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Flow and Sediment Transport at Hydraulic Jumps

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Flow and Sediment Transport at Hydraulic Jumps FLOW AND SEDIMENT TRANSPORT AT HYDRAULIC JUMPS BY ROBERT GORDON MACDONALD A thesis submitted to the School of Environmental Sciences at the University of East Anglia for the degree of Doctor of Philosophy © This copy of the thesis has been supplied on condition that anyone who consults it is understood to recognise that its copyright rests with the author and that no quotation from the thesis, nor any information derived therefrom, may be published without the author's prior, written consent. i Acknowledgements Thank you to Jan Alexander, Mark Cooker and John Bacon for all their help supervising this research. Jan has paid particular attention to provide me academic opportunities and I am grateful for the experience I have gained under her supervision. Mark has influenced me to present difficult discussions calmly and his quiet humour is an inspiration. John remained enthusiastic even after moving into a commercial job. Various people helped the physical undertaking of the research. Trevor Panter and Gareth Flowerdew made most of the equipment mounts for the UEA research flume, and provided engineering advice for my less than usual requests. Trevor also made the conveyor that I used to put sediment into the flume. Brendan, Emily, Estelle, James, John Brindle, Judith, Rob, Sheila and Stuart helped with the experiments. James had the dubious pleasure of being my best man and John Brindle the dubious pleasure of being my passenger the first time I drove a van, and of “reading the map”. I am grateful to Jan Alexander and Sheila Davies who took some of the laboratory photographs. This thesis is almost entirely sole authored, although numerous other people have helped with this thesis. Mark Cooker and I derived the equations in Appendix 1. Discussions with Matthieu Cartigny, Hubert Chanson, Joris Eggenhuisen, Andy Russell and Jutta Winsemann have been helpful. Hubert Chanson, Lucy Clarke, Maurits van Dijk and Jutta Winsemann generously let me use their field photos. Special thanks go to Fionnuala for managing three years at an adjacent desk and silently encouraging me. Gerrado managed two and a half years before seeking a window to look out of. Other people know the help they have been. The NERC funded my studentship (NER/S/A/2006/14111). The NWO, the British Council, the NERC, the IAS, the School of Environmental Sciences and OSIL gave money for conferences and a workshop. I also appreciate the varied speculation I have received on my research. SAND THIS WAY ii Abstract Where river discharge is highly variable or channels poorly confined, hydraulic jumps are common. Hydraulic jump deposits should be far more common in the rock record than has been documented, or than is implied by classical fluvial facies models. The only sedimentary structures classically recognised as originating from hydraulic jumps are backset bedding and chute-and-pool structures, whereas flume experiments reported in this thesis demonstrate that a far greater range of structures occur. Hydraulic jumps were formed downstream of a bed-attached hemisphere, acting as a boulder on a stream bed. Flow velocities and water surface shapes were recorded. Vorticity patterns were inferred from observations and theory. Sediment transport patterns were observed in runs with selected pumping rates, each with water surface patterns involving discrete forms of hydraulic jump. Small amounts of sediment were used, and the starved bedload features that formed are compared to published bedload features with a hemisphere but no hydraulic jump. Flow and sediment transport patterns were also measured in a hydraulic jump that spanned the channel width. Sediment fell from suspension and formed downstream-thickening wedges, which I term basal wedges. Bedload features formed, with an anatomy not seen in other bedload features, and are defined as hydraulic-jump unit bars. Growth of sediment deposit volume downstream of hydraulic jumps caused the hydraulic jump to move upstream and series of hydraulic-jump unit bars formed at intervals, above and upstream of the previous unit bars. The resulting hydraulic-jump bar complexes aggraded up to 0.5 m thick. Their formation preserved sets of shallow upstream dipping laminae that passed downstream into cosets of climbing and upward-thinning avalanche foresets with topset preservation. These cosets overlay the basal wedges. The architecture of hydraulic jump deposits, where preserved, provides diagnostic criteria to condition the 3D geological modelling of some important reservoirs for groundwater and hydrocarbons. iii Contents Title and copyright i Acknowledgements ii Abstract iii Symbols xii List of Figures xiv List of Tables xix Dedication xx Chapter 1 