to prohibit modern tangential Caribbean ooids from achieving grain sizes larger than coarse sand, 2) the radial crystal fabric that defines the internal structure of many ancient ooids, and 3) the first-order correlation of the abundance of large and giant ooids in the rock record to periods with predicted high porewater Ω. This model implies that photosynthetic microbes were unimportant for growth of large and giant ooid but it remains agnostic to the effect of other microbes. The physical and chemical milieu of modern marine ooid-forming environments is perhaps not the best analogue for ancient ooid-forming environments; this should be considered when using ancient ooids to reconstruct secular trends in ocean chemistry.
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de Leeuw, Jan, Michael P. Lamb, Gary Parker, Andrew J. Moodie, Daniel Haught, Jeremy G. Venditti, and Jeffrey A. Nittrouer. "Entrainment and suspension of sand and gravel." Earth Surface Dynamics 8, no. 2 (June 3, 2020): 485–504. http://dx.doi.org/10.5194/esurf-8-485-2020.
Повний текст джерелаАнотація:
Abstract. The entrainment and suspension of sand and gravel are important for the evolution of rivers, deltas, coastal areas, and submarine fans. The prediction of a vertical profile of suspended sediment concentration typically consists of assessing (1) the concentration near the bed using an entrainment relation and (2) the upward vertical distribution of sediment in the water column. Considerable uncertainty exists in regard to both of these steps, especially the near-bed concentration. Most entrainment relations have been tested against limited grain-size-specific data, and no relations have been evaluated for gravel suspension, which can be important in bedrock and mountain rivers. To address these issues, we compiled a database with suspended sediment data from natural rivers and flume experiments, taking advantage of the increasing availability of high-resolution grain size measurements. We evaluated 12 dimensionless parameters that may determine entrainment and suspension relations and applied multivariate regression analysis. A best-fit two-parameter equation (r2=0.79) shows that near-bed entrainment, evaluated at 10 % of the flow depth, decreases with the ratio of settling velocity to skin-friction shear velocity (wsi/u∗skin), as in previous relations, and increases with Froude number (Fr), possibly due to its role in determining bedload-layer concentrations. We used the Rouse equation to predict concentration upward from the reference level and evaluated the coefficient βi, which accounts for differences in the turbulent diffusivity of sediment from the parabolic eddy viscosity model used in the Rouse derivation. The best-fit relation for βi (r2=0.40) indicates greater relative sediment diffusivities for rivers with greater flow resistance, possibly due to bedform-induced turbulence, and larger wsi/u∗skin; the latter dependence is nonlinear and therefore different from standard Rouse theory. In addition, we used empirical relations for gravel saltation to show that our relation for near-bed concentration also provides good predictions for coarse-grained sediment. The new relations extend the calibrated parameter space over a wider range in sediment sizes and flow conditions compared to previous work and result in 95 % of concentration data throughout the water column predicted within a factor of 9.
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Florek, Jacek, and Maciej Wyrębek. "Procedure of Numerical Modelling and Estimation of Sieve Curve Changes as a Tool to Define Riverbed’s Erodibility." Sustainability 15, no. 2 (January 12, 2023): 1468. http://dx.doi.org/10.3390/su15021468.
Повний текст джерелаАнотація:
The numerical 1-D HEC-RAS modelling tool was supported by the estimation of the sieve curve changes procedure to measure the scale of predicted discharges along a stretch of stream in southern Poland on the Olkusz Upland. The procedure was calibrated in southern Poland on the mountain streams during high-stage events, using a radiotracer application in bedload transport. Particular terrain hypsometry, created by the dissolution of limestone, forced the deep erosion of the river valley bottom; it is here that the current shape of the riverbed of the Prądnik stream is placed. While numerical modelling is widely used in hydraulics, standards have been set for the estimation of flood risk zones; these estimations suggest that the densities of the measured cross-sections are less then optimal, and that the erosive processes are more frequent. This was proved by identifying a number of erosive sections. A new procedure proposed combining the prediction of grain size distribution with hydraulic modelling. Calculations using the estimation of sieve curves, based on the processes of creation and destruction in the armouring layer, have proven to be a challenge for the existing standards of hydraulic modelling. We believe that it is easy to expand the usefulness of the 1D model by utilising its results for this procedure. For the purpose of this type of analysis, dense cross-section measurements are involved, careful modelling is required and a wide range of additional in-field data has to be gathered. For the interpretation of the results, the relation between channel-forming discharge, bankfull discharge, present and critical shear stresses, as well as the mean diameter of the grain size and other estimated sieve curve parameters, were evaluated. Channel-forming discharge is smaller than the bankfull discharge in more than one third of the segment where the erosion process is more frequent and the stability of the riverbed is compromised. Channel-forming discharge was at least twice as high in the stable sections, compared to the erosive section. The presented method will help to find unstable riverbed sections, in order to mitigate the dimension of river training techniques and protect the natural state of the river. While we are in the period of development in this region of Europe, limiting the scope of interference in rivers and streams by applying this method may create an opportunity for the concept of river training close to nature.
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Ong, Muk Chen, Torbjørn Utnes, Lars Erik, Dag Myrhaug та Bjørnar Pettersen. "Near-Bed Flow Mechanisms Around a Circular Marine Pipeline Close to a Flat Seabed in the Subcritical Flow Regime Using a k-ɛ Model". Journal of Offshore Mechanics and Arctic Engineering 134, № 2 (5 грудня 2011). http://dx.doi.org/10.1115/1.4004631.
Повний текст джерелаАнотація:
Flow mechanisms around a two-dimensional (2D) circular marine pipeline close to a flat seabed have been investigated using the 2D unsteady Reynolds-averaged Navier–Stokes (URANS) equations with a standard high Reynolds number k-ɛ model. The Reynolds number (based on the free stream velocity and cylinder diameter) ranges from 1 × 104 to 4.8 × 104 in the subcritical flow regime. The objective of the present study is to show a thorough documentation of the applicability of the k-ɛ model for engineering design within this flow regime by means of a careful comparison with available experimental data. The inflow boundary layer thickness and the Reynolds numbers in the present simulations are set according to published experimental data, with which the simulations are compared. Detailed comparisons with the experimental data for small gap ratios are provided and discussed. The effects of the gap to diameter ratio and the inflow boundary layer thickness have been studied. Although under-predictions of the essential hydrodynamic quantities (e.g., time-averaged drag coefficient, time-averaged lift coefficient, root-mean-square fluctuating lift coefficient, and mean pressure coefficient at the back of the pipeline) are observed due to the limitation of the turbulence model, the present approach is capable of providing good qualitative agreement with the published experimental data. The vortex shedding mechanisms have been investigated, and satisfactory predictions are obtained. The mean pressure coefficient and the mean friction velocity along the flat seabed are predicted reasonably well as compared with published experimental and numerical results. The mean seabed friction velocity at the gap is much larger for small gaps than for large gaps; thus, the bedload sediment transport is much larger for small gaps than for large gaps.