DOCSLIB.ORG

Annotated Bibliography of River Avulsions Pat Dryer Geography 364 5/14/2007

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text

Load more

Annotated Bibliography of River Avulsions Pat Dryer Geography 364 5/14/2007 1 Table of Contents Introduction 2 Annotations I. River avulsions and their deposits 2 II. Channel avulsion on alluvial fans in southern Arizona 3 III. Modeling the effect of vegetation on channel pattern in bed 4 load rivers IV. Interrelations of channel processes, changes and sediments 6 in a proglacial braided river V. Channel morphology and bed load pulses in braided, 7 gravel-bed streams Conclusion 8 2 Introduction Channel avulsions are a very interesting geomorphic event. A river avulsion is a natural event in which stream flow gets diverted out of an established channel and forms a new permanent course on the adjacent floodplain. Avulsions are typically features of aggrading floodplains. Channel avulsions can happen frequently in some river systems and very rarely occur in others. The exact cause of river avulsions is not fully understood but there seems to be some contributing factors that influence avulsions. Avulsions can cause millions of dollars of damage and injure or kill numerous people. Annotations I. Slingerland, R., and Smith, N.D., 2004, River avulsions and their deposits: Annual Review of Earth Planet Science, v. 32, p. 254-285. This paper focuses on summaries the various styles of avulsions, review of present knowledge of avulsions, describing sedimentology and stratigraphy of alluvial floodplain deposits, and emphasis on the role avulsions play in creating them. To accurately understand river avulsions occur one must first understand several terms such as bed load, sedimentation, and channel patterns. In this paper the author’s quantify avulsions by sedimentation , bifurcation, and bed load transportation rates. 3 There are six main types of river avulsions including; partial, nodal, local, full, random, and regional. In a full avulsion all flow is diverted out of the parent channel into a new avulsion channel. A partial avulsion involves only part of the flow to be diverted typically resulting in anastomosing channels. Nodal avulsions are recurring events that originate from a fixed area of a floodplain such as a fan apex. Random avulsions happen throughout active channel systems. Local avulsions form new channels that rejoin the parent channel downstream. Regional avulsions happen at a very large scale and effect flow everywhere downstream from the avulsion. Avulsion frequencies vary greatly among modern river systems. The lowest rate is 28 years for the Kosi River in India to up to 1400 years for the Mississippi River. Stratagraphic records suggest much longer intervals between avulsions. Avulsions seem to be a function of aggrading floodplains and sedimentation rates. Avulsions occur more frequently when large amounts of sediment are introduced into systems, such as glacial outwash streams with braided channels. On the other hand avulsions may never happen on river systems with aggradation rates near or below zero. This article was very well written and clearly describes many key factors that influence river avulsions. The text was written for a scientific audience but easily understood by those who have some knowledge of the subject area. This paper was relevant to my topic and helped me understand many factors that influence avulsions. II. Field, J., 2001, Channel avulsion on alluvial fans in southern Arizona: Geomorphology, v. 37, p. 93-104. 4 This paper looks as channel avulsions on alluvial fans in southern Arizona and how they happen. John Field uses aerial photography to study channel patterns in the past and has also developed a descriptive model for explaining avulsions. Channel avulsions are of great interest when studying alluvial fans. The fan shape is a result of avulsions diverting flow to different portions of a fan. Avulsions occur very frequently on alluvial fans when sediment laden water reaches bankfull flow on channels. Channel abandonment occurs when overland flow form the main channel directs headward erosion of smaller channels on the fan surface. This headward erosion can eventually reach the parent channel and cause an avulsion to occur via stream capture. There are many stages to the avulsion process that can help identify areas of a fan surface that are more prone to flooding. These stages include; on-fan channels, “new” channels, adjusted channels, aggrading channels, and abandoned channels. Overtime the new channels become stabilized and the whole process starts over. Channel avulsions on fans are not completely random because of their relative position of low banks along the main channel and smaller channels draining the fan surface. This paper was written for scientific audiences which are experts on channel morphology. Some of the concepts were hard to understand. The research was well designed and would be easily recreated in other areas with alluvial fans. Some of the information in the paper is relevant to my topic but is not the most relevant topic for my source of river avulsions. III. Murry, A.B., and Paola, C., 2003, Modeling