Sediment Dynamics in Changing Environments

Sediment Dynamics in Changing Environments Edited by Jochen Schmidt, Tom Cochrane, Chris Phillips, Sandy Elliott, Tim Davies & Les Basher IAHS Publ. 325 (2008) ISBN 978-1-901502-84-8, 626 + xiv pp. Price £.00

To understand Sediment Dynamics in Changing Environments we need to advance our knowledge of sedimentary processes and systems, and in particular of associated scaling issues. This knowledge, derived from information and analysis of historical sediment archives and system analysis and modelling, enhances our abilities to assess impacts of global change on sedimentary systems. Most importantly, we need to find ways to link our understanding and models of sedimentary systems with impacts on human environments, including hazard and risk assessment, improvement of management, and feedback into policy frameworks. The Abstracts of the papers in this papers in this book, first presented at an IAHS Symposium in New Zealand in December 2008, volume can be seen at: document the international research efforts going into the themes of: www.iahs.info 1. Unlocking the archives – dating and source tracing technologies 2. Processes and scales in sedimentary systems – from point to continents with information about other IAHS 3. Global change and erosion publications and IAHS activities 4. Linking erosion with environmental and societal impacts

Preface

Mankind is facing environmental changes of undetermined magnitude and speed in the 21st century, particularly in terms of predicted climate change. With ongoing research, we are increasing our understanding of the processes and the magnitudes of human impacts on the environment and the related risks for societies worldwide. This century will thus be one of changing environments. We have an opportunity to manage these changes by our present actions, and to quantify and to prepare for future global changes. As more scientific evidence accumulates about the magnitude and speed of past environmental changes, including sedimentary histories, we can use this information to manage present and future changes. This century must be a century of concerted research and actions in order to manage and adapt to environmental, economic and social changes. This has to involve scientists from all disciplines – in particular water-related and Earth surface process science.

Sediment Dynamics in Changing Environments was chosen as the underlying theme for the 2008 Symposium of the International Commission on Continental Erosion (ICCE) held in Christchurch, New Zealand, 1–5 December 2008 (the history of ICCE symposia is detailed at the end of the Preface). Authors from over 40 countries around the globe, with a large range of institutional and disciplinary backgrounds, met in Christchurch to:  share their knowledge about sediment dynamics in changing environments;  inspire and to be inspired to research erosion and sediment dynamics; and  work together for a better future.

The 79 papers found in this book, which were presented at the Symposium, are a testimonial to the international extent and diversity of the IAHS organisation, and document the international research efforts going into the topics of sediment dynamics and global change. Over 50 additional posters presented at the conference further explored Sediment Dynamics in Changing Environments and enhanced the meeting by providing a stimulus to share research findings and to inspire future research.

To understand Sediment Dynamics in Changing Environments, we need to advance our knowledge of sedimentary processes and systems and in particular of scaling issues in sedimentary systems. This knowledge, derived from information and analysis of historical sediment archives, and system analysis and modelling, must enhance our abilities to assess impacts of Global Change on sedimentary systems. Finally, and most importantly, we need to find ways to link our understanding and our models of sedimentary systems with impacts on human environments, including hazard and risk assessment, improvement of management options, and feedback into policy frameworks. Thus, the scientific Symposium programme was organised around four themes.

Unlocking the archives – dating and source tracing technologies explores the utility of dating sediment sinks, such as flood-plain profiles, lake, and coastal-shelf sequences, to reconstruct long-term catchment erosion and sediment yield histories and budgets. Research on source tracing/fingerprinting for understanding catchment sediment generation and dispersal are also included. The papers presented in this theme range from evaluations and

improvements of techniques currently applied in the field of dating and tracing to applied studies utilizing dating and tracing techniques to understand catchment sediment budgets and to design appropriate conservation techniques for sustainable management.

Processes and scales in sedimentary systems – from point to continents tackles problems of understanding and scaling erosion, transport, and deposition processes within sedimentary systems, including the transfer of local process understanding to larger scales; global changes and their local effects; coupling and decoupling of processes on different scales; complex system behaviour and changes in sedimentary systems, and contrasts between extreme events and long- term changes. The research presented in this section ranges from detailed studies on process behaviour at small scales (like soil armouring), to investigations into the connectivities of the sediment cascade components over a range of scales, and to analyses of the behaviour of large- scale and long-term sedimentary systems.

Global change and erosion deals with effects of climate and land-use changes on erosion and sedimentation processes, including issues like the relative importance of land-use and climate change for sedimentary systems; the sensitivity of sedimentary systems in different environments; and signatures of past environmental changes in current records and sedimentary systems. Subjects discussed in this section range from catchment and regional scale impact studies of past environmental changes to assessments of magnitudes of expected future changes in sedimentary systems on various scales.

Political and environmental management agendas often move independently of the science base. It is critical to improve linkages between science outcomes and decision making on various levels. Therefore, the theme Linking erosion with environmental and societal impacts: sediment production, river regulation, depositional environments, hazards and risks, management and policy was added to the programme. The theme includes important issues such as sediment production and its impacts on societies, sedimentary systems and catchment management, and hazard and risk (mitigation), and tools to meet policy targets in areas such as erosion-transfer of sediment-associated contaminants. The editors hope that the examples presented in this section, including topics relating to flood plain restoration, river management, and control of coastal erosion, will contribute to bridging the gap between research and practice for delivery of improved strategies for sustainable development.

The editors are grateful to all the 150+ scientists for contributing their work to generate a Symposium and an IAHS publication of high scientific quality. The task of reviewing, editing, and compiling this volume has proved to be a major challenge and our thanks go to all the authors who helped by providing manuscripts in a timely manner and by promptly responding to reviewers’ and editors’ comments and queries. A number of reviewers should be thanked for their willingness and timeliness of providing constructive criticisms – we do not name you all – you know who you are! The keynote speakers, Professor Andreas Lang, Dr James P. M. Syvitski, Professor Des Walling and Professor Michael Crozier provided the “backbone” for this volume and for the Symposium by presenting high quality evaluations of the state-of-the-art in Sediment Dynamics in Changing Environments. Finally, we wish to

express our gratitude to all the “support staff” indispensible for completing this project: to Penny Perrins and Cate Gardner from IAHS Press for supporting us in all the stages of planning and putting this publication and the Symposium together; and to Claire McConchie, Merrin McAuley, and Julia Simmons from The Conference Office, Canterbury University, for all the local support work and conference organisation.

Jochen Schmidt National Institute of Water & Atmospheric Research (NIWA) 10 Kyle Street, Riccarton, Christchurch 8011, New Zealand Tom Cochrane Department of Civil and Natural Resources Engineering, University of Canterbury Civil/Mechanical Building, 67 Creyke Road, Ilam, Christchurch, New Zealand Chris Phillips Landcare Research Gerald Street, Lincoln 7608, New Zealand Sandy Elliott National Institute of Water & Atmospheric Research (NIWA) Gate 10 Silverdale Road, Hillcrest, Hamilton 3216, New Zealand Tim Davies Department of Geological Sciences, University of Canterbury Geology building, 67 Creyke Road, Ilam, Christchurch, New Zealand Les Basher Landcare Research 16 Paru Paru Road, Nelson 7010, New Zealand

ICCE SYMPOSIA SERIES Since the early 1980s, the International Commission on Continental Erosion (ICCE) of the International Association of Hydrological Sciences (IAHS) has organized a series of highly successful symposia dealing with various aspects of erosion and sedimentation. (Volumes marked with * are available for free download at http://iahs.info/publications/redbooks.)

In 1981, a Symposium was held in Christchurch, New Zealand, entitled: The Symposium on Erosion and Sediment Transport in Pacific Rim Steeplands, Christchurch, New Zealand, 1981 (IAHS Publ. 132*). After that a series of Symposia followed: The Symposium on Erosion and Sediment Transport Measurement, Florence, Italy, 1981 (IAHS Publ. 133*) The Symposium on Recent Developments in the Explanation and Prediction of Erosion and Sediment Yield, Exeter, UK, 1982 (IAHS Publ. 137*) The Symposium on Dissolved Loads of Rivers and Water Quantity/Quality Relationships, Hamburg, Germany, 1983 (IAHS Publ. 141*) The Symposium on Drainage Basin Sediment Delivery, Albuquerque, New Mexico, USA, 1986 (IAHS Publ. 159*) The Workshop on Erosion, Transport and Deposition Processes, Jerusalem, Israel, 1987 (IAHS Publ. 189*) The Symposium on Sediment Budgets, Porto Alegre, Brazil, 1988 (IAHS Publ. 174*) The Symposium on Sediment and the Environment, Baltimore, USA, 1989 (IAHS Publ. 184*) The Symposium on Erosion, Debris Flows and Environment in Mountain Regions, Chengdu, China, 1992 (IAHS Publ. 209*) The Symposium on Erosion and Sediment Transport Monitoring Programmes in River Basins, Oslo, Norway, 1992 (IAHS Publ. 210*) The Symposium on Sediment Problems: Strategies for Monitoring Prediction and Control, Yokohama, Japan, 1993 (IAHS Publ. 217*) The Symposium on Variability in Stream Erosion and Sediment Transport, Canberra, Australia, 1994 (IAHS Publ. 224*) The Symposium on the Effects of Scale on the Interpretation and Management of Sediment and Water Quality, Boulder, USA, 1995 (IAHS Publ. 226*) The Symposium on Erosion and Sediment Yield: Global and Regional Perspectives, Exeter, UK, 1996 (IAHS Publ. 236) The Symposium on Human Impact on Erosion and Sedimentation, Rabat, Morocco, 1997 (IAHS Publ. 245) The Symposium on Modelling Soil Erosion, Sediment Transport and Closely Related Hydrological Processes, Vienna, Austria, 1998 (IAHS Publ. 249) The Symposium on the Role of Erosion and Sediment Transfer in Nutrient and Contaminant Transfer, Waterloo, Canada, 2000 (IAHS Publ. 263) The Workshop on Erosion and Sediment Transport Measurement in Rivers: Technological and Methodological Advances, Oslo, Norway, 2002 (IAHS Publ. 283) The Symposium on the Structure, Function and Management Implications of Fluvial Sedimentary Systems, Alice Springs, Australia, 2002 (IAHS Publ. 276) The Symposium on Erosion Prediction in Ungauged Basins: Integrating Methods and Techniques, Sapporo, Japan, 2003 (IAHS Publ. 279) The Symposium on Sediment Transport through the Fluvial System, Moscow, Russia, 2004 (IAHS Publ. 288) The Symposium on Sediment Budgets, Foz do Iguaçu, Brazil, 2005 (IAHS Publs 291 and 292) The Symposium on Sediment Dynamics and the Hydromorphology of Fluvial Systems, Dundee, Scotland, 2006 (IAHS Publ. 306).

And finally in 2008, 27 years after the 1981 Christchurch Symposium, Christchurch again hosted a Symposium: The Symposium on Sediment Dynamics in Changing Environments, Christchurch, New Zealand, 2008 (IAHS Publ. 325). CONTENTS 1 Unlocking the archives – dating and source tracing technologies

Recent advances in dating and source tracing of fluvial deposits A. Lang Assessing the remobilisation of recently deposited sediment from river flood plains during single overbank flood events, using caesium-134 and cobalt-60 as tracers P. Greenwood, D. E. Walling & T. A. Quine Influence of particle size on geochemical suspended sediment tracing in Australia Baihua Fu, Lachlan T.H. Newham & John B. Field Sediment source fingerprinting: testing hypotheses about contributions from potential sediment sources Jean P. G. Minella, Robin T. Clarke, Gustavo H. Merten & Des E. Walling

210 Mass balance models for use with Pbex measurements to estimate soil loss from cultivated land Xinbao Zhang, Des Walling, Xiubin He & Yunqi Zhang Use of Beryllium-7 to assess soil redistribution by erosion in two contrasting Mediterranean environments A. Navas, D. E. Walling, L. Gaspar & J. Machin The sources and dispersal of sediment within a large flood plain complex M. C. Thoms, S. Brennan & S. W. Franks Determination and interpretation of sediment provenance in a sedimentary sequence affected by post-depositional changes R. Cossart, M. C. Thoms & M. A Reid Flood plain nutrient dynamics: patterns, controls and the influence of changing hydrology A. G. Lowes, M. R. Southwell & M. C. Thoms Recent tidal-flat evolution and mangrove-habitat expansion: application of radioisotope dating to environmental reconstruction A. Swales & S. J. Bentley Identifying relationships between flood history, flood frequency and the provenance of surface sediments in a semi-arid terminal wetland S. C. Rayburg & M. C. Thoms Uncertainty assessment in suspended sediment fingerprinting based on tracer mixing models: a case study from Luxembourg N. Martínez-Carreras, F. Gallart, J. F. Iffly, L. Pfister, D. E. Walling & A. Krein Response of a small arable catchment sediment budget to introduction of soil conservation measures V. N. Golosov, V. R. Belyaev, J. S. Kuznetsova, M. V. Markelov & E. N. Shamshurina Combining direct observations, modelling, and 137Cs tracer for evaluating individual event contribution to long-term sediment budgets

V. R. Belyaev, V. N. Golosov, K. S. Kislenko, J. S. Kuznetsova & M. V. Markelov Connecting the disconnected: longitudinal correlation of river terrace remnants M. D. Cheetham, A. F. Keene, W. D. Erskine, R. T. Bush & G. Jacobsen Intensity of soil erosion and sedimentation inferred from spatial distribution of radionuclide 137Cs in hillslope catchments, South Korea

A. Orkhonselenge, K. Kashiwaya & Y. K. Kim Redistribution of soil and soil organic carbon on agricultural landscapes J. C. Ritchie & G. W. McCarty Post-European settlement impacts on erosion and land degradation: a case study using farm reservoir sedimentation in the Eastern Cape, South Africa Kate Rowntree, Ian Foster, Tim Mighall, Leanne DuPreez & John Boardman Sediment fingerprinting in New Zealand: a pilot study into the feasibility of the application of the technique B. P. Roddy, J. L. McWhirter, V. G. Moon, M. R. Balks & F. J. Dyer 2 Processes and scales in sedimentary systems – from point to continents

Scaling sediment flux across landscapes J. P. M. Syvitski & A. J. Kettner Sediment yield modelling at micro-basin and basin scales in semi-arid regions of Brazil E. E. De Figueiredo Soil armouring and weathering: toward catchment scale computational modelling S. Cohen, G. R. Willgoose & G. R. Hancock An evaluation of the role of physical models in exploring form–process feedbacks in alluvial fans L. E. Clarke, T. A. Quine & A. P. Nicholas The signature of an extreme erosion event on suspended sediment loads: Motueka River Catchment, South Island, New Zealand D. M. Hicks & L. R. Basher Changing suspended sediment dynamics due to extreme flood events in a small pluvial-nival system in northern Japan A. C. Whitaker, H. Sato & H. Sugiyama The effect of local-scale valley constrictions on flood inundation and catchment-scale sediment delivery in the Fitzroy River Basin, Australia J. C. Croke, D. Purvis-Smith, C. J. Thompson & Leo Lymburner Sediment yield from seismically-disturbed mountainous watersheds revealed by multi-temporal aerial LiDAR surveys Akira Matsuoka, Takao Yamakoshi, Keiji Tamura, Jun Maruyama & Kiichiro Ogawa A study of spatial scaling in suspended sediment yield along a rural river system – the River Eden, Cumbria, UK C. F. Mills, J. C. Bathurst & P. F. Quinn Using remote sensing to quantify sediment budget components in a large tropical river – Mitchell River, Gulf of Carpentaria A. P. Brooks, J. Spencer, J. G. Shellberg, J. Knight & L. Lymburner Off-slope sediment delivery from landsliding during a storm, Muriwai Hills, North Island, New Zealand N. J. Preston SPARROW regional regression for sediment yields in New Zealand rivers A. H. Elliott, U. Shankar, D. M. Hicks, R. A. Woods & J. R. Dymond Morphometric analysis of interfluve topography for scaling soil erosion rates from local to regional scales Y. Kuznetsova & V. Golosov Sediment storage in Alpine sedimentary systems – quantification and scaling issues J.-C. Otto, J. Goetz & L. Schrott Stochastic sediment–vegetation dynamics in an Alpine braided river P. Perona, P. Molnar, M. Savina & P. Burlando Connectivity in steep-land environments: gully–fan coupling in the Tarndale system, Waipaoa catchment, New Zealand Ian C. Fuller & Mike Marden Channel incision and sand compartmentalization in an Australian sandstone basin subject to high flood variability W. D. Erskine Multi-scale sediment dynamics in an upland catchment, southeastern Australia: a synthesis Hugh G. Smith & Deirdre Dragovich Holocene alluvial sediment deposition in contrasting environments in northwestern Europe B. Notebaert & G. Verstraeten Flood-induced changes in the step-pool morphology of a steep mountain stream P. Molnar, A. L. Densmore, B. W. McArdell & P. Burlando Suspended sediment dynamics and transport into the Babitonga Bay, southern Brazil F. A. Oliveira & J. L. S. Ross Recent sedimentation rates for the Rees-Dart braided river delta Michelle Wild, Thomas Cochrane, Tim Davies, Murray Hicks, David Painter & Gavin Palmer Sediment movement from small catchments within the Moldavian Plateau of eastern Romania I. Ionita 3 Global change and erosion

The changing sediment loads of the world’s rivers D. E. Walling Gully erosion and sediment load: Waipaoa, Waiapu and Uawa rivers, eastern North Island, New Zealand Michael Marden, Harley Betts, Gregory Arnold & Randolph Hambling Sediment sources in a dry-tropical catchment: central Queensland, Australia A. O. Hughes, J. M. Olley, J. C. Croke & L. A. McKergow Chemical and physical weathering in a mountainous tributary of the Zhujiang (Pearl River), China Shu-Rong Zhang & X. X. Lu Sensitivity of Alpine fluvial environments in the Swiss Alps to climate forcing during the Late Holocene L. Schulte, R. Julià, M. Oliva, F. Burjachs, H. Veit & F. Carvalho An overlooked sediment trap in arid environments: ancient irrigation agriculture in the coastal desert of Peru Jussi Baade & Ralf Hesse Glacial–interglacial cycles, soil erosion and natural desertification in the Middle East Yoav Avni Changing sediment supply in Arctic rivers Irina Overeem & James P. M. Syvitski Mapping potential soil erosion in East Africa using the Universal Soil Loss Equation and secondary data Lieven Claessens, Paulo Van Breugel, An Notenbaert, Mario Herrero & Jeannette Van De Steeg The Waipaoa Sedimentary System: research review and future directions N. Litchfield, K. Berryman, H. Brackley, L. Carter, M. Marden, M. Page & N. Trustrum Climatic and anthropogenic effects on soil transport rates and hillslope evolution P. C. Almond, J. J. Roering, M. W. Hughes, F. S. Lutter & C. Lebouteiller Will human catalysts or climate change have a greater impact on the sediment load of the Waipaoa River in the 21st century? A. J. Kettner, B. Gomez & J. P. M. Syvitski The impact of climate change on glacial sediment delivery to rivers Jim Bogen Reconstructing historical sediment yields from the infilling of farm reservoirs, Eastern Cape, South Africa Ian D. L. Foster, John Boardman & John B. Gates National-scale sediment delivery to watercourses across England and Wales under recent (1970–2004) land-use change A. L. Collins, D. Duethmann & P. Taylor Land-use impacts on catchment erosion for the Waitetuna catchment, New Zealand J. Schmidt, S. Elliott & L. McKergow The effects of rapid and catastrophic sedimentation in tectonically active areas James Goff Impacts of the 921 Ji-Ji earthquake, Taiwan, on channel morphology and channel evolution Y. H. Hsu & Y. S. Hsu 4 Linking erosion with environmental and societal impacts: sediment production, river regulation, depositional environments, hazards and risks, management and policy

Linking erosion with environmental and societal impacts in a rapidly changing environment M. J. Crozier Erosion without sediment supply? The crux of a flood-plain restoration project downstream of dammed headwaters Bernd Cyffka & Florian Haas Sediment dynamics and improvised control technologies in the Athi River drainage basin, Kenya Shadrack Mulei Kithiia Recurrent displacement of a forested earthflow and implications for forest management, East Coast Region, New Zealand Michael Marden, Chris J. Phillips & Donna Rowan Estimating the spatial distribution of sediment concentration in the Manawatu River, New Zealand, under different land-use scenarios

A.-G. E. Ausseil & J. R. Dymond Impacts of wildfire and post-fire salvage logging on sediment transfer in the Oldman watershed, Alberta, Canada Uldis Silins, Micheal Stone, Monica Emelko & Kevin Bladon Managing coastal erosion: from long-term coastal evolution to seasonal shoreline changes L. S. Esteves, P. Teixeira & J. J. Williams Hydrological and sedimentological connectivity of unsealed roads C. J. Thompson, I. Takken & J. Croke Hydrological recovery of rangeland following cattle exclusion A. A. Hawdon, R. J. Keen, D. A. Post & S. N. Wilkinson Improved sediment-management strategies for the sustainable development of German waterways E. Goelz Predicting decadal-scale estuarine sedimentation for planning catchment development M. O. Green Testing the capability of a sediment budget model for targeting remediation measures to reduce suspended-sediment yield Scott N. Wilkinson Impacts of native forest harvesting on in-channel erosion and sediment yields in unmapped headwater catchments Ashley A. Webb Reformation of pool-riffle sequences and induced bed armouring in a sand-bed stream following river rehabilitation A. F. Keene, R. T. Bush, M. D. Cheetham & W. D. Erskine Evidence for catastrophic shifts in the trophic structure of flood-plain lakes associated with soil erosion Michael Reid The effect of increasing urbanization and population density on the concentrations of sediment-associated constituents for the conterminous US A. J. Horowitz & V. C. Stephens Towards improving the prediction of longshore sediment transport J. J. Williams, L. S. Esteves & M. A. Lisniowski Changes in sediment discharge after the collapse of Mount Bawakaraeng in South Sulawesi, Indonesia L. L. Dhanio, T. Mizuyama, K. Kosugi & D. A. Rampisela Influence of the changing environment on sediment loads of the Lower Mekong River J. J. Wang & X. X. Lu Modelling hillslope soil erosion at ANZAC Cove, Turkey S. Matthews & M. N. Neave ______Sediment Dynamics in Changing Environments (Proceedings of a symposium held in Christchurch, New Zealand, December 2008). IAHS Publ. 325, 2008, 3-12.

