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Leslie M. Reid; Thomas Dunne:

Rapid Evaluation of Sediment Budgets

1996. 164 pages, 30 figures, 17 tables, Catena ISBN 978-3-923381-39-5, US-ISBN 978-1-59326-256-3, 17x24cm, 420 g
Language: English

(GeoEcology paperback)

ISBN 978-3-510-65385-0, paperback, price: 35.00 €

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Keywords

hillslopechanneltransportstorageland managementerosion

Contents

Synopsis top ↑

Many land-management decisions would be aided by an understanding of the current sediment production and transport regime in a watershed and of the likely effects of planned land use on that regime. Sediment budgeting can provide this information quickly and at low cost if reconnaissance techniques are used to evaluate the budget. Efficient budget construction incorporates seven steps: careful definition of the problem to be addressed; collection of background information; subdivision of the project area into uniform sub-areas; interpretation of aerial photographs; fieldwork; analysis; and checking of results. Methods used in fieldwork and analysis must be selected according to the types of hillslope and channel processes active, the goals of the analysis, and the level of precision required. Methods for evaluating erosion and sediment transport rates are described, and four examples are given to demonstrate budget applications and construction.

Book review in Stream Notes, April 2004 top ↑

Rapid Evaluation of Sediment Budgets, does not pretend to be a complete guide to sediment budget construction, but it provides a comprehensive overview of strategies and tools useful for understanding sediment production and transport in watersheds.
The validity of a sediment budget then depends on how wisely these methods are employed. Effective construction and interpretation of sediment budgets requires a sound understanding of erosion and sedimentation processes, experience in field mapping and in the measurement and analysis techniques to be used, and above all, good professional judgment. Each area represents its own difficulties and opportunities, so analysts must have a strong enough background in geomorphology and hydrology to take advantage of the peculiarities of the area to be evaluated, and they must be creative and open-minded in their approach. An insufficient number of sediment budget studies exists to allow statistical evaluation of the accuracy and reproducibility of the general approach. However, Reid and Dunne have found that when several trained geomorphologists are asked to evaluate a process rate, results agree relatively closely, and certainly to well within an order of magnitude. Because many sediment budget applications require only approximate estimates, this level of accuracy is thought to be adequate.
Construction of sediment budgets is more difficult in some areas than others. At sites where sediment input is dominated by large, infrequent events, rates must be evaluated using as long a period of record as possible. In such cases, land use may cause small changes in process frequencies which can strongly affect long-term sediment yields, but which may not be observable over the time frame available for analysis.
The most difficult aspects of a sediment budget to quantify are those involving transport and storage of sediment in channels. In areas where these components are particularly important, sediment budgets can often reveal the process interactions that control channel response, the types of changes a channel may undergo, and the likely location of those changes, even if rates cannot be quantified.
Several examples of rapidly constructed sediment budgets are provided by the authors. Anyone interested in constructing sediment budgets for management applications should find this book useful as a guide to specific analysis techniques and as a source of ideas for applying those techniques to management problems.

STREAM NOTES, April 2004

Table of Contents top ↑

List of Figures
List of Tables
List of Boxes
List of Symbols
Abstract
Acknowledgements
1 INTRODUCTION 1
1.1 Definition and description 3
1.2 Relation to other methods 5
1.3 Misconceptions 6
1.4 How to use this volume 7
2 PROCEDURE FOR SEDIMENT BUDGET CONSTRUCTION 9
Step 1. Define the problem 9
Step 2. Acquire background information 10
Step 3. Subdivide area 13
Step 4. Interpret aerial photographs 14
Step 5. Conduct fieldwork 16
Step 6. Analyze data 19 Step 7. Check results 20
3 EVALUATING SEDIMENT PRODUCTION FROM HILLSLOPES
AND CHANNELS 20
3.1 Overview of shillslope sediment production 22
3.2 Identification of sediment sources 25
3.3 Rates of discrete erosion processes 27
3.3.1 Landslides 27
3.3.2 Debris flows 30
3.3.3 Gullies 31
3.3.4 Treethrow 34
3.3.5 Animal burrows 35
3.4 Rates of chronic erosion processes 36
3.4.1 Sheetwash erosion 36
3.4.2 Wind erosion 41
3.4.3 Dry ravel 43
3.4.4 Bank erosion 43
3.5 Other hillslope sediment transport processes 44
3.6 Sediment delivery from hillslopes to channels 47
3.7 Grain-size composition 50
3.8 Calculation of long-term rates 52
3.9 Predicting future erosion rates 59
4 EVALUATING SEDIMENT TRANSPORT AND STORAGE IN CHANNELS 60
4.1 Overview of channel processes 62
4.2 Characterization of channels 63
4.2.1 Qualitative characterization 63
4.2.2 Selection of measurement sites 65
4.2.3 Slope measurements 67
4.2.4 Channel geometry measurements 68
4.2.5 Channel roughness 69
4.2.6 Definition of flow characteristics 70
4.2.7 Identification of channel changes 71
4.3 Grain-size distributions 73
4.4 Initiation of bed-material transport 83
4.5 Determination of scour depths 90
4.6 Sediment transport rates in channels 92
4.6.1 Sediment transport equations 93
4.6.2 Comparison of transport predictions and measurements 94
4.6.3 Applying sediment transport equations 106
4.6.4 Use of field observations 113
4.6.5 Evaluation of the washload component 114
4.6.6 Limits of sediment transport predictions 116
4.7 Sediment storage 116
4.7.1 Identifying storage elements in channels 117
4.7.2 Defining trends in channel-related sediment storage 118
4.8 Computations of sediment yield 123
5 EXAMPLES OF SEDIMENT BUDGET APPLICATIONS 124
5.1 West slope of the Sierra Nevada, Californai 127
5.2 Shinyanga Region, Tanzania 130
5.3 Snoqualmie River basin, Washington 132
5.4 Olympic Peninsula rivers, Washington 133
6 CONCLUSIONS 135
APPENDIX 1. GLOSSARY 138
APPENDIX 2. ADDITIONAL READING AND USEFUL COMPENDIA 144
Background information 144
Manuals and descriptions of particular methods 146
Data compendia 147
REFERENCES 149