the effect of vegetation on channel pattern in 5 bed load rivers: Earth Surface Processes and Landforms, v. 28, p. 131-143. This paper looks at how vegetation can play a role in controlling avulsions. The main focus of this paper is on the role of vegetation in the development of single-thread channel patters either straight or sinuous. To study this relationship between vegetation presence and avulsions can be modeled with cellular modeling or rule-based modeling in non-linear dynamics. In each cell lattice the elevation, water and sediment discharge are defined in arbitrary units. This paper modified a simple numerical stream-pattern model to look at the sediment stabilization by roots on channel patterns in bed load streams. Vegetation enhances bank resistance to erosion resulting in one single incised channel instead of multiple channels typical of braided systems. Streams with a high sediment load can cause frequent avulsions that destroy vegetation along banks that limit erosion. The authors developed a stability chart that depicts if vegetation can anchor the stream banks before avulsions take away the vegetation and further promote erosion. This article was well written and makes some very interesting conclusions. Vegetation is often overlooked when looking at avulsion events. Once an avulsion occurs and takes away vegetation it takes time for the vegetation to regenerate and restabilize the banks. This article was written for a scientific audience interested in biological factors in river avulsions. I would have liked more information on how single channel streams can change into braided steams through avulsions. This article would be useful for my topic and would help create a well rounded paper from both the physical science of avulsions to biological factors. 6 IV. Ashworth P.J., and Ferguson, R.I., 1986, Interrelations of channel processes, changes and sediments in a proglacial braided river: Physical Geography, v. 68, p. 361-371. For this paper research was conducted in July and August 1984 on the Lyngsdalselva River, a braided proglacial river north of the Arctic Circle in Norway. The study area was downstream of the glacier snout at the head of the outwash plain, where bed load materials were cobble sized. This study focused on two main branches of the stream before an avulsion happened and then incorporated the new channel into the research as time progressed. Researches monitored discharge, velocity, shear stress, and transportation rates to try and quantify the avulsion. The researches placed 188 painted pebbles into the stream during the high flow event in August. The next morning only 50 of the pebbles could be located. The remaining pebbles were most likely buried during the event. When discharge decreased 88 more painted pebbles were introduced into the stream. After some time pebbles were found at or near the source and as far as 17 meters downstream from their initial position. This indicates decreasing mobility of sediment as discharge dropped. Results from this research indicate that discharge was mostly constant, but sunny weather in August produced larger diurnal peaks and higher discharge. During this time of high flow several new channels were formed through the process of avulsions and new bars were also deposited along the channel. The study showed that avulsion had a greater probability of occurring during times of high sedimentation and high discharge. No 7 avulsions were recorded during the times of constant discharge. This paper was very well written and was easily comprehendible. The research was well planned and executed. The way the writers presented the information made the data easily comprehendible. This paper would be relevant to a paper about stream avulsions and would provide useful information. V. Ashmore, P., 1991, Channel morphology and bed load pulses in braided, gravel-bed streams: Physical Geography, v. 73, p. 37-52. The researches in this paper used small-scale hydraulic laboratory models based on Froude modeling to investigate: the influence of gradient and discharge on cross sectional areas of graded streams, braided stream morphology, and occurrence of bed load pulses. The researches repeated several transect measurements of braided channels and found several different combinations of slope and discharge, which is an influential factor in local avulsions. Goals of this paper include using hydraulic modeling of braded streams to use as an approach to understand braided stream geometry and interaction of bed-load transfer. From this of understanding of the goals, the paper has three objectives; demonstrate experimentally that gravel-bed braided streams have stable cross-section geometry and braiding intensities, variations in morphological characteristics of a stream that occur at constant slope and discharge, and the downstream transfer of bed load. Periodic pulses in bed load over time can be related to avulsion events in braided streams. These pulses are generated by local erosion and aggradation of the stream bed. This process creates migrating bars and is the primary means of sediment transport.
Recommended publications
  • Geomorphic Classification of Rivers

