Aspects of Beach Sand Movement, at Gibraltar Point, Lincolnshire. By
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Aspects of beach sand movement, at Gibraltar Point, Lincolnshire. by Howard Re Fox, B, A, (Hons. ) Ce,..o Thesis submitted to the Department of Geography, University of Nottinghamq for the degree of Doctor of Philosophy. October 1978- 'If CONTENTS Page Abstract Acknowledgements List of Plates v List of Pigares vi List of Tables xiii Chapter 1: Introduction and background 1: 1 Introduction 1 6 1: 2 General physical background 1: 3 Waves and wind 10 1: 4 The offshore zone 18 1: 5 The beach 20 Part 1 Chapter 2: Data collection 2: 1 Introduction 43 2: 2 Tracer production 44 2: 3 Preliminary experimental procedure 51 2: 4 Measurement of process variables 56 2: 5 Sampling techniques 60 2: 6 Problems and efficiency of field procedure 68 Chapter 3: Data analysis and presentation 3: 1 Introduction 76 3: 2 Tracer grain counts 77 3: 3 Data presentation 84 3: 4 Numerical description of sand movement 89 3: 5 Data rejection 96 Page Chapter 8t Evaluation of the model 8: 1 Introduction 287 8: 2 The predictive model 287 6: 3 Summary of findings 297 8: 4 Conclusion 300 Appendix 1: Instrumentation 305 Appendix 2: Maps and diagrams not referred to in the text 320 Bibliography 345 ABSTRACT. In this study fluorescent sand tracer techniques were used to investigate sediment movement on the foreshore at two sites on the south Lincolnshire coast. Working over one tidal cycle, low water to low waterl tracer release at different points across the beach revealed a complexity of sand movement in this strongly tidal environ- ment. It was found that sand moved both at different rates and in contrasting dominant directions on different parts of the beach over the same tidal cycle. At Gibraltar Point there was confirmation from the tracer experiments of the importance of tidal generated currents on sand movements on the lower foreshore. Tests conducted to study the patterns and rates of movement of different grain sizes produced inconclusive results largely due to low recovery rates for the tracer. However, from the evidence avail- able, it appeared that sorting of sediment was taking place only in the sense that finer material was moved away from the release point at a faster rate than coarse material and not because different sized grains were moved in different directions. In a consideration of models for the prediction of longshore sand transport two of the most commonly used models were tested using data collected during the tracer experiments. The results confirmed the success of the two models, one based on the wave power equation and the other on an energetics approach, and coefficients produced were in (1969) close agreement with those obtained by Komar in a previous study. Finally, field measurements of a series of variables such as wave heighto wave longshore period and current velocity were combined with measures of sand direction movement and in a linear multiple regression analysis to study the associations present and to produce a simple I predictive model of sand movement. Using both stepwise and combina- torial methods of regression it was found that 801/6 of the variation of amount of longshore sand movement could be accounted for by the 'best' equation. Wave height alone explained 61-3Vo of the variation but beach slope, water temperature and longshore current velocity were also of importance. 595o' of the variation of average distance moved by sand grains normal to the shore was explained by beach slope, whilst wave period was seen to be the major factor in determining the direction of sand movement onshore or offshore. A set of equations was produced which together with longshore current flow direction, could be used to predict the average position of tracer on the beach face after one tidal cycle. At the same time individual equations could be used to model specific aspects of sand movement. / - iii - A CKNOVILEDGFTI UM Sincere thanks are due to the many people, colleagaes and friends9 who have assisted me throughout this project, Members of the staff in the Geography Department have helped in a variety of ways, Professor C. A, M. King read and commented upon the typescript of this thesis and as my joint supervisor provided valuable advice at different times during the study. Dr. R. E. 