DOCSLIB.ORG

Sediment Supply As a Driver of River Meandering and Floodplain

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Sediment Supply As a Driver of River Meandering and Floodplain LETTERS PUBLISHED ONLINE: 2 NOVEMBER 2014 | DOI: 10.1038/NGEO2282 Sediment supply as a driver of river meandering and floodplain evolution in the Amazon Basin José Antonio Constantine1*, Thomas Dunne2,3*, Joshua Ahmed1, Carl Legleiter4 and Eli D. Lazarus1 The role of externally imposed sediment supplies on the fine-grained Neogene sedimentary rocks of the Central Amazon evolution of meandering rivers and their floodplains is poorly Trough yield an order of magnitude less sediment per river each understood, despite analytical advances in our physical under- year9, and those that drain the Guiana Shield to the north and the standing of river meandering1,2. The Amazon river basin hosts Brazil Shield to the south of the Trough yield the least7. tributaries that are largely unaected by engineering controls As sedimentary deposits attached to the inner banks (convex and hold a range of sediment loads, allowing us to explore the relative to the channel centreline) of meander bends, point bars influence that sediment supply has on river evolution. Here we seem to be the link between changes in externally imposed calculate average annual rates of meander migration within 20 sediment supplies and adjustments in river behaviour. Modern reaches in the Amazon Basin from Landsat imagery spanning theory attributes the meandering behaviour of alluvial rivers to 1985–2013. We find that rivers with high sediment loads instabilities in river flow11 that arise either inherently12 or from experience annual migration rates that are higher than those of disruption of the flow field by bedforms13. Recent lab experiments rivers with lower sediment loads. Meander cutoalso occurs suggest that this latter influence may not be ubiquitous14,butthe more frequently along rivers with higher sediment loads. capacity for point bars to promote meandering by altering the flow Dierences in meander migration and cutorates between field15 has been observed both in the field16 and the laboratory17. the study reaches are not explained by dierences in channel A view of the Rio Mamoré, flowing through the Andean foreland slope or river discharge. Because faster meander migration basin of Bolivia, offers an illustration. The Rio Grande, a tributary and higher cutorates lead to increased sediment-storage of the Rio Mamoré, drains 7.2 104 km2 of the Bolivian Andes and 1 ⇥ space in the resulting oxbows, we suggest that sediment transports about 136 Mt yr− of suspended sediment as it enters the supply modulates the reshaping of floodplain environments foreland basin10. The substantial sediment load of the Rio Grande by meandering rivers. We conclude that imposed sediment has resulted in the enhanced development of point bars on the Rio loads influence planform changes in lowland rivers across Mamoré downstream of the confluence (Fig. 1a) that has instigated the Amazon. a nearly 1.7-fold increase in rates of meander migration (Fig. 1b). Decades of fluvial research have yielded physical insight Observations from the Sacramento River of California, USA, further into river behaviours associated with various channel patterns, from planform controls on meander migration, to mechanisms a responsible for dispersing sediment into the floodplain2,3 and the in-channel dynamics that produce sediment supply from local bank erosion4. By contrast, the role of externally imposed MamoréFlow RiverN sediment supplies in channel planform dynamics—that is, when Rio Grande 5 km sediment supplies are an imposed environmental variable to which b the channel planform must adjust—remains poorly understood. Puerto Ganadero Rio Chimoré −1 −1 (64 Mt yr ) (∼4 Mt yr ) Input into M1 M2 External sources of sediment may derive from mountain building, −1) −1 (∼82 Mt yr ch-w yr glacial and other climatic changes, volcanism, and land uses that −1 0.047 Puerto Villaroel 0.039 ch-wM0 r r (9 Mt yr−1) M1 -w y La Satísima accelerate landscape-scale soil loss. They may also be interrupted − 1 ) Mamoré Rive yr 1 − nde Trinidad 0.066 ch Flow N by water resource developments such as the large reservoirs under Flow 5 Rio Gra69 Mt yr 35 km consideration for many Amazonian tributaries . ∼ ( The Amazon Basin remains a unique opportunity to assess the role of externally imposed sediment supplies in river Figure 1 | Enhanced development of point bars on the Rio Mamoré evolution because of the generally undeveloped nature of its downstream of the confluence with the Rio Grande. a, Landsat image fluvial environments and the range of sediment supplies in its from 2013 of the Rio Mamoré and its confluence with the Rio Grande, various tributary