    Geomorphic Classification of Rivers

    9.36 Geomorphic Classification of Rivers JM Buffington, U.S. Forest Service, Boise, ID, USA DR Montgomery, University of Washington, Seattle, WA, USA Published by Elsevier Inc. 9.36.1 Introduction 730 9.36.2 Purpose of Classification 730 9.36.3 Types of Channel Classification 731 9.36.3.1 Stream Order 731 9.36.3.2 Process Domains 732 9.36.3.3 Channel Pattern 732 9.36.3.4 Channel–Floodplain Interactions 735 9.36.3.5 Bed Material and Mobility 737 9.36.3.6 Channel Units 739 9.36.3.7 Hierarchical Classifications 739 9.36.3.8 Statistical Classifications 745 9.36.4 Use and Compatibility of Channel Classifications 745 9.36.5 The Rise and Fall of Classifications: Why Are Some Channel Classifications More Used Than Others? 747 9.36.6 Future Needs and Directions 753 9.36.6.1 Standardization and Sample Size 753 9.36.6.2 Remote Sensing 754 9.36.7 Conclusion 755 Acknowledgements 756 References 756 Appendix 762 9.36.1 Introduction 9.36.2 Purpose of Classification Over the last several decades, environmental legislation and a A basic tenet in geomorphology is that ‘form implies process.’As growing awareness of historical human disturbance to rivers such, numerous geomorphic classifications have been de- worldwide (Schumm, 1977; Collins et al., 2003; Surian and veloped for landscapes (Davis, 1899), hillslopes (Varnes, 1958), Rinaldi, 2003; Nilsson et al., 2005; Chin, 2006; Walter and and rivers (Section 9.36.3). The form–process paradigm is a Merritts, 2008) have fostered unprecedented collaboration potentially powerful tool for conducting quantitative geo- among scientists, land managers, and stakeholders to better morphic investigations.
  • Morphologic Characteristics of the Blow River Delta, Yukon Territory, Canada

    Morphologic Characteristics of the Blow River Delta, Yukon Territory, Canada

    Louisiana State University LSU Digital Commons LSU Historical Dissertations and Theses Graduate School 1969 Morphologic Characteristics of the Blow River Delta, Yukon Territory, Canada. James Murl Mccloy Louisiana State University and Agricultural & Mechanical College Follow this and additional works at: https://digitalcommons.lsu.edu/gradschool_disstheses Recommended Citation Mccloy, James Murl, "Morphologic Characteristics of the Blow River Delta, Yukon Territory, Canada." (1969). LSU Historical Dissertations and Theses. 1605. https://digitalcommons.lsu.edu/gradschool_disstheses/1605 This Dissertation is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion in LSU Historical Dissertations and Theses by an authorized administrator of LSU Digital Commons. For more information, please contact [email protected]. This dissertation has been microfilmed exactly as received 70-252 McCLOY, James Murl, 1934- MORPHOLOGIC CHARACTERISTICS OF THE BLOW RIVER DELTA, YUKON TERRITORY, CANADA. The Louisiana State University and Agricultural and Mechanical College, Ph.D., 1969 Geography University Microfilms, Inc., Ann Arbor, Michigan Morphologic Characteristics of the Blow River Belta, Yukon Territory, Canada A Dissertation Submitted to the Graduate Faculty of the Louisiana State University and Agricultural and Mechanical College in partial fulfillment of the requirements for the degree of Doctor of Philosophy in The Department of Geography and Anthropology by James Murl McCloy B.A., State College at Los Angeles, 1961 May, 1969 ACKNOWLEDGEMENTS Research culminating in this dissertation was conducted under the auspices of the Arctic Institute of North America. The major portion of the financial support was received from the United States Army under contract no. BA-ARO-D-3I-I2I4.-G832, "Arctic Environmental Studies." Additional financial assistance during part of the writing stage was received in the form of a research assistantship from the Coastal Studies Institute, Louisi­ ana State University.
  • Coastal Wetland Trends in the Narragansett Bay Estuary During the 20Th Century