Recent advances in dating and source tracing of fluvial deposits

A. LANG Department of Geography, University of Liverpool, Liverpool L69 7ZT, UK [email protected]

Abstract Establishing well-resolved chronologies is essential for any kind of environmental reconstruction. Linking responses of sedimentary systems to climate change and human impacts requires independent age information: (i) to establish response types; (ii) to identify response lags; (iii) to quantify rates of change; and (iv) to estimate magnitudes of sediment flux within the systems. Here, current technological advances in dating approaches are reviewed and their applicability for a better understanding of fluvial systems are discussed. Rapid technological development has led to recent advances in many chronometric fields. These range from fundamental innovations that allow completely new applications to advances that improve the performance of existing techniques. Also discussed is the breakthrough achieved for constructing age- models from chronometric data based on statistical techniques and taking into account data precision and stratigraphic information. Key words U-series; cosmogenic nuclides; TCN; radiocarbon; luminescence; ESR; racemisation; dendrochronology; lichonometry; age-model

______Sediment Dynamics in Changing Environments (Proceedings of a symposium held in Christchurch, New Zealand, December 2008). IAHS Publ. 325, 2008, 13-22.

Assessing the remobilisation of recently deposited sediment from river flood plains during single overbank flood events, using caesium-134 and cobalt-60 as tracers

P. GREENWOOD, D. E. WALLING & T. A. QUINE Department of Geography, University of Exeter, Amory Building, Rennes Drive, Exeter EX4 4RJ, UK [email protected]

Abstract River flood plains can represent important stores of fine sediment and sediment-associated contaminants and there is therefore a need to develop an improved understanding of the rates and patterns of fine sediment deposition during overbank flood-events and its subsequent fate. Most existing studies have focused on deposition rates and only limited attention has been given to the potential for remobilisation of the recently deposited sediment during subsequent events. This communication reports an attempt to develop a tracing technique to address this problem. The approach employed involves placing small quantities of fine sediment, pre-labelled with artificial radioisotopes, on the flood plain surface and documenting the changes in the tracer inventories after subsequent overbank flood events. Reduced inventories provide evidence of sediment remobilisation. The magnitude of the reduction in the inventory provides information on the extent of the remobilisation, which can be related to the local physical conditions. This approach has been applied on two river flood plains in Devon, UK, where it was possible to document the change in tracer inventories after two subsequent overbank flood events. Remobilisation occurred at 80% and 87% of the measuring points on each flood plain during the first inundation event and at 67% and 73% during the second. The results confirm the potential importance of remobilisation of recently deposited sediment during subsequent overbank flood events. Key words caesium-134; cobalt-60; flood plain; sediment remobilisation; deposition; single overbank flood event; in situ gamma spectrometer

Influence of particle size on geochemical suspended sediment tracing in Australia

BAIHUA FU, LACHLAN T. H. NEWHAM & JOHN B. FIELD The Fenner School of Environment and Society, The Australian National University, Canberra, Australian Capital Territory 0200, Australia [email protected]

Abstract Suspended sediment tracing is a potentially useful method to identify the sources of suspended sediment in rivers. Sediment tracing relies on the use of representative and conservative tracers. Particle size is known to influence sediment geochemistry and yet its quantitative impact on sediment source discrimination is little known in Australia and worldwide. This paper investigates the influence of particle size on geochemical sediment tracing in southeastern Australia. The effects of particle size on sediment source discrimination are investigated using a multivariate mixing model. The results suggest geochemistry is a useful tracer for metasediment dominated catchments. Element concentrations are enriched in the finer fraction, but the differences of particle size distributions between sources and mixture are not sufficient to result in differences in source discrimination. The study demonstrates the less than 63 µm fraction to be a representative particle size for geochemical suspended sediment tracing in the lithologically-uniform catchments of Australia. Key words tracing; fingerprinting; sediment tracing; suspended sediment; particle size; geochemistry; metasediment

Sediment source fingerprinting: testing hypotheses about contributions from potential sediment sources

JEAN P. G. MINELLA1,2, ROBIN T. CLARKE1, GUSTAVO H. MERTEN1 & DES E. WALLING3 1 Institute of Hydraulic Research, Federal University of Rio Grande do Sul, PO Box 15029, 91501-970 Porto Alegre, RS, Brazil [email protected] 2 Department of Soils, Federal University of Santa Maria, 97105-900, Santa Maria, RS, Brazil 3 Department of Geography, Exeter University, Amory Building, Rennes Drive, Exeter EX4 4RJ, UK

Abstract Techniques involving composite fingerprints and multivariate mixing models are being increasingly used in catchment studies to establish the relative contributions of potential sources to the suspended sediment output. Such information is important both for understanding the fine sediment dynamics of a catchment and for targeting remediation measures required to reduce sediment-related environmental problems. A multivariate mixing model algorithm, which compares the concentrations of a range of geochemical properties of the suspended sediment load with those of a number s of potential sources, is commonly used to provide estimates of the relative contributions (P1, P2, ..., Ps) of those sources to the suspended sediment load. However, such models do not provide measures of the uncertainty associated with the P-values. This paper describes how the usual mixing model can be modified, such that the optimization procedure used to estimate the sediment proportions P1, P2 … contributed by different sources also provides measures of their uncertainty. This approach allows hypotheses concerning the P values to be tested, such as: (i) whether the individual P-values differ significantly from zero, and (ii) whether the P- values change significantly between events. To calculate the uncertainty associated with a P-value, a statistical model which considers the correlation between the tracer variables is used. This approach has been tested using data from a small rural catchment in southern Brazil where a sediment source investigation is in progress. Sediment samples collected during 48 storm events were used to establish the source contributions. Key words suspended sediment; source fingerprinting technique; multivariate mixing model; uncertainty analysis; optimization; soil management; Brazil

210 Mass balance models for use with Pbex measurements to estimate soil loss from cultivated land

XINBAO ZHANG1, DES WALLING2, XIUBIN HE1 & YUNQI ZHANG1 1 Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, Chengdu 610041, China [email protected] 2 Department of Geography, University of Exeter, Exeter EX4 4RJ, UK

Abstract 210Pb (half-life 22.3 years) is a natural product of the 238U decay series that is derived from the decay of gaseous 222Rn (half-life 3.8 days), the daughter of 226Ra (half-life 1622 years). Like fallout 137Cs, 210 Pbex reaching the land surface as fallout from the atmosphere will be rapidly adsorbed by the surface soil and its subsequent redistribution within the landscape will reflect the movement of soil and sediment particles associated with soil erosion and sediment transport processes. The radionuclide therefore offers considerable potential for use as a tracer for estimating soil erosion rates. It can be used in regions where 137Cs inventories are low, and therefore difficult to measure, or where they are complicated by additional Chernobyl inputs. Furthermore, due to its essentially constant input over time, it can provide information on erosion rates over a longer period of time. Conversion models utilizing a mass balance approach have 210 been developed for deriving estimates of soil redistribution rates on cultivated land from Pbex measurements. There is, however, a need to refine these models to take account of key features of the 210 210 redistribution of Pbex in the soil profile. In most cultivated soils Pbex is evenly distributed within the 210 plough layer, but a small proportion of the Pbex inventory is commonly found below the plough layer, 210 forming a tail to the depth distribution. This tail reflects the downward movement of Pbex into the soil below the plough layer by a range of mechanisms that can be represented as diffusion and migration 210 processes. Existing conversion models ignore this feature of the depth distribution of Pbex in cultivated soils and therefore overestimate rates of soil loss. This paper reports the development of a revised mass balance model that takes account of the tail of the depth distribution. Soil losses estimated by using the revised model are greater than those estimated by the existing models and the extent is determined by the 210 soil properties, which are related to transportation of the Pbex nuclide from the plough layer to the plough 210 pan layer, such as the plough depth (H), the Pbex depth distribution coefficient (h0) in the plough pan layer and the ratio of soil bulk densities between the plough pan layer and plough layer (γpp/γp). 210 Key words Pbex fallout; cultivated land; soil losses; mass balance model; revision

Use of Beryllium-7 to assess soil redistribution by erosion in two contrasting Mediterranean environments A. NAVAS1, D. E. WALLING2, L. GASPAR1 & J. MACHIN1 1 Estación Experimental de Aula Dei. CSIC Apartado 13034, 50080 Zaragoza, Spain [email protected] 2 Department of Geography, University of Exeter, Amory Building, Rennes Drive, Exeter EX4 4RJ, UK

Abstract In the Mediterranean region there is growing concern for the potential increase in erosion risk associated with climate change and increasing storm frequency. The central Ebro basin is the region facing the greatest problems of desertification in northern Spain and there is a need to assemble information on short-term erosion rates associated with individual storm events. The 7Be technique offers considerable potential to document short-term erosion rates, but to date there has been little attempt to use it in Spain. This contribution reports the results of a study aimed at using the 7Be technique to document short-term erosion rates associated with storm events in two study areas within the central Ebro basin and to investigate the influence of land use and slope gradient on the rates and patterns of soil redistribution. These study areas were located in the central gypsiferous plain and the mountainous area bordering the basin. In the mountain location, the 7Be areal activity density in the stony soils sampled along a 24% slope transect showed large variations (between 16.4 and 262.1 Bq m-2). Erosion dominated at most sampling points and estimated soil losses ranged between 5.5 and 40 Mg ha-1. On the gentler slopes of the central plain, 7Be inventories ranged between 20 and 170.3 Bq m-2 and there was greater evidence of deposition as well as erosion. The highest soil redistribution rates (–42 and 33 Mg ha-1) were found on cultivated soils. The 7Be inventories suggest that soil surface characteristics, such as stone and litter cover, in addition to land use and slope gradient, may affect the pattern of soil redistribution. The two case-studies reported provide evidence of relatively high short-term erosion and soil redistribution rates associated with individual storm events and confirm the potential for using 7Be to assemble information on erosion and soil redistribution rates in Mediterranean environments. Key words 7Be; fallout radionuclides; radiotracing; soil erosion; soil redistribution; stony soils; Mediterranean environments; central Ebro valley, Spain

The sources and dispersal of sediment within a large flood plain complex

M. C. THOMS1, S. BRENNAN1 & S. W. FRANKS2 1 Riverine Landscapes Research Laboratory, University of Canberra, Australian Capital Territory 2601, Australia [email protected] 2 School of Engineering, University of Newcastle, New South Wales 2308, Australia

Abstract Knowledge of sediment sources and their dispersal across the landscape is essential for understanding the dynamics of flood plain ecosystems. This is important for flood plain management because rates of upstream catchment erosion are predicted to increase considerably throughout much of inland Australia. In this study, the provenance and dispersal of sediment across a large lowland flood plain complex are investigated. A range of non-soluble geochemical elements were used in a Bayesian mixing model to determine the source and dispersal of very fine sand and clay sized particles across the lower Balonne flood plain in SE Australia. These two sediment fractions were chosen because they are the dominant material present within this flood plain complex. The relative contribution of the two main sediment sources differed for each of the sediment fractions. Clay sized particles were predominantly derived from the Maranoa catchment, whereas the very fine sand was derived from the Condamine catchment. In terms of the dispersal of these sediment fractions from the two main sources, very fine sands were dispersed relatively uniformly across the Lower Balonne flood plain, whereas the clay sized sediment was restricted to the main flow channels that dissect this flood plain. These spatial patterns are contrary to that expected in terms of the dispersal ability of sediment across flood plain surfaces and result from the complex hydrology of the flood plain surface along with the timing of flow events originating from the two tributaries. Key words sediment dispersal; complex systems; Murray Darling Basin ______Sediment Dynamics in Changing Environments (Proceedings of a symposium held in Christchurch, New Zealand, December 2008). IAHS Publ. 325, 2008, 60-67.

Determination and interpretation of sediment provenance in a sedimentary sequence affected by post-depositional changes

R. COSSART, M. C. THOMS & M. A. REID Riverine Landscapes Research Laboratory, University of Canberra, Australian Capital Territory 2601, Australia [email protected]

Abstract Post-depositional alteration of flood plain sedimentary deposits is a problem for the interpretation of environmental change. In particular, groundwater movement can alter the physical and chemical character of these deposits. This study considers the potential influence of post-depositional change on the geochemical character of sediments contained within the Narran flood plain, in semi-arid Australia, and the implications for interpreting environmental change. A series of 12 cores, ranging in length from 6 to 15 m, were collected from a number of different geomorphic regions across the flood plain. Stratigraphic analysis of the individual cores revealed extensive mottling and iron staining of sediments in all cores along with the presence of well developed carbonate nodules between 5 and 15 m below the surface. At this level of resolution it would appear that post-depositional processes have significantly influenced the geochemical character sediments within this flood plain deposit. However, a statistical comparison of the low and high solubility elements noted only small differences in the geochemistry of sediment within and between the different stratigraphic units of the individual cores. It appears that although the flood plain deposit has experienced post-depositional influences, as evident through the stratigraphic analysis, this has had little overall influence on sediment geochemistry. This highlights the importance of being scale aware when interpreting the environmental history of flood plain environments. In addition the study demonstrates the utility of integrating standard sedimentological and numerical techniques in unravelling environmental histories, possible post depositional processes and groundwater influences in flood plain depositional environments. Key words flood plain deposits; post depositional processes; multivariate analyses; groundwater

Flood plain nutrient dynamics: patterns, controls and the influence of changing hydrology

A. G. LOWES, M. R. SOUTHWELL & M. C. THOMS Riverine Landscapes Research Laboratory, Faculty of Science, University of Canberra, Australia Capital Territory 2601, Australia [email protected]

Abstract Dissolved nutrients are mobilised from flood plain surfaces during periods of inundation. These dissolved materials are an essential resource for the functioning of flood plain–river ecosystems. However, little is known of the dynamics of nutrient release during periods of flood plain inundation or the factors controlling their release. Patterns of total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) released from flood plain sediments were investigated in this study. In a series of experiments conducted over a 72-h period, sediments collected from various flood plain surfaces were wetted in order to assess possible controls, spatial patterns, and the influence of changing hydrology on the release of dissolved nutrients. Top-down constraints, including the reach location, degree of confinement and elevation above the river bed, all had a significant impact on release rates for TOC, as well as release rates and concentrations of TN. Sediment texture was significantly associated with TP concentrations only; although sediment texture was associated with TN and TOC release rates over time. These results indicate that larger scale constraints, such as position in the broader riverine landscape, influence spatial patterns of nutrient release rates over time more than smaller scale influences such as sediment texture. Using the release data for the various flood plain surfaces, combined with long-term flow data for several flow scenarios, simple budgets for dissolved nutrients were calculated for the study reach over the 1922–2000 period. A 43% reduction in the potential supply of dissolved nutrients was demonstrated with changes in river hydrology over this 78-year period associated with water resource developments. Key words flood plain–river exchanges; complex systems; water resource development

Recent tidal-flat evolution and mangrove-habitat expansion: application of radioisotope dating to environmental reconstruction

A. SWALES1 & S. J. BENTLEY2 1 NIWA, National Institute of Water and Atmospheric Research, PO Box 11-115, Hamilton, New Zealand [email protected] 2 Earth-Sciences Department, 6010 Alexander Murray Building, Memorial University of Newfoundland, St Johns, Newfoundland A1B 3X5, Canada

Abstract Mangrove-habitat expansion and tidal flat evolution in the Firth of Thames (North Island, New Zealand) is reconstructed using dated sediment cores (210Pb, 137Cs) and field observations to explore interactions between sediment processes and mangrove ecology. Mangrove habitat in the southern Firth has expanded rapidly over the last five decades, colonising prograding intertidal mudflats. The original lower- intertidal sand flat was transformed by the erosion of millions of m3 of mud following catchment deforestation (1850s–1920s). Sediment accumulation rates (SAR) on the tidal flats over the last 60 years have averaged approx. 20 mm year-1, outstripping sea level rise (1.3 mm year -1). Mangrove colonisation was delayed until the early 1950s when surface elevation reached approx. 0.5 m above mean sea level (MSL). Maximum SAR of approx. 100 mm year-1 occurs in the seaward edge of the mangrove forest. In contrast, SAR in the landward old-growth forest have averaged <10 mm year -1 since the 1970s as the forest was progressively isolated by distance and elevation from the tidal-flat. The forest today at 1.7 m above MSL is near the upper tidal limit and is infrequently inundated. Feedbacks between surface elevation, tidal inundation and sediment supply exert strong controls. The fate of the mangrove forest will depend on surface elevation increasing at a rate equal to or exceeding sea level rise. Key words 210Pb; 137Cs; dating; sedimentation; surface elevation; tidal inundation; sea level

Identifying relationships between flood history, flood frequency and the provenance of surface sediments in a semi- arid terminal wetland

S. C. RAYBURG & M. C. THOMS Riverine Landscapes Research Laboratory, University of Canberra, Australian Capital Territory 2601, Australia [email protected]