'Dugdale and Dr. M. J. McCullagh provided expertise in the field of instrumentation and tracer techniques in addition to maintaining a nautical presence at Gibraltar Point# Professor J. P. Cole encouraged and cajoled on many occasions and also subjected himself to the rigours of fieldwork. However, any merit contained in this piece of work is due almost entirely to the friendly advice and encouragement of my supervisor, Dr. P, M. Mather, Frequent discussion produced much needed boosts to flagging morale as well as a wealth of suggestions and ideas on all aspects of the work. Furthermore, Dr. Mather provided many of the computer programs used in the study and gave a great deal of construc- tive criticism of the thesis itself. In a physical geography project such as this a large amount of effort is expended in the field and this study would not have been possible without help with fieldwork, In this respect I gratefully acknowledge the invaluable help of my fellow researchers at Gibraltar Point, Mr, Richard Russell and Mrs. Elizabeth Fraser, who endured the horrors of night sampling and winter sea bathing with great good humour, Without their contribution to the corporate spirit little would have been achieved, Many others have willingly given of their time in helping with fieldwork and to them all I extend my deepest gratitude. Mro George Evans and more recently Mr. Peter Bain gave every assistance as wardens of the Lincolnshire Trust and Nature Conservancy Field - iv - Station at Gibraltar Pointv which on more than one occasion was a welcome haven during bad weather. I must also thank Dr. F. Palmer of the Chemistry Department and Dr. C. J, Paull of the Electrical Engineering Department who gave information and help with fluorescent tracers and electronic circuitrye Mrs. Morley and the staff of the Science Library were friendly and efficient in obtaining the more exotic literature and the technical staff of the Geography Department provided help at every stage of the study, In particular Mrs. E. Pyper gave much assistance with laboratory analysis. Mrs. E. O. Wigginton deserves much credit and grateful thanks for the deciphering of my handwriting and the able typing of this thesis. Finally, I must thank my wife, Kathryn, who has patiently endured the completion of this study over the past three years and has never ceased to be a source of encouragement and support. S- -'1- I LIST OF PLATES. Plate No, Page 17 1.1 Skegness is bracing a.. *oe see *so *oo ooe ooe 24 1.2 Aerial view of H2 profileg Gibraltar Point May 1978 1.3 View down the line of H2 profile from backshore 25 March 1978 *. 0 000 see see 000 000 000 aloe 1-4 View up the line of H2 profile from lower ridge 25 March 1978 see *00 Goo *so 000 see oee *00 26 1.5 Aerial view of El profile Skegness May 1978 000 000 1.6 View down the line of El profile from backshore 27 March 1978 00000 40 0000000000 00 0410 0 .0 1.7 View up the line of El profile from lower beach 27 March 1978 0000 400 *so a00 see 000 000 *00 tracer into beach face 2ol Emplacement of 00* see *00 57 2.2 Portable ultra-violet lamp 000 000 000 000 000 61 3.1 Spray glue and black sugar paper used in counting for procedure each sample 0*0 4100 000 000 4000 81 the thin 3,2 Spraying paper with coat of glue 0410 06* 81 3.3 Sample tipped onto sprayed surface ... ... 4000 0*0 82 3-4 Sand residue removed ... ... 000 000 0*0 0040 *00 82 thin from 83 3.5 Paper square with coating of sand sample 0400 3.6 Fluorescent grains counted using cotton grid and hand held fluorescent Honovia lamp 00* 0*0 00* 83 A1.1 Detail of completed wave pole (foreground). Pole fixed to beach surface with concrete base and guy (background) 306 ropes ... ... ... ... ... ... *so A1.2 Strainguage 311 current meter *a* @so #*@ @00 so* -, r-- ý-ýý- V1 - LIST Olt' FIGURES. Figure Page No. 2 1.1 Study area and location of profiles ... 1.2 beach Dynamic zones 000 4000a 00 00a000 000 0of 5 .a0.006*0 41 &&0 000 5 1.3 Beach terminology a&0 00 8 1.4 Geological section of coastal margin ... ooo as* oeo lo5 Percentage exceedance graph for wave height and wave direction rose taken from Inner Dowsing records 1974. 11 1.6 Percentage exceedance graph for wave height and wave direction rose taken from Inner Dowsing records 1975. 11 1.7 Percentage exceedance graph for wave height and wave direction rose taken from Inner Dowsing records 1976, 12 1.8 Wave fetch diagram for Gibraltar Point 14 000 .100 000 log Surface wind roses 1975 and 1976 for Gibraltar Point,,, 16 1.10 Comparison of offshore profiles for Skegness and Gibraltar Point 21 000 SO& 000 660 0400 Soo . 0.8 1.11 H2 6.10.75 18.3o76 profile surveyed and 000 see 000 29 lol2 H2 17.5.76 10.8-76 profile surveyed and ... ... ... 30 1.13 H2 22.9.76 23-10o76 profile surveyed and 0.0 00. .. o 31 lol4 El 18.5-76 25o8o76 profile surveyed and 006 0040 000 32 lol5 El 21.9-76 22.10o76 profile surveyed and .