basins. Rivers within the 6.9 106 km2 basin which drains the Bolivian Andes from the southeast. b, Study reaches ⇥ are generally free to modify their forms, and they drain distinct of the Mamoré (M0, green; M1, red; M2, blue), with average annual physiographic provinces, each of which supplies sediment to the meander migration rates provided for each (in units of channel widths channel network at different rates6,7. Rivers draining the highly per year) for the time period 1986–2010. The box shows the location erodible Andean Cordillera yield the greatest amount of sediment of the image in a. Estimates of total suspended sediment (TSS) flux are to the Amazon lowlands, on the order of 100 Mt of suspended shown in brackets. Details of TSS flux estimates can be found in the material per river each year8–10. Rivers with headwaters draining the Supplementary Information. 1School of Earth and Ocean Sciences, CardiUniversity, CardiCF10 3AT, UK, 2Bren School of Environmental Science and Management, University of California–Santa Barbara, Santa Barbara, California 93106, USA, 3Department of Earth Science, University of California–Santa Barbara, Santa Barbara, California 93106, USA, 4Department of Geography, University of Wyoming, Laramie, Wyoming 82071, USA. *e-mail: [email protected]; [email protected] NATURE GEOSCIENCE | ADVANCE ONLINE PUBLICATION | www.nature.com/naturegeoscience 1 LETTERS NATURE GEOSCIENCE DOI: 10.1038/NGEO2282 a b 0.4 Mean TSS 0.06 Mean MR (Mt yr−1 m−1) (ch-w yr−1) 0.3 0° Va Br 0.2 0.03 Pt 0.1 Na Jt P2 Cu It 0.0 0.00 Hu Ju Shield Trough Andes Shield Trough Andes Ir Uc P1 10° S Ma 0.4 Mean CR Mean NL Xi 0.002 (no. yr−1 ch-w−1) 0.3 (no. ch-w−1) Be M2 Ar M1 0.2 Shield M0 0.001 Central Trough 0.1 Andes–Foreland Basin 0.000 0.0 80° W70° W 60° W 50° W Shield Trough Andes Shield Trough Andes Ar, Araguaia; Va, Vaupés; Br, Branco; Ir, Iriri; Xi, Xingu; P1, Purus1; P2, Purus2; Ju, Juruá; Jt, Jutai; It , Ituí; Cu, Curuca; Na, Nanay; Pt, Putumayo; M0, Mamoré0; M1, Mamoré1; M2, Mamoré2; Be, Beni; Uc, Ucayali; Hu, Huallaga; Ma, Madre de Díos cd0.100 0.00500 0.28 0.43 MR = 0.043TSS CR = 0.0016TSS ρ = 0.73, = 0.53 M1 ρ = 0.66, = 0.51 M1 τB Uc τB Uc 0.050 α < 0.001 M2 0.00200 α < 0.002 Hu Be M0 Be M0 M2 ) 0.00100 Hu 1 − ) Ma 1 − 0.020 0.00050 Ma ch-w Br 1 P1 − Ju Cu Na It Va Na (ch-w yr (ch-w R 0.010 Ar 0.00020 It Ju P1 (no. yr (no. M Cu Ar R Ir Jt C Xi Pt 0.00010 Xi P2 Jt Pt 0.005 Br 0.00005 Va P2 Ir 0.0001 0.0010 0.0100 0.1000 1.0000 0.0001 0.0010 0.0100 0.1000 1.0000 TSS (Mt yr−1 m−1) TSS (Mt yr−1 m−1) Figure 2 | Study sites, river characteristics, and sediment fluxes. a, Locations of study reaches within the physiographic provinces with reach abbreviations defined. b, Mean values for total suspended sediment (TSS) flux (megatonnes per year per metre of channel width), average annual meander migration rate (MR; channel widths per year), average annual meander cutorate (CR) (number per year per channel width of down-valley distance), and total number of observable oxbow lakes (N ; number per channel width of down-valley distance). Error bars represent 1σ about the means. c, M plotted L ± R against TSS flux. d, CR plotted against TSS flux. highlight the role of point bars in facilitating bank erosion in reaches rates of lateral shifting. Cutoffrates (CR) were normalized by reach that experience a net accumulation of bed material18. valley-length, expressed in channel-width units (ch-w). TSS flux Within a given meander, curvature and shoaling of river flow estimates were normalized by RW to account for the ability of wider onto and over a point bar force high-momentum fluid to be channels with greater flows to convey more sediment. We used TSS advected outwards, increasing boundary shear stress along the outer data from the most extensive and systematically collected survey of (concave) riverbank and decreasing boundary shear stress over sediment supplies currently available for the Amazon Basin7. Details the inner-bank bar15. Elevated shear stresses near the outer bank of values from other sources are provided in the Supplementary promote the fluvial entrainment of the bank material primarily Information. TSS flux is the only widely (if sparsely) distributed responsible for bank erosion19, and the displacement of the zone measure of sediment supplies in the Amazon and other large river of maximum shear stress from the inner to the outer bank shifts systems. It includes both sandy bed material, which is the material of the zones of maximum bed-material transport and bank scour bar formation, and silt–clay washload, which is transported through accordingly15. As a result, the bar aggrades, growing laterally and the channel and into floodplains without being sequestered onto vertically20 until its surface is infrequently inundated, promoting the bars.