Abstract In semi-arid environments, dryland wetlands serve as key loci for biological diversity and productivity. This stems from their relative abundance of water and the comparative richness of their soils which are reinvigorated by the delivery of sediment and nutrients during relatively infrequent flood events. Therefore, to fully understand the nature of these environments, it is important to understand the links between the delivery of water and sediment (particularly with respect to varying sediment sources) to semi- arid wetlands and the physical and chemical properties of the surface sediments deposited within them. The purpose of this study was to: (1) determine the provenance (e.g. locally derived or fluvial sources) of surface sediments within a semi-arid wetland, the Narran Lakes Ecosystem in central eastern Australia; (2) determine how sediment provenance relates to flood frequency and flood history; and (3) identify variations in the physical and chemical properties of sediments with different sources. The study employs a set of 163 samples, collected along an irregular grid spaced at ~1.8 km, which were analysed to determine the physical and chemical properties of the surface sediments. The ratio of titanium to aluminium (Ti/Al) was used to differentiate between fluvial sub-catchment and locally derived sediment sources. The sourced sediments were then compared to flood frequency maps in the wetland and related to the flood history of the two principal source sub-catchments to see if sediment sourcing could be reliably linked with long term flood inundation patterns. The results of this study indicate that there are distinct and strong associations between the source of the sediments in a particular location of the wetland and the frequency of flooding that occurs there. These associations can be more completely understood by examining the flood history of the source sub-catchments. In addition, the sediments derived from each fluvial source and from locally derived hillslopes have distinct differences in their physical and chemical properties. Thus, the nature of the sediments and the resultant ecology of the Narran Lakes Ecosystem may be influenced by differential sediment sources. Key words sediment sourcing; Narran Lakes Ecosystem; Murray Darling Basin; Ti/Al ratio; fingerprinting

Uncertainty assessment in suspended sediment fingerprinting based on tracer mixing models: a case study from Luxembourg

N. MARTÍNEZ-CARRERAS1, F. GALLART2, J. F. IFFLY1, L. PFISTER1, D. E. WALLING3 & A. KREIN1 1 Public Research Centre - Gabriel Lippmann, Department of Environment and Agro-Biotechnologies, Research Unit GEOSAT, 41 rue du Brill, L-4422 Belvaux, Grand Duchy of Luxembourg [email protected] 2 Institute of Earth Sciences “Jaume Almera”, CSIC, Lluis Solé Sabarís s/n, 08028 Barcelona, Spain 3 School of Geography, Archaeology and Earth Resources, University of Exeter, Amory Building, Rennes Drive, Exeter EX4 4RJ, UK

Abstract The primary purpose of this paper is to explore the various sources of uncertainty associated with the use of the fingerprinting approach, based on multivariate mixing models, to establish suspended sediment sources. Model uncertainty has been investigated using a Monte Carlo simulation technique. A key aim of the study is to assess the relative importance to the uncertainty of the output of: (1) the number and type of tracers included in the mixing model, and (2) the spatial variability of the tracer signatures of individual sources. The results obtained showed that the main source of uncertainty was the number of tracers included in the model, and the spatial variability of the tracer signatures associated with an individual source, whereas the types of tracers included were shown to be of lesser importance. The various assessments of the uncertainty associated with sediment fingerprinting were, however, conditioned by the assumptions made. This study demonstrates that the precision and coherence of source ascription partitioning can be improved by: (1) incorporating tracer weightings to reflect the spatial variability of source signatures, and (2) constraining the mixing model to reflect current process understanding. Despite the uncertainties involved, the proposed methodology provides a formalized procedure by which sediment source contributions can be readily established using tracer mixing models. Key words suspended sediment sources; fingerprinting approach; multivariate mixing models; uncertainty analysis; Grand Duchy of Luxembourg ______Sediment Dynamics in Changing Environments (Proceedings of a symposium held in Christchurch, New Zealand, December 2008). IAHS Publ. 325, 2008, 106-113.

Response of a small arable catchment sediment budget to introduction of soil conservation measures

V. N. GOLOSOV, V. R. BELYAEV, J. S. KUZNETSOVA, M. V. MARKELOV & E. N. SHAMSHURINA Laboratory of Soil Erosion and Fluvial Processes, Faculty of Geography, Moscow State University, GSP-1, Leninskie Gory, 119991 Moscow, Russia [email protected]

Abstract This paper presents reconstructions of sediment budgets for a small arable catchment for two time periods: before and after the introduction of soil conservation measures in its upper part. The catchment is ideal for such a reconstruction because an earthen dam was built at its lower reach at the same time as planting forest belts at the beginning of 1986, making it a completely closed sedimentary system. At the same time, the Chernobyl 137Cs fallout occurred in European Russia, leaving an easily distinguishable concentration peak in the sediment stratigraphy. A USLE-based modelling approach was employed for calculating soil loss from arable slopes before and after changes of management practice. A 137Cs-based sediment stratigraphy provided information about volumes and average rates of valley aggradation above the dam for time intervals 1954–1986 and 1986–2006. Soil losses from the cultivated part of the catchment decreased by at least a factor of 2.8 after the introduction of soil conservation practices in 1986. Key words sediment budget; soil conservation measures; 137Cs technique; erosion model

Combining direct observations, modelling, and 137Cs tracer for evaluating individual event contribution to long-term sediment budgets

V. R. BELYAEV, V. N. GOLOSOV, K. S. KISLENKO, J. S. KUZNETSOVA & M. V. MARKELOV Laboratory of Soil Erosion and Fluvial Processes, Faculty of Geography, Moscow State University, GSP-1, Leninskie Gory, 119991 Moscow, Russia [email protected]

Abstract The contribution of individual extreme events to longer-term sediment budgets is difficult to evaluate without continuous records of precipitation, runoff, and sediment yield for a particular catchment. This imposes certain restrictions on the applicability of average soil redistribution rates obtained using the most widespread integrative approaches. The problem may partly be resolved by direct observations immediately after extreme runoff events, when their effects are still prominent. We attempted to combine such direct measurements of event erosion and deposition volumes with longer-term soil redistribution rates obtained by 137Cs tracer and empirical erosion models. Available meteorological data were obtained from official sources to evaluate recurrence periods of the observed events. Additional information obtained by other independent techniques, such as the soil profile comparison method, was also considered. Such a combination provides valuable information on the temporal variability of soil redistribution rates and the contribution of extreme events to long-term sediment budgets for the studied catchments. Key words soil erosion; direct measurements of erosion and deposition; 137Cs tracer; sediment redistribution ______Sediment Dynamics in Changing Environments (Proceedings of a symposium held in Christchurch, New Zealand, December 2008). IAHS Publ. 325, 2008, 123-129.

Connecting the disconnected: longitudinal correlation of river terrace remnants

M. D. CHEETHAM1, A. F. KEENE1, W. D. ERSKINE2, R. T. BUSH1 & G. JACOBSEN3 1 Southern Cross Geoscience, Southern Cross University, New South Wales, Australia [email protected] 2 School of Environmental and Life Sciences, University of Newcastle, New South Wales, Australia 3 Institute for Environmental Research, ANSTO, New South Wales, Australia.

Abstract Terrace sequences provide insights into flood plain development. Many studies have examined the cross-sectional morphology and correlation of terraces, but this is only part of the story. Longitudinal correlation can provide a far greater insight into flood plain development processes and the spatial significance of these processes. Here we examine flood plain development from the longitudinal correlation of river terrace sequences in a sand-dominated flood plain. The terrace remnants are discontinuous, having been separated longitudinally by the partial erosion of the flood plain. Terraces along the study reach ranged from recently abandoned (490 ± 60 yBP), poorly developed, vertically accreted flood plains to weathered, early Holocene deposits (10 050 ± 260 yBP). They occurred as inset, fill features which indicated successive phases of alluvial erosion and deposition as well as burial of previous terrace surfaces. Terrace morphology alone did not provide sufficient evidence of longitudinal correlation. Sedimentology and chronology were also vital in correlating these remnants. Four terraces (the Baramul Sequence) were identified in the reach showing progressively younger characteristics and ages. The longitudinal correlation of each discontinuous terrace remnant shows considerable variation over time in response to gradient changes, discharge, sediment size and stream sinuosity. Results show that climate and the local exceedence of geomorphic thresholds have influenced river terrace formation and highlight the significance of chronology in establishing longitudinal correlation of terrace remnants with varying morphology. The Baramul Sequence shows a progressive relative fall in bed-level and reduction in slope over the Holocene. This is likely to have been accompanied by progressive contraction of the channel and indicates a reduction in mean discharge over the last 6–7 ka. Key words stratigraphy; chronology, fluvial geomorphology, terrace sequences, sedimentology

Intensity of soil erosion and sedimentation inferred from spatial distribution of radionuclide 137Cs in hillslope catchments, South Korea

A. ORKHONSELENGE1, K. KASHIWAYA2 & Y. K. KIM3 1 Institute of Geography, Mongolian Academy of Sciences, Ulaanbaatar 210-620, Mongolia [email protected] 2 Institute of Nature & Environmental Technology, Kanazawa University, Kakuma-machi 920-1192, Japan 3 Korean Department of Nuclear Engineering, Hanyang University, Seoul 133-791, Korea

Abstract Erosion, transport and sedimentation of soil particles are considered for different bedrock catchments, underlain by granite, gneiss and sedimentary rocks, in South Korea. The spatial patterns of diffusion of the radionuclide 137Cs, and the inventory within soil profiles, particularly its loss from upper horizons and translocation intensity towards lower horizons, were measured with a germanium detector. The intensity of soil erosion, estimated by the spatial variability of the 137Cs inventory loss in these catchments, differs depending on bedrock, soil properties and runoff generation. Results indicate significantly higher rates of soil erosion and sedimentation in the granite and gneiss catchments than in the sedimentary rock catchment. Key words radionuclide 137Cs; soil erosion; sedimentation; South Korea

Redistribution of soil and soil organic carbon on agricultural landscapes

J. C. RITCHIE & G. W. MCCARTY USDA ARS Hydrology and Remote Sensing Laboratory, Beltsville, Maryland 20705, USA [email protected]

Abstract Patterns of soil organic carbon (SOC) vary widely across the landscape leading to large uncertainties in the SOC budgets for agricultural systems, especially for landscapes where water, tillage, and wind erosion redistributes soil and SOC across the landscape. It is often assumed that soil erosion results in a loss of SOC from agricultural ecosystems, but recent studies indicate that soil erosion on agricultural landscapes is not a source of carbon dioxide to the atmosphere, but that soil erosion and its subsequent redistribution within agricultural fields and watersheds can lead to limited carbon sequestration on agricultural landscapes. This study investigates the relationship between SOC and soil redistribution patterns on agricultural landscapes using fallout 137caesium (137Cs) to determine patterns of soil redistribution. SOC and 137Cs concentrations of soils were significantly correlated in our study areas. Soils in eroding areas have significantly less SOC than soils in depositional areas. SOC decreased as gradient slope increases and soils on concave slopes had higher SOC than soils on convex slopes. These data suggest that soil redistribution and topographic patterns may be used to help understand SOC dynamics on the landscape. The strong significant relationships between soil redistribution and SOC concentrations in the soils suggest that soil and soil organic matter are transported along similar physical pathways in agricultural systems. These transport processes move soils and SOC to sites of deposition within agricultural fields, riparian zones, and water bodies in the watershed, where SOC is buried, leading to more carbon being removed from the atmosphere than is emitted, creating a sink of atmospheric carbon. Our study indicates the importance of understanding soil movement and redistribution patterns within a field or watershed for understanding soil carbon cycles in agricultural ecosystems Key words soil organic carbon; caesium-137; soil erosion; soil redistribution; soil organic carbon redistribution

Post-European settlement impacts on erosion and land degradation; a case study using farm reservoir sedimentation in the Eastern Cape, South Africa

KATE ROWNTREE1, IAN FOSTER1,2, TIM MIGHALL3, LEANNE DUPREEZ1 & JOHN BOARDMAN4,5 1 Department of Geography, Rhodes University, PO Box 94, Grahamstown 6140, Eastern Cape, South Africa [email protected] 2 Department of Molecular and Applied Biosciences, School of Biosciences, University of Westminster, Cavendish Campus, 115 New Cavendish Street, London W1W 6UW, UK 3 Dept of Geography and Environment, University of Aberdeen, Elphinstone Road, Aberdeen AB24 3UF, UK 4 Environmental Change Institute, Oxford University Centre for the Environment, Dyson Perrins Building, South Parks Road, Oxford OX1 3QY, UK 5 Department of Environmental and Geographical Science, University of Cape Town, Rondebosch 7701, South Africa

Abstract We present data from a farm reservoir constructed in 1843, which retains a complete and undisturbed sedimentary record exceeding 4 m in depth. A small number (27) of potential sediment sources were sampled and characterised by their mineral magnetic fingerprints. Similar signatures were measured on the reservoir sediments. While yet to be dated, analysis of mineral magnetic properties of the reservoir sediments suggest that they contain significant quantities of super-paramagnetic minerals produced by pedogenesis, but are not strongly overprinted by magnetic signatures that could be attributed to bacterial magnetite or greigite produced within the reservoir. Preliminary results from the source tracing show that the sediments are probably derived from colluvial topsoils punctuated by inputs from river channels or badlands. Key words sediment sources; environmental magnetism; gamma-emitting radionuclides; Karoo; South Africa

Sediment fingerprinting in New Zealand: a pilot study into the feasibility of the application of the technique

B. P. RODDY1, J. L. MCWHIRTER2, V. G. MOON1, M. R. BALKS1 & F. J. DYER3 1 Department of Earth and Ocean Sciences, University of Waikato, Private Bag 3105, Hamilton 3240, New Zealand [email protected] 2 Department of Statistics, University of Waikato, Hamilton 3240, New Zealand 3 EarthTech, 1/72Wattle St. Lyneham Australian Capital Territory 2602, Australia

Abstract Statistically Verified Composite Fingerprinting (SVCF) has been attracting increased attention to identify catchment erosion sources, but to date has not been applied in a New Zealand setting. A pilot study was undertaken to investigate if different catchment land-uses (native forest, exotic forest, and pastoral agriculture) can be discriminated by their geochemical fingerprints. Seven elements were found to discriminate between the three land-use types, and a novel method of data resampling was successfully used to verify the selection of fingerprint properties. Key words sediment fingerprinting; land-use; erosion; discriminant function analysis; estuary sedimentation

Scaling sediment flux across landscapes

J. P. M. SYVITSKI & A. J. KETTNER CSDMS Integration Facility, INSTAAR, University of Colorado — Boulder, Boulder, Colorado 80309-0545, USA [email protected] Abstract The BQART model is applied for the first time to the world’s continents, to estimate the delivery of suspended sediment before (at 20 167 Mt/year) and after the interference by humans (presently at 12 838 Mt/year). Basin area is found to be the great integrator of relief, lithology, runoff, and humans. BQART is also used in a recursive manner to conceptually show the conveyance loss of suspended sediment along the pathway of rivers. Application of the Bagnold bed-material load equation to Space Shuttle Radar altimetry of river thalwegs is used to show the loss of sediment along the world’s flood plains and other intra-continental sinks. Key words coastal; modelling; global; sediment; flood plains; deltas

Sediment yield modelling at micro-basin and basin scales in semi-arid regions of Brazil

E. E. DE FIGUEIREDO Water Resources Research Engineering Area, Department of Civil Engineering, Federal University of Campina Grande, PO Box 505, 58100-970 Campina Grande/PB, Brazil [email protected]

Abstract Four distributed models, two event-oriented, KINEROS2 and WESP, and two continuous models, SHETRAN and MOSESS_D, have been utilized to investigate their capability in simulating hortonian flows, typical of semi-arid environments, and soil erosion in northeast semi-arid areas of Brazil. Parameters of the models were first determined for vegetated and non-vegetated plots (100 m2) of the experimental basin of Sumé (EBS) located within the representative basin of Sumé (RBS) in the state of Paraíba. For the event oriented models they were calibrated by comparing models results with observed values, while for the continuous models they were fixed, based on field data and used unchanged to simulate micro-basins (0.5–1.0 ha) and basin responses (10–140 km2) of the RBS. The MOSESS_D model was also applied to one sub-basin (19 km2) of the representative basin of Tauá (RBT), in the semi-arid region of the state of Ceará, as a validation test. In general, models results approached the observed values, which indicate that they would be useful in the semi-arid northeast Brazil. Good runoff results were obtained with the continuous models implying their suitability for simulating the dynamics of ephemeral rivers in the investigated areas, but the observed sediments were better approached by the event models. The sediment yields simulated with the continuous models decreased as basin area increased, at rates (1000–10 t km-2 year-1) comparable with those in other river systems worldwide. Key words flow dynamics; distributed model; runoff-erosion; semi-arid; scale effects

Soil armouring and weathering: toward catchment-scale computational modelling

S. COHEN1,2, G. R. WILLGOOSE1 & G. R. HANCOCK2 1 School of Engineering, The University of Newcastle, Callaghan, New South Wales 2308, Australia [email protected] 2 School of Environmental and Life Sciences, The University of Newcastle, Callaghan, New South Wales 2308, Australia

Abstract Hillslope surface armouring and weathering processes have been largely ignored in geomorphic and hydrological models due to their complexity and the uncertainty associated with them. However, their importance in a wide range of spatial processes is well recognised. An armouring and weathering computer model (ARMOUR) has previously been used to successfully simulate the effect of these processes on erosion and soil grading at a hillslope scale. In order to apply such a model across larger and more complex environments we used a Markov process conceptualisation to reduce the complexity of ARMOUR’s numerics. This new armouring-weathering model (named MrARM) is now capable of large-scale two- dimensional simulations. In this paper we describe the calibration and evaluation of MrARM as well as the results of multiple hillslope-scale simulations for varying weathering rates. The MrARM armouring component was calibrated against ARMOUR results, while its weathering component was validated against recently published laboratory results. A parametric study was conducted to evaluate model predictions under various conditions. The results described here demonstrate that the modelling approach used is effective and that the simulation of the armouring and weathering processes corresponds well with previous experience with ARMOUR and with generally accepted field understanding. Key words armouring; weathering; modelling; soil

An evaluation of the role of physical models in exploring form–process feedbacks in alluvial fans

L. E. CLARKE, T. A. QUINE & A. P. NICHOLAS Department of Geography, University of Exeter, Amory Building, Rennes Drive, Exeter EX4 4RJ, UK [email protected]

Abstract Alluvial fans represent small-scale coupled transport/depositional systems that provide the opportunity to undertake detailed studies of non-equilibrium landform behaviour. Previous interpretation of fans in the field has tended to emphasise the importance of external controls on their evolution (e.g. climate and tectonics). However, recent theoretical models have shown that internal process-driven feedbacks may be equally important. Using a physical model, image analysis reveals temporal and spatial patterns in flow patterns over the building and fully-developed fan surface, both in the presence and absence of external forcing (change in water–sediment ratios). The pattern observed from the physical model is compared to patterns observed in both numerical model simulations and field fans in the Avoca Valley and Poerua in the Southern Alps, New Zealand. These comparisons led to a preliminary evaluation of the role of physical models in exploring form–process feedbacks in alluvial fans. Key words alluvial fan; scaling; physical model; numerical model; field; New Zealand

The signature of an extreme erosion event on suspended sediment loads: Motueka River catchment, South Island, New Zealand

D. M. HICKS1 & L. R. BASHER2 1 National Institute of Water and Atmospheric Research, PO Box 8602, Christchurch, New Zealand [email protected] 2 Landcare Research, Private Bag 6, Nelson Mail Centre, Nelson 7042, New Zealand

