DOCSLIB.ORG

Flume Studies of Gravel Bed Surface Response to Flowing

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Flume Studies of Gravel Bed Surface Response to Flowing FLUME STUDIES OF GRAVEL BED SURFACE RESPONSE TO FLOWING WATER By JOHN FREDRIC WOLCOTT B.Sc, B.F.A., University of Washington, 1982 M.Sc, University of British Columbia, 1984 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES Department of Geography We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA January, 1990 ® John Fredric Wolcott, 1990 08 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Geography The University of British Columbia Vancouver, Canada Date Ffthrnary 7. DE-6 (2/88) ii ABSTRACT Almost all sediment transport equations incorporate the Shields parameter, which is a ratio of the total boundary shear stress as a driving force and the particle weight as a resisting force. Shields (1936) equated particle resistance to entrainment with particle weight, which is proportional to particle diameter, or bed texture. The present work analyses the particle resistance term in the Shields parameter. As the bed material adjusts to a given flow condition, bed stability increases. The arrangement of particles into more stable configurations is here termed geometric structure, and includes the formation of pebble clusters, and imbrication. After an initial surface coarsening, here termed textural structure, particle resistance to movement is a function primarily of geometric structure. The Shields number for entrainment is thus a measure of particle resistance due to both types of bed structure rather than the conventional notion of particle resistance due to particle weight. The response of a mobile bed surface composed of < 8 mm diameter gravels to flowing water was explored in a 6 meter by 0.5 meter flume using four different slopes and various water depths. Corrected bed shear stresses varied between 0.05 and 2.79 Pa. Step increases in discharge with a constant slope caused the bed surface to develop a structure which was more stable at the end of a run than at the beginning. Under these conditions, the Shields number for incipient motion was found to vary between 0.001 and 0.066. This variability can be explained by the degree of geometric structure present. Previous studies, including Shields' work (1936), have implicitly included the effects of geometric structure on incipient motion. iii Surface coarsening develops with very low flows, but subsequent coarsening in higher flows is minor, with less than 5% increase in median diameter following a 50% increase in bed shear stress. Calculations of Manning's n based on depth, slope, and velocity measurements show an increase in flow resistance as structure develops. The development of a coarse surface layer appears to be limited by flow characteristics near the bed which are in turn modified by the development of structure. Measurements of the area occupied by the largest stones show that they do not cover more than 14% of the surface during maximum coarsening. Froude scaling of the flume data indicates that the time necessary for development of maximum strength is on the order of a month for natural rivers under steady flow conditions. This suggests that gravel river beds are rarely in equilibrium with natural flow conditions. iv TABLE OF CONTENTS Abstract ii Table of Contents iv List of Tables vi List of Figures vii Acknowledgements ix CHAPTER ONE: INTRODUCTION 1 Prologue 1 Field Studies , 2 Flume Experiments 4 Shields' Work 6 Other Flume Studies 9 Objectives of This Study 14 CHAPTER TWO: METHODOLOGY 17 Justification of Approach 17 Models.... 18 A Note on Units 21 Experimental Apparatus 22 Experimental Procedure 28 Summary of Runs 34 CHAPTER THREE: OBSERVATIONS 41 Series One Runs 41 A Qualitative Model 54 CHAPTER FOUR: BED STABILITY AND INCIPIENT MOTION 57 An Overview 57 The Effect of Bed Structure Development 60 Bed Structure and Incipient Motion 63 V The Shields Parameter Re-Examined 71 Bed Structure and Manning's n 77 Summary 78 CHAPTER FIVE: LAG TIME 80 CHAPTER SIX: LIMITS TO COARSENING 88 CHAPTER SEVEN: CONCLUSIONS 96 REFERENCES 103 APPENDIX 108 VI LIST OF TABLES 2.1 Velocity Profiles Across the Test Section 25 2.2 Hydraulic Parameters of the Experiments 35 4.1 Measured and Calculated Sediment Transport Values for Later Runs 64 4.2 Shields Parameter Based on Various D50 68 4.3 The D50 and the Amounts of the +4 mm and +5.66 mm Material Captured in Series 3 Runs 69 5.1 Variations in Transport Rates through Time for Series 3 Runs 82 5.2 Variations in Transport Rates through Time for Series 4 Runs 83 5.3 r^ for Linearized Exponential and Power functions of Sediment Transport through Time 86 6.1 Weights and Percentage of the Total Area of the + 5.6 mm Size Class for Several Surface Samples 91 A.l Weights and Areas of Various Size Classes 110 A.2 Ratio of A and B Axes and Areas Occupied by weight Ill vii LIST OF FIGURES 1.1 Shields Curve, after Shields (1936) 8 1.2 Illustration of a particle cluster and imbrication 12 2.1 Sketch of flume 23 2.2 Cumulative grain size distribution curves for sediment used in the experimental runs 29 3.1 Loose, well mixed material (top) and armored, and settled material after Run 1-3 (bottom) 42 3.2 Surface web of larger stones as seen on bed (top), and with smaller stones removed for clarity (bottom) 44 3.3 Photograph of incipient web development after Run 4-3 45 3.4 Comparison of bulk sample with surface samples after 0.02 m, 0.03 m, 0.05 m deep flows (Runs 1-1 to 1-4), and thalweg from degrading run (Run 1-5) 49 3.5 Textural differences between channel surface (above) and bar top surface (below). Flow from left to right 52 3.6 Comparison of bulk sample, sediment trapped during degrading run, and surface sample from thalweg and top of bar 53 4.1 Proposed relation between hydraulic variables and sediment supply (Parker, 1987, pers. com.) 58 4.2 Cumulative grain size distribution of trapped material during Series 4 runs 62 4.3 Decline in transport rate through time 66 4.4 Proposed model of bed structure development 73 viii 4.5 Shields parameter based on material moved compared to Shields parameter based on subsurface D50 74 4.6 Difference in Shields parameters of Figure 4.5 (which is the excess bed strength due to geometric structure) compared to Shields parameter based on subsurface D50 75 5.1 Coarsening of the surface median sizes following disturbance by three major storms, with discharges of 0.068, 0.039, and 0.056 m3/s 84 6.1 Comparison of typical surface (top, after 0.02 m flow depth, Run 1-2) and very well sorted surface (bottom, after Run 1-5) 95 ix ACKNOWLEDGEMENTS Since it is probable that this is the most read page of any thesis, I feel compelled to mention two things, before getting on with the traditional thank yous. First, in my two and half decades of doing research in two countries, which included one province and three states, the most enjoyable experience was completing the M.Sc. The most miserable was dealing with the examining committee during and following the PhD defense, and the administration. The bitterness has not yet dissipated. In fact, it is only through incredible encouragement of a small circle of very good friends that this thesis has continued to the final stage. May it rest in peace on some dark and dusty library shelf. Second, Dr. Humphrey of Cal. Tech. has pointed out the following irony. Since an examiner has asked that the centimeter/gram/second system of units be changed to SI units, this thesis has grown in length and therefore stature simply by the addition of zeros. Think about this when you try and figure out what 0.000158 m^/s means (it is 9.5 liters per minute or 2.5 gallons per minute), or recognize that if a 2.3 mm particle rolls 0.005 m, it has gone 2 grain diameters. To the examiner who edited the original acknowledgements page I apologize. I guess the thesis was dropped on the way to the library and the wrong page inserted. The success of this thesis is the result of generous help from many individuals, a few of whom are mentioned here. First and foremost, I would like to thank Dr. M. Church, one of the best supervisors I have ever met. He supported my initial explorations into this subject in spite of no clear objective on my part, other than curiosity. Later, through suggested readings and provocative questions, he guided me to the point where everything fell into place, and even I could see the way home. Dr. O. Slaymaker of UBC and Dr. T. Hicken of SFU provided moral support and helpful suggestions during Dr. Church's sabbatical leave, and I am very grateful for their encouragement during a discouraging period. Dr. P. Ward of Ward and Associates, Vancouver, was extremely helpful with pump and motor calculations and the design of fluid flow systems. In addition to my committee, I would like to thank Dr.
