Rhythmic Patterns of Beach Topography. Johannes Laurens Van Beek Louisiana State University and Agricultural & Mechanical College
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Louisiana State University LSU Digital Commons LSU Historical Dissertations and Theses Graduate School 1973 Rhythmic Patterns of Beach Topography. Johannes Laurens Van beek Louisiana State University and Agricultural & Mechanical College Follow this and additional works at: https://digitalcommons.lsu.edu/gradschool_disstheses Recommended Citation Van beek, Johannes Laurens, "Rhythmic Patterns of Beach Topography." (1973). LSU Historical Dissertations and Theses. 2508. https://digitalcommons.lsu.edu/gradschool_disstheses/2508 This Dissertation is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion in LSU Historical Dissertations and Theses by an authorized administrator of LSU Digital Commons. For more information, please contact [email protected]. INFORMATION TO USERS This material was produced from a microfilm copy of the original document. 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Michigan 48106 74-7270 VAN BEEK, Johannes Laurens, 1940- RHYTHMIC PATTERNS OF BEACH TOPOGRAPHY. The Louisiana State University and Agricultural and Mechanical College, Ph.D., 1973 Geology University Microfilms, A XEROX Company , Ann Arbor, Michigan RHYTHMIC PATTERNS OF BEACH TOPOGRAPHY A Dissertation Submitted to the Graduate Faculty of the Louisiana State University and Agricultural and Mechanical College in partial fulfillment of the requirements for the degree of Doctor of Philosophy in The Department of Geography by Johannes Laurens van Beek Drs. Rijks Universiteit at Utrecht, 1966 August, 1973 ACKNOWLEDGMENT The present study was conducted under the super vision of Professor W. G. Mclntire. His encouragement and advice have been invaluable contributions that are greatly appreciated. Discussions with Professor C. J. Honu, who first introduced me to the problems of rnytnmic beach topography, and encouragement from Professor 0. V.. Galliano have aided substantially in data analysis anu preparation of this report. The field propram could not have been accomplished without the resourceful assistance given by R. D. Adams under often trying conditions. The contribution of field time by Dr. N. Meland is also gratefully acknowledged. The study was supported by the Office of Naval Research, Geography Programs, under Contract Nonr lbYb(03), Project HR 388 002, with the Coastal Studies Institute, .jouisiana State University. ii TABLE OF CONTENTS LIST OF FIGUKES...............................................iv ABSTRACT......................................................vl INTRODUCTION ..................... -L MOHPHOLOGIC AND DYNAMIC ASPECTS OF RHYTHMIC BEACH TOPOGRAPHY............................ ACQUISITION AND REDUCTION OF FIELD DATA................... 17 SEQUENTIAL FIELD OBSERVATIONS............................2 2 Wind, Tide, and Wave Re g i m e....................... 2 2 Beach Topography and Circulation Patterns .... 27 PERIOD I ............................................ 2d PERIOD II............................................ 40 PERIOD I I I .......................................... 50 PROCESS-FORM RELATIONSHIPS .............................. 59 Development of Rhythmic Bars.......................... 59 Beach Face Topography and C u s p s ..................... o3 Modification of Rhythmic Bars and Surf Zone Circulation............................ 72 Occurrence and Scale of Rhythmic Forms.............. 70 SUMMARY AND CONCLUSIONS..................................... 85 REFERENCES................................................... 91 lii LIST OF FIGURES Figure Papo i. Morphologic characteristics of rhythmic beach topography................................... o P. Diagrammatic representation of a standing edge wave........................................... 11 5. Location map of study s i t e .........................lb ‘i. Time histories of tidal stage and wave and wind characteristics......................... 2b 5. Dissolution of rhythmic bar topography during Period I................................ 2 9 o. Resolution of beach topography into constituent rhythmic patterns.................... 32 7. Nearshore circulation as Indicated by dye dispersion.....................................35 d. Schematic representation of beach change during Period I................................... 3d 9. Dispersion of tracer sediment, Period I......... 39 1U. Development of rhythmic bar during Period II . 9l 11. Modification of rhythmic bar during Period II. 47 12. Disruption of rhythmic bar topography during Period I I I . ................................ 91 13. Ne.irshore circulation cells as Indicated by dye dispersion.................................. 53 19. Dispersion of tracer sediment, Period III. 5o 15. Surf zone with compound rhythmic bar topography......................................... 57 ID. Relationship between cuspate patterns of the beach face and rhythmic bar.................. 65 iv !■' i gur< ■ 1’ai i V . Ywo types of beach cusps................................do is. iiuacii cusps attributed to erosion................. od Id. oencn cusps attributed to deposition............ /’ i :j . Modifications of rhythmic bar ana related circulation pattern:;.................. ai. Modified rhytnrnic bar topography................. li ?2 . Reach cusps in embayment.......................... 61 CO Relationship between order and wave length of rhythmic patterns. .........................Rf v ABSTRACT Many beaches feature a rhythmic pattern of topo graphic variation. The pattern may be apparent simulta neously in a longshore alternation of cuspate projections and arcuate embayments along the beach face, j.n a rhytnmic longsnore bar composed of an alternate series of arcs anu cusps, ana in longshore undulation of the nearshore bca. development anu modification of this type of rhythmic topography was monitored over a 3-week period along, the Sulf coast (Seagrove Beach, Florida). Theoretical considerations and laboratory experi ments have suggested that formation of rhytnmic topography is governed by drift velocities related to tne presence of standing edge waves in the nearshore zone (Bowen anu i-nman, 1971). This study provides evidence that tne con cept can be extended to the natural environment. Dimen sions of observed topography are in general agreement witn those' derived theoretically, and the relative magnituue and distribution of deposition and erosion involved in liar formation correspond to those expected on the basis of uistribution and relative magnituue of predicted drift velocities. The suggested necessity for a stationary uni ft pattern appears to be substantiated by repeated con currence of rhythmic bar formation with neap tide phases. vi j-'leld observations reveal formation and modifica tion of rhythmic bar topography according to a character istic sequence related primarily to wave height, ancle of wave incidence, tide phase, and nearshore circulation, no1lowing oar formation, during the neap tiae phase the oar cusps become subject to a general shoreward expan sion. This process is commensurate with development of a nearsnore circulation system composed of discrete cells anu produced as a result of interaction between incident waves and rhythmic bar topography (donu, 1972). hxpansion of the cusps and intensity of the circulation are mutuuiiy supportive and are both enhanced by successive decrease.of low-tide water depths following neap tide. Combined expansion of the cusps and increasing, Intensity of the circulation produce a topograpny that tends increasingly toward longshore alternation of elongate shoals and well-defined channels. Orientation and shape of the shoals are predominantly a function of wave1 incidence. Rhythmic topography appears to attenuate when