Abstract Five years of continuously monitoring turbidity and suspended sediment (SS) at four sites in the Motueka River catchment, northern South Island, New Zealand, has characterised the downstream and temporal dispersion of high SS inputs from an extreme rainfall event. The rainstorm, of >50 year recurrence interval, was concentrated in the upper Motueka and Motupiko tributaries and delivered high sediment outputs from re-activated gully complexes and landslides. These only appear to activate when a rainfall threshold is exceeded. Monitoring stations in these tributaries captured a ~20- to 30-fold increase in SS concentrations and event sediment yields, whereas the monitoring station at the coast recorded only a 2- to 5-fold increase. The high concentrations and event yields decayed exponentially back towards normal levels over ~2–3 years at both upstream and downstream sites. Field observations suggest that this erosion recovery trend relates more to the exhaustion/stabilisation of transient riparian sediment storage than to “healing” of the primary erosion sites by surface-armouring and/or re-vegetation. The downstream decay relates both to dilution (from other tributaries carrying lower SS concentrations) and dispersion processes. Similar space–time patterns have been observed in other New Zealand catchments and have implications for the reliability of sediment yield estimates based on short monitoring records. A method is suggested for incorporating such extreme erosion events into estimates of long-term average sediment yield. Key words erosion thresholds; suspended sediment ratings; event sediment yields; non-stationary yields; Motueka

Changing suspended sediment dynamics due to extreme flood events in a small pluvial-nival system in northern Japan

A. C. WHITAKER1, H. SATO1 & H. SUGIYAMA2 1 Faculty of Agriculture, Niigata University, 8050 Ikarashi 2-nocho, Niigata 950-2181, Japan [email protected] 2 Japan International Cooperation Agency, Tsukuba International Center, 3-6 Koyadai, Tsukuba City, Ibaraki Prefecture 305-0074, Japan

Abstract Suspended sediment concentration (SSC) has been monitored in a small, steep and forested pluvial-nival system from 2001 to 2007. The hydrological regime is characterized by rain-on-snow and snowmelt, in addition to high intensity summer rains that normally produce the maximum annual flood. Turbidity and stage were logged every 5–10 minutes, with flood stage activating a pump sampler for determining SSC by filtration. Total suspended sediment yield was estimated by the SSC-turbidity relationship, if possible, or by separate discharge-rating curves (SSC-Q) on rising and falling limbs. Shifts in the SSC-Q rating curves were detected after three extreme flood events occurred during 2004 and 2005, causing a period of channel instability. Channel aggradation and bank erosion appear to have been caused by chronic supply of sediment where re-activated landslides feed directly into the channel, and subsequently by a large pulse of sediment entering the channel as a meander cut-off was formed. Key words suspended sediment concentration; suspended sediment yield; turbidity; sediment-rating curves; sediment supply; channel instability; Japan

The effect of local-scale valley constrictions on flood inundation and catchment-scale sediment delivery in the Fitzroy River Basin, Australia

J. C. CROKE1, D. PURVIS-SMITH1, C. J. THOMPSON1 & LEO LYMBURNER2 1 School of Physical, Environmental and Mathematical Sciences, UNSW@ADFA, Canberra, Australia [email protected] 2 Australian Center for Remote Sensing, Geoscience Australia, Canberra, Australia

Abstract Sediment delivery patterns and rates of sediment accumulation within a basin are significantly affected by features which physically act to prevent and/or enhance the downstream transfer of flow, sediment and attached nutrients. Such features include major within-valley constrictions, or “bottlenecks”, which have developed where valley width reduces dramatically relative to the upstream reaches. Several of these features have been previously identified in the Fitzroy River Basin, Queensland. In many of these bottlenecks, channel pattern upstream and downstream of the bottleneck is notably different, with a propensity for change from multi-channel anabranching to single meandering. Using a representative example from the Nogoa sub-catchment, one-dimensional hydraulic modelling is used to describe the affect of the bottleneck on flood inundation and flow routing downstream. Flow hydrographs indicate a spatially and temporally variable flow regime where discharge dominance alternates between the trunk and main channel. Key words valley constrictions; flood inundation; back-water; HEC-RAS; flood plain storage

Sediment yield from seismically-disturbed mountainous watersheds revealed by multi-temporal aerial LiDAR surveys

AKIRA MATSUOKA1, TAKAO YAMAKOSHI1, KEIJI TAMURA1, JUN MARUYAMA2 & KIICHIRO OGAWA3 1 Public Works Research Institute, Erosion and Sediment Control Research Group, Volcano and Debris Flow Team, 1-6 Minamihara, Tsukuba, Ibaraki 305-8516, Japan [email protected] 2 Hokuriku Regional Development Bureau, Ministry of Land, Infrastructure, Transport and Tourism, 1-1-1, Misaki cho, Chuo ward, Niigata City, Niigata Prefecture 950-8801, Japan 3 Asia Air Survey, Co.,Ltd., 1-2-2 Manpukuji, Asao Ward, Kawasaki City, Kanagawa Prefecture 215-0004, Japan

Abstract The Mid Niigata Prefecture Earthquake (M = 6.8) that occurred on 23 October 2004 caused numerous landslides and landslide dams in the Imo River basin (A = 38 km2) of Niigata Prefecture, Japan, altering sediment yield and discharge processes. Snowmelt and rain events produced more landslides in the basin in following years. We conducted multi-temporal aerial LiDAR surveys to clarify the post-seismic sediment dynamics in this seismically-disturbed mountainous watershed. The surveys revealed the following: in the 19 months after the earthquake, snowmelt and heavy rainfall events yielded 1.4 Mm 3 of sediment (about 19% of that by seismic origin based on fieldwork and aerial photographic interpretation); landslides of seismic origin and those of rainfall or snowmelt origin had very similar distributions; as of May 2006, 70% of the sediment yielded by landslides had not been transported downstream, but remained under the scarps or beside the streams and throughout the periods after the earthquake, river bed deformation in the stream part is larger than the sediment runoff to river course in slope part; and the total amount of post-seismic sediment discharge obtained by the multi-temporal bathymetric surveys coincided fairly well with that of the post-seismic sediment runoff, as revealed by the multi-temporal aerial LiDAR surveys. Key words aerial LiDAR survey; DEM; earthquake; rainfall; sediment yield rate; shallow landslides; snowmelt

A study of spatial scaling in suspended sediment yield along a rural river system – the River Eden, Cumbria, UK

C. F. MILLS, J. C. BATHURST & P. F. QUINN School of Civil Engineering and Geosciences, Newcastle University, Newcastle upon Tyne NE1 7RU, UK [email protected]

Abstract Specific suspended sediment yield was calculated for sub-catchments at a range of scales within the Eden catchment, northwest England. Suspended sediment load was calculated using the flow duration/sediment rating curve method. Specific sediment yield did not show a significant relationship with catchment area, but was found to be spatially variable, particularly between smaller catchments. In order to explain the observed pattern, spatial analysis of catchment characteristics thought to influence sediment yield was carried out. Some variables were derived from GIS data; others were surveyed in the field. No individual variables had a significant relationship with specific sediment yield, suggesting that the factors affecting sediment yield are complex. However, no variables had a significant relationship with catchment area either, indicating the complex nature of the catchment morphology. It is suggested that the catchment area–sediment yield relationship provides a poor basis for understanding spatial variability in sediment yield because of the variability in the underlying processes both within and between catchments. An alternative method of conceptualising spatial variability in sediment yield is now being developed. Key words specific sediment yield; River Eden; spatial variability; scale; land use

Using remote sensing to quantify sediment budget components in a large tropical river – Mitchell River, Gulf of Carpentaria

A. P. BROOKS1, J. SPENCER1, J. G. SHELLBERG1, J. KNIGHT1 & L. LYMBURNER2 1 Australian Rivers Institute, Griffith University, Nathan, Queensland 4111, Australia [email protected] 2 Geosciences Australia, Canberra, Australia

Abstract The recent drought in southern Australia and the increasing realisation that this may be the norm as a result of global warming has led to increased interest in developing the land and water resource of the tropical savannah in northern Australia. Intensive land and water resource development in tropical savannahs in other parts of the world has been shown to lead to significant land degradation, and there are signs this has already occurred with the comparatively moderate levels of historic grazing and agriculture in northern Australia. It is critical that we understand contemporary and historical landscape dynamics before land use is intensified in this region. As a way of beginning to quantify key sediment sources and to start to understand potential changes in relative contributions associated with land use and other drivers, we have begun to construct a sediment budget for the Mitchell River, a 71 360 km2 catchment draining into the Gulf of Carpentaria. We present some preliminary results from two key components of the sediment budget: alluvial gully erosion and channel erosion. A remote sensing analysis has identified around 130 km2 of active alluvial gullies within the Mitchell megafan, which has an estimated active front length of around 5560 km. Preliminary measurements suggest the average rate of scarp retreat to be 0.34 m per year, with scarp heights ranging between 0.3 and 8 m. Using a spatially distributed method we calculated an annual catchment sediment yield from alluvial gullying of >5 Mt/year. Estimates of minimum river channel bed turnover were also determined using a remote sensing approach from Landsat archival data. A measure of minimum annual bed turnover of 15 Mm3/year was derived from analysis of bed area change between 1988 and 2005 (i.e. from either pools to sand bars and vice versa, or vegetated island to pools and vice versa). When analysed at a tributary scale, these data show a pattern of net sediment scour from the Walsh and Palmer rivers, and net accumulation within all other mainstem channels in the period between 1988 and 2005. These data support the anecdotal evidence that there has been a trend towards sediment accumulation within the lower Mitchell River in recent times, with a resulting net reduction in total pool area of 0.6 km 2. While preliminary, these data highlight the value of remote sensing for constructing sediment budgets in large dynamic tropical rivers. Key words sediment budget; Mitchell River; alluvial gully erosion; bed load; remote sensing; Landsat; ASTER

Off-slope sediment delivery from landsliding during a storm, Muriwai Hills, North Island, New Zealand

N. J. PRESTON School of Geography, Environment and Earth Sciences, Victoria University of Wellington, PO Box 600, Wellington, New Zealand [email protected]

Abstract One of the critical aspects of regional sediment transport that must be addressed is the issue of sediment delivery. Although both the mechanics of, and systematic controls on, sediment transport are well understood, there is little data on sediment delivery available. In August 2002 a high intensity rainfall event induced widespread shallow landsliding on the coastal hills south of Gisborne in the North Island of New Zealand, presenting an opportunity to obtain first-hand estimates of sediment delivery from landslides. Many of the failures were shallow and extremely fluid in nature, suggesting that high pore water pressure was the triggering mechanism, and in some cases sub-surface flow was clearly a factor. Field estimates of off-slope sediment delivery to channels, including ephemeral channels that were thought to have been present during the peak of storm runoff, were made for 220 individual failures within three catchment areas of uniform lithology and vegetation cover. One of the more important controls on sediment delivery is the timing of landsliding relative to duration of storm runoff, and therefore transport capacity. Related to this are issues of slope/channel coupling and connectivity within the landscape, and the location of landslides relative to channels, which is a function of the erosional history in the catchment, is clearly important. The average estimated sediment delivery ratio was ~26%. Although this figure is low, it applies to a single event, and implies that landsliding produces considerably more sediment that will be available for attenuated delivery through the fluvial system. Key words rainfall-triggered landsliding; fluid failure; sediment delivery ratio; slope-channel coupling

SPARROW regional regression for sediment yields in New Zealand rivers

A. H. ELLIOTT1, U. SHANKAR2, D. M. HICKS2, R. A. WOODS2 & J. R. DYMOND3 1 National Institute of Water and Atmospheric Research (NIWA), PO Box 11115, Hamilton, New Zealand [email protected] 2 National Institute of Water and Atmospheric Research (NIWA), PO Box 8602, Christchurch, New Zealand 3 Landcare Research, Private Bag 11052, Palmerston North 4442, New Zealand

Abstract This paper reports on the application of the SPARROW regression model for predicting mean annual sediment yield in streams throughout New Zealand. SPARROW generates sediment (or nutrient) sources as a function of subcatchment parameters such as areas of different erosion terrains, modifies the loads according to generation and land-to-water delivery factors, and routes the sediment down a dendritic stream network, allowing for stream and lake erosion or deposition. The parameters for the model are determined by nonlinear calibration to measured yields at stream monitoring stations (over 220 sites in New Zealand). Areas of different erosion terrains were the key source in the model, while the mean annual rainfall and slope were key source modifiers. Land cover also emerged as a significant source modifier. A model with these terms gave a regression R2 of 0.925 to the measured yields, in log space. Stream erosion and deposition terms were not statistically significant, so they would have to be imposed rather than calibrated to stream yield data. Key words regression; model; stream; SPARROW

Morphometric analysis of interfluve topography for scaling soil erosion rates from local to regional scales

Y. KUZNETSOVA & V. GOLOSOV Laboratory of Soil Erosion and Channel Processes, Faculty of Geography, Moscow State University, Moscow, Russia [email protected]

Abstract Intensively cultivated areas are often affected by human-accelerated soil erosion. In European Russia most of the arable land occupies interfluves and relatively gentle interfluvial slopes. There are a number of case study sites within the Central Russian Plain for which detailed information on local soil redistribution rates have been obtained. However, transition from local-scale to regional-scale assessment of soil erosion rates still presents a serious problem as it cannot be satisfactorily achieved by simple interpolation between the case study points. Analysis of the variability of interfluvial morphometry enabled us to identify criteria for extrapolation of locally derived erosion and soil redistribution rates. We identified a key morphometric parameter at the 1:500 000 scale, i.e. the area of elementary interfluvial slope unit connected with the Hortonian first-order stream thalweg. We also discuss other morphometric parameters relevant at different spatial scales. Key words geomorphometry; interfluves; soil erosion; upscaling

Sediment storage in Alpine sedimentary systems – quantification and scaling issues

J.-C. OTTO, J. GOETZ & L. SCHROTT Department of Geography and Geology, University of Salzburg, Hellbrunner Strasse 34, A-5020 Salzburg, Austria [email protected]

Abstract The role of sediment storage is considered to be crucial for the construction of sediment budgets, and for linking sediment dynamics to landform evolution. In Alpine sedimentary systems, dynamic and highly-complex system behaviour, combined with changing climate and process regimes, lead to the formation of numerous types and generations of storage landforms. The strong impact of Quaternary glaciation on the sediment flux is very often still observable in the reworking of glacial sediments, as described by the concept of paraglacial sedimentation. Controlled by changing process rates and variable coupling conditions through time, storage landforms strongly affect sediment output from Alpine catchments. Sedimentary deposits may be temporarily decoupled or preserved, from erosion by climatic (e.g. permafrost), vegetation, or topographic (hanging valleys, cirques) conditions leading to a complex distribution of sediment storages and cascades. Changing climate or sediment availability may also result in a remobilisation of these deposits modifying the sediment flux dynamics. Various approaches to quantify storage volumes have been applied, with changing efficiency and accuracy at different spatial scales. Whereas at small scales (<10 km2) higher accuracies can be reached, the assessment of storage volumes on large scales is still problematic and often based on rough estimations. Methods of quantification range from high resolution techniques using field geophysics, to less accurate techniques applying simple geometries and DEM analysis. However, few approaches tackle the gap between scales and provide ways to integrate between them. Paying special attention to Alpine sedimentary systems, we review the most frequently applied methods of storage quantification at various scales, in order to evaluate their usability and accuracy in sediment budget studies. To initiate a discussion on the quantification of sediment storage in large Alpine drainage basins, we present a simple approach to approximate the storage volume of the Upper Rhone catchment, Swiss Alps. Key words sediment budget; sediment storage; scaling issues; large Alpine drainage basins

Stochastic sediment–vegetation dynamics in an Alpine braided river

P. PERONA, P. MOLNAR, M. SAVINA & P. BURLANDO Institute of Environmental Engineering, ETH Zurich, W. Pauli Strasse 15, CH-8093 Zurich, Switzerland [email protected]

Abstract We propose a stochastic modelling framework to simulate the spatially lumped sediment and vegetation dynamics in a flood plain of a braided gravel bed river as an alternative to detailed morphodynamic modelling. The idea is that floods intermittently erode the river bed and expose sediment on gravel bars, while riparian vegetation continuously recolonises the exposed area. The exposed sediment and water stochastic dynamics can be analytically solved in terms of their probability density function (pdf), and later used to force a vegetation model, together forming a so-called coupled “Master–Slave” stochastic dynamical system in continuous time. We apply and validate the master model by using a historical record of aerial photographs of the Maggia River (Tessin, Switzerland) and daily streamflow measurements. This approach is useful to statistically quantify the amount of sediment that is reworked by flood events, as well as the effects of changes in the flood disturbance regime on flood-plain dynamics. Key words flood plain processes; river–vegetation interactions; sediment dynamics; stochastic models

Connectivity in steep-land environments: gully–fan coupling in the Tarndale system, Waipaoa catchment, New Zealand

IAN C. FULLER1 & MIKE MARDEN2 1 School of People, Environment & Planning, Massey University, Palmerston North, New Zealand [email protected] 2 Landcare Research, Gisborne, New Zealand

Abstract Digital Elevation Models (DEMs) of the Tarndale Fan derived from nine RTK-dGPS surveys between 2004 and 2007 demonstrate a rapid cutting and filling of the fan surface over the course of two and a half years. Repeat DEM analysis permits an assessment of the transfer of sediment supplied from a fluvio-mass movement gully complex (Tarndale Slip) through the fan to the Te Weraroa Stream. This demonstrates considerable complexity in patterns of erosion and deposition on the fan and, ultimately, sediment delivery to the stream system. Discrete mass movements in the gully complex, triggered by rainstorm events, frequently deliver sediment to the upper fan. Extreme rainfall events are particularly effective at delivering large quantities of sediment. Enhanced sediment delivery promotes rapid aggradation (up to ~30 000 m3) of the upper fan. This infilling may then propagate down-fan, particularly when the upper fan equally rapidly incises these deposits. However, floods generated in the Te Weraroa Stream by the same extreme rainstorm may trim the lower fan prompting up-fan incision in response to changed local base level. This process may evacuate up to ~10 000 m3 of sediment to the stream. This see-saw behaviour in response to sediment supply and evacuation is superimposed on an overall aggradational trend in which the Tarndale Fan is buffering the trunk channel system from the full quantity of sediment supplied by the Tarndale Slip. This study demonstrates a need for intensive investigation of such systems so as to understand more fully complex behaviour at this critical nexus within the fluvial system. Key words gully complex; fan; DEM; sediment transfer; sediment cascade

Channel incision and sand compartmentalization in an Australian sandstone basin subject to high flood variability

W. D. ERSKINE School of Environmental and Life Sciences, University of Newcastle – Ourimbah Campus, PO Box 127, Ourimbah, New South Wales 2258, Australia [email protected]

Abstract Wollombi Brook in the Hunter Valley, New South Wales, Australia, is characterised by high flood variability on a global scale (Flash Flood Magnitude Index of at least 0.86). Channel incision has occurred throughout the 2000-km2 basin since initial European settlement in the early 1820s. On the main stream, discontinuous incision occurred in the upper basin in a 7-km long reach and was caused by the localised exceedence of a valley-floor slope threshold by a large flood in 1927. Since then, 900 000 m3 of valley fill has been eroded by knick-zone migration and subsequent channel widening, but the whole sand fraction has been deposited immediately downstream in a sand slug or intermediate floodout. Between 1927 and 1982, incision moved 7 km upstream, but has since stabilised due to engineering works. Non-synchronous incision of tributaries was recorded between 1838 and 1977, but the generated sand often did not reach the main stream because of deposition in intermediate floodouts/sand slugs on the tributaries. Incision of the largest tributary, Congewai Creek, was initiated by a catastrophic flood in June 1949, and was integrated with the main stream downstream of the intermediate floodout. Sand from Congewai Creek and Wollombi Brook, downstream of their junction, was transported continuously out of the basin until 1996 when channel recovery from the catastrophic 1949 flood was accelerated by substantial vegetation colonization and sand anchorage. Key words Wollombi Brook, NSW, Australia; chain of ponds; floodouts; sand slugs; sand compartment; channel recovery