Load more

Recommended publications
  • Two-Phase Modeling of Granular Sediment for Sheet Flows and Scour
    TWO-PHASE MODELING OF GRANULAR SEDIMENT FOR SHEET FLOWS AND SCOUR. A Dissertation Presented to the Faculty of the Graduate School of Cornell University in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy by Laurent Olivier Amoudry January 2008 c 2008 Laurent Olivier Amoudry ALL RIGHTS RESERVED TWO-PHASE MODELING OF GRANULAR SEDIMENT FOR SHEET FLOWS AND SCOUR. Laurent Olivier Amoudry, Ph.D. Cornell University 2008 Even though sediment transport has been studied extensively in the past decades, not all physical processes involved are yet well understood and repre- sented. This results in a modeling deficiency in that few models include complete and detailed descriptions of the necessary physical processes and in that mod- els that do usually focus on the specific case of sheet flows. We seek to address this modeling issue by developing a model that would describe appropriately the physics and would not only focus on sheet flows. To that end, we employ a two-phase approach, for which concentration- weighted averaged equations of motion are solved for a sediment and a fluid phase. The two phases are assumed to only interact through drag forces. The correlations between fluctuating quantities are modeled using the turbulent viscosity and the gradient diffusion hypotheses. The fluid turbulent stresses are calculated using a modified k−ε model that accounts for the two-way particle-turbulence interaction, and the sediment stresses are calculated using a collisional granular flow theory. This approach is used to study three different problems: dilute flow modeling, sheet flows and scouring. In dilute models sediment stresses are neglected.
    [Show full text]
  • Numerical Study of Particle Bed Scour by Vortices Daniel S
    University of Vermont ScholarWorks @ UVM Graduate College Dissertations and Theses Dissertations and Theses 2014 Numerical study of particle bed scour by vortices Daniel S. Hagan University of Vermont Follow this and additional works at: https://scholarworks.uvm.edu/graddis Part of the Mechanical Engineering Commons Recommended Citation Hagan, Daniel S., "Numerical study of particle bed scour by vortices" (2014). Graduate College Dissertations and Theses. 267. https://scholarworks.uvm.edu/graddis/267 This Thesis is brought to you for free and open access by the Dissertations and Theses at ScholarWorks @ UVM. It has been accepted for inclusion in Graduate College Dissertations and Theses by an authorized administrator of ScholarWorks @ UVM. For more information, please contact [email protected]. NUMERICAL STUDY OF PARTICLE BED SCOUR BY VORTICES A Thesis Presented by Dan Hagan to The Faculty of the Graduate College of The University of Vermont In Partial Fullfillment of the Requirements for the Degree of Master of Science Specializing in Mechanical Engineering October, 2014 Accepted by the Faculty of the Graduate College, The University of Vermont, in partial fulfillment of the requirements for the degree of Master of Science, specializing in Mechanical Engineering. Thesis Examination Committee: Advisor Yves Dubief, Ph.D. Advisor Mandar Dewoolkar, Ph.D. Darren Hitt, Ph.D. Chairperson George Pinder, Ph.D. Dean, Graduate College Cynthia J. Forehand, Ph.D. Date: July 2, 2014 Abstract Scouring is the process of soil or sediment erosion due to flowing water, which can lead to bed degradation and compromised transportation infrastructure. In the decade before 2000, over half of the 500 bridge failures in the United States were caused by flooding or scouring.