Load more

Recommended publications
  • (P 117-140) Flood Pulse.Qxp
    117 THE FLOOD PULSE CONCEPT: NEW ASPECTS, APPROACHES AND APPLICATIONS - AN UPDATE Junk W.J. Wantzen K.M. Max-Planck-Institute for Limnology, Working Group Tropical Ecology, P.O. Box 165, 24302 Plön, Germany E-mail: [email protected] ABSTRACT The flood pulse concept (FPC), published in 1989, was based on the scientific experience of the authors and published data worldwide. Since then, knowledge on floodplains has increased considerably, creating a large database for testing the predictions of the concept. The FPC has proved to be an integrative approach for studying highly diverse and complex ecological processes in river-floodplain systems; however, the concept has been modified, extended and restricted by several authors. Major advances have been achieved through detailed studies on the effects of hydrology and hydrochemistry, climate, paleoclimate, biogeography, biodi- versity and landscape ecology and also through wetland restoration and sustainable management of flood- plains in different latitudes and continents. Discussions on floodplain ecology and management are greatly influenced by data obtained on flow pulses and connectivity, the Riverine Productivity Model and the Multiple Use Concept. This paper summarizes the predictions of the FPC, evaluates their value in the light of recent data and new concepts and discusses further developments in floodplain theory. 118 The flood pulse concept: New aspects, INTRODUCTION plain, where production and degradation of organic matter also takes place. Rivers and floodplain wetlands are among the most threatened ecosystems. For example, 77 percent These characteristics are reflected for lakes in of the water discharge of the 139 largest river systems the “Seentypenlehre” (Lake typology), elaborated by in North America and Europe is affected by fragmen- Thienemann and Naumann between 1915 and 1935 tation of the river channels by dams and river regula- (e.g.
    [Show full text]
  • Deposition Patterns and Rates of Mining-Contaminated Sediment Within a Sedimentation Basin System, S.E
    BearWorks Institutional Repository MSU Graduate Theses Spring 2017 Deposition Patterns and Rates of Mining- Contaminated Sediment within a Sedimentation Basin System, S.E. Missouri Joshua Carl Voss Missouri State University - Springfield, [email protected] Follow this and additional works at: http://bearworks.missouristate.edu/theses Part of the Environmental Indicators and Impact Assessment Commons, Environmental Monitoring Commons, and the Hydrology Commons Recommended Citation Voss, Joshua Carl, "Deposition Patterns and Rates of Mining-Contaminated Sediment within a Sedimentation Basin System, S.E. Missouri" (2017). MSU Graduate Theses. 3074. http://bearworks.missouristate.edu/theses/3074 This article or document was made available through BearWorks, the institutional repository of Missouri State University. The orkw contained in it may be protected by copyright and require permission of the copyright holder for reuse or redistribution. For more information, please contact [email protected]. DEPOSITION PATTERNS AND RATES OF MINING-CONTAMINATED SEDIMENT WITHIN A SEDIMENTATION BASIN SYSTEM, BIG RIVER, S.E. MISSOURI A Masters Thesis Presented to The Graduate College of Missouri State University ATE In Partial Fulfillment Of the Requirements for the Degree Master of Science, Geospatial Sciences in Geography, Geology, and Planning By Josh C. Voss May 2017 Copyright 2017 by Joshua Carl Voss ii DEPOSITION PATTERNS AND RATES OF MINING-CONTAMINATED SEDIMENT WITHIN A SEDIMENTATION BASIN SYSTEM, BIG RIVER, S.E. MISSOURI Geography, Geology, and Planning Missouri State University, May 2017 Master of Science Josh C. Voss ABSTRACT Flooding events exert a dominant control over the deposition and formation of floodplains. The rate at which floodplains form depends on flood magnitude, frequency, and duration, and associated sediment transport capacity and supply.