    Coastal Wetland Trends in the Narragansett Bay Estuary During the 20Th Century

    u.s. Fish and Wildlife Service Co l\Ietland Trends In the Narragansett Bay Estuary During the 20th Century Coastal Wetland Trends in the Narragansett Bay Estuary During the 20th Century November 2004 A National Wetlands Inventory Cooperative Interagency Report Coastal Wetland Trends in the Narragansett Bay Estuary During the 20th Century Ralph W. Tiner1, Irene J. Huber2, Todd Nuerminger2, and Aimée L. Mandeville3 1U.S. Fish & Wildlife Service National Wetlands Inventory Program Northeast Region 300 Westgate Center Drive Hadley, MA 01035 2Natural Resources Assessment Group Department of Plant and Soil Sciences University of Massachusetts Stockbridge Hall Amherst, MA 01003 3Department of Natural Resources Science Environmental Data Center University of Rhode Island 1 Greenhouse Road, Room 105 Kingston, RI 02881 November 2004 National Wetlands Inventory Cooperative Interagency Report between U.S. Fish & Wildlife Service, University of Massachusetts-Amherst, University of Rhode Island, and Rhode Island Department of Environmental Management This report should be cited as: Tiner, R.W., I.J. Huber, T. Nuerminger, and A.L. Mandeville. 2004. Coastal Wetland Trends in the Narragansett Bay Estuary During the 20th Century. U.S. Fish and Wildlife Service, Northeast Region, Hadley, MA. In cooperation with the University of Massachusetts-Amherst and the University of Rhode Island. National Wetlands Inventory Cooperative Interagency Report. 37 pp. plus appendices. Table of Contents Page Introduction 1 Study Area 1 Methods 5 Data Compilation 5 Geospatial Database Construction and GIS Analysis 8 Results 9 Baywide 1996 Status 9 Coastal Wetlands and Waters 9 500-foot Buffer Zone 9 Baywide Trends 1951/2 to 1996 15 Coastal Wetland Trends 15 500-foot Buffer Zone Around Coastal Wetlands 15 Trends for Pilot Study Areas 25 Conclusions 35 Acknowledgments 36 References 37 Appendices A.
  • New York State Artificial Reef Plan and Generic Environmental Impact

    New York State Artificial Reef Plan and Generic Environmental Impact

    TABLE OF CONTENTS EXECUTIVE SUMMARY ...................... vi 1. INTRODUCTION .......................1 2. MANAGEMENT ENVIRONMENT ..................4 2.1. HISTORICAL PERSPECTIVE. ..............4 2.2. LOCATION. .....................7 2.3. NATURAL RESOURCES. .................7 2.3.1 Physical Characteristics. ..........7 2.3.2 Living Resources. ............. 11 2.4. HUMAN RESOURCES. ................. 14 2.4.1 Fisheries. ................. 14 2.4.2 Archaeological Resources. ......... 17 2.4.3 Sand and Gravel Mining. .......... 18 2.4.4 Marine Disposal of Waste. ......... 18 2.4.5 Navigation. ................ 18 2.5. ARTIFICIAL REEF RESOURCES. ............ 20 3. GOALS AND OBJECTIVES .................. 26 3.1 GOALS ....................... 26 3.2 OBJECTIVES .................... 26 4. POLICY ......................... 28 4.1 PROGRAM ADMINISTRATION .............. 28 4.1.1 Permits. .................. 29 4.1.2 Materials Donations and Acquisitions. ... 31 4.1.3 Citizen Participation. ........... 33 4.1.4 Liability. ................. 35 4.1.5 Intra/Interagency Coordination. ...... 36 4.1.6 Program Costs and Funding. ......... 38 4.1.7 Research. ................. 40 4.2 DEVELOPMENT GUIDELINES .............. 44 4.2.1 Siting. .................. 44 4.2.2 Materials. ................. 55 4.2.3 Design. .................. 63 4.3 MANAGEMENT .................... 70 4.3.1 Monitoring. ................ 70 4.3.2 Maintenance. ................ 72 4.3.3 Reefs in the Exclusive Economic Zone. ... 74 4.3.4 Special Management Concerns. ........ 76 4.3.41 Estuarine reefs. ........... 76 4.3.42 Mitigation. ............. 77 4.3.43 Fish aggregating devices. ...... 80 i 4.3.44 User group conflicts. ........ 82 4.3.45 Illegal and destructive practices. .. 85 4.4 PLAN REVIEW .................... 88 5. ACTIONS ........................ 89 5.1 ADMINISTRATION .................. 89 5.2 RESEARCH ..................... 89 5.3 DEVELOPMENT .................... 91 5.4 MANAGEMENT .................... 96 6. ENVIRONMENTAL IMPACTS ................. 97 6.1 ECOSYSTEM IMPACTS.
  • Morphological Bedload Transport in Gravel-Bed Braided Rivers