    [Show full text]
  • Large Eddy Simulation of Oscillatory Flow Over a Mobile Rippled Bed Using an Euler-Lagrange Approach Daniel S
    University of Vermont ScholarWorks @ UVM Graduate College Dissertations and Theses Dissertations and Theses 2018 Large Eddy Simulation of Oscillatory Flow over a Mobile Rippled Bed using an Euler-Lagrange Approach Daniel S. Hagan University of Vermont Follow this and additional works at: https://scholarworks.uvm.edu/graddis Part of the Aerodynamics and Fluid Mechanics Commons, and the Ocean Engineering Commons Recommended Citation Hagan, Daniel S., "Large Eddy Simulation of Oscillatory Flow over a Mobile Rippled Bed using an Euler-Lagrange Approach" (2018). Graduate College Dissertations and Theses. 848. https://scholarworks.uvm.edu/graddis/848 This Dissertation is brought to you for free and open access by the Dissertations and Theses at ScholarWorks @ UVM. It has been accepted for inclusion in Graduate College Dissertations and Theses by an authorized administrator of ScholarWorks @ UVM. For more information, please contact [email protected]. LARGE EDDY SIMULATION OF OSCILLATORY FLOW OVER A MOBILE RIPPLED BED USING AN EULER-LAGRANGE APPROACH A Dissertation Presented by Daniel Stokes Hagan to The Faculty of the Graduate College of The University of Vermont In Partial Fullfillment of the Requirements for the Degree of Doctor of Philosophy Specializing in Mechanical Engineering May, 2018 Defense Date: January 9, 2018 Dissertation Examination Committee: Yves Dubief, Ph.D., Advisor Erik Monsen, Ph.D., Chairperson Mandar Dewoolkar, Ph.D. Douglas Fletcher, Ph.D. Cynthia J. Forehand, Ph.D., Dean of the Graduate College Abstract A volume-filtered Large-Eddy Simulation (LES) of oscillatory flow over a rippled mobile bed is conducted using an Euler-Lagrange approach. As in unsteady marine flows over sedimentary beds, the experimental data, referenced in this work for validation, shows quasi-steady state ripples in the sand bed under oscillatory flow.
    [Show full text]
  • Field Investigation on Hydroabrasion in High-Speed Sediment-Laden Flows at Sediment Bypass Tunnels
    water Article Field Investigation on Hydroabrasion in High-Speed Sediment-Laden Flows at Sediment Bypass Tunnels Michelle Müller-Hagmann 1,* , Ismail Albayrak 1 , Christian Auel 2 and Robert M. Boes 1 1 Laboratory of Hydraulics, Hydrology and Glaciology, ETH Zurich, 8093 Zurich, Switzerland; [email protected] (I.A.); [email protected] (R.M.B.) 2 ILF Consulting Engineers, 6063 Rum/Innsbruck, Austria; [email protected] * Correspondence: [email protected] Received: 13 January 2020; Accepted: 1 February 2020; Published: 10 February 2020 Abstract: Wear due to sediment particles in fluid flows, also termed ‘hydroabrasion’ or simply ‘abrasion’, is an omnipresent issue at hydraulic structures as well as in bedrock rivers. However, interactions between flow field, particle motion, channel topography, material properties and abrasion have rarely been investigated on a prototype scale, leaving many open questions as to their quantitative interrelations. Therefore, we investigated hydroabrasion in a multi-year field study at two Swiss Sediment Bypass Tunnels (SBTs). Abrasion depths of various invert materials, hydraulics and sediment transport conditions were determined and used to compute the abrasion coefficients kv of different abrasion models for high-strength concrete and granite. The results reveal that these models are useful to estimate spatially averaged abrasion rates. The kv-value is about one order of magnitude higher for granite than for high-strength concrete, hence, using material-specific abrasion coefficients enhances the prediction accuracy. Three-dimensional flow structures, i.e., secondary currents occurring both, in the straight and curved sections of the tunnels cause incision channels, while also longitudinally undulating abrasion patterns were observed.