    [Show full text]
  • Lesson 4: Sediment Deposition and River Structures
    LESSON 4: SEDIMENT DEPOSITION AND RIVER STRUCTURES ESSENTIAL QUESTION: What combination of factors both natural and manmade is necessary for healthy river restoration and how does this enhance the sustainability of natural and human communities? GUIDING QUESTION: As rivers age and slow they deposit sediment and form sediment structures, how are sediments and sediment structures important to the river ecosystem? OVERVIEW: The focus of this lesson is the deposition and erosional effects of slow-moving water in low gradient areas. These “mature rivers” with decreasing gradient result in the settling and deposition of sediments and the formation sediment structures. The river’s fast-flowing zone, the thalweg, causes erosion of the river banks forming cliffs called cut-banks. On slower inside turns, sediment is deposited as point-bars. Where the gradient is particularly level, the river will branch into many separate channels that weave in and out, leaving gravel bar islands. Where two meanders meet, the river will straighten, leaving oxbow lakes in the former meander bends. TIME: One class period MATERIALS: . Lesson 4- Sediment Deposition and River Structures.pptx . Lesson 4a- Sediment Deposition and River Structures.pdf . StreamTable.pptx . StreamTable.pdf . Mass Wasting and Flash Floods.pptx . Mass Wasting and Flash Floods.pdf . Stream Table . Sand . Reflection Journal Pages (printable handout) . Vocabulary Notes (printable handout) PROCEDURE: 1. Review Essential Question and introduce Guiding Question. 2. Hand out first Reflection Journal page and have students take a minute to consider and respond to the questions then discuss responses and questions generated. 3. Handout and go over the Vocabulary Notes. Students will define the vocabulary words as they watch the PowerPoint Lesson.
    [Show full text]
  • River Dynamics 101 - Fact Sheet River Management Program Vermont Agency of Natural Resources
    River Dynamics 101 - Fact Sheet River Management Program Vermont Agency of Natural Resources Overview In the discussion of river, or fluvial systems, and the strategies that may be used in the management of fluvial systems, it is important to have a basic understanding of the fundamental principals of how river systems work. This fact sheet will illustrate how sediment moves in the river, and the general response of the fluvial system when changes are imposed on or occur in the watershed, river channel, and the sediment supply. The Working River The complex river network that is an integral component of Vermont’s landscape is created as water flows from higher to lower elevations. There is an inherent supply of potential energy in the river systems created by the change in elevation between the beginning and ending points of the river or within any discrete stream reach. This potential energy is expressed in a variety of ways as the river moves through and shapes the landscape, developing a complex fluvial network, with a variety of channel and valley forms and associated aquatic and riparian habitats. Excess energy is dissipated in many ways: contact with vegetation along the banks, in turbulence at steps and riffles in the river profiles, in erosion at meander bends, in irregularities, or roughness of the channel bed and banks, and in sediment, ice and debris transport (Kondolf, 2002). Sediment Production, Transport, and Storage in the Working River Sediment production is influenced by many factors, including soil type, vegetation type and coverage, land use, climate, and weathering/erosion rates.
