Downstream Change in the Processes of Riverbank Erosion Along the River Swale, Uk
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DOWNSTREAM CHANGE IN THE PROCESSES OF RIVERBANK EROSION ALONG THE RIVER SWALE, UK by James Robin Grove A thesis submitted to The University of Birmingham for the degree of DOCTOR OF PHILOSOPHY School of Geography and Environmental Sciences University of Birmingham Edgbaston Birmingham UK November 2000 University of Birmingham Research Archive e-theses repository This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder. ABSTRACT This study was designed to test the hypothesis that riverbank erosion processes altered with increasing distance from a river source. The River Swale, northern England, was monitored at nine sites throughout its 109-km length, from December 1995 – March 1998. Erosion pins, bank-edge surveying, and Photo-Electronic Erosion Pins (PEEPs) were used to determine rates and timings of erosion. The rates were compared against a range of environmental variables based on temperature, river stage, and precipitation at 14-day intervals for erosion pins and 15- minute intervals for PEEPs. This allowed processes of erosion to be inferred. Catchment erosion rates were modelled using quadratic equations, simulating a mid-basin peak of 3.58 m a-1. Rates of erosion were low upstream, 0.07 m a-1, and also downstream, 0.12 m a-1. Subaerial processes, especially frost action, dominated upstream. Fluvial entrainment was most influential mid-catchment. Mass failures were most efficient downstream, but were more frequent mid-catchment. Piping, sapping and cantilever failures did not follow the same trends and were modelled separately. The length of the erosion season increased downstream as the number of active processes increased. ACKNOWLEDGEMENTS I would like to thank NERC for funding my studentship GT4/95/20/F, and the Centre for Ecology and Hydrology (CEH) for being CASE sponsors. The Environmental Change Network, British Atmospheric Data Centre, Environment Agency, CEH, and Yorkshire Dales National Park Authority all efficiently provided essential data and information. The landowners that let me dig up and tramp over their land are much appreciated. Damian Lawler, Graham Leeks, and John Gerrard all supervised this project. Damian helped getting the project started, especially with advice on PEEPs. He provided comprehensive corrections on drafts of Chapters 2-7, despite numerous mental and physical illnesses. John allowed much needed opportunities to discuss concepts and valuable moral support. I hope Graham is pleased with the results. Colin Thorne and Chris Bradley gave an educational viva, entertaining corrections, and a lot of relief to me by approving this work. All fellow postgraduates, and the support staff at the School of Geography and Environmental Science, Birmingham University are thanked especially my office mates for putting up with my mess. Neil Harris’ fantastic work was a guide in the darkness and he is remembered for his help and kindness. Everyone at the Department of Geography, University of Durham, especially Bob Allison, office mates Toru-Matt-Dave, postgraduates, and housemates should get medals. Louise Bull deserves sainthood for her understanding of my plight, and for acting as a surrogate supervisor. My sister (Sarah), Adam Sawyer, John Couperthwaite, John Livesey, Iqbal Hamaddudin, Sharon Woodruffe, Dave Tickner, Jenny Clayman, Conor, and Barney were all dragged to the beautiful Yorkshire Dales to get covered in mud. On my way round the country Chris, Laura, Frances, and Clay offered a roof over my head and a counselling service. You are all stars. Yvette Parkes has managed to put up with permanent Ph.D. crises, after 3 years of B.Sc. moaning. She has been a constant support, and provider of food, especially through all my little accidents. Caroline and Yvette deserve awards for managing the fort whilst I was in intensive care, and for finding Bangor Hospital in the end. I owe my life to Kirsty Jones, plus an unknown climber and his mobile phone, and the Mountain Rescue team at Cader Idris. Words cannot describe my thanks to you all and everyone who put me back together at Bangor Hospital, I also thank the Physios and Dermatologists at Cirencester and Dryburn Hospitals, Oral and Maxillofacial Dept. at Cheltenham Hospital, A+E at Selly Oak and Sheffield Hospitals, my dentist, and the Infectious and Tropical Diseases Dept. at Heartlands Hospital. To the special people on BSES Svalbard Spring ’96, and Greenland ’98 especially Sally Mackay, Christina Hennessey, Tim Stott, and Frobisher Fire, I