Beach Morphology and Sediments of the West Wellington Coast: Wanganui to Paekakariki
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Copyright is owned by the Author of the thesis. Permission is given for a copy to be downloaded by an individual for the purpose of research and private study only. The thesis may not be reproduced elsewhere without the permission of the Author. Frontispiece: Aerial view of Otaki river mouth and beach foreshore. Photo courtesy of Pr ofessor D. W. McKenzie , Victoria Univer sity, Wellington. Massey University library New Zeaiand & Pacific Colleci:1on BEACH MORPHOLOGY AND SEDIMENTS OF THE WEST WELLINGTON COAST: WANGANUI TO PAEKAKARIKI A thesis presented in partial fulfilment of the requirements for the Degree of Master of Science in Geography at Massey University by RONALD GRAEME GIBBARD 1972. ACKNOWLEDGEMENTS I wish to thank the many people who gave assistance in the course of my research and this presentation of results. In particular I wish to acknowledge: The following staff members of Massey University: Dr. J.L. McArthur, Geography Department, for his valued supervision of field and laboratory procedures, and whose suggestions and constructive criticism were greatly appreciated; Professor K.W. Thomson, Geography Department, for the provision of transport; and Dr. c. Fife, former Head of Soil Science Department, for the use of the Soil Science Laboratory facilities. The staff of the N.Z. Meteorological Service and the N.Z. Oceanographic Ins titute, Wellington, for the supplying of climatic data and bathymetric charts, respectively; and Mr. S. Ellen, Area Engineer (Paraparaumu), Hutt County Council, for providing background information and personal comments on beach conditions in the vicinity of Paraparaumu. Fellow students at Massey University, especially Nanyang Lee, A. Taylor, P. Tayler and D. Stewart, who gave assistance in the field. Professor D.W. McKenzie of the Geography Department, Victoria University, for the frontispiece photograph; Mrs M. McCamish, Massey Illustrator, who completed a number of diagrams; and Mrs R. McGee for typing the thesis copy. iii. TABLE OF CONTENTS Page ACKNOWLEDGEMENTS ii TABLE OF CONTENTS iii List of Tables vi List of Figures vii List of Plates ix 1 • INTRODUCTION 1 1.1 Introduction 2 1.2 Thesis Format 3 1.3 Previous Research 3 2. THE ENVIRONMENT 6 2.1 THE TERRESTRIAL ENVIRONMENT 7 2 . 11 Introduction 7 2 .1 2 Geologic and Geomorphic History 8 2 . 121 Development of the Wnnganui Bc:. sin 9 2 . 122 Hnwera St.:i.ge 9 2 . 123 Post-Glacial Development of the Sand Country 10 2.13 Climi:tte 12 2,131 \H ind 12 2. 132 Rainfall 13 2 .133 Temperature 13 2.14 The Drainage System 14 2 .141 Northern Rivers 14 2 .142 Southern Rivers 15 2.143 Sand Country Drainage 16 2. 15 Summary 16 2.2 THE MARINE ENVIRONMENT 18 2.21 Introduction 18 2.22 Bathymetry 18 2.23 Offshore Sediments 20 2.24 Coastal Currents 23 iv. Page 2 .25 Waves 24 2 . 251 General Setting 24 2.252 Environmental Factors 25 2 .253 Wave Climate 27 2.254 Survey Data 28 2.26 Wave Refraction 30 2 . 27 Summary 34 3. FIELD AND LABORATORY INVESTIGATION OF BEACH SEDIMENT AND BEACH MORPHOLOGY 40 3 .1 FIELD AND LABORATORY PROCEDURES 41 3 . 11 Field Procedures 41 3.12 La boratory Procedures 42 3.2 BEACH SEDIMENTS 44 3 . 21 I ntroduc tion 44 3 . 22 Mineral Composition and Source Areas 45 3 . 23 Hydr aulic Equivalence 46 3 . 24 Justifica tion of Sieve Analysis 47 3 . 25 Mean Grain Size Vuriation 48 3 . 251 Longshore Va riation 49 3 .252 Se~sonal Vari a tion 51 3 . 26 Environmental Differentiation 52 3 . 27 Summary 55 3 . 3 BEACH MORPHOLOGY 57 Introduction 57 Beach Profiles 58 3.321 Monthly and Seasonal Variation 59 3 . 322 ~ind Patterns and Vo lumetric Change 62 Foreshore Slope , Grain Size and Sorting 64 Summary 67 v . Page 4. RECENT COASTAL CHANGE 71 4 . 1 Introduction 72 4.2 Coastal Change 72 4. 3 Effects of Erosion near Raumati 74 4. 4 Erosion Factors 75 I+ . 41 Sub-Aerial Beach 75 4. 42 Offshore Conditions 76 4. 43 Energy Consider ations 77 4. 44 Sediment Supply, Deposition and 78 Depletion 4. 5 Summary Bo CONCLUSIONS 84 APPENDICES 87 BI BLIOGRAPHY 93 vi. LIST OF TABLES page Table I Tempera ture statistics of sel ected Sand Country stations . 13 II Offsh ore gradients to 50 f a thom c ontour a t four loca lities . 19 III Swe ll ~ave heights at ~aipipi Poin t, 1959. 28 IV Breaker wav e hei ghts for Surveys 1 t o 6. 29 v Co mparison of titano - magnetite and r esi dual samp le p roperties . 1+7 VI ApplicQtion o f t-test t o Gr a i n - size pcr nme ters of samp l es obtained from mi d -tide , backshore a n d dune environments . VII Aver a g e depth c hange per unit l engt h of p rof ile on the basis of station sets . 