Multi-scale sediment dynamics in an upland catchment, southeastern Australia: a synthesis

HUGH G. SMITH1,2 & DEIRDRE DRAGOVICH1 1 School of Geosciences, University of Sydney, Sydney, New South Wales 2006, Australia 2 Current address: Department of Forest and Ecosystem Science, University of Melbourne, Melbourne, Victoria, 3010, Australia [email protected] Abstract This paper presents a synthesis of multi-scale sediment dynamics within an upland catchment in southeastern Australia. Various process-based techniques were utilised for a period of nearly two years to monitor three nested spatial scales: hillslope (<250 m), sub-catchment (1.64 km2) and catchment (53.5 km2). Hillslope erosion rates were low, with sub-catchment and catchment-scale sediment dynamics dominated by sediment supply from channel banks. Assessment of sub-catchment to catchment sediment delivery was based on comparison of specific sediment yields, with peak yields and delivery in spring 2005. In-channel sediment storage responded to seasonal and drought-dependent discharge patterns, with storage increasing during extended low flow periods. Seasonal variation in processes and controls was observed across all spatial scales examined, demonstrating the important effect of seasonality in rainfall patterns, vegetation growth, and antecedent soil moisture, for sediment dynamics in the study catchment. Key words scale; catchment sediment dynamics; sediment delivery; Australia

Holocene alluvial sediment deposition in contrasting environments in northwestern Europe

B. NOTEBAERT & G. VERSTRAETEN Department of Earth and Environmental Sciences, K.U. Leuven, Celestijnenlaan 200E, B-3001 Leuven, Belgium [email protected]

Abstract The total mass of Holocene alluvial sediment storage was estimated for three Belgian catchments (Dijle, Gulp and Amblève), with areas ranging between 47 and 1070 km 2. The Dijle and Gulp catchments have comparable, rather intensive, land-use histories, while the land use in the Amblève catchment is less intensive and developed more recently. Topography is more pronounced in the Amblève catchment and more gentle in the Dijle catchment. In total, 1070 hand augerings were made to study fluvial deposition at 96 cross-sections across the flood plain. Average flood-plain deposition masses for the different catchments were calculated at different spatial scales. The results show that alluvial sediment storage is much higher for the Dijle catchment (464 103 Mg/km2 catchment area) compared to the Gulp (128 103 Mg/km2) and Amblève catchment (33 103 Mg/km2). Comparison with other data from West European catchments shows that alluvial sediment storage is much larger for the Dijle catchment, while that for the Amblève is very low. These differences between catchments can be attributed to their land-use history. Land use plays a role in both the soil erosion rates and in the sediment transport towards the fluvial system. Radiocarbon dating results for the Dijle flood plain indicate that major changes in land use are responsible for changing flood plain sedimentation. Key words Holocene; alluvial sediment deposition; land-use change

Flood-induced changes in the step-pool morphology of a steep mountain stream

P. MOLNAR1, A. L. DENSMORE2, B. W. McARDELL3 & P. BURLANDO1 1 Institute of Environmental Engineering, ETH Zurich, CH-Zurich Switzerland [email protected] 2 Department of Geography, Durham University, Durham, UK 3 Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, Switzerland Abstract The step-pool morphology of steep mountain streams is reorganized during large floods by scouring of the river bed and deposition of step-forming grains. We compare the statistical properties of step-pool sequences before and after a large flood in the Erlenbach stream, in Switzerland, to document this effect. We show that the flood has led to substantial overall erosion of the river bed. Steps were completely reorganized, although their total number did not change. More small and large steps were formed, with a wider statistical distribution of step spacing. The location of the largest steps before and after the flood remained constrained to the middle reaches of the stream where hillslope landslides are most active. We also applied scaling techniques to the increments of the longitudinal profile to detect statistical differences between the pre- and post-flood sequences. We found a multiscaling signature in the step sequences both before and after the flood, which is an indication of complex structure in the bed morphology. Overall, our results show that a large flood may reorganize the bed, build complex step risers and fill pools. Subsequent lower floods will structure and extend the pools, remove small steps and regularize the step-pool sequence. Key words channel morphology; step-pool streams; mountain rivers; scaling processes

Suspended sediment dynamics and transport into the Babitonga Bay, southern Brazil

F. A. OLIVEIRA1 & J. L. S. ROSS2 1 Department of Geography, University of the Region of Joinville, Campus Universitário s/n, 89201-972 Joinville SC, Brazil [email protected] 2 Department of Geography, University of São Paulo, Av. Prof. Lineu Prestes 338, 05508-900 São Paulo SP, Brazil

Abstract This study aims to estimate suspended sediment yield entering the Babitonga Bay, an estuarine system located on the southern coast of Brazil. Discharge and suspended sediment were monitored monthly in nine watersheds over a period of three years. Monitoring was accomplished on a more frequent basis in the major watershed with monthly, daily, and hourly measurements and sampling. The discharge and suspended-sediment values for each watershed were compared with morphology and morphometry, rainfall, and land-use data. The studied watersheds show distinct hydrological and sedimentological features leading to specific signals of suspended sediment yields for each individual watershed contributing to the overall sediment budget of the bay. Key words suspended sediment; discharge; Babitonga Bay, Brazil

Recent sedimentation rates for the Rees-Dart braided river delta

MICHELLE WILD1, THOMAS COCHRANE1, TIM DAVIES2, MURRAY HICKS3, DAVID PAINTER4 & GAVIN PALMER5 1 Department of Civil & Natural Resources Engineering, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand [email protected] 2 Department of Geological Sciences, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand 3 National Institute of Water & Atmospheric Research, PO Box 8602, Christchurch 8011, New Zealand 4 David Painter Consulting Ltd, PO Box 29012, Christchurch 8540, New Zealand 5 Otago Regional Council, Private Bag 1954, Dunedin, New Zealand

Abstract An estimate of the recent sedimentation rates for the Rees–Dart river delta (New Zealand) is required for use in future physical and numerical models studying delta growth. A combination of historic aerial photos and a recent sonar bathymetric survey of the delta front were used to determine volumetric rates of sedimentation. Between 1966 and 2007, the average annual rate of sedimentation was approximately 2.7  105 m3/year, which equates to a catchment denudation rate of 0.3 mm/year. The results also suggest that the delta growth may be dominated by large events, such as the November 1999 flood, because the average annual rate of sedimentation between 1998 and 2007 is significantly higher. Key words sedimentation; deltas; rivers; braided; coarse-grained sediment

Sediment movement from small catchments within the Moldavian Plateau of eastern Romania

I. IONITA Department of Geography, “Alexandru Ioan Cuza” University of Iasi, Carol I Blv., No 20A, 700505 Iasi, Romania [email protected]

Abstract Soil erosion, gullying, landslides, and reservoir sedimentation have been recognized as the most important environmental threat in the Moldavian Plateau of eastern Romania. A long-term field study of runoff and gully erosion rates under flash streamflow in small catchments, each less than about 3000 ha, showed much variability of sediment movement over time and among catchments. Two types of sediment delivery mode were identified. During the synchronous mode, erosion generation and sediment cleanout occur simultaneously, whereas during the more common asynchronous mode an eroding stage during late winter and early spring is followed by a channel debris cleanout stage with warm season rainstorms. Key words runoff; soil erosion; gullying; sediment concentration; sediment movement

The changing sediment loads of the world’s rivers

D. E. WALLING Department of Geography, University of Exeter, Amory Building, Rennes Drive, Exeter EX4 4RJ, Devon, UK [email protected]

Abstract Recent anthropogenic pressures on the Earth’s surface, including population growth, wide ranging disturbance of the land surface by land use activities, infrastructure development and mineral exploitation, and modification of the hydrological cycle caused by water resource exploitation, have resulted in significant changes to the sediment loads of some of the world’s rivers. In some cases loads have increased, whereas in others loads have reduced. Examples of such changes are provided and an attempt is made to identify the key drivers of changing sediment loads at the global scale. Situations that can lead to blurred signals of upstream changes in sediment flux at the catchment outlet are also considered. Recent changes in the sediment loads of the world’s rivers, as demonstrated by existing short- term records, may represent only the recent phase of longer-term changes and there is therefore a need to place recent changes into a longer-term context. The implications of changing sediment fluxes, and particularly sediment trapping by dams, for land–ocean sediment transfer and the global sediment budget are assessed. Key words world rivers; erosion; sediment yield; sediment load; human impact; reservoir sedimentation; land disturbance; global sediment budget

Gully erosion and sediment load: Waipaoa, Waiapu and Uawa rivers, eastern North Island, New Zealand

MICHAEL MARDEN1, HARLEY BETTS2, GREGORY ARNOLD2 & RANDOLPH HAMBLING3 1 Landcare Research, PO Box 445, Gisborne 4040, New Zealand [email protected] 2 Landcare Research, Private Bag 11-052, Palmerston North 4442, New Zealand 3 Ministry of Agriculture and Forestry, PO Box 2122, Gisborne 4040, New Zealand

Abstract The onset of gully erosion following deforestation was mapped for the three largest and heaviest sediment-laden rivers within the East Coast Region, North Island, New Zealand. Gullies were then re- mapped after a ~40-year reforestation period (~1957–1997) and sediment production from gullies was calculated from these data bases using a degradation rate based on DEMs of gullies at differing stages of development in each of two different geologic/tectonic terrains. At the end of the measurement period the total composite gully area for the Waipaoa, Waiapu and Uawa catchments was 5%, 33% and 39% greater than before reforestation, and for the study period, gullies in both terrains collectively contributed the equivalent of 43%, 49% and 54% of the average annual suspended sediment yield from just 0.8%, 2.4% and 1.7% of hill country areas in these respective river systems. A potentially significant reduction in sediment production and yield at catchment-scale could be achieved through a more targeted approach to reforestation, particularly of gullies in the most highly erodible and unstable pastoral hill country areas of Waiapu catchment. Key words gullies; sediment production and yield; reforestation; eastern New Zealand

Sediment sources in a dry-tropical catchment: central Queensland, Australia

A. O. HUGHES1, J. M. OLLEY2, J. C. CROKE1 & L. A. MCKERGOW3 1 School of Physical, Environmental and Mathematical Sciences, University of New South Wales@ADFA, Canberra, Australian Capital Territory 2600, Australia [email protected] 2 Australian Rivers Institute, Griffith University, Nathan, Queensland 4111, Australia 3 National Institute of Water and Atmospheric Research, Hamilton, New Zealand

Abstract Rivers draining into the Great Barrier Reef lagoon are receiving increased attention from catchment managers and scientists, with the realisation that European land use changes over the last ~150 years may have increased river sediment yields with resultant adverse effects on the receiving marine environment. Mitigation of the effects associated with such changes is only possible if information on the spatial provenance and dominant types of erosion is known. This study uses fallout radionuclide ( 137Cs and 210 Pbex) and geochemical tracing of river bed sediments to examine sediment sources for Theresa Creek, a subcatchment of the Fitzroy River basin, central Queensland, Australia. Sheetwash and rill erosion from cultivated basaltic land and channel erosion from non-basaltic parts of the catchment were found to be contributing most sediment to the river system. Evidence indicates that the dominant form of channel erosion is gully head-cut and sidewall erosion. Sheetwash and rill erosion from uncultivated land (i.e. grazed pasture/woodland) is a comparatively minor contributor of sediment to the river network. Due to the limited extent of cultivation, on a basin-wide scale, channel sources are likely to be the largest contributor of sediment to the Fitzroy River basin; accordingly catchment managers should focus their efforts on reducing the sediment yield from these sources. Key words geochemical tracing; fallout radionuclide tracing; channel erosion; human impact; Great Barrier Reef

Chemical and physical weathering in a mountainous tributary of the Zhujiang (Pearl River), China

SHU-RONG ZHANG & X. X. LU Department of Geography, National University of Singapore, Arts Link 1, Singapore 117570, Singapore [email protected]

Abstract The historical records of dissolved and particulate solids transported in rivers can provide important information about long-term chemical and physical denudation in the drainage basins, as well as the atmospheric CO2 consumption. In this study, temporal variations of major ions and suspended sediment between two separate periods 1959–1967 and 1991–1999 in a mountainous tributary of the Zhujiang (Pearl River) in China were examined using statistical methods. Suspended sediment and most major ions, as well as total dissolved solids (TDS) showed significant downward step changes between these two periods. Chemical weathering rate, especially silicate weathering rate, and atmospheric CO2 consumption rate decreased in the later period, coinciding with the decreasing of mechanical erosion rate. The positive relationship between dissolved and suspended solids suggests a strong coupling between chemical and physical weathering rate in the drainage basin. Key words trend analysis; major ions; suspended sediment; chemical and physical weathering; the Zhujiang (Pearl River); atmospheric CO2 consumption rate

Sensitivity of Alpine fluvial environments in the Swiss Alps to climate forcing during the Late Holocene

L. SCHULTE1, R. JULIÀ2, M. OLIVA1, F. BURJACHS3, H. VEIT4 & F. CARVALHO1 1 Department of Physical and Regional Geography and Laboratory of Landscape Research, University of Barcelona, Carrer de Montalegre 6, E-08001 Barcelona, Spain [email protected] 2 Institute of Earth Science “Jaume Almera”, CSIC, C/Lluis Sole i Sabaris s/n., E-08028 Barcelona, Spain 3 Catalan Institution for Research and Advanced Studies at the Department of Prehistory, University Rovira i Virgili, Plaça Imperial Tarraco 1, E-43005 Tarragona, Spain 4 Institute of Geography, University of Bern, Hallerstrasse 12, CH-3012 Bern, Switzerland Abstract The variability of Late Holocene fluvial dynamics in the Swiss Alps is traced from fan delta deposits using a multi-proxy approach. The spatial coexistence of wetland, alluvial and fluvial environments on the low-gradient Lütschine fan delta provides a high-resolution fluvial record. The sedimentary record shows seven major aggradation pulses from 3600 cal year BP to the present. Furthermore, 19 minor burial episodes occur between 3600 and 1050 cal year BP at intervals of between 100 and 130 years, suggesting that aggradation during the period of interest was triggered by centennial flood events. Nine coarse-grained flood layers, deposited at a recurrence interval of between 200 and 600 years, coincide with positive radiocarbon anomalies and cold phases in the Alps. The solar influence on the regional hydrological regime is proposed as the main factor triggering the flooding events. Key words Late Holocene; fluvial environments; multi-proxy record; solar forcing; climate; fan delta; Swiss Alps

An overlooked sediment trap in arid environments: ancient irrigation agriculture in the coastal desert of Peru

JUSSI BAADE & RALF HESSE Department of Geography, Friedrich Schiller University Jena, Löbdergraben 32, D-07743 Jena, Germany [email protected]

Abstract The fluvial transfer of sediment from the land surface to the ocean is a complex process, and in many regions of the world, this process has been strongly influenced by man. In humid regions, the onset and expansion of agriculture coincided with deforestation, accelerated soil erosion, and an increase in sediment yield. In arid regions, agriculture is based on irrigation and thus the withdrawal of water and sediment from the rivers. Several metre thick irragric anthrosols are evidence of the continuous and long lasting trapping of sediments on irrigated fields. Investigations of irragric anthrosols in the Palpa Valley, southern Peru, have shown that trapping of sediments started around 3000 cal BP. Based on these investigations and other published data, this paper assesses the amount of sediment trapped in the river oases of the Rio Grande de Nazca drainage basin (11 164 km2) in the coastal desert of Peru. Key words arid environments; sediment transport; irrigation agriculture; irragric anthrosols; human impact; Peru

Glacial–interglacial cycles, soil erosion and natural desertification in the Middle East

YOAV AVNI Geological Survey of Israel, 30 Malkhe Yisrael St, Jerusalem 95501, Israel [email protected]

Abstract Field observations and luminescence dating indicate that, during the Late Pleistocene glacial period (OIS 4 and 3), deposition of fluvio-loess sediments, with minor erosion cycles, occurred in the arid and semi-arid regions of the Middle East. Severe erosion started during OIS 2 and continued into the Holocene. Since the mid-Holocene, the co-existence of soil and runoff created unique geomorphic conditions, which enabled the establishment of runoff-harvesting agricultural farms in the arid regions of the Middle East. This led to the redeposition of fine alluvial loess sediments originating from Late Pleistocene loess sections. This accumulation, which contributed to soil conservation, is not related to any apparent Late Holocene pluvial climatic phase. The human impact, contributing either to land degradation or to soil conservation, is super-imposed on the natural long-term trend of geomorphic change leading toward natural desertification. Similar processes are operating in other semi-arid regions worldwide. Key words continental erosion; global climate change; geomorphic change; gully incision; desertification; loess sediments; Negev Highlands; Middle East

Changing sediment supply in Arctic rivers

IRINA OVEREEM & JAMES P. M. SYVITSKI CSDMS Integration Facility, INSTAAR, University of Colorado – Boulder, Boulder, Colorado 80309-0545, USA [email protected]

Abstract Changes in Arctic rivers are integrated signals of changing hydrological conditions in their drainage areas. Water and sediment fluxes are assessed for 50 high-latitude rivers (>55ºN) under conditions of rapid Arctic warming. Controlling parameters have been analysed from regional data sets, i.e. GTOPO30 DEM, UNDel climate grids, combined monthly discharge data, WGI glacier data and a circum-arctic map of permafrost. Based on derived parameters, the BQARTmodel calculates suspended sediment loads. High- latitude river systems contribute 4.86 × 1012 m3/s of water to the ocean annually. Calculated suspended sediment fluxes are 347 MT/year for the Arctic Ocean, and 88 and 53 MT/year for the Pacific and Atlantic oceans, respectively. Changes in outflux of water and sediment load are spatially variable between the late 1970s and early 1990s. Large Eurasian and Pacific rivers show pronounced flux increase, whereas the MacKenzie River basin is stable. Validation of these model predictions is typically limited by sparse observations. Strong nonlinear response of sediment flux to environmental changes is recognized. Small rivers are much more sensitive to changes in glacial area and extreme events affecting loads, whereas sinks dampen these signals in continental-scale basins. Key words rivers; modelling; Arctic; sediment; extreme events; scaling

Mapping potential soil erosion in East Africa using the Universal Soil Loss Equation and secondary data

LIEVEN CLAESSENS1,2, PAULO VAN BREUGEL3, AN NOTENBAERT3, MARIO HERRERO3 & JEANNETTE VAN DE STEEG3 1 International Potato Center (CIP), PO Box 25171, Nairobi, Kenya [email protected] 2 Land Dynamics Group, Wageningen University, PO Box 47, 6700AA Wageningen, The Netherlands 3 International Livestock Research Institute (ILRI), PO Box 30709, Nairobi, Kenya

Abstract Soil erosion is a serious threat of increasing dimensions and tends to blunt efforts to counter global population growth with increased and sustainable agricultural production. The tropics are especially vulnerable because of the circumstantial convergence of intense climatic regimes, frequently fragile soils, low levels of fertilizer use and conservation practices and strong dependence on soil quality for livelihoods. In addition, climate change is expected to aggravate the already existing vulnerabilities of the poorest people, who depend on semi-subsistence agriculture for their survival. Tools for assessing spatially explicit erosion patterns would be a great help for planning soil conservation measures, or targeting agricultural technology or policy interventions that mitigate the adverse effects of soil erosion and could help farmers to adapt. Because extensive measurement of soil erosion is expensive and time consuming, erosion models that make use of secondary data available in a Geographic Information System can offer a useful alternative. In this paper, an attempt is made to analyse and map current soil erosion potential on the sub- continental scale. We use principles of the Universal Soil Loss Equation (USLE) and its reformulations to make a qualitative assessment of soil erosion in East Africa. Data on climate, soils, topography, hydrology and land cover are derived from existing secondary data sources that are spatially explicit and have an adequate resolution to be linked, at least as proxies, to important drivers of soil erosion as represented in the USLE. Obvious limitations of methodology and data, as well as the lack of validation possibilities are discussed. The results have value in reflecting broad patterns of soil erosion across East Africa. The methodology also permits the highlighting of hotspots of soil erosion risk where agricultural research can focus efforts of developing or applying soil conservation measures and target agricultural technology, and policy interventions that can mitigate the adverse effects of soil erosion on poor people’s livelihoods. Key words USLE; erosion; erosion risk; East Africa