    [Show full text]
  • Proquest Dissertations
    Essays on nonlinear waves: Patterns under water; pulse propagation through random media Item Type text; Dissertation-Reproduction (electronic) Authors Komarova, Natalia, 1971- Publisher The University of Arizona. Rights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 30/09/2021 16:49:01 Link to Item http://hdl.handle.net/10150/282787 INFORMATION TO USERS This manuscript has been reproduced from the microfikn master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter fece, while others may be from any type of computer printer. The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely a£fect reproduction. In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand comer and continuing from left to right in equal sections with small overlaps. Each original is also photographed in one exposure and is included in reduced form at the back of the book. Photographs included in the original manuscript have been reproduced xerographically in this copy.
    [Show full text]
  • An Index Concentration Method for Suspended Load Monitoring in Large Rivers of the Amazonian Foreland
    Earth Surf. Dynam., 7, 515–536, 2019 https://doi.org/10.5194/esurf-7-515-2019 © Author(s) 2019. This work is distributed under the Creative Commons Attribution 4.0 License. An index concentration method for suspended load monitoring in large rivers of the Amazonian foreland William Santini1,2, Benoît Camenen3, Jérôme Le Coz3, Philippe Vauchel1,2, Jean-Loup Guyot1,2, Waldo Lavado4, Jorge Carranza4, Marco A. Paredes5, Jhonatan J. Pérez Arévalo5, Nore Arévalo6, Raul Espinoza Villar6,7, Frédéric Julien8, and Jean-Michel Martinez1,2 1IRD, Toulouse, 31400, France 2Laboratoire GET, CNRS, IRD, UPS, OMP, Toulouse, 31400, France 3Irstea, UR RiverLy, Lyon-Villeurbanne, 69625 Villeurbanne, France 4SENAMHI, Lima, Lima 11, Peru 5SENAMHI, Iquitos, Peru 6Facultad de Ingeniería Agrícola, UNALM, La Molina, Lima 12, Peru 7IGP, Ate, Lima 15012, Peru 8Laboratoire ECOLAB, CNRS, INPT, UPS, Toulouse, 31400, France Correspondence: William Santini ([email protected]) Received: 15 December 2018 – Discussion started: 21 January 2019 Revised: 30 March 2019 – Accepted: 21 May 2019 – Published: 4 June 2019 Abstract. Because increasing climatic variability and anthropic pressures have affected the sediment dynam- ics of large tropical rivers, long-term sediment concentration series have become crucial for understanding the related socioeconomic and environmental impacts. For operational and cost rationalization purposes, index con- centrations are often sampled in the flow and used as a surrogate of the cross-sectional average concentration. However, in large rivers where suspended sands are responsible for vertical concentration gradients, this index method can induce large uncertainties in the matter fluxes. Assuming that physical laws describing the suspension of grains in turbulent flow are valid for large rivers, a simple formulation is derived to model the ratio (α) between the depth-averaged and index concentrations.
    [Show full text]
  • SERDP Project MR-2410
    FINAL REPORT Large-Scale Laboratory Experiments of Incipient Motion, Transport, and Fate of Underwater Munitions under Waves, Currents, and Combined-Flows SERDP Project MR-2410 APRIL 2018 Marcelo H. Garcia, PhD Blake J. Landry, PhD University of Illinois at Urbana-Champaign Distribution Statement A Page Intentionally Left Blank This report was prepared under contract to the Department of Defense Strategic Environmental Research and Development Program (SERDP). The publication of this report does not indicate endorsement by the Department of Defense, nor should the contents be construed as reflecting the official policy or position of the Department of Defense. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the Department of Defense. Page Intentionally Left Blank 117 Page Intentionally Left Blank SERDP FINAL REPORT – PROJECT NUMBER: MR-2410 Table of Contents Table of Contents ............................................................................................................................ ii List of Tables ................................................................................................................................. iii List of Figures ................................................................................................................................ iv List of Acronyms .........................................................................................................................
