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A Continental Shelf Bottom Boundary Layer Model

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A Continental Shelf Bottom Boundary Layer Model A CONTINENTAL SHELF BOTTOM BOUNDARY LAYER MODEL: DEVELOPMENT, CALIBRATION AND APPLICATIONS TO SEDIMENT TRANSPORT IN THE MIDDLE ATLANTIC BIGHT by RICHARD BRENT STYLES A Dissertation submitted to the Graduate School-New Brunswick Rutgers, The State University of New Jersey in partial fulfillment of the requirements for the degree of Doctor of Philosophy Graduate Program in Oceanography written under the direction of Scott M. Glenn and approved by New Brunswick, New Jersey May 1998 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. OMI Number: 9900705 UMI Microform 9900705 Copyright 1998, by UMI Company. Ail rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. UMI 300 North Zeeb Road Ann Arbor, MI 48103 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT OF THE DISSERTATION A Continental Shelf Bottom Boundary Layer Model: Development, Calibration and Applications to Sediment Transport in the Middle Atlantic Bight by RICHARD BRENT STYLES Dissertation Director: Scott M. Glenn A continental shelf bottom boundary layer model is presented for use over a non- cohesive movable sediment bed. Model features include a continuous eddy viscosity, a correction for suspended sediment-induced stratification and improved bottom roughness and reference concentration models. Predicted concentration and current profiles are sensitive to changes in selected internal model parameters and grain size. High-resolution current and concentration profile data collected simultaneously over a 6-week summer deployment in 1995 off the southern coast of New Jersey are used to calibrated sensitive model coefficients and to determine the accuracy of the model at predicting the shear velocity and hydrodynamic roughness. Calibration of the internal parameters a, which regulates the cutoff point of the eddy viscosity near the bed, and y, which regulates the vertical decay of the suspended sediment concentration, are shown to be consistent with past estimates obtained in the field. Estimates of ripple height, r|, and ripple length, X are also shown to give good agreement with available field data. ii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Bottom roughness is shown to be a function of not only ripple height, but also of the angle between the wave and combined wave and current shear stress components. Nearly two-years of current and wave data collected on the inner shelf offshore of New Jersey are used to run the model to investigate long-term sediment transport. Model results indicate that all transport events are related to waves and that the seasonal distribution includes a number of summer storms that are comparable in sediment transport potential to other systems in the spring and fall. Modes of longshore transport follow established patterns for a wide, gently sloping continental shelf with the transport directed primarily alongshore. Cross-shore patterns exhibit an onshore bias which may be caused by multi-scale topographic features that may introduce 3-dimensional flow effects. iii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGMENTS I would first like to thank the Office of Naval Research/Augmentation Awards for Science and Engineering Research Training (ONR/AASERT) and the National Oceanographic and Atmospheric Administration National Undersea Research Program (NOAA/NURP) for providing funding to support this research. I also wish to thank Drs. Dale Haidvogel, James Lynch and Andreas Miinchow for serving on my thesis committee and reviewing my dissertation in a professional and objective manner. I would like to thank Mr. Peter Traykovski of the Woods Hole Oceanographic Institution for graciously providing the suspended sediment concentration and the ripple geometry data. These datasets contributed significantly to the quality of the work presented in these pages. I would like to thank my family for their support of my career choice and for patiently waiting for my commencement to finally arrive. I want to thank the staff and research faculty of the Institute of Marine and Coastal Sciences, Rutgers University for providing an atmosphere teeming with a collaborative spirit and enthusiasm for the ocean sciences. The inaugural days of the marine science program at Rutgers are sure to be regarded as a mile stone in the shifting focus to coastal oceanography that has recently swept through the U.S. oceanographic community. I want to pay special tribute to my advisor and friend Dr. Scott Glenn. Scott has served as a source of inspiration since the conception of this dissertation. He has demonstrated impeccable leadership and has given me a strong foundation on which to Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. build my own independent research program. My career as an oceanographer will always reflect what I have learned as a student from Scott. I would finally like to thank my wife Renee for her support, patience and comfort during this trying odyssey known as graduate school. v Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS ABSTRACT OF THE DISSERTATION.............................................................................. ii ACKNOW LEDGM ENTS..........................................................................................................iv LIST OF TABLES ...................................................................................................................... xi LIST OF ILLUSTRATIONS............................................................................................... xii 1.0 INTRODUCTION ......................................................................................................... 1 1.1 Objective of present study ............................................................................. 6 2.0 BA CK G RO U N D ........................................................................................................... 8 2.1 Historical development of bottom boundary layer models ....................... 8 2.2 Observational studies of boundary layer processes ................................... 9 2.3 Related calibration studies of key model parameters ............................ 12 2.4 Justification and need .................................................................................. 14 3.0 THEORETICAL MODEL DEVELOPMENT ..................................................... 16 3.1 Governing equations .................................................................................... 16 3.1.1 Eddy viscosity ................................................................................ 28 vi Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3.1.2 Stability parameter ........................................................................ 31 3.2 Solution for the wave ................................................................................. 34 3.3 Wave friction factor and the determination of the bottom stress . 43 3.4 Solution for the mean current and suspended sediment concentration ......................................................................................................................... 58 3.5 Determination of the stability parameter .................................................. 62 3.5.1 Stability parameter convergence tests ...................................... 73 3.6 Solution procedure for the mean current and concentration ................. 81 3.7 Theoretical model comparisons ................................................................. 84 3.8 Influence of multiple sediment grain size classes ................................ 91 3.8.1 Effect of reducing particle s i z e ................................................... 91 3.8.2 Effect of increasing the number of grain size classes 95 3.9 Sensitivity of the solution to P and y .................................................... 98 3.9.1 Sensitivity to P with y held fix e d .............................................. 99 3.9.2 Sensitivity to y with P held fixed ........................................... 102 3.9.3 Effect of varying y and grain size ........................................... 104 3.10 S u m m ary..................................................................................................... 107 4.0 MODEL AND DATA COMPARISONS ......................................................... 110 4.1 Study site and instrumentation ............................................................... 110 4.1.1 BASS current meter array ........................................................ I l l 4.1.2 ABS sediment concentration profiler ...................................... 113 4.1.3 SSS acoustic imaging system ................................................... 114 vii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4.2 Bed reference concentration .................................................................. 114 4.3 Determination of model input parameters ............................................. 118 4.4 Field estimates of y0, y and a .................................................................. 120 4.4.1 Reference concentration m o d e l ................................................
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