3Y A SEDIMENT CIRCULATION IN MIXED GRAVEL AND SHINGLE BAYHEAD BEACHES ON THE SOUTH EAST DORSET COAST Carolyn Heeps, B. Sc. (Hons). ý*ýýý Thesis submitted to the Council-for National Academic Awards for the degree of Doctor of Philosophy ý**ý* ve..r ' wý Sponsored by the Dorset Institute of Higher Education, Department of Tourism and Field Sciences. In Collaboration with the University of Wales, Institute of Science and Technology, Cardiff, Department of Maritime Studies. April, 1986. DORSETINSTITUTE' Of H!GI EREDUCATION LIBRARY SEDIMENT CIRCULATION III-=ED G HINGLE BAYHEAD BEACHES ON THE SOUTH EAST DORSET COAST Carolyn Heeps ABSTRACT This thesis investigates and attempts to clarify the morphological characteristics, processes and sedimentology of five local mixed gravel and shingle beaches. A conceptual framework of process- response has been adopted which considers energy inputs, sediment transport and coastal morphology, under conditions of limited sediment supply and a "closed cell" situation. Onshore field investigations using conventional methods of surface sediment sampling, together with beach profiling, platform and cliff measurements provided quantitative data with respect to contemporary sediment inputs, sediment characteristics and trans- port. Extensive and intensive measurements of beach sections described spatial and temporal morphological and volumetric change and revealed a neutral sediment budget at the scale of 12-14 months. The beaches are in equilibrium with prevailing and dominant south westerly wave regimes; prolonged periods of south easterly wave climates influence the foci of wave energy and cause significant littoral drift and exposure of the chalk platform. The offshore data used were derived from available sources and supplemented by fieldwork by the author. Investigations in the nearshore zone by side-scan sonar and echosounder revealed the morphological and sedimentological nature of the seafloor along the northern shore of Weymouth Bay. Sediment distribution and bedforms suggested preferred sediment transport paths. Within each bay sediment sampling by grab and/or divers elucidated the nature of each sediment cell. The distinct differences of textural composition and the presence of natural offshore barriers to sediment movement highlighted the sedimentological/morphological containment of each bayhead unit. Theoretical considerations and field data have helped to gain a better understanding of the relationship between cliff, beach, platform and nearshore processes and illustrate that selected embayments along the northern shore of Weymouth Bay are morpho- logically contained sediment cells sharing the same hydrodynamic system. It I declare that while registered as a candidate for the degree of Doctor of Philosophy I have not been registered for another award of the Council for National Academic Awards or of a University during the research programme, nor has any of the material contained within this thesis been submitted for any other award. Any assistance received has been duly acknowledged. CONTENTS VOLUME 1. CHAPTER PAGE 1. PROCESS-RESPONSE MODELS AND APPROACHES TO COASTAL GEOMORPHOLOGY. 1 2. INTRODUCTION. 