    Morphological Bedload Transport in Gravel-Bed Braided Rivers

    Western University Scholarship@Western Electronic Thesis and Dissertation Repository 6-16-2017 12:00 AM Morphological Bedload Transport in Gravel-Bed Braided Rivers Sarah E. K. Peirce The University of Western Ontario Supervisor Dr. Peter Ashmore The University of Western Ontario Graduate Program in Geography A thesis submitted in partial fulfillment of the equirr ements for the degree in Doctor of Philosophy © Sarah E. K. Peirce 2017 Follow this and additional works at: https://ir.lib.uwo.ca/etd Part of the Physical and Environmental Geography Commons Recommended Citation Peirce, Sarah E. K., "Morphological Bedload Transport in Gravel-Bed Braided Rivers" (2017). Electronic Thesis and Dissertation Repository. 4595. https://ir.lib.uwo.ca/etd/4595 This Dissertation/Thesis is brought to you for free and open access by Scholarship@Western. It has been accepted for inclusion in Electronic Thesis and Dissertation Repository by an authorized administrator of Scholarship@Western. For more information, please contact [email protected]. Abstract Gravel-bed braided rivers, defined by their multi-thread planform and dynamic morphology, are commonly found in proglacial mountainous areas. With little cohesive sediment and a lack of stabilizing vegetation, the dynamic morphology of these rivers is the result of bedload transport processes. Yet, our understanding of the fundamental relationships between channel form and bedload processes in these rivers remains incomplete. For example, the area of the bed actively transporting bedload, known as the active width, is strongly linked to bedload transport rates but these relationships have not been investigated systematically in braided rivers. This research builds on previous research to investigate the relationships between morphology, bedload transport rates, and bed-material mobility using physical models of braided rivers over a range of constant channel-forming discharges and event hydrographs.
  • Understanding the Temporal Dynamics of the Wandering Renous River, New Brunswick, Canada

    Understanding the Temporal Dynamics of the Wandering Renous River, New Brunswick, Canada

    Earth Surface Processes and Landforms EarthTemporal Surf. dynamicsProcess. Landforms of a wandering 30, 1227–1250 river (2005) 1227 Published online 23 June 2005 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/esp.1196 Understanding the temporal dynamics of the wandering Renous River, New Brunswick, Canada Leif M. Burge1* and Michel F. Lapointe2 1 Department of Geography and Program in Planning, University of Toronto, 100 St. George Street, Toronto, Ontario, M5S 3G3, Canada 2 Department of Geography McGill University, 805 Sherbrooke Street West, Montreal, Quebec, H3A 2K6, Canada *Correspondence to: L. M. Burge, Abstract Department of Geography and Program in Planning, University Wandering rivers are composed of individual anabranches surrounding semi-permanent of Toronto, 100 St. George St., islands, linked by single channel reaches. Wandering rivers are important because they Toronto, M5S 3G3, Canada. provide habitat complexity for aquatic organisms, including salmonids. An anabranch cycle E-mail: [email protected] model was developed from previous literature and field observations to illustrate how anabranches within the wandering pattern change from single to multiple channels and vice versa over a number of decades. The model was used to investigate the temporal dynamics of a wandering river through historical case studies and channel characteristics from field data. The wandering Renous River, New Brunswick, was mapped from aerial photographs (1945, 1965, 1983 and 1999) to determine river pattern statistics and for historical analysis of case studies. Five case studies consisting of a stable single channel, newly formed anabranches, anabranches gaining stability following creation, stable anabranches, and an abandoning anabranch were investigated in detail.
  • Appendix E Fish Habitat Utilization Literature Review

    Appendix E Fish Habitat Utilization Literature Review

    Appendix E Fish Habitat Utilization Literature Review East Kitsap Nearshore Assessment Appendix E Appendix E - Fish Habitat Utilization Literature Review Toft et al. (2007) City Shoreline Fish Distribution Study objective: study the abundance and behavior of juvenile salmon and other fishes among various marine shoreline habitat types near the city of Seattle. Focused on 5 types of shorelines - cobble beach - sand beach - riprap extending into the upper intertidal zone - deep riprap extending into the subtidal - edge of overwater structures Also examined stomach contents of juvenile salmon. Fish sampling methods included enclosure nets and snorkel surveys. Riprap often results in greater beach slopes and steep embankments which effectively reduces the intertidal zone. These characteristics in turn, result in habitat loss for juvenile flatfishes. At high intertidal habitats, more crab were encountered at cobble beaches compared to sand beaches and riprap. Demersal fishes (cottids) were found in greater numbers at riprap. Differences in species density between habitat type were more apparent for demersal fishes than for pelagic species. Densities of salmon were significantly different among habitat types. The highest densities occurred at the edge of overwater structures and in deep riprap. Deep riprap creates some structured habitat which seems to attract surfperches and gunnels. Threespine stickleback, tubesnout, and bay pipefish were also more prevalent at deep riprap than at cobble, sand, and high elevation riprap. Beamer et al. (2006) – Habitat and fish use of pocket estuaries in the Whidbey basin and north Skagit county bays, 2004 and 2005 Pocket estuaries are characterized as having more dilute marine water relative to the surrounding estuary.
  • Hydrodynamics of Braiding River