    [Show full text]
  • Stream Restoration, a Natural Channel Design
    Stream Restoration Prep8AICI by the North Carolina Stream Restonltlon Institute and North Carolina Sea Grant INC STATE UNIVERSITY I North Carolina State University and North Carolina A&T State University commit themselves to positive action to secure equal opportunity regardless of race, color, creed, national origin, religion, sex, age or disability. In addition, the two Universities welcome all persons without regard to sexual orientation. Contents Introduction to Fluvial Processes 1 Stream Assessment and Survey Procedures 2 Rosgen Stream-Classification Systems/ Channel Assessment and Validation Procedures 3 Bankfull Verification and Gage Station Analyses 4 Priority Options for Restoring Incised Streams 5 Reference Reach Survey 6 Design Procedures 7 Structures 8 Vegetation Stabilization and Riparian-Buffer Re-establishment 9 Erosion and Sediment-Control Plan 10 Flood Studies 11 Restoration Evaluation and Monitoring 12 References and Resources 13 Appendices Preface Streams and rivers serve many purposes, including water supply, The authors would like to thank the following people for reviewing wildlife habitat, energy generation, transportation and recreation. the document: A stream is a dynamic, complex system that includes not only Micky Clemmons the active channel but also the floodplain and the vegetation Rockie English, Ph.D. along its edges. A natural stream system remains stable while Chris Estes transporting a wide range of flows and sediment produced in its Angela Jessup, P.E. watershed, maintaining a state of "dynamic equilibrium." When Joseph Mickey changes to the channel, floodplain, vegetation, flow or sediment David Penrose supply significantly affect this equilibrium, the stream may Todd St. John become unstable and start adjusting toward a new equilibrium state.
    [Show full text]
  • Scour and Fill in Ephemeral Streams
    SCOUR AND FILL IN EPHEMERAL STREAMS by Michael G. Foley , , " W. M. Keck Laboratory of Hydraulics and Water Resources Division of Engineering and Applied Science CALIFORNIA INSTITUTE OF TECHNOLOGY Pasadena, California 91125 Report No. KH-R-33 November 1975 SCOUR AND FILL IN EPHEMERAL STREAMS by Michael G. Foley Project Supervisors: Robert P. Sharp Professor of Geology and Vito A. Vanoni Professor of Hydraulics Technical Report to: U. S. Army Research Office, Research Triangle Park, N. C. (under Grant No. DAHC04-74-G-0189) and National Science Foundation (under Grant No. GK3l802) Contribution No. 2695 of the Division of Geological and Planetary Sciences, California Institute of Technology W. M. Keck Laboratory of Hydraulics and Water Resources Division of Engineering and Applied Science California Institute of Technology Pasadena, California 91125 Report No. KH-R-33 November 1975 ACKNOWLEDGMENTS The writer would like to express his deep appreciation to his advisor, Dr. Robert P. Sharp, for suggesting this project and providing patient guidance, encouragement, support, and kind criticism during its execution. Similar appreciation is due Dr. Vito A. Vanoni for his guidance and suggestions, and for generously sharing his great experience with sediment transport problems and laboratory experiments. Drs. Norman H. Brooks and C. Hewitt Dix read the first draft of this report, and their helpful comments are appreciated. Mr. Elton F. Daly was instrumental in the design of the laboratory apparatus and the success of the laboratory experiments. Valuable assistance in the field was given by Mrs. Katherine E. Foley and Mr. Charles D. Wasserburg. Laboratory experiments were conducted with the assistance of Ms.
    [Show full text]
  • Logistic Analysis of Channel Pattern Thresholds: Meandering, Braiding, and Incising
    Geomorphology 38Ž. 2001 281–300 www.elsevier.nlrlocatergeomorph Logistic analysis of channel pattern thresholds: meandering, braiding, and incising Brian P. Bledsoe), Chester C. Watson 1 Department of CiÕil Engineering, Colorado State UniÕersity, Fort Collins, CO 80523, USA Received 22 April 2000; received in revised form 10 October 2000; accepted 8 November 2000 Abstract A large and geographically diverse data set consisting of meandering, braiding, incising, and post-incision equilibrium streams was used in conjunction with logistic regression analysis to develop a probabilistic approach to predicting thresholds of channel pattern and instability. An energy-based index was developed for estimating the risk of channel instability associated with specific stream power relative to sedimentary characteristics. The strong significance of the 74 statistical models examined suggests that logistic regression analysis is an appropriate and effective technique for associating basic hydraulic data with various channel forms. The probabilistic diagrams resulting from these analyses depict a more realistic assessment of the uncertainty associated with previously identified thresholds of channel form and instability and provide a means of gauging channel sensitivity to changes in controlling variables. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Channel stability; Braiding; Incision; Stream power; Logistic regression 1. Introduction loads, loss of riparian habitat because of stream bank erosion, and changes in the predictability and vari- Excess stream power may result in a transition ability of flow and sediment transport characteristics from a meandering channel to a braiding or incising relative to aquatic life cyclesŽ. Waters, 1995 . In channel that is characteristically unstableŽ Schumm, addition, braiding and incising channels frequently 1977; Werritty, 1997.
