Modelling erosion, sediment transport and sediment yield ... modelling erosion, sediment transport and

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  • INTERNATIONAL HYDROLOGICAL PROGRAMME _____________________________________________________________

    Modelling erosion, sediment transport and sediment yield

    Edited by Wolfgang Summer and Desmond E. Walling

    A contribution to IHP-V Projects 2.1 and 6.2 _____________________________________________________________ IHP-VI  Technical Documents in Hydrology  No. 60 UNESCO, Paris, 2002

  • The designations employed and the presentation of material throughout the publication do not imply the expression of any

    opinion whatsoever on the part of UNESCO concerning the legal status of any country, territory, city or of its authorities, or

    concerning the delimitation of its frontiers or boundaries.

    SC-2002/WS/48

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    CONTENTS

    INTRODUCTION iii

    What approach to the modelling of catchment scale erosion and sediment transport should be adopted? R.J. Wasson 1

    Soil erosion by water prediction technology developments in the United States D.C. Flanagan, M.A.Nearing and L.D. Norton 13

    Erosion and sediment yield modelling in the former USSR N.N. Bobrovitskaya 31

    Physically-based erosion and sediment yield modelling: the SHETRAN concept J.C. Bathurst 47

    Multiscale Green’s function Monte Carlo approach to erosion modelling and its application to land use optimization L. Mitas and H. Mitasova 69

    Developments in physically-based overland flow modelling W. Summer 87

    Sediment transport modelling – combination of theoretical concepts and practical approach

    C.T. Yang 101

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    Sediment transport analysed by energy derived concepts W. Zhang and W. Summer 137

    The linkage between hydrological processes and sediment transport at the river basin scale – a modelling study V. Krysanova, J. Williams, G. Bürger and H. Österle 147

    Essai de modélisation du risque d’érosion hydrique utilisant des paramèters socio-économiques. Cas d’une zone rural sénégalaise A. Thioubou and M.W. Ostrowski 175

    Trends in soil erosion and sediment yield in the alpine basin of the Austrian Danube E. Klaghofer, K. Hintersteiner and W. Summer 195

    Suspended sediment structure: implications for sediment transport/yield modelling I.G. Droppo, D.E. Walling and E.D. Ongley 205

    On assessment of erosion and model validation B. Hasholt 229

    Using 137Cs measurements to test distributed soil erosion and sediment delivery models D.E. Walling and Q. He 243

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  • iii

    INTRODUCTION

    In July 1998, the International Commission on Continental Erosion of the International Association of Hydrological Sciences organised a symposium in Vienna, Austria, with the theme Modelling Soil Erosion, Sediment Transport and Closely Related Hydrological Processes. The symposium was co-sponsored by UNESCO, as a contribution to IHP-V and more particularly to IHP-V Project 2.1 dealing with Vegetation, Land-Water Use and Erosion Processes and Project 6.2 concerned with Land Use, Deforestation, Erosion and Sedimentation in the Humid Tropics. The symposium was held at the headquarters of the IAEA, and was widely agreed to have been a very successful meeting. The proceedings were published by IAHS Press (Modelling Soil Erosion, Sediment Transport and Closely Related Hydrological Processes, Proceedings of the Vienna Symposium, July 13-17, 1998, eds. W. Summer, E. Klaghofer and W. Zhang, IAHS Publication no. 249, 1998) and the 50 papers were contributed by authors from many different regions of the world.

    The formal and informal discussion sessions at the meeting emphasised the diversity of the approach to modelling erosion and sediment yield and the need for closer integration of field monitoring and modelling activities, but nevertheless provided clear evidence of many significant advances and achievements within the general area. The discussions also highlighted the central role that modelling must play in dealing with the many environmental problems associated with erosion and sediment transport and in the development of effective catchment management and sediment control strategies.

    To build on the success of the symposium and to contribute further to IHP-V Projects 2.1 and 6.2, it was agreed to assemble a collection of papers dealing with recent work on the field of modelling erosion, sediment transport and sediment yield, that could be published in the UNESCO Technical Documents in Hydrology Series, in order to demonstrate the state-of-the-art in this important area. Many of the papers built on contributions to the symposium, but others were solicited to extend the scope of the collection.

    The process of collating the papers into the final electronic form proved a lengthy task and the editors are grateful to the authors for their forbearance in accepting the resulting delays and in responding to requests for additional material. Particular thanks are extended to Dr Adrian Collins from the Department of Geography at the University of Exeter, UK, for his help with the final stages of the collation process.

    Wolfgang Summer Hagenbrunn, Austria

    Desmond Walling Department of Geography, University of Exeter, UK.

  • 1

    What approach to the modelling of catchment scale erosion and sediment transport should be adopted?

    R. J. Wasson Centre for Resource and Environmental Studies,

    Australian National University, Canberra, Australia

    Abstract

    At the catchment scale, spatial and temporal organisation emerges from a large number of physical and biological processes operating at lower levels. The long-standing method of understanding and modelling these lower level processes, from which it is claimed higher level organisation can be simulated, has thus far not produced the anticipated results. Many landscape modellers remain stuck at lower levels, and the catchment scale models required for management and scientific understanding are either not available or are too complex for meaningful use. Emphasis should now be given to either directly modelling the high level, or emergent, properties of catchments, or producing models that can reproduce these high level properties. Sediment budgets are used to explore these ideas.

    Introduction

    A commonplace assumption in the modern world of hydrological and sediment transport modelling is that processes understood at point scale can be scaled to basin areas of tens to hundreds of thousands of square kilometres. Large and expensive modelling efforts in many countries are based on this assumption, following a tradition that comes largely from classical physics. Once constructed, such models are seen as useful tools for understanding particular catchments and for predicting the impact of land use and climate change on erosion and sediment transport.

    There are two reasons for questioning the assumption that bottom-up process-based modelling is the best and only way to produce useful models:

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    1. A practical objection – models of the natural variability of rainfall infiltration, run off, erodibility, cover, channel characteristics, and sediment storage demand enormous data inputs. Such data are rarely if ever available for areas much larger than a few tens of square kilometres, and the cost of data collection is prohibitive in most countries. Highly parameterised models of the kind needed to exploit such data are essentially untestable, and while the accurate simulation of measured runoff and/or sediment yield may be obtained, it is not possible to know if it is because of correct model configuration or because of the tuning that is almost always needed to successfully simulate outputs.

    2. A philosophical objection – catchments are complex systems in which the dynamics are likely to be best understood by examining across - system organisation rather than concentrating on the parts from which a whole system view is constructed. The interaction of components produces results that generally cannot be simulated from the components; that is, the whole is emergent from a wide range of processes and interactions that are neither predictable from, deducible from, nor reducible to the parts alone (Anderson, 1992).

    In what follows, the top-down approach is adopted, whereby emergent properties of catchment are identified as a starting point for modelling, rather than the traditional approach of continuum mechanics in which processes are modelled and combined, usually in a spatial setting, using GIS, to reproduce an emergent property such as runoff or sediment yield.

    Support for the top-down approach