The Coastal Geomorphology of North Cornwall: St. Ives Head to Trevose Head
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The Coastal Geomorphology of North Cornwall: St. Ives Head to Trevose Head. by DANIEL D. BUSCOMBE & TIMOTHY M. SCOTT Wave Hub Impact on Seabed and Shoreline Processes (WHISSP) University of Plymouth. c University of Plymouth, 2008. ii A review of the scenery and coastal geomorphology of north Cornwall between St. Ives and Trevose Head, an area in the potential shadow of the proposed Wave Hub wave farm. This report comes ahead of the Wave Hub’s proposed installation offshore of St. Ives in early 2009, and is made as part of the WHISSP (Wave Hub Impact on Seabed and Shoreline Processes) project at the University of Plymouth. A special emphasis is given to the character and phys- ical attributes of the fifty-three individual beaches and coves in the study area, as well as the physical coastal processes in the region. c University of Plymouth, 2008. Table of Contents 1 Overview 3 1.1 The‘WaveHub’andWHISSP. 3 1.2 PhysiographyandGeology. 5 1.3 Waveandtidalregime.............................. 7 1.4 Sediment and sediment transport . .... 10 1.5 Morphodynamic classification of WHISSP beaches . ........ 13 1.6 Human Intervention and Shoreline Management . ....... 13 2 St Ives Head to Godrevy Head 25 2.1 Porthmeor .................................... 27 2.2 PorthGwidden.................................. 30 2.3 HarbourSand .................................. 32 2.4 PorthMinster .................................. 35 2.5 CarbisBay .................................... 37 2.6 Porth Kidney Sands and Hayle Estuary . .... 41 2.7 PhillackTowans ................................. 45 2.8 Uptonor‘Mexico’Towans. 47 2.9 GwithianTowans................................. 50 2.10GodrevyCove .................................. 53 3 Godrevy Head to St. Agnes Head 57 3.1 MuttonCove................................... 59 3.2 FishingCove ................................... 61 3.3 HudderDown .................................. 62 3.4 Hell’sMouth................................... 63 3.5 HudderCove................................... 64 3.6 Basset’sCove .................................. 66 3.7 Porth-CadjackCove ............................... 67 3.8 WesternCove .................................. 69 3.9 Portreath..................................... 71 3.10GoodenHeaneCove ............................... 74 3.11Sally’sBottom .................................. 76 3.12PorthTowan................................... 78 3.13ChapelPorth................................... 82 iii iv TABLE OF CONTENTS 4 St Agnes Head to Penhale Head 87 4.1 TrevaunanceCove ................................ 89 4.2 GreanIsland ................................... 92 4.3 HanoverCove .................................. 93 4.4 PerranporthBeach................................ 95 4.5 Hoblyn’sCove .................................. 101 4.6 HolywellBeach.................................. 103 5 Penhale Head to Porthcothan 105 5.1 PorthJoke .................................... 106 5.2 CrantockBeach ................................. 108 5.3 Fistralbeach................................... 112 5.4 TowanBeach................................... 116 5.5 TolcarneBeach.................................. 119 5.6 LustyGlaze.................................... 120 5.7 PorthBeach ................................... 122 5.8 WhipsiderryBeach................................ 123 5.9 WatergateBeach................................. 125 5.10StemCove.................................... 128 5.11BeaconCove................................... 129 5.12MawganPorth .................................. 131 5.13TrerathickCove ................................. 133 5.14WhitestoneCove................................. 134 5.15 Bedruthan Steps or ‘Pendarves’ . ..... 136 5.16Diggory’sIsland ................................ 138 5.17PentireSteps................................... 139 5.18TheSaddle.................................... 140 5.19PorthMear.................................... 142 6 Porthcothan to Trevose Head 145 6.1 PorthcothanBay................................. 147 6.2 FoxCove..................................... 148 6.3 PepperCove ................................... 150 6.4 TreyarnonBay .................................. 151 6.5 ConstantineBay ................................. 153 6.6 Booby’sBay ................................... 155 Bibliography 160 List of Figures & Plates 1.1 The proposed location of the wave hub site is marked with an arrow. 4 1.2 WHISSP study area (scale 1:230220) . ........ 6 1.3 Tidal residuals within the study area, according to Halcrow [2002]. Arrow size is relative to magnitude of the tidal flux. Map extent is 100km. ............ 8 1.4 Main rivers and tidal co-range lines in the WHISSP area. Source: Marine Digimap. 