The Waipaoa Sedimentary System: research review and future directions

N. LITCHFIELD1, K. BERRYMAN1, H. BRACKLEY1, L. CARTER2, M. MARDEN3, M. PAGE1 & N. TRUSTRUM1 1 GNS Science, PO Box 30368, Lower Hut 5040, New Zealand [email protected] 2 Antarctic Research Centre, Victoria University of Wellington, PO Box 600, Wellington 6001, New Zealand 3 Landcare Research, PO Box 445, Gisborne 4040, New Zealand

Abstract The Waipaoa Sedimentary System is an ideal natural laboratory for determining the processes that affect sediment delivery and deposition across a high sediment input, active continental margin. As such it was chosen as one of two focus sites for the NSF- and FRST-supported MARGINS Source-to-Sink Initiative. Key research outcomes-to-date are described here, and can be broadly grouped into four themes: (i) long-term (≤100 ka) fluvial processes; (ii) post-18 ka sediment budgets; (iii) contemporary sedimentary processes; and (iv) the response to major events including the impacts of human colonisation. Research gaps include quantification of post-18 ka hillslope erosion, hillslope-channel linkages, and the landscape response to rapid changes in climate and large earthquakes. A new research programme is summarised which aims to fill some of these gaps in the terrestrial part of the Waipaoa SS, to extend understanding of sedimentary systems through numerical modelling, and to appraise the likely changes in sediment delivery through various mitigation strategies. Key words sedimentary system; erosion; sediment budget; Waipaoa; New Zealand

Climatic and anthropogenic effects on soil transport rates and hillslope evolution

P. C. ALMOND1, J. J. ROERING2, M. W. HUGHES1, F. S. LUTTER3 & C. LEBOUTEILLER4 1 Agriculture and Life Sciences Division, Lincoln University, PO Box 84, Lincoln University 7647, New Zealand [email protected] 2 Department of Geological Sciences, University of Oregon, Eugene, Oregon 97403-1272, USA 3 University of Natural Resources and Applied Life Sciences (BOKU), Vienna, Austria 4 Cemagref ETNA, BP 76, F-38402 St Martin d’Heres, France

Abstract Vegetation change, whether it be of anthropogenic or climatic origin, can have dramatic effects on landscape form, processes and sediment yield. General conceptual models for relationships between climate, vegetation and sediment yield exist for whole landscapes, but no rigorous analysis of the effects of vegetation change on sediment transport, in the absence of overland flow, has been done from soil-mantled hillslopes. Here we investigate the rate of erosion and sediment delivery from soil-mantled hillslopes underlain by loess, over long (27 ka) and historic (50 year) time scales. In a humid environment the change from grassland/shrubland to tall forest across the Pleistocene/Holocene boundary resulted in a 60% increase in sediment flux. We attribute this to increased soil disturbance and transport by tree-throw. In a presently subhumid landscape, average soil transport efficiency over the same 27 ka period, as quantified by the soil transport coefficient (the proportionality constant relating soil flux to hillslope gradient), was very similar to the humid area, despite a semi-arid or even drier phase prevailing during the Late Glacial in the subhumid region. This result suggests that any differences in soil fluxes and erosion rates during the Late Glacial, imbued by the very different climates in the two regions, have been overwhelmed by processes associated with the Holocene forest phase. The soil transport coefficient for the historical (last 50-year) period at the subhumid site, quantified by 137Cs analysis, indicates the present erosion rate under introduced grazed pasture is higher than the long-term averages at both sites, higher than that which occurs under native tussock grasslands and comparable to rates under forest. We propose a general scheme to describe the relationship between climate/vegetation and sediment yield on soil mantled hillslopes that have a trough form: the minimum coincides with subhumid grassland/shrubland, while sediment flux maxima may be associated with climatic extremes (humid forested landscapes and arid and hyperarid deserts). Key words climate change; vegetation change; soil erosion; 137Cs; hillslope evolution

Will human catalysts or climate change have a greater impact on the sediment load of the Waipaoa River in the 21st century?

A. J. KETTNER1, B. GOMEZ2 & J. P. M. SYVITSKI1 1 Community Surface Dynamics Modeling System Integration Facility (CSDMS), Institute of Arctic and Alpine Research (INSTAAR), University of Colorado, Boulder, Colorado 80309-0450, USA [email protected] 2 Geomorphology Laboratory, Indiana State University, Terre Haute, Indiana 47809, USA

Abstract We use a climate-driven hydrologic-transport model, HydroTrend, that is able to compute water and sediment discharges in daily increments, to assess the effect that the change in climate (mean annual temperature and precipitation) forecast for the 2030s and 2080s will have on the water discharge and suspended sediment load of the Waipaoa River, New Zealand. Given the prospects of a warmer and drier climate, the magnitude of extreme events, such as the one-in-200 year flood, could be reduced by as much as 63–68%, and the mean flow in the Waipaoa River could decline to 78–96% of its present value by the 2030s and to 64– 100% by the 2080s. Our simulations indicate that the mean annual suspended sediment load could be 91–108% and 84–126% of the present value (13.4  7.3 Mt year-1) by the 2030s and 2080s, respectively. Given the large variation in the present mean annual suspended sediment load, the former change may be difficult to discern and, overall, the forecast effect of 21st century climate change on the suspended sediment load of the Waipaoa River is less than the magnitude of the change that is thought to have occurred at the beginning of the Anthropocene. Thus the legacy of past human activities will continue to dominate. Key words modelling; HydroTrend; sediment transport; climate change; suspended sediment; peak discharge ______Sediment Dynamics in Changing Environments (Proceedings of a symposium held in Christchurch, New Zealand, December 2008). IAHS Publ. 325, 2008, 432-439.

The impact of climate change on glacial sediment delivery to rivers

JIM BOGEN Norwegian Water Resources and Energy Directorate, PO Box 5091, Maj. 0301 Oslo, Norway [email protected]

Abstract Climate change scenarios indicate that most glaciers in Norway will have disappeared by the year 2100. As the downstream river reaches are often completely dominated by glacial sediments, large environmental changes are expected. This paper discusses and reviews sediment transport studies in order to deduce the impact of climate change on the sediment delivery of glaciers. Sediment monitoring programmes have revealed large seasonal and year-to-year changes in sediment transport that reflect the rate of melt-out and flushing of sediments in the subglacial conduits and cavity systems. Long-term changes in sediment delivery were revealed by sedimentation rates in proglacial lakes. It was found that the reduction in the glacier volumes during the last 300 years and the increased meltwater runoff, were accompanied by an increase in suspended sediment supply. A doubling of the sediment yield is estimated for the Nigardsbreen Glacier during the period 2070–2100, due to predicted temperature rise. Key words glacial erosion; sediment delivery; climate change; sediment transport

Reconstructing historical sediment yields from the infilling of farm reservoirs, Eastern Cape, South Africa

IAN D. L. FOSTER1,2, JOHN BOARDMAN3,4 & JOHN B. GATES5 1 Department of Molecular and Applied Biosciences, School of Biosciences, University of Westminster, Cavendish Campus, 115 New Cavendish Street, London W1W 6UW, UK [email protected] 2 Department of Geography, Rhodes University, PO Box 94, Grahamstown 6140, Eastern Cape, South Africa 3 Environmental Change Institute, Oxford University Centre for the Environment, Dyson Perrins Building, South Parks Road, Oxford OX1 3QY, UK 4 Department of Environmental and Geographical Science, University of Cape Town, Rondebosch 7701, South Africa 5 Bureau of Economic Geology, Jackson School of Geosciences, University of Texas at Austin, University Station, Box X, Austin, Texas 78713-8924, USA

Abstract In order to calculate sediment yields, a chronology was established for sediments accumulating in two farm reservoirs at single coring locations in each reservoir. The chronology has been transferred to six adjacent cores in each reservoir using magnetic core correlation, particle size and visual stratigraphy. Reservoir sediment volumes corresponding to variable surface levels behind the two dams were estimated using GPS-based measurement of the contemporary reservoir in-fill, combined with coarse assumptions about underlying reservoir geometry derived from aerial photographs and topographic maps. Upper limits on volume were calculated for the hypothetical case of a reservoir with near-vertical sides, and lower limits for the case of linearly-sloping sides (i.e. a v-shaped cross-section). The arithmetic mean of these two boundary cases was taken as the best estimate. Reservoir sediment volumes, and volumes of sediment accumulating between dated horizons in the sediment cores, were obtained from the best estimate of changing sediment volumes derived from these assumptions. The volume of sediment accumulating between each time zone was adjusted by combining sedimentation rates with trap efficiency estimates. These data were subsequently converted to specific sediment yields using the average sediment density. Results from the two reservoirs to which this methodology has been applied show that the historical timing of increased sediment yields is different and that yields have not declined significantly over the last ~50 years, despite reductions in stocking density and the abandonment of rain-fed agriculture. Key words sediment yields; reservoir sedimentation; Karoo; South Africa

National-scale sediment delivery to watercourses across England and Wales under recent (1970–2004) land-use change

A. L. COLLINS, D. DUETHMANN & P. TAYLOR Environment Group, ADAS, Woodthorne, Wergs Road, Wolverhampton WV6 8TQ, UK [email protected]

Abstract Land-use change has been widely reported as a key driver of temporal trends in soil erosion and sediment delivery. As a means of generating strategic information on sediment pressures, the process-based PSYCHIC (Phosphorus and Sediment Yield CHaracterisation In Catchments) model was used to simulate sediment delivery from agricultural land, excluding channel banks, to all rivers across England and Wales. Evaluation of PSYCHIC using available field-scale monitoring data is ongoing (r2 = 70%). Scenario analyses employed a national land-use database assembled for the years 1970, 1980, 1995, 2000 and 2004. The total sediment loading delivered to all rivers for these reference years was estimated at 2774 kt, 2890 kt, 2720 kt, 2659 kt and 2518 kt, respectively. On the basis of the hindcasting, PSYCHIC therefore predicted that total sediment delivery to watercourses from agricultural sources peaked in 1980 and decreased by 9% between 1970 and 2004. Key words land-use change; sediment delivery; modelling; River Basin Districts

Land-use impacts on catchment erosion for the Waitetuna catchment, New Zealand

J. SCHMIDT1, S. ELLIOTT2 & L. McKERGOW2 1 National Institute of Water and Atmospheric Research (NIWA), PO Box 8602, Christchurch, New Zealand [email protected] 2 National Institute of Water and Atmospheric Research (NIWA), PO Box 11115, Hamilton, New Zealand

Abstract In this study the detailed physically-based model SHETRAN was applied and tested for the Waitetuna catchment of the Raglan Harbour/Whaingaroa (170 km2), with the aim of representing signals in terrestrial sediment generation. Records of streamflow, turbidity, and transported sediment monitored under intensive rainfall conditions served as validation data. We used model set-ups using different land-use scenarios to explore land-use impacts on sediment generation and to suggest catchment management alternatives to minimize impacts of erosion and sediment transport on the Raglan estuary. Key words land-use change; catchment erosion; SHETRAN; Raglan, New Zealand ______Sediment Dynamics in Changing Environments (Proceedings of a symposium held in Christchurch, New Zealand, December 2008). IAHS Publ. 325, 2008, 458-461.

The effects of rapid and catastrophic sedimentation in tectonically active areas

JAMES GOFF Natural Hazards Research Laboratory and Australian Tsunami Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney 2052, NSW, Australia [email protected]

Abstract Tectonic activity can have a marked direct and indirect control upon region-wide geomorphology and human activity. A seismic driving model for sediment movement is discussed and key examples are given from two regions in New Zealand. In South Westland, regional episodes of coastal progradation and dune formation have quickly followed all known Alpine fault earthquakes since at least c. 1220 AD. On the other side of the Southern Alps the rapid transfer of sand to the coast following the same fault ruptures again caused coastal dune formation. While dune system development occurs soon after tectonic activity, other geomorphological changes such as river channel avulsion and spit/barrier formation can be delayed by many years. The interaction between fine and coarse sediment delivery systems causes significant and often rapid changes to coastal geomorphology and ecosystems that have serious implications for human populations living at or near the coast. Key words tectonics; dunes; aggradation; geomorphology; coastal change; human settlements

Impacts of the 921 Ji-Ji earthquake, Taiwan, on channel morphology and channel evolution

Y. H. HSU1 & Y. S. HSU2 1 Civil and Hydraulic Engineering and Construction and Disaster Prevention Research Center, Feng-Chia University, Taichung 407, Taiwan, Republic of China yuhsiung @mail 2000 . com .tw 2 Department of Water Resources Engineering, Feng-Chia University, Taiwan, Republic of China

Abstract On 21 September 1999, an earthquake, that measured 7.3 on the Richter scale, erupted with the epicentre located at Ji-Ji Township in central Taiwan. A large-scale landslide took place during the Ji-Ji earthquake. Landslide masses plugged the original channel of the Chingshui River and created an upstream dammed reservoir – the Tasoling Lake – with a water volume of 42 000 000 m3. Subsequently, the area was affected by a series of typhoons and associated floods in 2001 and 2004. The newly formed channels show disparate patterns of channel evolution, and provide a rare opportunity for field observation and data collection. In this paper, the landslide-dammed lake was reconstructed using historic documents and geomorphic channel evolution. The result shows the channel is at a stage where the bed-slope is going through self- adjustment. Backward erosion at the spillway notch leads to lowering of the longitudinal bed slope. Key words landslide-dammed lake; channel evolution; Ji-Ji earthquake, Taiwan

______Sediment Dynamics in Changing Environments (Proceedings of a symposium held in Christchurch, New Zealand, December 2008). IAHS Publ. 325, 2008, 469-476. Linking erosion with environmental and societal impacts in a rapidly changing environment

M. J. CROZIER School of Geography, Environment and Earth Sciences, Victoria University of Wellington, PO Box 600, Wellington 6040, New Zealand [email protected]

Abstract In global terms, unprecedented rates of population growth and development, with their incessant demands on the land resource, are increasingly exposing society to the adverse consequences of erosion. In this paper, I review previous work on the degree and rate of change of the mega drivers of erosion (climate and human activity) in a historical context and analyse the geo-social system’s response from a hazard perspective. The geo-social system faces increased complexity, resulting from population growth, urbanisation, climate change, escalating oil and grain prices, as well as increased physical and political intervention within the natural environment. Costs of erosion and mitigating measures are increasing and the cost of food production is becoming unsustainable. This rapidly changing environment has enhanced the risks associated with the erosion hazard by accelerating physical processes, increasing the elements at risk, compounding social vulnerability and increasing exposure to hazard. Key words erosion; population growth; climate change; food production; sustainability; hazard; risk

Erosion without sediment supply? The crux of a flood-plain restoration project downstream of dammed headwaters

BERND CYFFKA1 & FLORIAN HAAS2 1 Floodplain Institute Neuburg, Schloss Gruenau, D-86633 Neuburg/Danube, Germany [email protected] 2 Divsion of Physical Geography, Catholic University of Eichstaett-Ingolstadt, D-85072 Eichstaett, Germany

Abstract During the first half of the 19th century, work started to embank the main parts of the Upper Danube River completely. Since that time, the river has flowed in levees. The second half of the 20th century was characterized by dam building for hydro-power stations. Since then, only sandy material has reached the banks of the Danube. In 2006, a pilot project named “Remediation of riparian areas on the Danube flood plain between Neuburg and Ingolstadt” started. About 1200 ha of forests are used for controlled artificial flooding to improve biodiversity in the riparian forest. Besides the controlled artificial flooding, a new distributary will be installed using old ox-bow structures. Meander migration, erosion and sedimentation are explicitly allowed. But what if the material from the upper part of the restoration area is completely eroded and transported downstream? This question is still to be answered. This contribution illustrates the scope and problems of this flood-plain remediation pilot project. Key words erosion; sedimentation; flood-plain remediation; laser scanning; cross-profiles

Sediment dynamics and improvised control technologies in the Athi River drainage basin, Kenya SHADRACK MULEI KITHIIA Postgraduate Programme in Hydrology, Department of Geography and Environmental Studies, University of Nairobi, PO Box 30197, 00100 GPO, Nairobi, Kenya [email protected]

Abstract In Kenya, the changing of land-use systems from the more traditional systems of the 1960s to the present mechanized status, contributes enormous amounts of sediments due to water inundations. The Athi River drains areas that are subject to intense agricultural, industrial, commercial and population settlement activities. These activities contribute immensely to the processes of soil erosion and sediment transport, a phenomenon more pronounced in the middle and lower reaches of the river where the soils are much more fragile and the river tributaries are seasonal in nature. Total Suspended Sediments (TSS) equivalent to sediment fluxes of 13 457, 131 089 and 2 057 487 t year-1 were recorded in the headwater areas, middle and lower reaches of the river, respectively. These varying trends in sediment transport and amount are mainly due to the chemical composition of the soil coupled with the land-soil conservation measures already in practice, and which started in the 1930s and reached their peak in the early 1980s. This paper examines trends in soil erosion and sediment transport dynamics progressively downstream. The land-use activities and soil conservation, control and management technologies, which focus on minimizing the impacts of overland flow, are examined to assess the economic and environmental sustainability of these areas, communal societal benefits and the country in general. Key words land-use systems; soil erosion; sediment dynamics; improvised control technologies

Recurrent displacement of a forested earthflow and implications for forest management, East Coast Region, New Zealand

MICHAEL MARDEN1, CHRIS J. PHILLIPS2 & DONNA ROWAN1 1 Landcare Research, PO Box 445, Gisborne 4010, New Zealand [email protected] 2 Landcare Research, PO Box 40, Lincoln 7640, New Zealand

Abstract Recurrent movement of a forested earthflow is documented over a 21-year period when two phases of activity were recorded, each separated by an interval of inactivity. Horizontal, vertical, and real- time surface displacements were measured. On both occasions the initiation of movement began in the headscarp region and activity propagated the 700-m length of this flow at times when soil moisture surplus exceeded the long-term winter average. Movement occurred as a series of “surges” followed by periods of deceleration. Our findings suggest that the critical failure threshold leading to the initiation of movement under closed-canopy forest is determined by the duration of antecedent soil moisture surplus and elevated pore water pressure, and is less a response to rainfall. Once initiated, however, surge-like movements are accelerated by heavy rainfall events and activity overlaps with periods of soil moisture deficit. There was no relationship between the initiation of earthflow activity and forest practices. Key words earthflow; displacement rates; rainfall; soil moisture; forest harvesting

Estimating the spatial distribution of sediment concentration in the Manawatu River, New Zealand, under different land-use scenarios

A.-G. E. AUSSEIL & J. R. DYMOND Landcare Research Ltd, Private Bag 11052, Palmerston North, New Zealand [email protected]

Abstract To mitigate sedimentation in waterways, catchment-wide approaches to reducing soil erosion are required. We propose a method to estimate sediment concentration at mean and high discharge, at the subcatchment level, resulting from scenarios of land uses. Sediment concentration is predicted as a function of discharge and sediment yield. The discharge was estimated for 655 subcatchments of the Manawatu River by fitting a regression model between mean annual discharge and mean annual rainfall for 21 gauging sites. The sediment yield was derived from a long-term mean erosion rate model that took into consideration rainfall, land cover, and erosion terrains. The correlation coefficients between the predicted sediment concentration from our model, and the sediment concentration estimated from the rating curves at mean and high discharge, were 0.84 and 0.77, respectively. The model prediction was used to assess the implications of land use change and farm plans scenarios on sediment concentrations in the Manawatu River. Key words sediment concentration; spatial distribution; land use; land management; water quality; soil erosion