Introduction to the thesis 1 1.1 Rationale for studying hydraulic jumps 1 1.1.1 Rationale for selecting rivers as the context for the study 4 1.2 Aims 5 1.3 Objectives 5 1.4 Theoretical description of hydraulic jumps 6 1.4.1 The Froude number 6 1.4.2 The anatomy of hydraulic jumps 10 1.4.3 Designing the position of a hydraulic jump in a channel 10 1.4.4 Turbulence properties of hydraulic jumps in rivers 12 1.4.5 Energy transformations within hydraulic jumps 14 1.5 Characteristics of supercritical flows in open channels 15 1.5.1 Most characteristics of supercritical flows are predicted by theory 15 1.5.2 Mechanism of formation of supercritical open channel flows 16 1.5.3 Spatial prevalence of supercritical flows in rivers 20 1.5.4 Time persistence of supercritical flows in rivers 20 1.5.5 The shape of supercritical flows in rivers 22 1.6 Documentation of hydraulic jumps 25 1.6.1 Position of formation of hydraulic jumps 26 1.6.2 Spatial prevalence of hydraulic jumps in rivers 26 iv 1.6.3 The shape of hydraulic jumps in rivers 29 1.6.4 Time persistence of shapes of hydraulic jumps 30 1.7 Sediment transport patterns at hydraulic jumps 31 1.8 Sedimentary structures inferred to have been formed in association with a 35 hydraulic jump 1.9 Breaking barriers in communication 35 1.9.1 Standing waves: A common misconception in terminology 35 1.9.2 Cylindrical: Another common misconception in terminology 36 1.9.3 Use of the word “bed” 36 1.9.4 Use of the word “jet” 36 1.9.5 Terms used to describe the shape of curved surfaces 36 1.10 General content of the following six chapters 37 Chapter 2 Equipment, deployment, accuracy and coordinates 38 2.1 Introduction 38 2.2 The flumes used in the experiments 38 2.2.1 The small flume used for trial experiments 38 2.2.2 The flume used for the main experiments 39 2.2.3 Coordinate systems and dimensions in the flumes 43 2.2.4 Reynolds number is constant in the test channels 43 2.3 The conveyor used to put sand into the flume 43 2.4 Acoustic equipment used to monitor velocity 44 2.4.1 Acoustic Doppler velocimeters 46 2.4.2 Ultrasonic Doppler velocity profilers 47 2.5 Non-acoustic equipment deployed in the experiments 49 2.5.1 The point gauge 49 2.5.2 The video recorders 50 2.6 The laser diffraction particle sizer 50 2.7 Designing the initial position of hydraulic jumps in the flume test channel 51 2.8 Post-processing velocity data 52 2.8.1 Defining and removing erroneous data 52 v 2.8.2 Time-averaging velocity data 53 2.8.3 Calculating turbulent kinetic energy and Reynolds shear 53 2.9 Trial experiments for sediment patterns 54 2.9.1 Objectives of making trial experiments 54 2.9.2 The setup used for the sediment trial experiments 54 2.9.3 Observations of sediment transport through a hydraulic jump 55 2.10 The style of the experiments reported in the following three chapters 55 Chapter 3 The flow field around a hemisphere where a hydraulic jump is created and 57 implications for sediment deposition 3.1 Introduction 57 3.1.1 Flow patterns around immobile boulders in subcritical flows 58 3.1.2 Sediment features around immobile boulders in subcritical flows 59 3.2 Experimental procedure 60 3.2.1 Runs to characterise flows around the hemisphere 60 3.2.2 Runs to characterise bedload transport patterns around the 62 hemisphere 3.3 General changes to flow characteristics with increasing pumping rate 63 3.4 Observations of the water surface pattern as pumping rate increased 68 3.4.1 The water surface patterns in Series H1 68 3.4.2 The water surface patterns in Series H2 70 3.4.3 The water surface patterns in Series H3 70 3.4.4 The water surface patterns in Series H4 71 3.5 Flow patterns highlighted by bubbles 74 3.6 Details of the flow in the hydraulic jumps 75 3.6.1 Run H2.2: The undular jump (Fru = 0.30) 75 3.6.2 Run H2.4: The arcuate-fronted jump (Fru = 0.44) 80 3.6.3 Run H2.6: The overturning arcs (Fru = 0.53) 81 3.7 The patterns of sediment transport 86 3.7.1 Runs MH2.2 and MH2.2a: Transport of medium sand involving an 89 undular jump vi 3.7.2 Run MH2.4: Transport of medium sand involving an arcuate- 91 fronted jump 3.7.3 Run MH2.6: Transport of medium sand involving arcs of 93 overturning water 3.7.4 Run CH2.2: Transport of coarse sand and fine gravel involving an 93 undular jump 3.8 Water surface patterns without the hemisphere or hydraulic jump 94 3.9 Sediment transport patterns without the hemisphere or hydraulic jump 94 3.10 Discussion of the patterns of the flow 96 3.10.1 Influence of the hemisphere and hydraulic jump on vorticity 96 patterns 3.10.2 Water surface patterns with and without the hemisphere 98 3.10.3 Shape and plan position of the hydraulic jumps 98 3.10.4 The change in form between undular jumps, arcuate fronted jumps 99 and arcs of overturning water 3.11 Discussion of the patterns of sediment transport 101 3.11.1 Comparisons of bedload transport
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