6 3. PHYSICAL BACKGROUND. 9 4. COASTAL SEDIMENT TRANSPORT. 23 5. SIDEWAYS-LOOKING SONAR. 55 6. CLIFFS AND SHORE PLATFORMS. 66 7. BEACH SEDIMENTOLOGY. 95 8. BEACHES: PROFILE AND PROCESSES. 152 9. SUMMARY AND CONCLUSIONS. 200 ACKNOWLEDGEMENTS. 208 REFERENCES. 209 VOLUME 2. TABLES FIGURES PLATES APPENDICES. VOLUME 2: LIST OF FIGURES FIGURE 1. CONCEPTUAL BEACH MODEL (KRUMBEIN 1964) 2. INTER-RELATIONS AMONG ELEMENTS OF KRUMBEIN'S BEACH MODEL 3. ENERGY FACTORS OF KRUMBEIN'S BEACH MODEL 4. LOCATION OF STUDY AREA 5. SITE MAP-RINGSTEAD BAY 6. SITE MAP-DURDLE DOOR/BAT'S HEAD BAY 7. SITE MAP-MAN O'WAR COVE 8. SITE MAP-MUPE BAY 9. SITE MAP-WORBARROWBAY 10. OFFSHORE GEOLOGY-WEYMOUTHBAY 11. ENGLISH CHANNEL GEOLOGY 12. BATHYMETRY OF WEYMOUTH BAY 13. RELATIONSHIPS BETWEEN GRAIN DIAMETER AND THE CRITICAL FORCE REQUIRED FOR ITS MOVEMENT 14. EFFECTIVE FETCH CHARACTERISTICS AT WORBARROW BAY 15. WAVE PREDICTION CHART FOR COASTAL WATERS 16. WIND ROSE (SEPTEMBER1982/1984) 17. WAVE REFRACTION IN WEYMOUTHBAY (South-west wave train, 10 sec. period) 18. WAVE REFRACTION IN WORBARROWBAY 19. WAVE REFRACTION IN WEYMOUTHBAY (South-east wave train, 5 sec. period). 20. COMPUTERGENERATED BATHYMETRIC MOSAIC OF THE STUDY AREA 21. THRESHOLDS OF SEDIMENT MOVEMENT IN WATER 22. SOME PRINCIPLES OF SIDE-SCAN SONAR 23. SIDE SCAN SONAR TRACK-WEYMOUTH BAY JULY 1984 FIGURE 24. MORPHOLOGICAL AND SEDIMENTOLOGICAL FEATURES ALONG SIDE-SCAN TRACK 25. FACTORS AFFECTING CLIFF EROSION (SUNAMURA 1977) 26. CLIFF TYPE ACCORDING TO PRECHEUR(1960) 27. PROFILE VARIATION IN HARD CHALK CLIFFS OF THE DORSET COAST. 28. CROSS SECTION THROUGH CLIFF FALL AT SWYRE HEAD 1983 29. CHALK CLIFF-PLATFORM JUNCTIONS (DURDLE DOOR) 30. PARTICLE SIZE CLASSIFICATION 31. PILOT STUDY BEACH SECTIONS 32. MAIN STUDY BEACH SECTIONS 33a. NEARSHORE PROFILE 1, RINGSTEAD BAY 33b. NEARSHORE PROFILE 2, RINGSTEAD BAY 34. NEARSHORE PROFILE 1, WORBARROWBAY 35. GRAB SAMPLE SITES AT WORBARROW BAY 36. GRAB SAMPLE SITES AT DURDLE DOOR BAY 37. A. E. R. E. SEDIMENT SURVEY(ARISH MELL)1956 38. A. E. R. E. SEDIMENT SURVEY(WEYMOUTHBAY) 1960/1961 39. A. E. R. E. SEDIMENT SURVEY(198L) 40. MODIFIED BEACH PRISM(AFTER CLAYTON 1977) 41. WIND ROSE : ONE MONTH SURVEY, DURDLE DOOR 1983 42. WIND ROSE : STORM EVENT SURVEY, SEPTEMBER 1983 43. TYPICAL MORPHOLOGY OF MIXED GRAVEL AND SHINGLE BEACH; a. -IN FRONT OF CLAY CLIFF. b. -ON CHALK'PLATFORM. 44. BAYHEAD BEACH MODEL. LIST OF TABLES: 1. VELOCITY PROFILE AND THE QUADRATIC STRESS LAW. 2. SHIELDS' ENTRAINMENT FUNCTION(1936) AND BAGNOLDS BEDLOAD TRANSPORT RATE(1963)- 3. GEOMETRIC AND EFFECTIVE FETCHES FOR WORBARROW BAY. 4. PREDICTED WAVE HEIGHTS FOR WORBARROWBAY. 5. CHALK COASTLINES(MAY 1964) 6. SWYRE HEAD DEBRIS SIZE. (1983) 7. DEVELOPMENT OF SPHERICITY INDICES. 8. DEVELOPMENT OF ROUNDNESS INDICES. 9. OTHER SHAPE INDICES. 10. SAMPLE PREPARATION. 11. MEASURES OF CENTRAL TENDENCY AND SCATTER. 12. GRAPHICAL MEASURES AND DESCRIPTIVE TERMS FOR MEAN, SKEWNESS, SORTING, AND KURTOSIS. 13a. RINGSTEAD PARTICLE SIZE ANALYSIS 23/9/82. b. RINGSTEAD PARTICLE SHAPE ANALYSIS 23/9/82. 14a. DURDLE DOOR PARTICLE SIZE ANALYSIS 23/9/82. b. DURDLE DOOR PARTICLE SHAPE ANALYSIS 23/9/82. 15a. MAN 0' WAR PARTICLE SIZE ANALYSIS 23/9/82. b. MAN 0' WAR PARTICLE SHAPE ANALYSIS 23/9/82. 