Impacts of wildfire and post-fire salvage logging on sediment transfer in the Oldman watershed, Alberta, Canada

ULDIS SILINS1, MICHEAL STONE2, MONICA EMELKO3 & KEVIN BLADON1 1 Department of Renewable Resources, University of Alberta, Edmonton, Alberta T6G 2H1, Canada 2 School of Planning and Department of Geography, University of Waterloo, Waterloo N2L 3G1, Canada [email protected] 3 Department of Civil and Environmental Engineering, University of Waterloo, Waterloo N2L 3G1, Canada

Abstract The 2003 Lost Creek fire burned 21 000 ha of forested land in the Oldman River basin, Alberta, Canada. Seven watersheds, with varying degrees of natural and man-made land disturbance (burned, post- fire salvage logged, unburned) were monitored for three years to assess sediment concentrations and production (export and yield) over a range of flow regimes (spring melt, baseflow and stormflow). Suspended sediment concentrations were 6-times higher in burned watersheds and 11-times higher in post- fire salvage logged watersheds than in unburned watersheds. Sediment availability was greater in both burned and post-fire salvage logged watersheds but varied with flow condition; particularly during the snowmelt freshet and stormflow. In burned watersheds, sediment yield was 5-times higher during snowmelt and 13-times higher during stormflow than in unburned watersheds. Post-fire salvage logging produced much greater impacts than wildfire alone, with mean sediment yield 19-times higher during snowmelt and 9-times higher during stormflow compared to unburned watersheds. Key words Canada; Rocky Mountains; salvage logging; sediment concentration; sediment export; sediment yield; wildfire

______Sediment Dynamics in Changing Environments (Proceedings of a symposium held in Christchurch, New Zealand, December 2008). IAHS Publ. 325, 2008, 516-523. Managing coastal erosion: from long-term coastal evolution to seasonal shoreline changes

L. S. ESTEVES1, P. TEIXEIRA2 & J. J. WILLIAMS1 1 School of Geography, University of Plymouth, Drake Circus, Plymouth PL4 8AA, UK [email protected] 2 Pós-Graduação em Oceanografia Física, Química e Geológica, FURG, CP 474, Rio Grande, RS 9201-900, Brazil

Abstract Erosion problems along the southern Brazilian coast are evaluated, taking into account the complex interactions of long- and short-term natural processes and socio-economic factors. Coastal evolution during the Holocene are considered, together with shoreline changes in the shorter term, to measure magnitudes of changes relevant to coastal management (using aerial photographs, DGPS mapping and beach profiles). This study focuses on specific sites to illustrate the importance of integrating processes acting at different spatial and temporal scales to define the best management practice to deal with coastal erosion. One of the case studies is the area of Hermenegildo, a small beach village built on top of the dunes, in a flat, low-lying coastal plain. The settlement is experiencing long-term coastal retreat and often is threatened by erosion during storms. As the local government does not have a policy to regulate construction of coastal defences, the Hermenegildo coastline is protected by a range of amateur schemes initiated by individual property owners. Due to a public action filed in 2005, the local government now is obliged by law to map and deal with illegal occupation in dune areas (which are protected by the Federal Constitution), and to establish a plan of coastal uses and regulations. Based on the available data, potential management approaches are evaluated in terms of long-term sustainability, and economic and technical viability. Key words beach erosion; coastal protection; integrated coastal management; GIS; public perception; Brazil

Hydrological and sedimentological connectivity of unsealed roads

C. J. THOMPSON, I. TAKKEN & J. CROKE School of Physical, Environmental and Mathematical Sciences, University of New South Wales at Australian Defence Force Academy, Northcott Drive. Campbell, Australian Capital Territory 2600, Australia [email protected]

Abstract Unsealed roads are an important source of runoff and sediment and may affect the hydrology and water quality of streams. A recently-developed conceptual framework to model the hydrological connectivity between roads and streams in managed forest environments allows identification of the different types of delivery pathways and estimation of the runoff volumes delivered through them. While the model does not include sediment delivery explicitly, it is generally assumed that sedimentological connectivity can only be equal to, or smaller than hydrological connectivity. The objectives of this study are to quantify road runoff and sediment generation, and to investigate runoff and sediment travel distance below drain outlets. Preliminary field monitoring results show that roads in this catchment produce an order of magnitude more sediment compared to findings from other studies. Results from field experiments indicate that drains located within 40 m of the stream have very high probability of connecting to the stream during an event with a 10-year recurrence interval. The experimental results also indicate that the current modelling approach may over-predict connectivity, as observed flow losses down the hillslope were higher than would be predicted based on current model assumptions. Key words overland flow; connectivity; modelling; bed load; suspended sediment; road drains; erosion ______Sediment Dynamics in Changing Environments (Proceedings of a symposium held in Christchurch, New Zealand, December 2008). IAHS Publ. 325, 2008, 532-539.

Hydrological recovery of rangeland following cattle exclusion

A. A. HAWDON1, R. J. KEEN1, D. A. POST2 & S. N. WILKINSON1 1 CSIRO Land and Water, Davies Laboratory, PMB Aitkenvale, Queensland 4814, Australia [email protected] 2 CSIRO Land and Water, GPO Box 1666, Canberra, Australian Capital Territory 2601, Australia

Abstract There is concern that the Great Barrier Reef World Heritage Area (GBRWHA) is being impacted by a decline in the quality of water exported from adjacent catchments. Approximately 90% of the catchment area draining to the GBRWHA is used for cattle production, and at present there is a limited understanding of the time periods required for water and sediment runoff to respond to changes in pasture management and over what period changes in grazing land management may impact water and sediment runoff. The quantity and quality of water exported from two hillslopes in the Burdekin River catchment was monitored for a period of seven years. Both hillslopes were grazed during the first two years of monitoring and cattle were excluded from the treated hillslope prior to the beginning of the third year. The suspended sediment yield of the treated hillslope declined from 150% to 50% of the control hillslope after the first year of treatment and remained at this level or less for the following four years. However, hillslope runoff of water showed little response to treatment despite the surface pasture condition having improved. This means that the amount of runoff available to cause downstream gully and river bank erosion would not be affected within five years. Key words recovery; hillslope; grazing; runoff; sediment; Great Barrier Reef World Heritage Area

Improved sediment-management strategies for the sustainable development of German waterways

E. GOELZ Federal Institute of Hydrology, Am Mainzer Tor 1, D-56068 Koblenz, Germany [email protected]

Abstract Apart from the coastal waters, the German waterway system consists of large navigable rivers and of canals connecting the individual basins. The main arteries are the Rhine River and the tidal Elbe River. In the impounded section of the Upper Rhine, relocation of sediments causes major problems as the fine-grained deposits are contaminated by hexachlorobenzene (HCB). Furthermore, an increasing frequency and intensity of extreme events might increase the sediment input into the impoundment chains and enhance deposition there. Hence, new strategies to reduce maintenance costs and to minimize ecological risks are required. Due to sediment retention in the impounded section, the free-flowing Rhine is subject to severe bed degradation. Here the goal is to achieve a dynamic stabilization of the river bed by combining training works with bed-load management measures, such as artificial sediment supply. In the estuaries of north-western Germany, regulation and deepening of the fairways have enforced tidal pumping leading to enhanced upstream transport of sediments and to increasing dredging volumes in the inner parts of the estuaries. In the tidal Elbe River, the strategy is to accomplish measures to damp the incoming tide and to optimize relocation of dredged sediment from both ecological and economic aspects. Key words Rhine; tidal Elbe; contaminated sediments; relocation; bed-load management; residual transport ______Sediment Dynamics in Changing Environments (Proceedings of a symposium held in Christchurch, New Zealand, December 2008). IAHS Publ. 325, 2008, 550-558.

Predicting decadal-scale estuarine sedimentation for planning catchment development

M. O. GREEN National Institute of Water & Atmospheric Research (NIWA), PO Box 11-115, Hamilton, New Zealand [email protected]

Abstract Deposition of typically fine-grained terrigenous sediment in coastal-plain estuaries can smother habitats, chronically raise turbidity and change substrate texture. To help plan catchment development and choose mitigation measures that will secure environmental goals in the estuary, we have built a model that predicts rates and locations of estuarine sedimentation on the decadal time scale. The USC model combines information from several underlying models, including a catchment model (based on GLEAMS) for predicting daily sediment runoff, and an estuary hydrodynamics/sediment-transport model. The estuary model is used to evaluate event-scale sediment transport and deposition patterns under a range of weather conditions, which are held in a database that the USC model accesses. Multiple grainsizes are treated in the USC model. A bed-sediment weighted mean grainsize controls erosion of the mixed-grain bed, but, once in suspension, the constituent grainsizes disperse according to their respective fall speeds. These features allow for bed armouring, which reduces the resuspension of all grainsizes, and for different constituent grainsizes to “unmix” while in suspension. The USC model is run in a Monte Carlo mode to capture extreme sediment-generation events. The USC model has been implemented for the Central Waitemata Harbour (Auckland, New Zealand) in a study to predict sedimentation and heavy-metal accumulation in the harbour as the Auckland region continues to grow over the next 100 years. The model predictions are being used for, amongst other things, identifying significant sediment and metal sources in the catchment, and testing the efficacy of different types of stormwater treatment and options for controlling heavy-metal generation at source. The model was calibrated against measured (radioisotopic) sedimentation rates over the past 50 years. The calibration primarily consists of relaxing and strengthening sediment-transport pathways in the model until all of the dynamic sinks in the model simultaneously accumulate sediment at realistic rates. The hindcast sedimentation rates are generally smaller than the radioisotopic sedimentation rates; however, the patterns of sedimentation are similar in all important respects. A further reality check on the model performance is provided by examining patterns of sediment dispersal, specifically, the origins of sediments that deposit in the various parts of the harbour. The model predictions for the period 2001–2100 show a complicated response in the harbour to a reduction in catchment sediment runoff expected over the next 15–20 years, which in turn is due to the supply of greenfield development sites becoming exhausted and development as a consequence turning exclusively to infill housing. In some parts of the harbour the sedimentation rate is predicted to be virtually unchanged by this reduction, but in other parts a change in depositional regime is predicted. This has significant implications for the accumulation of heavy metals in the harbour bed sediments. Key words estuary; sediment transport; sedimentation; model; planning; catchment development; New Zealand

Testing the capability of a sediment budget model for targeting remediation measures to reduce suspended-sediment yield

SCOTT N. WILKINSON CSIRO Land and Water and eWater CRC, PMB Aitkenvale, Queensland 4814 Australia [email protected] Abstract Targeting and achieving reductions in suspended-sediment yield (wash load) requires identification of the sediment sources and their connectivity to the catchment outlet. This paper assesses the strengths and limitations of a spatially-distributed model of suspended-sediment budgets (SedNet) for targeting remediation actions by reviewing five recent Australian model applications. Compared with suspended- sediment yields estimated from river discharge and concentration data, the root-mean-square relative error in predicted yield is 36–99% for catchments below 2000 km2 in area and 24–32% for larger catchments. Spatial variation in sediment supply within each river basin is 2–9 times larger than model error, and so the model can reliably differentiate between the areas contributing most and least to basin yield. Quality input data on vegetation cover, gully extent and bank erosion rates are important to obtain reliable model predictions. Geomorphic studies and sediment tracing can provide process understanding to test model predictions and refine parameter values. Key words sediment budget; modelling; erosion; land use; watershed management; uncertainty

Impacts of native forest harvesting on in-channel erosion and sediment yields in unmapped headwater catchments

ASHLEY A. WEBB Forests NSW, Department of Primary Industries, PO Box J19, Coffs Harbour Jetty, New South Wales 2450, Australia [email protected]

Abstract The outlets of five unmapped headwater forest catchments on the Mid-North coast of New South Wales, Australia, 0.9–4.2 ha in area, were instrumented between 2002 and 2006 with flat-v weirs to measure streamflow; bed-load traps to measure bed load; and stage-activated automatic pump-samplers to allow water sample collection for analysis of turbidity and suspended-sediment concentration. Pressure transducers were installed in groundwater monitoring wells beneath the surface of each channel to measure subsurface flow. Additionally, 70 channel cross-sections were surveyed at least annually during the trial period while a total of 1037 erosion pins was installed at 180 locations of likely bank or nickpoint erosion and measured at 6-monthly intervals. Harvesting using BMPs occurred in three catchments in 2004, while two catchments were harvested, but total exclusion zones 10 m wide maintained on either side of the channels. On average, the channels flowed for 2–5% of the time. They are ephemeral features and surface flows that did occur were dominated by stormflows (79–95%) with a minor baseflow component. Groundwater monitoring indicated that 58–79% of annual channel flow was transmitted beneath the channel sediments as opposed to surface runoff. Because they flowed infrequently, sediment yields from the channels were extremely low. Pre-harvest values were recorded between 0.001 and 0.05 tonnes per ha per year, which are lower than typically recorded in larger forest catchments. Sediment yields and streamflow peaks increased in all channels following harvesting. However, harvesting using BMPs in selected catchments did not significantly alter the magnitude of the sediment response to harvesting, while channel bank and nickpoint erosion rates remained consistently low during the monitoring period. Key words unmapped drainage lines; channel erosion; sediment yields; buffer strips; forestry impacts; southeastern Australia

Reformation of pool-riffle sequences and induced bed armouring in a sand-bed stream following river rehabilitation

A. F. KEENE1, R. T. BUSH1, M. D. CHEETHAM1 & W. D. ERSKINE2 1 Southern Cross Geoscience, School of Environmental Science and Management, Southern Cross University, PO Box 157, Lismore, Australia [email protected] 2 School of Environmental and Life Sciences, University of Newcastle, PO Box 127, Ourimbah, Australia

Abstract A series of structures was built along Widden Brook to trap sandy bed load as part of a river rehabilitation project. Stock-proof fencing of the riparian corridor was also carried out. The combination of in-stream structures and riparian revegetation has successfully sequestered large volumes of sand over the last six years, causing a substantial reduction in downstream sand supply. Downstream channel response to sand sequestration has included up to 1 m of bed degradation, channel contraction to less than half of the initial channel width, formation of marginal in-channel benches, reformation of a well-defined, rhythmic- ally-spaced pool-riffle sequence and creation of a partially gravel-armoured bed surface. Sand storage in the study reach has starved the river immediately downstream, inducing bed erosion and the size-selective transport of sand and fine gravel. Residual pool depths now store four times the volume of water that was present before the start of river rehabilitation. Key words channel response; sand storage; residual pool depth; grain size analysis; longitudinal profile; Widden Brook

Evidence for catastrophic shifts in the trophic structure of flood-plain lakes associated with soil erosion

MICHAEL REID Riverine Landscapes Research Lab, University of Canberra, Australian Capital Territory 2601, Australia [email protected]

Abstract The introduction of European agricultural practices to southeastern Australia during the 1800s was associated with a period of extensive erosion in upland areas. The effects of this erosion on aquatic systems were substantial. Deep gullies replaced natural “chain of ponds” systems in headwaters, and the resultant “sand slugs” reduced substrate complexity and stability in middle reaches. The impact of this period of intensive erosion in lowland reaches is less obvious. This study presents the results of palaeoecological reconstructions from several flood-plain lakes on the Murray River that cover the period prior to the introduction of agriculture to the present. These records show a consistent pattern whereby benthic algae are replaced by planktonic algae concomitant with peaks in indicators of high sediment input. This pattern supports studies which have utilised different indicators at other sites in the region and is interpreted as resulting from light attenuation due to high suspended-sediment loads during a phase of intensive sediment erosion and transport during the mid to late 1800s. The maintenance of this macrophyte- free state in the absence of continued high sediment loads up to the present day is thought to reflect the existence of “alternative stable states” in these systems. Key words erosion; flood plains; billabongs; aquatic plants; diatoms; palaeolimnology

Recurrent displacement of a forested earthflow and implications for forest management, East Coast Region, New Zealand MICHAEL MARDEN1, CHRIS J. PHILLIPS2 & DONNA ROWAN1 1 Landcare Research, PO Box 445, Gisborne 4010, New Zealand [email protected] 2 Landcare Research, PO Box 40, Lincoln 7640, New Zealand

Abstract Recurrent movement of a forested earthflow is documented over a 21-year period when two phases of activity were recorded, each separated by an interval of inactivity. Horizontal, vertical, and real- time surface displacements were measured. On both occasions the initiation of movement began in the headscarp region and activity propagated the 700-m length of this flow at times when soil moisture surplus exceeded the long-term winter average. Movement occurred as a series of “surges” followed by periods of deceleration. Our findings suggest that the critical failure threshold leading to the initiation of movement under closed-canopy forest is determined by the duration of antecedent soil moisture surplus and elevated pore water pressure, and is less a response to rainfall. Once initiated, however, surge-like movements are accelerated by heavy rainfall events and activity overlaps with periods of soil moisture deficit. There was no relationship between the initiation of earthflow activity and forest practices. Key words earthflow; displacement rates; rainfall; soil moisture; forest harvesting

Impacts of wildfire and post-fire salvage logging on sediment transfer in the Oldman watershed, Alberta, Canada

ULDIS SILINS1, MICHEAL STONE2, MONICA EMELKO3 & KEVIN BLADON1 1 Department of Renewable Resources, University of Alberta, Edmonton, Alberta T6G 2H1, Canada 2 School of Planning and Department of Geography, University of Waterloo, Waterloo N2L 3G1, Canada [email protected] 3 Department of Civil and Environmental Engineering, University of Waterloo, Waterloo N2L 3G1, Canada

Abstract The 2003 Lost Creek fire burned 21 000 ha of forested land in the Oldman River basin, Alberta, Canada. Seven watersheds, with varying degrees of natural and man-made land disturbance (burned, post- fire salvage logged, unburned) were monitored for three years to assess sediment concentrations and production (export and yield) over a range of flow regimes (spring melt, baseflow and stormflow). Suspended sediment concentrations were 6-times higher in burned watersheds and 11-times higher in post- fire salvage logged watersheds than in unburned watersheds. Sediment availability was greater in both burned and post-fire salvage logged watersheds but varied with flow condition; particularly during the snowmelt freshet and stormflow. In burned watersheds, sediment yield was 5-times higher during snowmelt and 13-times higher during stormflow than in unburned watersheds. Post-fire salvage logging produced much greater impacts than wildfire alone, with mean sediment yield 19-times higher during snowmelt and 9-times higher during stormflow compared to unburned watersheds. Key words Canada; Rocky Mountains; salvage logging; sediment concentration; sediment export; sediment yield; wildfire

Managing coastal erosion: from long-term coastal evolution to seasonal shoreline changes L. S. ESTEVES1, P. TEIXEIRA2 & J. J. WILLIAMS1 1 School of Geography, University of Plymouth, Drake Circus, Plymouth PL4 8AA, UK [email protected] 2 Pós-Graduação em Oceanografia Física, Química e Geológica, FURG, CP 474, Rio Grande, RS 9201-900, Brazil