    [Show full text]
  • This Is a Text Test of the Font
    INDEX active layer 238, 493 cross stratification 498 aerodynamic threshold 332 debris flow 490 aggradation 491 degradation 491, 496 Airy waves 203 deposition ratio 491 amalgamation 498 depth-limited sea 189 angle of climb 505 differential transport 486 angular velocity 205 diffusion 15 antidunes 357 dimensional analysis 31 armor 459 displacement height 385 backwater curve 182 drag 264 barchans 433 drag coefficient 25 bed 497 drag crisis 74 bed configuration 350 drag partition 249 bedding 497 dunes 356, 432 bed-form transport rate 398 dynamic pressure 4 bed forms 350 dynamically rough flow 109 bed load 285, 286, 294 dynamically smooth flow 108 bed phase 350 eddies 53 bed state 350 eddy diffusion coefficient 116 bed-material load 286 eddy viscosity 116 Bernoulli equation 43, 48 Ekman layer 227, 228 boundary layer 53 Ekman spiral 218 boundary Reynolds number 109 elevation head 165 boundary shear stress 104 energy cascade 120 brink 355 energy grade line 166 buffer layer 102 energy gradient 166, 179 buoyancy 8 energy slope 166, 179 burst 150 equal mobility 460 burst–sweep cycle 150 equation of motion 34 Chézy coefficient 115 equivalent sand roughness 114, 136 Chézy equation 115 fall velocity 75 climbing-ripple cross stratification 507 fetch 189 coherent structures 149 flow intensity 285 combined flow 194 flow regimes 71, 379 competence 260 flow resistance 117 conservation of sediment volume 486 flow separation 65, 381 continua 2 fluid threshold 332 core region 102 flumes 254 Coriolis acceleration 204 form drag 19, 249 Coriolis effect 204 fractional transport rate 459 Coriolis force 204 fractionation 494 Coriolis parameter 211 free body 7 creeping flow 37 free stream 53 critical flow 169 free surface 84, 157 critical shear stress 260 friction factor 112 cross bedding 497 friction velocity 109 cross lamination 497 Froude number 30.
    [Show full text]
  • CFD–DEM Simulations of Current-Induced Dune Formation and Morphological Evolution
    CFD{DEM Simulations of Current-Induced Dune Formation and Morphological Evolution Rui Sun, Heng Xiao∗ Department of Aerospace and Ocean Engineering, Virginia Tech, Blacksburg, VA 24060, United States Abstract Understanding the fundamental mechanisms of sediment transport, particularly those during the formation and evolution of bedforms, is of critical scientific importance and has engi- neering relevance. Traditional approaches of sediment transport simulations heavily rely on empirical models, which are not able to capture the physics-rich, regime-dependent behaviors of the process. With the increase of available computational resources in the past decade, CFD{DEM (computational fluid dynamics{discrete element method) has emerged as a vi- able high-fidelity method for the study of sediment transport. However, a comprehensive, quantitative study of the generation and migration of different sediment bed patterns using CFD{DEM is still lacking. In this work, current-induced sediment transport problems in a wide range of regimes are simulated, including ‘flat bed in motion', `small dune', `vortex dune' and suspended transport. Simulations are performed by using SediFoam, an open-source, massively parallel CFD{DEM solver developed by the authors. This is a general-purpose solver for particle-laden flows tailed for particle transport problems. Validation tests are per- formed to demonstrate the capability of CFD{DEM in the full range of sediment transport regimes. Comparison of simulation results with experimental and numerical benchmark data demonstrates the merits of CFD{DEM approach. In addition, the improvements of the present simulations over existing studies using CFD{DEM are presented. The present arXiv:1510.07201v3 [physics.flu-dyn] 11 Apr 2016 solver gives more accurate prediction of sediment transport rate by properly accounting for the influence of particle volume fraction on the fluid flow.
