University of New Hampshire University of New Hampshire Scholars' Repository Doctoral Dissertations Student Scholarship Spring 2018 Bedform Geometry and Bedload Sediment Flux in Coastal Wave, Current, and Combined Wave- Current Flows Meagan Wengrove University of New Hampshire, Durham Follow this and additional works at: https://scholars.unh.edu/dissertation Recommended Citation Wengrove, Meagan, "Bedform Geometry and Bedload Sediment Flux in Coastal Wave, Current, and Combined Wave-Current Flows" (2018). Doctoral Dissertations. 2405. https://scholars.unh.edu/dissertation/2405 This Dissertation is brought to you for free and open access by the Student Scholarship at University of New Hampshire Scholars' Repository. It has been accepted for inclusion in Doctoral Dissertations by an authorized administrator of University of New Hampshire Scholars' Repository. For more information, please contact [email protected]. BEDFORM GEOMETRY AND BEDLOAD SEDIMENT FLUX IN COASTAL WAVE, CURRENT, AND COMBINED WAVE-CURRENT FLOWS BY MEAGAN E. WENGROVE M.S. Civil Engineering, University of New Hampshire, 2012 B.S. Civil Engineering and International Affairs, University of New Hampshire, 2010 DISSERTATION Submitted to the University of New Hampshire in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Ocean Engineering May 2018 ALL RIGHTS RESERVED ©2018 Meagan E. Wengrove This dissertation has been examined and approved in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Ocean Engineering by: Dissertation Director, Diane L. Foster, Director of the Ocean Engineering Program and Professor of Mechanical Engineering Thomas C. Lippmann, Associate Professor of Oceanography Matthieu A. de Schipper, Assistant Professor of Coastal Engineering Christopher M. White, Associate Professor of Mechanical Engineering Anthony Lyons, Research Professor on 13 April 2018. Original approval signatures are on file with the University of New Hampshire Graduate School. iii To the ocean-human connection... may enhanced physical understanding of coastal dynamics aid in a resilient relationship between people and the shorelines we occupy. iv ACKNOWLEDGMENTS First off, I would like to acknowledge my advisor, Diane Foster, for her continuous support in my academic and personal endeavors. From the highs of receiving fellowships and job offers to the lows of being offered a clean sock from your floor... Diane, your mentoring in science and interpersonal connections has truly helped me to grow over the past eight years since we met. I look forward to passing along lessons and larks I have learned from you to my own students. I would like to truly thank my insightful committee members Tom Lippmann, Matthieu de Schipper, Chris White, and Tony Lyons, for their guidance and intellectual input over the duration of my Ph.D. From deploying a bunch of instruments in the field and interpreting their data to discussing the interplay between small-scale and large-scale morphology and the momentum and transport gradients that play a role in shaping them, you each have significantly shaped the direction of my work. I would like to acknowledge other intellectual input and field help from faculty, re- searchers, and graduate students over the last four and a half years. Jim Irish, Joe Calantoni, Rob Holman, Marcel Stive, Tom Weber, Sylvia Rodriguez-Abudo, Donya Frank, Reza Ebadi, Dan Hagan, Ad Reniers, Drummond Biles, Emily Carlson, Alex Padilla, Joe Klewicki, John Hughs-Clark, Larry Mayer, Brian Calder, Dirk-Jan Walstra, Larry Ward, Mike Allard, Max Radermacher, Martijn Henriquez, Jon Hunt, Nick Cohn, Bonnie Ludka, Bas Hoonhout, Steph Gilooly, Brandon Montemuro, Marion Tessier, Simion Moons, Kara Koetje, Salme Cook, Josh Humberston, John Turner, Kate von Krusenstiern, Sarah Blagdon, Sierd de Vries, and other past and present UNH OE, ME, and CCOM graduate students and faculty as well as TUDelft Hydraulic Engineering graduate students and faculty. My Ph.D. could not have been completed without funding from the Department of De- fense National Defense Science and Engineering Graduate Fellowship Program for three years of personal support, and The PADI Foundation grant that funded much of the field v experiment data collection in the Netherlands. Additionally, UNH Mechanical and Ocean Engineering and TUDelft Hydraulic Engineering have financially supported me at times while working toward my Ph.D. I would also like to acknowledge the UNH Marine School and the UNH Graduate School for financially supporting much of my travel to present my work at national and international conferences. Finally, I am very grateful to my friends and family for their emotional support, ability to have fun, and laugh over the last four and a half years. Thank you to my mom, dad, and sister, Kim, Jim, and Ashley Wengrove, my adventure and life partner, Drummond Biles, and my close friends from childhood through graduate school from around the country and the world. My sanity at times depended on you, thank you. vi TABLE OF CONTENTS Page ACKNOWLEDGEMENTS ..................................................v LIST OF TABLES .......................................................... xi LIST OF FIGURES........................................................ xii ABSTRACT ............................................................. xxiv CHAPTER 1. INTRODUCTION ........................................................ 1 1.1 Motivation and Background..............................................1 1.2 Dissertation Propositions................................................3 1.3 Dissertation Organization................................................4 2. SAND RIPPLES: SMALL-SCALE FEATURES FEEDING LARGE-SCALE MORPHOLOGY .....................................7 2.1 Abstract..............................................................7 2.2 Introduction...........................................................7 2.3 The Spectrum of Morphologic Scales......................................9 2.4 How much sand do bedforms move?...................................... 11 2.5 The Net Flux......................................................... 13 2.6 Conclusion........................................................... 19 3. OBSERVATIONS OF TIME DEPENDENT BEDFORM TRANSFORMATION IN COMBINED WAVE-CURRENT FLOWS ............................................................. 21 3.1 Abstract............................................................. 21 3.2 Introduction.......................................................... 22 3.3 Methods............................................................. 23 3.3.1 Experiment and Instrumentation.................................. 23 3.3.2 Hydrodynamics................................................. 26 vii 3.3.3 Measured Bedform Statistics...................................... 27 3.3.4 Sediment Continuity Equation.................................... 29 3.3.5 Existing Time-Dependent Bedform Geometry Models................ 31 3.4 Results............................................................... 33 3.4.1 Observations of Bedform Geometry................................ 33 3.4.2 Bedform Characterization........................................ 34 3.4.3 Observations of Bedform Orientation............................... 39 3.5 Discussion............................................................ 44 3.5.1 Time-evolving Bedform Geometry and the Sediment Continuity Equation.................................................... 44 3.5.2 Existing Time-Dependent Bedform Geometry Model Comparisons..... 48 3.6 Conclusions........................................................... 52 4. OBSERVATIONS OF BEDFORM MIGRATION AND BEDLOAD SEDIMENT TRANSPORT IN COMBINED WAVE-CURRENT FLOWS ............................................................. 55 4.1 Abstract............................................................. 55 4.2 Introduction.......................................................... 55 4.3 Methods............................................................. 58 4.3.1 Experiment and Instrumentation.................................. 58 4.3.2 Wave Dominant, Current Dominant, and Combined Flows............ 58 4.3.3 Bedform Migration and Sediment Flux............................. 59 4.3.4 Prediction of Bedload Transport Magnitude......................... 60 4.3.5 Prediction of Bedload Transport Direction.......................... 63 4.4 Results............................................................... 64 4.4.1 Flow Forcing Bedform Shape and Migration........................ 64 4.4.2 Observations of Bedform Migration Direction....................... 66 4.5 Discussion............................................................ 73 4.5.1 Statistics of Bedform Migration and Implications for Transport........ 73 4.5.2 Bedform Sediment Flux Compared with Existing Bedload Transport Models..................................................... 75 4.5.3 Bedform Migration Direction Compared with MGBNT............... 80 4.6 Conclusions........................................................... 85 viii 5. ESTIMATING BED STRESS IN UNIDIRECTIONAL- AND OSCILLATORY- SEPARATED FLOWS OVER FIXED AND MOBILE BOUNDARIES ............................................ 88 5.1 Abstract............................................................. 88 5.2 Introduction.......................................................... 89 5.3 Methods............................................................. 91 5.3.1 The Momentum Integral Method.................................. 91 5.3.1.1