9 1.5 Bathymetric overview of the study area, according to Halcrow [2002]. The -5, -10, -20, -30, -50m depth contours are shown. Map extent is 100km. ........... 10 1.6 Bathymetric contours of the WHISSP area. Source: Marine Digimap. 11 1.7 Overview of the seabed sediments in the study area, according to Halcrow [2002]. Darkest shading is bedrock, intermediate is gravel, and light shading is sand. Map extent is 100km, and the information has largely been gathered from the British GeologicalSurveyof1987. 12 1.8 Morphodynamic classification of beach types (from Scott [in prep]) I: type and de- scription.......................................... 14 1.9 Morphodynamic classification of beach types (from Scott [in prep]) II: conceptual matrixofbeachtypes................................. 15 1.10 Protected areas and national limits. Source: Marine Digimap. ............ 16 1.11 Locations of wrecked ships in the WHISSP study area. Source: Marine Digimap. 23 1.12 Locations of construction, obstructions and installations in the WHISSP study area. Source:MarineDigimap. .. .. .. .. .. .. .. .. .. 24 2.1 St Ives Head to Godrevy Head (scale 1:38794) . .......... 25 2.2 Bathymetry of St Ives Bay. Source: Marine Digimap . ........... 26 2.3 Digital Elevation Model of Porthmeor Beach, 2007. Elevations in m (ODN) —0 ODN (MSL) marked. Data courtesy of the Plymouth Coastal Observatory.. 28 2.4 Porthmeor Beach (scale 1:7831) . ....... 29 2.5 Porth Gwidden Beach (scale 1:7831) . ........ 31 2.6 Digital Elevation Model of St Ives Harbour Beach, 2007. Elevations in m (ODN) —0 ODN (MSL) marked. Data courtesy of the Plymouth Coastal Observatory. 33 2.7 HarbourSandBeach(scale1:7831) . ....... 34 2.8 Porthminster Beach (scale 1:7831) . ......... 36 2.9 Digital Elevation Model of Carbis Bay Beach, 2007. Elevations in m (ODN) —0 ODN (MSL) marked. Data courtesy of the Plymouth Coastal Observatory.. 38 2.10 CarbisBeachatlowtide. ...... 39 2.11 Carbis Bay or Barrepta Cove Beach (scale 1:7831) . ............. 40 v vi LIST OF FIGURES & PLATES 2.12 Digital Elevation Model of Hayle, 2007. Elevations in m (ODN) —0 ODN (MSL) marked. Data courtesy of the Plymouth Coastal Observatory. ............. 43 2.13 Porth Kidney or Hayle Beach (scale 1:7831) . ........... 44 2.14 PhillackTowans(scale1:7831) . ......... 46 2.15 Digital Elevation Model of Hayle to Gwithian, 2007. Elevations in m (ODN) —0 ODN (MSL) marked. Data courtesy of the Plymouth Coastal Observatory. 48 2.16 UptonTowans(scale1:7831) . ....... 49 2.17 Digital Elevation Model of Gwithian Beach, 11/02/2008. Elevations in m (ODN) —0 ODN(MSL)marked. .................................. 51 2.18 GwithianTowans(scale1:7831) . ........ 52 2.19 GodrevyBeachatlowtide . ..... 54 2.20 GodrevyCove(scale1:7831) . ....... 55 3.1 Godrevy Head to St. Agnes Head (scale 1:55358) . .......... 57 3.2 Bathymetry of Godrevy to St Agnes. Source: Marine Digimap ............ 58 3.3 MuttonCove(scale1:7831). ...... 60 3.4 FishingCovetoHudder Cove(scale1:7831) . .......... 65 3.5 Basset’s Cove to Porth-Cadjack Cove (scale 1:7831) . .............. 68 3.6 WesternCove(scale1:7831) . ...... 70 3.7 Portreath Beach (scale 1:7831) . ........ 72 3.8 PortreathBeach(atlowtide . ...... 73 3.9 GoodenHeaneCove(scale1:7831) . ....... 75 3.10 Sally’sBottom(scale1:7831) . ......... 77 3.11 Digital Elevation Model of Porth Towan Beach, 10/02/2008. Elevations in m (ODN) -0ODN(MSL)marked. ................................ 79 3.12 PorthTowanBeachatlowtide . ...... 80 3.13 Porth Towan Beach (scale 1:7831) . ........ 81 3.14 Digital Elevation Model of Chapel Porth Beach, 09/02/2008. Elevations in m (ODN) -0ODN(MSL)marked. ................................ 83 3.15 ChapelPorthBeachatlowtide. ....... 84 3.16 Chapel Porth Beach (scale 1:7831) . ......... 85 4.1 St. Agnes Head to Penhale Head (scale 1:55358) . .......... 87 4.2 Bathymetry of St Agnes to Porthcothan. Source: Marine Digimap .......... 88 4.3 TrevaunanceCoveBeachatlowtide . ....... 90 4.4 Trevaunance Cove and Grean Island (scale 1:7831) . ............ 91 4.5 HanoverCove(scale1:7831) . ...... 94 4.6 Digital Elevation Model of Perranporth Beach, 08/02/2008. Elevations in m (ODN) —0ODN(MSL)marked. ................................ 96 4.7 PerranporthBeachatlowtide . ...... 97 4.8 Perran Sands/South Perranporth (scale 1:7831) . ............. 98 4.9 Central Perranporth (scale 1:7831) . .......... 99 4.10 North Perranporth (scale 1:7831) . .......... 100 4.11 Hoblyn’sCove(scale1:7831) . ........ 102 4.12 Holywell Bay Beach (scale 1:7831) . ......... 104 5.1 Penhale Head to Porthcothan (scale 1:67458) . ........... 105 5.2 Porth Joke Beach (scale 1:7831) . ....... 107 5.3 Digital Elevation Model of Crantock Beach, 2007. Elevations in m (ODN) - 0 ODN (MSL) marked. Data courtesy of the Plymouth Coastal Observatory.. 109 LIST OF FIGURES & PLATES 1 5.4 CrantockBeachatlowtide. ..... 110