love you all. Richard Burt managed to keep me out of Birmingham and sane for a multitude of weekends, without falling off anything. Bob Allison and Graham Philip on the other hand had the brilliant idea of sending me to Syria and Jordan where I could do nothing in my spare time but Ph.D. work. Thank-you. Finally, to my parents and Oonagh the dog. Despite never quite understanding exactly what I was doing you have always been there. What more could I ask. “ Facts may lead to truth just as bricks may finally produce a wall. Facts are to truth what traffic lights and the red tape of government are to order – they are necessities, a cause of more bookkeeping, often way out of proportion to the ends to be gained and a reason why men grow old before their time.” (Talcott, 1936, p.173) “ Every particle of hitherto unknown information obtained in any direction whatever is supposed to, and undoubtedly can if properly pieced together, further the advance of science. But in turn, let me ask, of what use is science except as a means to further the enjoyment of life? I wonder in this connection who it is who really comes closest to the final truth - the man who ecstatically watches the flight of a bird for the sheer sensation of pleasure derived from the way it banks its corners (and is not that the essence of scientifically apportioned effort?) or the man who cannot afford time to enjoy the sight in his nervous haste to run and fetch a book? – a book that will tell him what the bird’s name is, how many toes it has and where else it is known to breed. ” (Talcott, 1936, p.172) “ Exploration is the physical expression of the Intellectual Passion. And I tell you, if you have the desire for knowledge and the power to give it physical expression, go out and explore. If you are a brave man you will do nothing, for none but cowards have need to prove their bravery. Some will tell you that you are mad, and nearly all will say, ‘What is the use?’ For we are a nation of shopkeepers, and no shopkeeper will look at research which does not promise him a financial return within a year. And so you will sledge nearly alone, but those with whom you sledge will not be shopkeepers: that is worth a good deal. If you march your Winters Journeys you will have your reward, so long as all you want is a penguin’s egg. ” (Cherry-Garrard, 1994, p.597-598) CONTENTS Table of Contents List of Figures List of Tables List of Plates Chapter 1 Introduction___________________________________________ 1 1.1 Research Background ____________________________________________ 1 1.1.1 The Importance of Bank Erosion in the Fluvial System ______________________ 1 1.1.2 The Influence of Catchment Scale on Bank Erosion _________________________ 3 1.1.3 Seasonal Changes in Bank Erosion ______________________________________ 6 1.2 Aims and Objectives______________________________________________ 8 1.3 Thesis Structure _________________________________________________ 9 Chapter 2 Theoretical and Empirical Studies of Bank Erosion Processes 10 2.1 Introduction ___________________________________________________ 10 2.2 Subaerial Processes _____________________________________________ 10 2.2.1 Introduction ______________________________________________________ 10 2.2.2 Cryergic Processes__________________________________________________ 11 2.2.3 Pore Water Associated Processes ______________________________________ 14 2.2.4 Rainsplash Processes ________________________________________________ 18 2.3 Fluid Entrainment ______________________________________________ 20 2.3.1 Introduction ______________________________________________________ 20 2.3.2 Sediment Influences on Entrainment ___________________________________ 20 2.3.3 Entrainment Fluid Dynamics _________________________________________ 23 2.3.4 Basal Endpoint Control _____________________________________________ 27 2.4 Mass Failure Processes __________________________________________ 28 2.4.1 Introduction ______________________________________________________ 28 2.4.2 Cantilever Failures__________________________________________________ 29 2.4.3 Planar Failures_____________________________________________________ 31 2.4.4 Pop-out or Draw-down Failures _______________________________________ 34 2.4.5 Rotational Failures__________________________________________________ 35 2.4.6 Sediment Flows____________________________________________________ 36 2.5 The Influence and Variability of Riparian Vegetation _________________ 37 2.6 Anthropogenic Influences on Erosion Processes _____________________ 40 2.7 Process Combinations and Interactions_____________________________