    [Show full text]
  • Chapter 7 Sediment Transport Model
    Chapter 7 Sediment transport model 7.1 Introduction This chapter describes the sediment transport model implemented in COHE- RENS. There are six sections. In the first one, a discussion is given of phys- ical parameters and processes (bed shear stress, molecular viscosity, waves) which are of importance for the sediment and the influence of sediments on the physics through density gradients. In the next section a description is given of the basic sediment parameters (Shield parameter, fall velocity, critical shear stress), related to sediment transport. This is followed by an overview of the bed and total load equations available in COHERENS. Then, the suspended sediment transport module is presented. Finally, numerical techniques, specific for the sediment module, are described. 7.2 Physical aspects 7.2.1 Bed shear stresses The bed shear stress is considered as the physical parameter which has the largest impact on sediment transport, since it controls how much of the se- diment in the bed layer becomes suspended in the water column. In the physical part of COHERENS, bottom stresses are calculated using either a linear or a quadratic friction law (see Section 4.9). In the sediment transport module, however, a quadratic friction law is always taken, as given by equa- tion (4.340) in 3-D or (4.341) in 2-D mode. The magnitude of the bottom stress can then be written as 2 2 2 2 τb = ρu∗b = ρCdbub or τb = ρu∗b = ρCdbj¯uj (7.1) 311 312 CHAPTER 7. SEDIMENT TRANSPORT MODEL for the 3-D, respectively 2-D case.
    [Show full text]
  • Entrainment of Sediment Particles from a Flat Mobile Bed with the Influence of Near-Wall Turbulence
    School of Civil Engineering The University of New South Wales a ? Sydney, Australia Entrainment of Sediment Particles from a Flat Mobile Bed with the Influence of Near-wall Turbulence by Alireza Keshavarzy B.Eng., Shiraz University, Shiraz, Iran M.Eng. Sc., The University of New South Wales, Sydney A thesis submitted in partial fulfilment of the requirement for the degree of Doctor of Philosophy 1997 L S W 18 APS 1303 Li UR ARY CERTIFICATE OF ORIGINALITY I hereby declare that this submission is my own work and that, to the best of my knowledge and belief, it contains no material previously published or written by another person nor material which to a substantial extent has been accepted for the award of any other degree or diploma of a university or other institute of higher learning, except where due acknowledgment is made in the text. (Signed) CERTIFICATE OF ORIGINALITY 3 hereby declare that this submission is my own work and to the best of my knowledge it contains no materials previously published or written by another person, nor material which to a substantial extent has been accepted for the award of any other degree or diploma at UNSW or any other educational institution, except where due acknowledgement is made in the thesis. Any contribution made to die research by others, with whom I have worked at UNSW or elsewhere, is explicitly acknowledged in the thesis. I also declare that the intellectual content of this thesis is the product of my own work, except to the extent that assistance from others in the project’s design and conception or in style, presentation and linguistic expression is acknowledged.
    [Show full text]
  • Introduction to Numerical and Physical Modelling Helmut Habersack
    Introduction to Numerical and Physical Modelling Helmut Habersack Michael Tritthart, Christine Sindelar, Christoph Hauer, Marcel Liedermann BOKU University of Natural Resources and Life Sciences Vienna Helmut Habersack Outline 1. Introduction 2. Problems and boundary conditions 3. Physical Modelling 4. Numerical Modelling 5. Examples 6. Summary and outlook Helmut Habersack Sediment needs management Due to: Too much sediment Too little sediment Sediment as resource Obstruction of channels Beaches erode Construction material Storages Riverbanks erode Sand for beaches Rivers fill and flood Wetlands are lost Wetland nourishment Reefs get smothered River profile degradation Soil enrichment Turbidity Habitat and food for life Sediment = “no waste” = essential & integral element of river-sea systems Source scheme: Martin (2002) Helmut Habersack S u r p l u s D e f i c i t Helmut Habersack Purpose and types of physical models Purpose Determination of hydraulic impacts on hydraulic structures before they are built (hydro-engineering facilities are very expensive and require a lot of planning in most cases) under controlled conditions (the experiment can be repeated as often as necessary): ▪ Occurence of flow is very complex / not entirely covered by theoretical considerations ▪ Verification or proof of theoretical approach to the calculation Evaluation of complex 3D flow processes by: ▪ Physical models: ▪ Numerical models ▪ Reproduction of nature at a reasonable scale ▪ Hybrid models ▪ Analogy models Helmut Habersack 5 Purpose and types of models
    [Show full text]