61 VIII Uind reg imes and volumetr ic chan ge , May -July , AuGu st- October incl., 1971 . IX Statistics, tests of hypotheses and estimates of s amp l e par~meters for slope and gr ain size regression nnalysis . 66 vii. LIST OF FIGURES following page Figure 1 Location of west Wellington coast study area . 2 2 Percentage fr e quency of wind speed and direction at Ohakea , 1940- 49. 12 3 Mean annual rain f a ll distribution , west We llington province. 13 4 Offshore bathymetry of eastern Cook Strait. 18 5 Sediment distribution over the continental shelf west of central Ne~ Zeala nd. 20 6 Surface coastal currents of central New Zealand. 23 7 Linenr fetch at selected sites . 8 Refraction diagram of north-westerly wave system : period ten seconds. 32 9 Refraction diagram of westerly wave system: period ten seconds. 32 10 Refr action diagram of south- westerly wave system: period ten seconds . 32 11 Refraction di agram of southerly wave system: period ten seconds . 32 12 Location of s ampling stations. 41 13 Source a reas of mineral suites supplied to the west We llington coast. 45 14 Levels of hydraulic equivalence of selected heavy minerals . 46 15 Longshore mean grain size v a riation of foreshore samples. 16 Idea lised profile types. 17 Average inter- survey change across each profile . 60 18 Net volumetric change per profile on basis of station sets . 61 viii. LIST OF FIGURES (continued) following page Figure 19 Rel utionshi p bet ween mean grain s i ze ( Mz ) a n d beach foreshore slope.. 65 20 Na ture of inter action bet ween the major elements of a 3each- e rosion model . 75 21 Refr a ction of west e rly wave t r a i n a round Ka p iti Island: period ten seconds . 77 22 Sediment source-sink a r eas f or the Waikanae-Paekakariki foreshore zone . 78 ix. LIST OF PLATES foll owing page Plate frontispiece Aerial view of Otaki river mouth and beach foreshore. 1 View of foreshore berms and beach cusp development, south of Otaki river. 59 2 View of beach conditions, Raumati South. 75 1 . INTRODUCTION 2. 1 • 1 Introduction During the past two decades the coastal districts of New Zealand have received increasing attention , in terms of recreation, settlement, pollution and the evaluation of mineral deposits. This trend is clearl y in evidence along the west ~e llington coast, especially in r e lation to the pressure of a rapidly increasing population on coastal facilities. The region considered in this thesis as the west Wellington coast is shown in Figure 1. For the southern coastal section, recently-mooted development proposals include the offshore siting of a Jumbo Jet airport and the establishment of a marina complex, with accompanying breakwater , in the vicinity of Kapiti Island. This southern section has a documented history of incipient erosion since the 1930's, the consequences of which have been accentuated by widespread road, housing and property development on the foredunes. In recent months there has been renewed discussion on groyne and breakwater construction to protect these beaches. Whether or not these proposals are eventually realised , they have highlighted the fact t hat , with the exception of work by Donnelley (1 959 ) and Burgess (1971), little basic investigation has been made into the movement of material contributing to foreshore change along the west Wellington coast. The aim of this thesis is therefore to provide further information on the coastal environment and to discuss the possible processes which may contribute to coastal change in the district. It is hoped also that this work will fulfil a number of related functions. ll1/ hangaehu COOK STRAIT t Manawa tu Otaki 20 Kilometres Sand Country of the Wellington West Coast (Hocking,1964) FIG. 1 LOCATION WEST VI/ELLINGTON COAST. (1) Provide a basis for future surveys involving long term change along the coast. (2) Assist planners in the development of coastal recreation and protection schemes, (3) Enable the west Wellington coastal environment to be examined in the context of other New Zealand coastal areas , and to contribute towards a greater comprehension of the national coastal environment . 1.2 Thesis Format The thesis i s divided into five sections . Section One includes an i ntroduction to the top ic a nd a review of beach sediment litera ture. The various components of the material and energy sets of the environment a re described i n Section Two. Section Three is a discussion of field and labora tory inves tiga tion of beach sediment a nd bea ch morphology along the west We llington coast . Sec tion Four discusses the nature of, and the contributing factors for , r e cent coastline change ; special reference is made to the Wa ikanae- Paekakariki district .