    Hydrodynamics of Braiding River

    International Journal of Hydrology Review Article Open Access Hydrodynamics of braiding river Abstract Volume 5 Issue 3 - 2021 Braided river reaches and alluvial systems are characterized by their multi-threaded planform LUO Ching-Ruey and agents of sediment transport due to eroding and deposing to form the bars and riffles. In Associate Professor of Department of Civil Engineering, braided river, frequent sediment transport and the quick shifting of the positions about the National Chi-Nan University, Taiwan river channel induce many attentions discussion and relating a complicated consideration of the combinations of disciplines. In this article we introduce its fundamental characteristics Correspondence: LUO Ching-Ruey, Associate Professor of and further the complicated mechanism in the literature and methodologies. The braided Department of Civil Engineering, National Chi-Nan University, channel ecology and the management of braided river are mentioned and discussed, Taiwan, Email especially, the secondary currents, in this paper we explain in detail, the combinations on multiplying of 2-D flow of the velocity fluctuations. The interdisciplinary approach Received: April 28, 2021 | Published: May 10, 2021 on linking engineers, earth scientists and social scientists concerned with environmental economics, planning, and societal and political strategies in order to fully evaluate the validity and reliability of different selections to various timescales is really sensitive. Furthermore, the requirements of public education on reinforcing
  • Grain Sorting in the Morphological Active Layer of a Braided River Physical Model

    Grain Sorting in the Morphological Active Layer of a Braided River Physical Model

    Earth Surf. Dynam., 3, 577–585, 2015 www.earth-surf-dynam.net/3/577/2015/ doi:10.5194/esurf-3-577-2015 © Author(s) 2015. CC Attribution 3.0 License. Grain sorting in the morphological active layer of a braided river physical model P. Leduc, P. Ashmore, and J. T. Gardner University of Western Ontario, Department of Geography, London, Ontario, Canada Correspondence to: P. Leduc ([email protected]) Received: 8 June 2015 – Published in Earth Surf. Dynam. Discuss.: 10 July 2015 Revised: 22 October 2015 – Accepted: 23 November 2015 – Published: 15 December 2015 Abstract. A physical scale model of a gravel-bed braided river was used to measure vertical grain size sorting in the morphological active layer aggregated over the width of the river. This vertical sorting is important for ana- lyzing braided river sedimentology, for numerical modeling of braided river morphodynamics, and for measuring and predicting bedload transport rate. We define the morphological active layer as the bed material between the maximum and minimum bed elevations at a point over extended time periods sufficient for braiding processes to rework the river bed. The vertical extent of the active layer was measured using 40 hourly high-resolution DEMs (digital elevation models) of the model river bed. An image texture algorithm was used to map bed material grain size of each DEM. Analysis of the 40 DEMs and texture maps provides data on the geometry of the morpho- logical active layer and variation in grain size in three dimensions. By normalizing active layer thickness and dividing into 10 sublayers, we show that all grain sizes occur with almost equal frequency in all sublayers.
  • Modelling Confluence Dynamics in Large Sand-Bed Braided Rivers

