Downstream change in the processes of riverbank erosion along the River Swale, UK

327 Pages·2013·6.76 MB·English

by  James Robin Grove

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

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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_____________________________42
2.7 Summary______________________________________________________44
Chapter 3 Methodology_________________________________________45
3.1 Introduction ___________________________________________________45
3.2 Study Area Selection_____________________________________________45
3.3 Study Area Characteristics________________________________________48
3.3.1 Geology and Pedology_______________________________________________ 48
3.3.2 Hydrology, Water Quality and Meteorology ______________________________ 50
3.3.3 Vegetation and Land-use_____________________________________________ 54
3.3.4 Anthropogenic Activity______________________________________________ 56
3.4 Instrumentation _______________________________________________56
3.4.1 Monitoring Rationale________________________________________________ 56
3.4.2 Site Selection Criteria________________________________________________ 57
3.4.3 Erosion Pins ______________________________________________________ 67
3.3.4 Photo-Electronic Erosion Pins (PEEPs)_________________________________ 70
3.3.5 Stage Measurements ________________________________________________ 74
3.3.6 Air and Bankface Temperature ________________________________________ 75
3.5 Channel Morphology and Vegetation Assessment ____________________76
3.5.1 Planform Bank-top Re-survey_________________________________________ 76
3.5.2 Cross-sectional Survey_______________________________________________ 77
3.5.3 Vegetational Survey_________________________________________________ 77
3.6 Channel Boundary Sediment Sampling _____________________________78
3.6.1 Bank Sediment Sampling_____________________________________________ 78
3.6.2 Riverbed Sediment Sampling__________________________________________ 80
3.7 Summary______________________________________________________ 81

Chapter 4 Spatial Variability in Bank Erosion Rates at the Catchment Scale
_____________________________________________________________83
4.1 Introduction ___________________________________________________83
4.2 Downstream change in Erosion Rates______________________________83
4.2.1 Erosion Pin Results_________________________________________________ 83
4.2.2 Planform Re-survey Results___________________________________________ 88
4.3 Downstream Trends in Bank Sediment Properties____________________93
4.3.1 Introduction ______________________________________________________ 93
4.3.2 Upper Bank Trends_________________________________________________ 95
4.3.3 Mid-bank Trends___________________________________________________ 97
4.3.4 Lower Bank Trends_________________________________________________ 99
4.3.5 Downstream Change in the Organic Content of the Riverbank Sediment_______ 101
4.4 Downstream Changes in Bankfull Flow Efficiency___________________ 102
4.4.1 Introduction _____________________________________________________ 102
4.4.2 Downstream Variability in Channel Dimensions__________________________ 102
4.4.3 Downstream Trends in Bed Sediment__________________________________ 103
4.4.4 Downstream Variability in Stream Power _______________________________ 105
4.4.5 Downstream Changes in Bank Vegetation_______________________________ 111
4.5 Summary_____________________________________________________ 113

Chapter 5 Seasonal Variability in Bank Erosion Rates________________114
5.1 Introduction __________________________________________________ 114
5.2 Bank Erosion Seasonality _______________________________________ 114
5.3 Regression Techniques and Selection of Indices ____________________ 118
5.3.1 Introduction _____________________________________________________ 118
5.3.2 Linear Stepwise Regression Methodology _______________________________ 118
5.3.3 Erosion Variable Selection __________________________________________ 121
5.3.4 Derivation and Selection of Independent Variables________________________ 121
5.3.4.1 Temperature Indices__________________________________________________ 124
5.3.4.2 Streamflow Indices ___________________________________________________ 126
5.3.4.3 Precipitation Indices __________________________________________________ 130
5.3.4.4 Antecedent Precipitation Indices_________________________________________ 131
5.4 Correlation and Regression Results _______________________________ 133
5.4.1 Time Series of Independent Variables__________________________________ 133
5.4.1.1 Temperature Indices__________________________________________________ 133
5.4.1.2.Streamflow Indices ___________________________________________________ 133
5.4.1.3.Precipitation Indices __________________________________________________ 134
5.4.1.4 Antecedent Precipitation Indices_________________________________________ 134
5.4.2 Correlation Analysis _______________________________________________ 135
5.4.3 Regression of Average Erosion Rates (ERRATE)_________________________ 154
5.4.4 Regression of Maximum Erosion Rates (ERMAX) ________________________ 159
5.4.5 Regression of the 84th Percentile of Erosion Rates (ERODE84) ______________ 164
5.4.6 Regression of the Spatial Extent of Erosion (ERODE%) ___________________ 169
5.5 Summary____________________________________________________ 174