Abstract Erosion problems along the southern Brazilian coast are evaluated, taking into account the complex interactions of long- and short-term natural processes and socio-economic factors. Coastal evolution during the Holocene are considered, together with shoreline changes in the shorter term, to measure magnitudes of changes relevant to coastal management (using aerial photographs, DGPS mapping and beach profiles). This study focuses on specific sites to illustrate the importance of integrating processes acting at different spatial and temporal scales to define the best management practice to deal with coastal erosion. One of the case studies is the area of Hermenegildo, a small beach village built on top of the dunes, in a flat, low-lying coastal plain. The settlement is experiencing long-term coastal retreat and often is threatened by erosion during storms. As the local government does not have a policy to regulate construction of coastal defences, the Hermenegildo coastline is protected by a range of amateur schemes initiated by individual property owners. Due to a public action filed in 2005, the local government now is obliged by law to map and deal with illegal occupation in dune areas (which are protected by the Federal Constitution), and to establish a plan of coastal uses and regulations. Based on the available data, potential management approaches are evaluated in terms of long-term sustainability, and economic and technical viability. Key words beach erosion; coastal protection; integrated coastal management; GIS; public perception; Brazil

Hydrological and sedimentological connectivity of unsealed roads

C. J. THOMPSON, I. TAKKEN & J. CROKE School of Physical, Environmental and Mathematical Sciences, University of New South Wales at Australian Defence Force Academy, Northcott Drive. Campbell, Australian Capital Territory 2600, Australia [email protected]

Abstract Unsealed roads are an important source of runoff and sediment and may affect the hydrology and water quality of streams. A recently-developed conceptual framework to model the hydrological connectivity between roads and streams in managed forest environments allows identification of the different types of delivery pathways and estimation of the runoff volumes delivered through them. While the model does not include sediment delivery explicitly, it is generally assumed that sedimentological connectivity can only be equal to, or smaller than hydrological connectivity. The objectives of this study are to quantify road runoff and sediment generation, and to investigate runoff and sediment travel distance below drain outlets. Preliminary field monitoring results show that roads in this catchment produce an order of magnitude more sediment compared to findings from other studies. Results from field experiments indicate that drains located within 40 m of the stream have very high probability of connecting to the stream during an event with a 10-year recurrence interval. The experimental results also indicate that the current modelling approach may over-predict connectivity, as observed flow losses down the hillslope were higher than would be predicted based on current model assumptions. Key words overland flow; connectivity; modelling; bed load; suspended sediment; road drains; erosion

______Sediment Dynamics in Changing Environments (Proceedings of a symposium held in Christchurch, New Zealand, December 2008). IAHS Publ. 325, 2008, 532-539. Hydrological recovery of rangeland following cattle exclusion

A. A. HAWDON1, R. J. KEEN1, D. A. POST2 & S. N. WILKINSON1 1 CSIRO Land and Water, Davies Laboratory, PMB Aitkenvale, Queensland 4814, Australia [email protected] 2 CSIRO Land and Water, GPO Box 1666, Canberra, Australian Capital Territory 2601, Australia

Abstract There is concern that the Great Barrier Reef World Heritage Area (GBRWHA) is being impacted by a decline in the quality of water exported from adjacent catchments. Approximately 90% of the catchment area draining to the GBRWHA is used for cattle production, and at present there is a limited understanding of the time periods required for water and sediment runoff to respond to changes in pasture management and over what period changes in grazing land management may impact water and sediment runoff. The quantity and quality of water exported from two hillslopes in the Burdekin River catchment was monitored for a period of seven years. Both hillslopes were grazed during the first two years of monitoring and cattle were excluded from the treated hillslope prior to the beginning of the third year. The suspended sediment yield of the treated hillslope declined from 150% to 50% of the control hillslope after the first year of treatment and remained at this level or less for the following four years. However, hillslope runoff of water showed little response to treatment despite the surface pasture condition having improved. This means that the amount of runoff available to cause downstream gully and river bank erosion would not be affected within five years. Key words recovery; hillslope; grazing; runoff; sediment; Great Barrier Reef World Heritage Area

Improved sediment-management strategies for the sustainable development of German waterways

E. GOELZ Federal Institute of Hydrology, Am Mainzer Tor 1, D-56068 Koblenz, Germany [email protected]

Abstract Apart from the coastal waters, the German waterway system consists of large navigable rivers and of canals connecting the individual basins. The main arteries are the Rhine River and the tidal Elbe River. In the impounded section of the Upper Rhine, relocation of sediments causes major problems as the fine-grained deposits are contaminated by hexachlorobenzene (HCB). Furthermore, an increasing frequency and intensity of extreme events might increase the sediment input into the impoundment chains and enhance deposition there. Hence, new strategies to reduce maintenance costs and to minimize ecological risks are required. Due to sediment retention in the impounded section, the free-flowing Rhine is subject to severe bed degradation. Here the goal is to achieve a dynamic stabilization of the river bed by combining training works with bed-load management measures, such as artificial sediment supply. In the estuaries of north-western Germany, regulation and deepening of the fairways have enforced tidal pumping leading to enhanced upstream transport of sediments and to increasing dredging volumes in the inner parts of the estuaries. In the tidal Elbe River, the strategy is to accomplish measures to damp the incoming tide and to optimize relocation of dredged sediment from both ecological and economic aspects. Key words Rhine; tidal Elbe; contaminated sediments; relocation; bed-load management; residual transport

______Sediment Dynamics in Changing Environments (Proceedings of a symposium held in Christchurch, New Zealand, December 2008). IAHS Publ. 325, 2008, 550-558. Predicting decadal-scale estuarine sedimentation for planning catchment development

M. O. GREEN National Institute of Water & Atmospheric Research (NIWA), PO Box 11-115, Hamilton, New Zealand [email protected]

Abstract Deposition of typically fine-grained terrigenous sediment in coastal-plain estuaries can smother habitats, chronically raise turbidity and change substrate texture. To help plan catchment development and choose mitigation measures that will secure environmental goals in the estuary, we have built a model that predicts rates and locations of estuarine sedimentation on the decadal time scale. The USC model combines information from several underlying models, including a catchment model (based on GLEAMS) for predicting daily sediment runoff, and an estuary hydrodynamics/sediment-transport model. The estuary model is used to evaluate event-scale sediment transport and deposition patterns under a range of weather conditions, which are held in a database that the USC model accesses. Multiple grainsizes are treated in the USC model. A bed-sediment weighted mean grainsize controls erosion of the mixed-grain bed, but, once in suspension, the constituent grainsizes disperse according to their respective fall speeds. These features allow for bed armouring, which reduces the resuspension of all grainsizes, and for different constituent grainsizes to “unmix” while in suspension. The USC model is run in a Monte Carlo mode to capture extreme sediment-generation events. The USC model has been implemented for the Central Waitemata Harbour (Auckland, New Zealand) in a study to predict sedimentation and heavy-metal accumulation in the harbour as the Auckland region continues to grow over the next 100 years. The model predictions are being used for, amongst other things, identifying significant sediment and metal sources in the catchment, and testing the efficacy of different types of stormwater treatment and options for controlling heavy-metal generation at source. The model was calibrated against measured (radioisotopic) sedimentation rates over the past 50 years. The calibration primarily consists of relaxing and strengthening sediment-transport pathways in the model until all of the dynamic sinks in the model simultaneously accumulate sediment at realistic rates. The hindcast sedimentation rates are generally smaller than the radioisotopic sedimentation rates; however, the patterns of sedimentation are similar in all important respects. A further reality check on the model performance is provided by examining patterns of sediment dispersal, specifically, the origins of sediments that deposit in the various parts of the harbour. The model predictions for the period 2001–2100 show a complicated response in the harbour to a reduction in catchment sediment runoff expected over the next 15–20 years, which in turn is due to the supply of greenfield development sites becoming exhausted and development as a consequence turning exclusively to infill housing. In some parts of the harbour the sedimentation rate is predicted to be virtually unchanged by this reduction, but in other parts a change in depositional regime is predicted. This has significant implications for the accumulation of heavy metals in the harbour bed sediments. Key words estuary; sediment transport; sedimentation; model; planning; catchment development; New Zealand

Testing the capability of a sediment budget model for targeting remediation measures to reduce suspended-sediment yield

SCOTT N. WILKINSON CSIRO Land and Water and eWater CRC, PMB Aitkenvale, Queensland 4814 Australia [email protected]

Abstract Targeting and achieving reductions in suspended-sediment yield (wash load) requires identification of the sediment sources and their connectivity to the catchment outlet. This paper assesses the strengths and limitations of a spatially-distributed model of suspended-sediment budgets (SedNet) for targeting remediation actions by reviewing five recent Australian model applications. Compared with suspended- sediment yields estimated from river discharge and concentration data, the root-mean-square relative error in predicted yield is 36–99% for catchments below 2000 km2 in area and 24–32% for larger catchments. Spatial variation in sediment supply within each river basin is 2–9 times larger than model error, and so the model can reliably differentiate between the areas contributing most and least to basin yield. Quality input data on vegetation cover, gully extent and bank erosion rates are important to obtain reliable model predictions. Geomorphic studies and sediment tracing can provide process understanding to test model predictions and refine parameter values. Key words sediment budget; modelling; erosion; land use; watershed management; uncertainty

Impacts of native forest harvesting on in-channel erosion and sediment yields in unmapped headwater catchments

ASHLEY A. WEBB Forests NSW, Department of Primary Industries, PO Box J19, Coffs Harbour Jetty, New South Wales 2450, Australia [email protected]

Abstract The outlets of five unmapped headwater forest catchments on the Mid-North coast of New South Wales, Australia, 0.9–4.2 ha in area, were instrumented between 2002 and 2006 with flat-v weirs to measure streamflow; bed-load traps to measure bed load; and stage-activated automatic pump-samplers to allow water sample collection for analysis of turbidity and suspended-sediment concentration. Pressure transducers were installed in groundwater monitoring wells beneath the surface of each channel to measure subsurface flow. Additionally, 70 channel cross-sections were surveyed at least annually during the trial period while a total of 1037 erosion pins was installed at 180 locations of likely bank or nickpoint erosion and measured at 6-monthly intervals. Harvesting using BMPs occurred in three catchments in 2004, while two catchments were harvested, but total exclusion zones 10 m wide maintained on either side of the channels. On average, the channels flowed for 2–5% of the time. They are ephemeral features and surface flows that did occur were dominated by stormflows (79–95%) with a minor baseflow component. Groundwater monitoring indicated that 58–79% of annual channel flow was transmitted beneath the channel sediments as opposed to surface runoff. Because they flowed infrequently, sediment yields from the channels were extremely low. Pre-harvest values were recorded between 0.001 and 0.05 tonnes per ha per year, which are lower than typically recorded in larger forest catchments. Sediment yields and streamflow peaks increased in all channels following harvesting. However, harvesting using BMPs in selected catchments did not significantly alter the magnitude of the sediment response to harvesting, while channel bank and nickpoint erosion rates remained consistently low during the monitoring period. Key words unmapped drainage lines; channel erosion; sediment yields; buffer strips; forestry impacts; southeastern Australia

Reformation of pool-riffle sequences and induced bed armouring in a sand-bed stream following river rehabilitation

A. F. KEENE1, R. T. BUSH1, M. D. CHEETHAM1 & W. D. ERSKINE2 1 Southern Cross Geoscience, School of Environmental Science and Management, Southern Cross University, PO Box 157, Lismore, Australia [email protected] 2 School of Environmental and Life Sciences, University of Newcastle, PO Box 127, Ourimbah, Australia Abstract A series of structures was built along Widden Brook to trap sandy bed load as part of a river rehabilitation project. Stock-proof fencing of the riparian corridor was also carried out. The combination of in-stream structures and riparian revegetation has successfully sequestered large volumes of sand over the last six years, causing a substantial reduction in downstream sand supply. Downstream channel response to sand sequestration has included up to 1 m of bed degradation, channel contraction to less than half of the initial channel width, formation of marginal in-channel benches, reformation of a well-defined, rhythmic- ally-spaced pool-riffle sequence and creation of a partially gravel-armoured bed surface. Sand storage in the study reach has starved the river immediately downstream, inducing bed erosion and the size-selective transport of sand and fine gravel. Residual pool depths now store four times the volume of water that was present before the start of river rehabilitation. Key words channel response; sand storage; residual pool depth; grain size analysis; longitudinal profile; Widden Brook

Evidence for catastrophic shifts in the trophic structure of flood-plain lakes associated with soil erosion

MICHAEL REID Riverine Landscapes Research Lab, University of Canberra, Australian Capital Territory 2601, Australia [email protected]

Abstract The introduction of European agricultural practices to southeastern Australia during the 1800s was associated with a period of extensive erosion in upland areas. The effects of this erosion on aquatic systems were substantial. Deep gullies replaced natural “chain of ponds” systems in headwaters, and the resultant “sand slugs” reduced substrate complexity and stability in middle reaches. The impact of this period of intensive erosion in lowland reaches is less obvious. This study presents the results of palaeoecological reconstructions from several flood-plain lakes on the Murray River that cover the period prior to the introduction of agriculture to the present. These records show a consistent pattern whereby benthic algae are replaced by planktonic algae concomitant with peaks in indicators of high sediment input. This pattern supports studies which have utilised different indicators at other sites in the region and is interpreted as resulting from light attenuation due to high suspended-sediment loads during a phase of intensive sediment erosion and transport during the mid to late 1800s. The maintenance of this macrophyte- free state in the absence of continued high sediment loads up to the present day is thought to reflect the existence of “alternative stable states” in these systems. Key words erosion; flood plains; billabongs; aquatic plants; diatoms; palaeolimnology

The effect of increasing urbanization and population density on the concentrations of sediment-associated constituents for the conterminous USA

A. J. HOROWITZ1 & V. C. STEPHENS2 1 US Geological Survey, Peachtree Business Center, 3039 Amwiler Road, Atlanta, Georgia 30360, USA [email protected] 2 US Geological Survey, Denver Federal Center, MS 415, Lakewood, Colorado 80225, USA Abstract In 1991, the US Geological Survey began the first cycle of its multidisciplinary National Water Quality Assessment Program. The Program encompasses 51 river basins that collectively account for >70% of the total water use (excluding power generation), and >50% of the drinking water supply in the USA. One aspect of the first cycle included representative bed-sediment sampling within each of the river basins. Sampling sites were selected to represent the most important land-use categories (e.g. agriculture, undeveloped, urban) in each river basin. Both urban percentage and population density were the only land- use/socio-economic factors that significantly affect sediment-associated chemical concentrations, with the latter appearing to be more significant/consistent than the former. The affected constituents, in decreasing order were: Pb > Hg > Ag > Zn > Cd > Cu > Sb > S > Ni > Sn > Cr > As = TC > Co = Fe = P = TOC. Key words sediment chemistry; land use; trace elements; major elements; carbon; sulfur

Towards improving the prediction of longshore sediment transport

J. J. WILLIAMS1, L. S. ESTEVES1 & M. A. LISNIOWSKI2 1 School of Geography, University of Plymouth, Drake Circus, Plymouth PL4 8AA, UK [email protected] 2 Faculty of Science, University of Plymouth, Plymouth PL4 8AA, UK

Abstract Bulk formulae are often used in coastal studies to estimate the net longshore sediment transport (LST) rate. For the same hydrodynamic conditions at a given beach, rates of LST predicted by different bulk formula can vary by factors in a range between 2 and 10, and may not actually reflect the real LST rate. This can have serious economic consequences when designing, for example, beach nourishment schemes. The present paper attempts to reduce these errors and presents a more accurate, site-specific methodology to estimate LST. The study, from four contrasting locations, draws on existing theory and field measurements of hydrodynamics and suspended sediments in the surf zone to develop a new longshore transport model, LT-MOD. Case studies are used to compare the performance of LT-MOD against existing bulk LST formulae at daily time scales. This inter-comparison is then extended over much larger temporal and spatial scales by examining measured and predicted shoreline changes attributable to LST. Key words longshore sediment transport; modelling; field measurements; suspended sediment concentration profile

Changes in sediment discharge after the collapse of Mount Bawakaraeng in South Sulawesi, Indonesia

L. L. DHANIO, T. MIZUYAMA, K. KOSUGI & D. A. RAMPISELA Department of Forestry, Laboratory of Erosion Control, Graduate School of Agriculture, Kyoto University, Kitashirakawa Oiwake-cho, Kyoto 606-8502, Japan [email protected]

Abstract The inner side of a caldera wall at Mount Bawakaraeng collapsed on a large scale in Sulawesi Island in the Republic of Indonesia on 26 March 2004. There were two landslides, located in the Jeneberang River basin (727 km2), and the total volume of the collapse was 232 million m3. The soil covered a wide area of the basin and it has since been eroded by rainfall and flowed into Bili-bili dam, 30 km downstream. Data of rainfall, flow discharge, turbidity of inflow water and water taken to supply Makassar City were recorded since before the collapse. These data were analysed to evaluate the magnitude of the impact of the change of the basin and how the impact decreases over subsequent years. How the basin and the condition of the river bed have changed was analysed in terms of restoration of vegetation, gully formation and armouring of the river bed. The relationship of rainfall and runoff was also analysed and compared from before and after the collapse. The turbidity increased sharply and was 400-times larger after the landslides. The turbidity decreased gradually through three rainy seasons, but it is still much higher than before the collapse. It is estimated that it will take several more years for it to fall back to the level of before the landslide. The rate of water discharge to rainfall decreased after the landslide, probably because the soil retained a lot of rainwater. Key words Bawakaraeng; Bili-bili dam; sedimentation; turbidity; water discharge

Influence of the changing environment on sediment loads of the Lower Mekong River

J. J. WANG & X. X. LU Department of Geography, National University of Singapore 119260, Singapore [email protected]

Abstract With the operation of the Chinese dams in the Upper Mekong River, the sediment issues of the Lower Mekong River (LMR) have attracted more attention. The reports of the impact of the Chinese dams are inconsistent or even contradictory, mainly due to scarcity of sediment measurements and lack of analysis of climate variations. This study employed a newly developed data set to overcome the data scarcity, and investigated both the influence of human activities and climate variations, as well as possible impacts of the Chinese dams on the sediment loads (SL) in the LMR. We differentiated the contributions of human activities and climate factors to the SL during 1962 to 2003 at Chiang Saen in Thailand, closest to the Chinese dams. The combined effects of human activities, including the Chinese dams, as a whole have increased the SL, while climate variations have decreased the SL. This suggests that the construction of the Chinese dams has slowed the increasing rate. Other stations further downstream have also been investigated. Key words Lower Mekong River; Chinese dams; sediment loads; human activities; climate variations

Modelling hillslope soil erosion at ANZAC Cove, Turkey

S. MATTHEWS & M. N. NEAVE Division of Geography, School of Geosciences, University of Sydney, New South Wales 2006, Australia [email protected]

Abstract The Gallipoli Peninsula Peace Park in Turkey is becoming an increasingly popular tourist destination, particularly around ANZAC day when thousands of Australian and New Zealand visitors attend memorial ceremonies. The Peace Park currently faces the difficult issue of balancing public access to its battlefield sites with the desire to conserve their natural and archaeological value. An important aspect of this management is a perceived need to control soil erosion, which has been identified as a problem within the Park. Although potentially important, very little work has been undertaken to determine the extent to which erosion is occurring or to quantify erosion rates. This study aims to remotely predict erosion susceptibility at ANZAC Cove, a site within the Gallipoli Peninsula Peace Park, using a hillslope soil erosion model: Silsoe. The model was built in an ArcGIS framework using a Digital Elevation Model (DEM) that enabled output in the form of erosion prediction maps. Initial results indicate that slopes around ANZAC Cove are vulnerable to extensive erosion, rates of which are primarily limited by sediment transport capacities. Some of the highest rates of erosion coincide with the occurrence of important historic sites, reflecting the significance of topography in the Gallipoli campaign. The results of this study can be used to provide an initial risk assessment for soil erosion in the Gallipoli Peninsula Peace Park and information for the emplacement of erosion control measures in the Park. Key words Silsoe model; sediment transport; Gallipoli Peninsular Peace Park, Turkey; erosion susceptibility