    Modelling Confluence Dynamics in Large Sand-Bed Braided Rivers

    Earth Surf. Dynam. Discuss., https://doi.org/10.5194/esurf-2018-85 Manuscript under review for journal Earth Surf. Dynam. Discussion started: 18 December 2018 c Author(s) 2018. CC BY 4.0 License. 1 Modelling confluence dynamics in large sand-bed braided rivers 2 Haiyan Yang1, Zhenhuan Liu2 3 1College of Water Conservancy and Civil Engineering, South China Agricultural 4 University, Guangzhou 510642, China; [email protected] 5 2 Guangdong Provincial Key Laboratory of Urbanization and Geo-simulation, School 6 of Geography and Planning, Sun Yat-sen University, Guangzhou 510275, China 7 Correspondence: [email protected] 8 Abstract 9 Confluences are key morphological nodes in braided rivers where flow converges, 10 creating complex flow patterns and rapid bed deformation. Field survey and laboratory 11 experimental studies have been carried out to investigate the morphodynamic features 12 in individual confluences, but few have investigated the evolution process of 13 confluences in large braided rivers. In the current study a physics-based numerical 14 model was applied to simulate a large lowland braided river dominated by suspended 15 sediment transport, and analyzed the morphologic changes at confluences and their 16 controlling factors. It was found that the confluences in large braided rivers exhibit 17 some dynamic processes and geometric characteristics that are similar to those observed 18 in individual confluences arising from two tributaries. However, they also show some 19 unique characteristics that are result from the influence of the overall braided pattern 20 and especially of neighboring upstream channels. 21 Key words: braided river, numerical model, confluence, dynamics, geometry, scour 22 hole 1 Earth Surf.
  • Braided River Management: from Assessment of River Behaviour to Improved Sustainable Development

    Braided River Management: from Assessment of River Behaviour to Improved Sustainable Development

    BR_C12.qxd 08/06/2006 16:29 Page 257 Braided river management: from assessment of river behaviour to improved sustainable development HERVÉ PIÉGAY*, GORDON GRANT†, FUTOSHI NAKAMURA‡ and NOEL TRUSTRUM§ *UMR 5600—CNRS, 18 rue Chevreul, 69362 Lyon, cedex 07, France (Email: [email protected]) †USDA Forest Service, Corvallis, USA ‡University of Hokkaido, Japan §Institute of Geological and Natural Sciences, Lower Hatt, New Zealand ABSTRACT Braided rivers change their geometry so rapidly, thereby modifying their boundaries and flood- plains, that key management questions are difficult to resolve. This paper discusses aspects of braided channel evolution, considers management issues and problems posed by this evolution, and develops these ideas using several contrasting case studies drawn from around the world. In some cases, management is designed to reduce braiding activity because of economic considerations, a desire to reduce hazards, and an absence of ecological constraints. In other parts of the world, the eco- logical benefits of braided rivers are prompting scientists and managers to develop strategies to preserve and, in some cases, to restore them. Management strategies that have been proposed for controlling braided rivers include protecting the developed floodplain by engineered structures, mining gravel from braided channels, regulat- ing sediment from contributing tributaries, and afforesting the catchment. Conversely, braiding and its attendant benefits can be promoted by removing channel vegetation, increasing coarse sediment supply, promoting bank erosion, mitigating ecological disruption, and improving planning and devel- opment. These different examples show that there is no unique solution to managing braided rivers, but that management depends on the stage of geomorphological evolution of the river, ecological dynamics and concerns, and human needs and safety.
  • Dune Nourishment Fact Sheet

    Dune Nourishment Fact Sheet

    StormSmart Coasts StormSmart Properties Fact Sheet 1: Artificial Dunes and Dune Nourishment The coast is a very dynamic environment and coastal shorelines—especially beaches, dunes, and banks—change constantly in response to wind, waves, tides, and other factors such as seasonal variation, sea level rise, and human alterations to the shoreline system. Consequently, many coastal properties are at risk from storm damage, erosion, and flooding. Inappropriate shoreline stabilization methods can actually do more harm than good by exacerbating beach erosion, damaging neighboring properties, impacting marine habitats, and diminishing the capacity of beaches, dunes, and other natural landforms to protect inland areas from storm damage and flooding. StormSmart Properties—part of the Massachusetts Office of Coastal Zone Management’s (CZM) StormSmart Coasts program—provides coastal property owners with important information on a range of shoreline stabilization techniques that can effectively reduce erosion and storm damage while minimizing impacts to shoreline systems. This information is intended to help property owners work with consultants and other design professionals to select the best option for their circumstances. What Are Artificial Dunes and Dune Nourishment? A dune is a hill, mound, or ridge of sediment that No shoreline stabilization option permanently stops has been deposited by wind or waves landward of all erosion or storm damage. The level of protection a coastal beach. In Massachusetts, the sediments provided depends on the option chosen, project design, that form beaches and dunes range from sand to and site-specific conditions such as the exposure to gravel- and cobble-sized material. An artificial dune storms. All options require maintenance, and many is a shoreline protection option where a new mound also require steps to address adverse impacts to of compatible sediment (i.e., sediment of similar the shoreline system, called mitigation.