    [Show full text]
  • Field Studies and 3D Modelling of Morphodynamics in a Meandering River Reach Dominated by Tides and Suspended Load
    fluids Article Field Studies and 3D Modelling of Morphodynamics in a Meandering River Reach Dominated by Tides and Suspended Load Qiancheng Xie 1,* , James Yang 2,3 and T. Staffan Lundström 1 1 Division of Fluid and Experimental Mechanics, Luleå University of Technology, 97187 Luleå, Sweden; [email protected] 2 Vattenfall AB, Research and Development, Hydraulic Laboratory, 81426 Älvkarleby, Sweden; [email protected] 3 Resources, Energy and Infrastructure, Royal Institute of Technology, 10044 Stockholm, Sweden * Correspondence: [email protected]; Tel.: +4672-2870-381 Received: 9 December 2018; Accepted: 20 January 2019; Published: 22 January 2019 Abstract: Meandering is a common feature in natural alluvial streams. This study deals with alluvial behaviors of a meander reach subjected to both fresh-water flow and strong tides from the coast. Field measurements are carried out to obtain flow and sediment data. Approximately 95% of the sediment in the river is suspended load of silt and clay. The results indicate that, due to the tidal currents, the flow velocity and sediment concentration are always out of phase with each other. The cross-sectional asymmetry and bi-directional flow result in higher sediment concentration along inner banks than along outer banks of the main stream. For a given location, the near-bed concentration is 2−5 times the surface value. Based on Froude number, a sediment carrying capacity formula is derived for the flood and ebb tides. The tidal flow stirs the sediment and modifies its concentration and transport. A 3D hydrodynamic model of flow and suspended sediment transport is established to compute the flow patterns and morphology changes.
    [Show full text]
  • Bedload Transport and Large Organic Debris in Steep Mountain Streams in Forested Watersheds on the Olympic Penisula, Washington
    77 TFW-SH7-94-001 Bedload Transport and Large Organic Debris in Steep Mountain Streams in Forested Watersheds on the Olympic Penisula, Washington Final Report By Matthew O’Connor and R. Dennis Harr October 1994 BEDLOAD TRANSPORT AND LARGE ORGANIC DEBRIS IN STEEP MOUNTAIN STREAMS IN FORESTED WATERSHEDS ON THE OLYMPIC PENINSULA, WASHINGTON FINAL REPORT Submitted by Matthew O’Connor College of Forest Resources, AR-10 University of Washington Seattle, WA 98195 and R. Dennis Harr Research Hydrologist USDA Forest Service Pacific Northwest Research Station and Professor, College of Forest Resources University of Washington Seattle, WA 98195 to Timber/Fish/Wildlife Sediment, Hydrology and Mass Wasting Steering Committee and State of Washington Department of Natural Resources October 31, 1994 TABLE OF CONTENTS LIST OF FIGURES iv LIST OF TABLES vi ACKNOWLEDGEMENTS vii OVERVIEW 1 INTRODUCTION 2 BACKGROUND 3 Sediment Routing in Low-Order Channels 3 Timber/Fish/Wildlife Literature Review of Sediment Dynamics in Low-order Streams 5 Conceptual Model of Bedload Routing 6 Effects of Timber Harvest on LOD Accumulation Rates 8 MONITORING SEDIMENT TRANSPORT IN LOW-ORDER CHANNELS 11 Monitoring Objectives 11 Field Sites for Monitoring Program 12 BEDLOAD TRANSPORT MODEL 16 Model Overview 16 Stochastic Model Outputs from Predictive Relationships 17 24-Hour Precipitation 17 Synthesis of Frequency of Threshold 24-Hour Precipitation 18 Peak Discharge as a Function of 24-Hour Precipitation 21 Excess Unit Stream Power as a Function of Peak Discharge 28 Mean Scour
    [Show full text]
  • Variability of Bed Mobility in Natural Gravel-Bed Channels
    WATER RESOURCES RESEARCH, VOL. 36, NO. 12, PAGES 3743–3755, DECEMBER 2000 Variability of bed mobility in natural, gravel-bed channels and adjustments to sediment load at local and reach scales Thomas E. Lisle,1 Jonathan M. Nelson,2 John Pitlick,3 Mary Ann Madej,4 and Brent L. Barkett3 Abstract. Local variations in boundary shear stress acting on bed-surface particles control patterns of bed load transport and channel evolution during varying stream discharges. At the reach scale a channel adjusts to imposed water and sediment supply through mutual interactions among channel form, local grain size, and local flow dynamics that govern bed mobility. In order to explore these adjustments, we used a numerical flow ␶ model to examine relations between model-predicted local boundary shear stress ( j) and measured surface particle size (D50) at bank-full discharge in six gravel-bed, alternate-bar ␶ channels with widely differing annual sediment yields. Values of j and D50 were poorly correlated such that small areas conveyed large proportions of the total bed load, especially in sediment-poor channels with low mobility. Sediment-rich channels had greater areas of full mobility; sediment-poor channels had greater areas of partial mobility; and both types had significant areas that were essentially immobile. Two reach- mean mobility parameters (Shields stress and Q*) correlated reasonably well with sediment supply. Values which can be practicably obtained from carefully measured mean hydraulic variables and particle size would provide first-order assessments of bed mobility that would broadly distinguish the channels in this study according to their sediment yield and bed mobility.
