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Sedimentary Geology 202 (2007) 333–336www.elsevier.com/locate/sedgeo

Foreword

From particle size to sediment dynamics: An introduction

1. Introduction

This special issue presents a selection of paperspresented at an International Workshop entitled “FromParticle Size to Sediment Dynamics” which was heldfrom 15–18 April 2004 at the Hanse Institute forAdvanced Study in Delmenhorst, Germany.

2. Rationale

With the invention of physical mechanics some250 years ago, the ancient art of water engineeringbecame the modern science of hydraulics. Sedimentswere initially of little concern because flowing waterwas harnessed by fixed channels with rigid boundaries.The experience and knowledge gained by such fixedboundary hydraulics was later applied to naturalstreams. However, there are three main elementswhich interact in dynamic sedimentary systems, namelythe external physical forces acting upon the system, thetwo- and three-dimensional morphology of the system,and sedimentary particles. Because such systemscommonly have movable beds with constant morpho-logical adjustment, sediment transport phenomenabegan to interest both engineers and sedimentologists,the former to control sediment movement by speciallydesigned structures, the latter to understand and explaindepositional processes and products. In this way thescience of loose boundary hydraulics was born.

From the start it was evident that the response ofwater-borne and wind-blown sediments was in somemanner reflected in their particle size distributions. As aresult, grain-size analysis became a matter of routine andover the past century numerous attempts were made tointerpret grain-size distributions, or various statisticaldescriptors thereof, in terms of hydraulic processes.Many promising theoretical concepts evolved and wereapplied with apparent success for some time, only to be

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discarded as more about the transport behaviour ofsediments became known. For a start, there was thetechnical and analytical problem of grain-size analysis,different measurement techniques and statistical meth-ods producing different looking particle size distribu-tions. As a result, it not only is difficult to compare suchgrain-size data, but it also obscures the hydraulicprocess-response mechanisms affecting particle disper-sions and sorting during transport.

It has to be conceded that the empirical understand-ing and modelling of sedimentary morphodynamicprocess-response systems through their particle-sizedistributions has remained an elusive problem to thisday. It is therefore not surprising that this eventually ledto resignation in some scientific quarters where grain-size studies were sacrificed for other, supposedly moreproductive empirical investigations or modellingapproaches. For example, it is not uncommon thatdiscussions deal with the discrepancies between theo-retical and empirical morphodynamic approachesconcerning coastal sedimentary behaviour and howinept theoretical modelling is even in predicting long-term hindcasting, let alone forecasting. In spite of this, asmall group of scientists persisted in the search for asolution, being convinced that it existed but realizingthat it would not be easily found.

With the advent of computers, which enabled rapiddata processing with new and increasingly moresophisticated statistical procedures, the availability ofvarious modern particle-size analysis techniques and anestablished scientific community focusing on morpho-dynamics using rapidly evolving modelling techniques,the initiators of this workshop felt that – after two earlierworkshops held in 1986 and 1987 (Syvitski, 1991) – thetime had come for the sedimentological community toonce more tackle the issue of process-based interpreta-tions of particle-size distributions, this time in an inter-nationally concerted effort.

334 Foreword

3. Objectives

The workshop focused on one fundamental theme,namely “the extraction of process-related information andknowledge from temporal and spatial particle dispersionpatterns.” Because this theme has many facets, it requiresinput at a variety of levels affecting sediments between theirphysical or chemical generation, or dynamic reactivation ata variety of sources and their ultimate deposition in sinks onland and in the oceans. Such aspects range from the natureof the source materials themselves and the processes andconditions affecting them, through sampling strategies,grain-size analysis methods, statistical treatment anddescription of grain-size data, imprints imposed by erosionand transport, to the environmental conditions duringdeposition. One major objective of the workshop thus wasto present state-of-the-art overviews of selected topics inorder to provide a basis for critical evaluations, the iden-tification of major gaps in our knowledge, and recommen-dations for future research.

The ultimate aim was to gain a better understanding ofthe processes which generate and control particle-sizedistributions along transport pathways between sourcesand sinks. Such fundamental understanding is consideredessential for the development of innovative sedimenttransport models, both for the prediction of sedimentarymorphodynamic changes due to climate change or humaninterference and management, as well as the quantitativeinterpretation of modern and ancient sedimentary depo-sitional processes.