16a. RINGSTEAD PARTICLE SIZE ANALYSIS 14/10/82. b. RINGSTEAD PARTICLE SHAPE ANALYSIS 14/10/82. 17a. DURDLE DOOR PARTICLE SIZE ANALYSIS 14/10/82. b. DURDLE DOOR PARTICLE SHAPE ANALYSIS 14/10/82 18a. MAN 0' WAR PARTICLE SIZE ANALYSIS 14/10/82. b. MAN 0' WAR PARTICLE SHAPE ANALYAIS 14/10/82. 19(a-f)DURDLE DOOR ONE MONTH SURVEY-PARTICLE SIZE ANALYSIS. 20(a-f)DURDLE DOOR ONE MONTH SURVEY-PARTICLE SIZE ANALYSIS. TABLE 21. DURDLE DOOR ONE MONTH SURVEY-LITTORAL OBSERVATION DATA. 22. RINGSTEAD SUMMER SURVEY (1984) PARTICLE SIZE ANALYSIS. 23. DURDLE DOOR SUMMER SURVEY (1984) PARTICLE SIZE ANALYSIS. 24. MAN 0' WAR SUMMER SURVEY (1984) PARTICLE SIZE ANALYSIS. 25. MUPE SUMMER SURVEY (1984) PARTICLE SIZE ANALYSIS. 26. WORBARROW SUMMER SURVEY (1984) PARTICLE SIZE ANALYSIS. 27. SEDIMENT CHARACTERISTICS ALONG UNDERWATER TRANSECTS(RINGSTEAD BAY AND WORBARROW BAY) 28. GRAB SAMPLE DATA WORBARROW BAY. 29. GRAB SAMPLE DATA DURDLE DOOR. 30. BEACH DEFINITIONS. 31. PROFILE SECTIONS REDUCED TO ORDNANCE DATUM.. 32. PROFILE CLASSIFICATION BY MACROFORM. 33. DURDLE DOOR ONE MONTH SURVEY, VOLUMETRIC CHANGE. 34. DURDLE DOOR ONE MONTH SURVEY, PROFILE CLASSIFICATION BY MACROFORM. 35. DURDLE DOOR ONE MONTH SURVEY, BRUUN INDEX & MEAN DEPTH VALUES. 36. WORBARROWSTORM EVENT SURVEY, VOLUMETRIC CHANGE. 37. WORBARROW STORM EVENT SURVEY, BRUUN INDEX & MEAN DEPTH VALUES. 38. WORBARROW STORM EVENT SURVEY, PROFILE CLASSIFICATION BY MACROFORM. 39. RINGSTEAD MONTHLY SURVEY, VOLUMETRIC CHANGE. 40. RINGSTEAD MONTHLY SURVEY, PROFILE CLASSIFICATION BY MACROFORM. 41. RINGSTEAD MONTHLY SURVEY, BRUUN INDEX & MEAN DEPTH VALUES. TABLE 42. DURDLE DOOR MONTHLY SURVEY, VOLUMETRIC CHANGE '13. DURDLE DOOR MONTHLY SURVEY, PROFILE CLASSIFICATION BY MACROFORM. 44. DURDLE DOOR MONTHLY SURVEY, BRUUN INDEX & MEAN DEPTH VALUES. 45. MAN 0' WAR MONTHLY SURVEY, VOLUMETRIC CHANGE. 46. MAN 0' WAR MONTHLY SURVEY, PROFILE CLASSIFICATION BY MACROFORM. 47. MAN 01 WAR MONTHLY SURVEY, BRUUN INDEX & MEAN DEPTH VALUES. 48. MUPE MONTHLY SURVEY, VOLUMETRIC CHANGE. 49. MUPE MONTHLY SURVEY, PROFILE CLASSIFICATION BY MACROFORM. 50. MUPE MONTHLY SURVEY, BRUUN INDEX & MEAN DEPTH VALUES. - 51. WORBARROWMONTHLY SURVEY, VOLUMETRIC CHANGE. 52. WORBARROW MONTHLY SURVEY, PROFILE CLASSIFICATION BY MACROFORM. 53. WORBARROWMONTHLY SURVEY, BRUUN INDEX & MEAN DEPTH VALUES. LIST OF PLATES: PLATE 1. RINGSTEAD BAY(looking west). 2. DURDLE DOOR-BAT'S HEAD(looking west). 3. MAN O'WAR COVE(looking east). 4. HUPE BAY(looking east). 5. WORBARROWBAY(looking west). 6. MUPE ROCKS TO WORBARROWTOUT(along line of submerged Portland Stone barrier). 7. SONOGRAPH AND ECHOGRAPH OF THE PURBECK MONOCLINE(east of Bat's Head). 8. SONOGRAPHAND ECHOGRAPHOF SEABED OFF LULWORTH COVE. 9. SONOGRAPH AND ECHOGRAPH OF FLAT BED SANDS, WORBARROW BAY. 10. SONOGRAPH AND ECHOGRAPH OF SUBMERGED PORTLAND STONE REEF OPPOSITE ARISH HELL GAP, WORBARROW BAY. 11. SONOGRAPHAND ECHOGRAPHOF PORTLAND STONE REEF WITH RIPPLED AND FLAT BED SANDS. 12. SONOGRAPH AND ECHOGRAPH OF THE PORTLAND STONE BARRIER, WESTERN SECTION OF WORBARROW BAY. 13. SONOGRAPHILLUSTRATING YAW DISTORTION OVER BOULDER FIELD, OFF COW CORNER,WORBARROW BAY. 14. ECHOGRAPHOF