    [Show full text]
  • Biogeochemical and Metabolic Responses to the Flood Pulse in a Semi-Arid Floodplain
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by DigitalCommons@USU 1 Running Head: Semi-arid floodplain response to flood pulse 2 3 4 5 6 Biogeochemical and Metabolic Responses 7 to the Flood Pulse in a Semi-Arid Floodplain 8 9 10 11 with 7 Figures and 3 Tables 12 13 14 15 H. M. Valett1, M.A. Baker2, J.A. Morrice3, C.S. Crawford, 16 M.C. Molles, Jr., C.N. Dahm, D.L. Moyer4, J.R. Thibault, and Lisa M. Ellis 17 18 19 20 21 22 Department of Biology 23 University of New Mexico 24 Albuquerque, New Mexico 87131 USA 25 26 27 28 29 30 31 present addresses: 32 33 1Department of Biology 2Department of Biology 3U.S. EPA 34 Virginia Tech Utah State University Mid-Continent Ecology Division 35 Blacksburg, Virginia 24061 USA Logan, Utah 84322 USA Duluth, Minnesota 55804 USA 36 540-231-2065, 540-231-9307 fax 37 [email protected] 38 4Water Resources Division 39 United States Geological Survey 40 Richmond, Virginia 23228 USA 41 1 1 Abstract: Flood pulse inundation of riparian forests alters rates of nutrient retention and 2 organic matter processing in the aquatic ecosystems formed in the forest interior. Along the 3 Middle Rio Grande (New Mexico, USA), impoundment and levee construction have created 4 riparian forests that differ in their inter-flood intervals (IFIs) because some floodplains are 5 still regularly inundated by the flood pulse (i.e., connected), while other floodplains remain 6 isolated from flooding (i.e., disconnected).
    [Show full text]
  • Classifying Rivers - Three Stages of River Development
    Classifying Rivers - Three Stages of River Development River Characteristics - Sediment Transport - River Velocity - Terminology The illustrations below represent the 3 general classifications into which rivers are placed according to specific characteristics. These categories are: Youthful, Mature and Old Age. A Rejuvenated River, one with a gradient that is raised by the earth's movement, can be an old age river that returns to a Youthful State, and which repeats the cycle of stages once again. A brief overview of each stage of river development begins after the images. A list of pertinent vocabulary appears at the bottom of this document. You may wish to consult it so that you will be aware of terminology used in the descriptive text that follows. Characteristics found in the 3 Stages of River Development: L. Immoor 2006 Geoteach.com 1 Youthful River: Perhaps the most dynamic of all rivers is a Youthful River. Rafters seeking an exciting ride will surely gravitate towards a young river for their recreational thrills. Characteristically youthful rivers are found at higher elevations, in mountainous areas, where the slope of the land is steeper. Water that flows over such a landscape will flow very fast. Youthful rivers can be a tributary of a larger and older river, hundreds of miles away and, in fact, they may be close to the headwaters (the beginning) of that larger river. Upon observation of a Youthful River, here is what one might see: 1. The river flowing down a steep gradient (slope). 2. The channel is deeper than it is wide and V-shaped due to downcutting rather than lateral (side-to-side) erosion.
    [Show full text]