4. Topics of particular interest

Topics and questions of particular interest, which wereconsidered among the more important to be addressedwhen investigating the information contained in particle-size distributions as an indicator for progressive sizesorting and size-sorting differentiation along sedimenttransport pathways, are summarized below:

4.1. From rocks to grains: the source problem

What are the particle-size spectra of different rocktypes and how are these affected by different weatheringprocesses? Are there typical size spectra associated withparticular rock types? What kinds of source distributionsoccur and are they environment and process sensitive?

4.2. From source to sink: the transport problem

To what extent are source signals carried along thetransport path and how can these be recognized? How

are inherited size characteristics and source distributionsmodified in the course of transport? How do they re-spond to different transport modes?

4.3. From field to lab: the sampling and analysisproblem

Which sampling strategy is appropriate for whichpurpose? How should samples be recovered in the field inorder to satisfy specific objectives? Do sampling methodsaffect the nature of size distributions? How do differentgrain-size analysis techniques affect the nature of grain-size distributions? Are there quantitative ways oftransforming one into another? How should we handlethe sand–mud problem or mixtures of aggregated andnon-aggregated particles?

4.4. From reality to model: the parameterizationproblem

What are the most accepted statistical models in thescientific literature and what kind of quality assuranceprocedures do we use to make a concise choice? Whichstatistical model is appropriate for the description ofunimodal particle-size distributions? How should non-unimodal distributions be handled? Which samplestatistical descriptors serve what purpose and how welldo they reflect the nature of a grain-size population?What does the shape of a single grain-size distributionmean, considering that different techniques producedifferent distributions?

4.5. From point to area: the spatial trend problem

How can point data be most meaningfully transformedinto coherent spatial patterns? What spatial and temporalscales are involved and how should one deal with thevarious scales? What do spatial grain-size patterns revealabout the mixture of concurrent depositional and erosionprocesses?How canwe determine transport pathways andsorting from spatial patterns? What sediment trendanalysis and sorting procedures are available and howdo they perform? Have critical comparisons been carriedout and, if yes, with what results?

4.6. From now to later: the temporal trend problem

What is the natural variability of a grain-size dis-tribution at one location over various time scales? Howmuch of this is due to short-term processes and howmuch is due to sampling and analytical noise? How canwe cope with this problem? How do we interpret

335Foreword

temporal grain size trends in cores? How can continuouschanges in local sedimentation conditions be recognizedand held apart from non-continuous sequences?

4.7. From good to better: the ground-truthing problem

How can we make sure that our ex-situ analyticalresults actually reflect the real situation in nature? Arethere any in-situ analytical techniques which can improveour understanding? How do different analytical techni-ques perform in this respect? How does sedimentaryresearch combine with morphodynamic research? Howcan we test whether the outcome of a sediment trendanalysis actually conforms to trends in nature? How canwe test whether the outcome of sediment transportmodelling actually conforms to trends in nature? Whatprocedures are available to check this?

4.8. From here to everywhere: the universal applic-ability problem

To what extent are models biased towards the data(and hence locality) on the basis of which they wereconceptualized, calibrated or validated? How universalare current models?

5. Contributions

Eighteen of altogether 39 presentations at theworkshop (Flemming et al., 2005) are contained in thisspecial issue. Although some topics received less at-tention than expected, every contribution touches on atleast one of them. Overall, seven papers essentially dealwith conceptual models, measuring techniques andanalytical methodologies, the remaining eleven dealingwith case studies from a variety of terrestrial and marineenvironments.

Of several possible alternatives, we decided to groupthe contributions according to the eight themes of theworkshop. Group a): “From rocks to grains: the sourceproblem” is dealt with by Janet S. Wright whoinvestigated the role of weathering in the productionof quartz silt, and by Martin H. Iriondo and Daniela M.Kröhling who studied the generation and aeoliandistribution of “non-classical” types of Loess. Groupb): “From source to sink: the transport problem” ismostly dealt with by Edward J. Anthony and ArnaudHéquette in their work on the grain-size characterisa-tion, sediment sorting processes and mixing in the tide-and storm-dominated coast between the Somme estuaryand the Belgium border. Group c): “From field to lab:the sampling and analysis problem” is oriented towards