Chapter 6 The Distribution of Erosion Processes in Space and Time____178
6.1 Introduction __________________________________________________ 178
6.2 Comparisons between PEEP and Erosion Pin Measurements _________ 178
6.3 Rates of Erosion_______________________________________________ 182
6.3.1 PEEP Data Reduction Methodology___________________________________ 182
6.3.2 Seasonal Trends in Manual and Automatically Monitored Erosion ____________ 184
6.4 Erosion Process Identification using PEEP Data and Environmental
Variables________________________________________________________ 191
6.4.1 Introduction _____________________________________________________ 191
6.4.2 A Flow Diagram for Process Inference_________________________________ 191
6.4.3 Inferences and Observations of Upstream Erosion Processes________________ 194
6.4.4 Inferences and Observations of Mid-Catchment Erosion Processes____________ 201
6.4.5 Inferences and Observations of Lower Catchment Erosion Processes _________ 208
6.5 Summary_____________________________________________________ 216
Chapter 7 An Empirical Model of Bank Erosion Process Efficacy throughout
a Catchment__________________________________________________225
7.1 Introduction __________________________________________________ 225
7.2 Models of Bank Erosion Process Efficacy at a Catchment Scale________ 225
7.2.1 An Empirical Model for the River Swale________________________________ 225
7.2.2 A Model of Erosion Process Efficacy in an Idealised Catchment _____________ 229
7.2.3 The Catchment Scale Distribution of Preparation Processes_________________ 232
7.2.4 The Catchment Scale Distribution of Fluid Entrainment____________________ 236
7.2.5 The Catchment Scale Distribution of Mass Failures _______________________ 239
7.3 The Downstream Change in the Magnitude and Frequency of Bank Erosion
________________________________________________________________ 244
7.3.1 Introduction _____________________________________________________ 244
7.3.2 Upper Catchment Seasonal Erosion Variability___________________________ 244
7.3.3 Mid-Catchment Seasonal Erosion Variability_____________________________ 248
7.3.4 Lower Catchment Seasonal Erosion Variability___________________________ 249
7.4 Comparative Studies of Bank Erosion Rates and Processes____________ 250
7.4.1 A Global Bibliography of Bank Erosion Rates ___________________________ 250
7.4.2 A Global Bibliography of Bank Erosion Processes ________________________ 258
7.5 Comparative Studies of Bank Erosion Process Efficacy at a Catchment Scale
________________________________________________________________ 261
7.6 Summary_____________________________________________________ 267

Chapter 8 Conclusions_________________________________________268
8.1 Introduction __________________________________________________ 268
8.2 Main Project Findings__________________________________________ 269
8.2.1 Erosion Process Spatial Domains _____________________________________ 269
8.2.2 Erosion Process Temporal Domains___________________________________ 271
8.2.3 Catchment Geomorphological Characteristics____________________________ 272
8.2.4 Catchment Trends in Rates of Erosion _________________________________ 274
8.3 Implications of the Study________________________________________ 274
8.4 Future Research Suggestions ____________________________________ 276

References___________________________________________________279
Appendices
I Grove, J.R. and Sedgwick, C. (1998) Downstream spatial and temporal remobilisation of heavy metal
contaminated sediments in the River Swale, England. In IRTCES (Ed), Proc. International Symposium
on Comprehensive Watershed Management, Patent Documentation, Beijing, September 1998, 505-512.

II Lawler, D.M., Grove, J.R., Couperthwaite, J.S. and Leeks, G.J.L. (1999) Downstream change in river
bank erosion rates in the Swale-Ouse system, northern England. Hydrological Processes, 13, 977-992.