SEDIMENT YIELDS AND STREAM CATCHMENT VARIATION IN SOUTH-EASTERN TASMANIA By L.J. OLIVE B.Sc. (NE.) Submitted in fulfilment of the requirements for the degree of Master of Science University of Tasmania Hobart 1973 Except as stated herein this thesis contains no material which has been accepted for the award of any other degree or diploma in any other university, and that, to the best of my knowledge and belief, the thesis contains no copy or paraphrase of material previously published or written by another person, except when due reference is made in the text of the thesis. L.j. Olive ACKNOWLEDGEMENTS I would like to acknowledge the assistance given by the staff of the Geography Department, University of Tasmania in the preparation of this thesis, particularly in the collection of field samples. Special thanks are due to my supervisor Professor J.L. Davies and to Dr. E.A. Colhoun who took over the supervision in the final stages. My appreciation is also extended to the Rivers and Water Supply Commission of Tasmania for their invaluable support and particularly to the assistance giveh by Mr. J. Koebon. Finally, I wish to thank Mrs. J. Kemp and Mrs. L. Arcus who typed the manuscript. ABSTRACT The study is an examination of the sediment loads and erosion rates of three small catchments in south-eastern Tasmania. Only that part of the load known as the wash load has been considered. Also, the suspension and solution load components of the wash load have been determined. The bed load has not been examined because of the absence of any accurate method for its determination. The previous literature on sediment yields is examined showing the dominance of work carried out in the United States of America in this field. Only a small number of studies have been carried out in Australia, • with no previous studies in Tasmania. A review of methods used in sediment studies revealed a wide range, many of which proved unsatisfactory for this study. The method used in this study, involving the use of ashless filters, was the most accurate known to the author at the time of the study although it is subject to some limitations. A description of the environment of the area is given. The landforms, geology, vegetation and climate of the three catchments are similar varying only in the proportions of each catchment which are made up of the various lithological and vegetational units. The wash load of the streams was sampled over a period of twelve months- while the suspension and solution loads were examined for only three months. From the information obtained sediment rating curves and daily sediment yields were determined. The computed daily sediment yields revealed the dominance of individual run-off episodes where up to 20 per cent of the annual load was removed in one episode. These episodes were separated by long periods of basal flow when sediment transport was minimal. It also illustrated the importance of the solution load which made up 65 to 85 per cent of the total wash load. This high figure is due to some degree to the inability of the laboratory method to separate colloidal material from the solution load. The solution load was much more constant than total wash load with individual run-off episodes not being so dominant. The suspension load however was extremely concentrated in individual run-off episodes with only negligible transport during basal flows. Erosion rates were also determined ranging from 140 to 156 tons per square mile. These fall into a similar range to those found elsewhere in Australia. A linear relationship was found between erosion rates and rainfall in Australia. This contrasts with results obtained in America where erosion rates increased with rainfall to a maximum at 12 inches per annum and then decreased as rainfall increased. These differences are due to differences in vegetation with the American vegetation changing with climate while that in Australia is relatively constant. An examination of the influence of various catchments revealed significant relationships with lithology and vegetation. Erosion rates were greatest on sandstone and mudstone areas and lower from dolerite areas. Also, a greater proportion of the sandstone and mudstone was carried in suspension while the dolerite was transported in solution or colloidal suspension. Wash load was also greater from forest areas than from the other vegetational types. This is due to the lack of ground cover in the forest area. TABLE OF CONTENTS Page Chapter 1 THE PROBLEM 1-19 Bed load 1 Suspension load 5 Solution load 13 Wash load 18 Chapter 2 THE STUDY AREAS 20-39 Previous studies :- 2,0 1 the world 20 2 Australia 25 The Study Area 27 The Physical Environment 30 1 Geology 30 2 Climate 33 1 Topography 34 • 4 Soils 36 5 Vegetation 38 Chapter 