the group of methodological and technical topics, beingtreated by Daniel Hartmann in his exposé on operation-alism and the value chain of particle-size analysis, andby David M. Rubin, Henry Chezar, Jodi N. Harney,David J. Topping, Theodore S. Melis, and ChristopherR. Sherwood in the application of an underwatermicroscope for measuring spatial and temporal changesin bed-sediment grain sizes in rivers. Group d): “Fromreality to model: the parameterization problem” istreated by Gert Jan Weltje and Maarten A. Prins intheir study of genetically meaningful decomposition ofgrain-size distributions, by Burghard W. Flemming inhis evaluation of the influence of grain-size analysismethods and sediment mixing on curve shapes andtextural parameters and the implications thereof forsediment trend analysis, and by Jesper Bartholdy,Christian Christiansen, Jørn B.T. Pedersen who, forthe first time, have systematically compared spatial sizetrends on the basis of textural parameters generated byboth percentile statistics and the log-hyperbolic method.Group e): “From point to area: the spatial trendproblem” has received the greatest attention of all thetopics. Thus, Tae Soo Chang, Burghard W. Flemmingand Alexander Bartholomä present the results of a fieldstudy on the distinction between sortable silts andaggregated particles in muddy intertidal sediments.Alexander Bartholomä and Burghard W. Flemmingdocument and discuss progressive grain-size sortingalong an intertidal energy gradient. Jacobus P. le Rouxand Eduardo M. Rojas present a state-of-the-artoverview on sediment transport patterns determinedfrom grain size parameters, while Patrick McLaren,Steven H. Hill and Donald Bowles discuss the issue ofderiving transport pathways from sediment trendanalysis. Group f): “From now to later: the temporaltrend problem” is addressed by Christine Holz, Jan-Berend W. Stuut, Rüdiger Henrich and Helge Meggersin a study on the variability in terrigenous sedimentationprocesses off northwest Africa and its relation toHolocene climate changes, and by Diane P. Horn andSusan M. Walton who try to unravel the spatial andtemporal variations in sediment size on a mixed sandand gravel beach. Group g): “From good to better: theground-truthing problem” is dealt with by Jianhong Renand Aaron I. Packman in a study on the changes in finesediment size distributions due to interactions withstreambed sediments. And finally, Group h): “From hereto everywhere: the universal applicability problem”withDavid J. Topping, Dave M. Rubin and Theodore S.Melis who present new insights into coupled changes insand grain size and sand transport driven by changes inthe upstream supply of sand in the Colorado River,

336 Foreword

Christian Winter who evaluates sediment transportmodels in tidal environments, and Joanna C. Curranwho shows that shear stresses decrease and transportrates increase subsequent to an increase in sand supplyto a gravel-bed channel.

6. Discussion and summary

We can conclude that although particle-size analysis(PSA) is fundamental to the understanding of sedimen-tary processes, as well as being a basic tool in bothacademic and applied scientific earth sciences andengineering, there is still no generally accepted andstandardized mode of operationalism after more than acentury of intensive scientific work. We believe that themost common error in debating particle-size analysisand its contribution to the study and understanding ofsedimentary processes is the confusion between meth-odology and theory.

This volume seeks to generate debate by summariz-ing and reviewing key issues about PSA concepts,paradigms and models, as well as measurements andparameterization of PSA. We may ask once againwhether the crisis in PSA is the result of a fundamentalfailure of concepts and paradigms related to sedimentaryparticles and their textural attributes, or whether it ismerely a technical issue related to how PSA isperformed. If the latter assumption were correct, thenthe question is whether the problem can be solved bysimply improving our methods and techniques.

Therefore, one of the main achievements of theworkshop may be the realization that a unified andstandardized approach for the generation of suitableparticle-size data is one of the major challenges for thefuture. By joining forces, geoscientists may eventuallyarrive at such a unified methodology and its application.Although PSA has been fundamental to the study ofsedimentary processes, having provided a practical toolin earth sciences and engineering for over a century, itstill lacks a standardized mode of operationalism.

References

Flemming, B.W., Hartmann, D., Delafontaine, M.T. (Eds.), 2005.From particle size to sediment dynamics. Extended Abstracts,International Workshop, 15–18 April 2004, Hanse Institute forAdvanced Study, Delmenhorst, Germany. Research CentreTerramare Reports, vol. 13. 173 pp.

Syvitski, J.M.P. (Ed.), 1991. Principles, methods and application ofparticle size analysis. Cambridge University Press, New York.

Daniel HartmannLehavim 85338, Israel

Corresponding author. Tel.: +972 523932373;fax: +972 86472821.

E-mail address: danielh@bgu.ac.il.

Burg FlemmingSenckenberg Institute, Suedstrand 40, 26382

Wilhelmshaven, GermanyE-mail address: bflemming@senckenberg.de.