3 METHODS AND TEaHNIQUES 40-60 Streamflow measurement 40 Wash load sampling 46 Laboratory analysis of sediment 55 1 Wash load 56 2 Suspension and solution loads 58 Chapter 4 BROWNS RIVER 61-85 General environment • 61 Rainfall and runoff • 67 Sediment Data 73 Wash load 75 2 Suspension load 81 3I Solution load 82 Denudation Rates 83 Summary of Results 84 Page Chapter 5 . SNUG RIVULET 86-112 General environment 86 Rainfall and runoff 91 Sediment data 99 Wash load 99 2 Suspension load 107 3I Solution load 109 Denudation Rates 110 Summary of Results 110 Chapter 6 MOUNTAIN, RIVER 113-136 General environment 113 Rainfall and runoff 119 SEidiment data 124 1. Mountain River below the tributary 124 i) Wash load 124 ii) Suspension load 131 iii) Solution load 132 iv) Denudation rates 133 2. Mountain River tributary 133 3. Mountain River above the tributary 134 Summary of results 135 Chapter 7 DISCUSSION OF RESULTS 137-171 f Rainfall and runoff 137 Sediment data 139 Wash load 139 2 Suspension load 148 3I Solution load 152 Comparison with other studies 155 Chapter 8 c.ocursIonp 172-177 Bibliography 178-184 Appendices' 185-19 6 MAPS AND DIAGRAMS Page Figure 1 Vertical distribution of varying sediment sizes 8 2 Vertical distribution of sediment 9 3 Transverse distribution of pediment 11 4 Variation of sediment with changing bed form 12 5 Catchment variables 14 6 Location of the study area 29 7 Rainfall of south-east Tasmania 35 8 V.-notch weir rating curve 42 9 Mountain River rating curve 43 10 UNE sediment sampler 48 11 Relationship between sampler intake velocity and water velocity with constant depth 12 Relationship between sampler intake velocity and depth 54 13 Browns River catchment area 62 14 Browns River geology 64 15 Browns River vegetation 66 16 Browns River hydrographs 71 17 Browns River double mass curves 74 18 Browns River runoff episode 15th-30th May 1969 79 19 Browns River sediment rating curves 80 20 Snug Rivulet catchment area 87 Page 21 Snug RivUlet geology 89 22 Snug Rivulet vegetation 92 23 Snug Rivulet hydrographs 96 24 Snug RivLet double mass curve 97 25 Snug Rivulet - Browns River rainfall double mass curve 99 26 Snug Rivulet - Browns River discharge double mass curve 100 27 Snug Rivulet runoff episode 15th-30th May 1969 105 28 Snug Rivulet sediment rating curves 106 29 Mountain River catchment area 114 30 Mountain River geology 116 31 Mountain River vegetation 118 32 Mountain River hydrographs' 123 33 Mountain River runoff episode 15th-30th May 1969 128 34 Mountain River sediment rating curves 130 35 Wash load rating curves of the three streams 144 36 Suspension load rating curves of the three streams 150 37 Solution load rating curves of the three streams. 154 38 Variation: ofsediment concentration with annual predpitation in the United States 158 39 Relationship between sediment 'Ifield and pmacipitation in Australia 162 1)age 40 Relationship between sediment yield and precipitation in the Uhited States 163 41 Relationship between solution load and runoff in the United States 171 TABLES Page 1. Browns River rainfall data 69 2. Browns River wash load data 77 3. Browns River suspension and solution load data 78 4. Snug Rivmlet rainfall data 94 5. Snug Riv'Olet wash load data 102 6. Snug RivUlet suspension and solutipn data 103 7. Mountain River rainfall data \._,•„,.120 • 8. Mountain River wash load data 125 ' 9.. Wuntain,River suspension and solution load data 126 • 10. Mountain River tributary and the Mountain • River above the tributary. - wash load data 127 11. Denudation rates in Australia 159 12. Siitation rates in Australian reservoirs 160 13. Denudation rates in the Unites States 165 14. Suspension load data for Australia and the United States 167 15. Solution load data for the United States 170 CHAPTER 1 THE PROBLEM Sediment can be transported in a stream as bed load, suspension load or solution load. Generally these three types ape related to • different, variables and in many ways operate in distinctive ways. Although three types Of transport have been proposed there are no distinct boundaries between them and it is possible for particular 'sediment particles to fluctuate between two types. Relatively fine bea load material may pass into suspension if stream velocity is increased. Also colloid particles which are theoretically part of the suspension load are often difficult to separate from the solution load' due to their weak electrical bonds with the water. A further type of sediment load known as the "wash load" has been. proposed by 1 Einstein . This load is that which can be carried by the stream independent of the Stream velocity and is made up of the solution load and the greater proportion of the suspension load. It is the wash load that this thesis is primarily concerned with.