DOCSLIB.ORG

Total Bed-Material Discharge in Alluvial Channels

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Total Bed-Material Discharge in Alluvial Channels Total Bed-Material Discharge in Alluvial Channels GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1498-1 Total Bed-Material Discharge in Alluvial Channels By F. M. CHANG, D. B. SIMONS, and E. V. RICHARDSON STUDIES OF FLOW IN ALLUVIAL CHANNELS GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1498-1 UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1965 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C., 20402 - Price 20 cents (paper cover) CONTENTS Page Symbols_ _______________________________________________________ iv Abstract__ _____________________________________________________ I 1 Introduction._ ____________________________________________________ 1 Scope._______________________________________________________ 1 Acknowledgments. ____________________________________________ 3 Analysis of sediment size.__________________________________________ 3 Velocity distribution in alluvial channels____________________________ 5 Bed-material discharge._------__-______-_-_________________________ 8 Contact-bed-material discharge________________________________ 10 Suspended-bed-material discharge.______________________________ 13 Total bed-material discharge._________-_____-_-___________----__ 16 Evaluation.__________________________________________________ 18 Summary and conclusions__--_-__________-_-__-___-_______--_-___ 20 References_ _ ____________________________________________________ 22 ILLUSTRATIONS Page FIGURE 1. Bed-material size distribution of sands for flume data____ 12 2. Relation of sediment Reynolds number and von Karman's coefficient. ______________________________ _ ______ 7 3-6. Comparison of theoretical and measured velocity dis­ tribution for flume data 3. For de=0.19-mm sand ___ ___________________ 7 4. For de=0.33-, 0.35-mm sand. _________------_- 8 5. For de=0.50-, 0.52-mm sand___._._ _ ___._.__ 9 6. For rfe=0.93-mm sand ____ __._ ______ _-__ 9 7. Comparison of theoretical and measured velocity distri­ bution for canal data. _ __________________---_-_-- 10 8. Function Ii in terms of £ for various values of z ____ -___ 15 9. Function 72 in terms of £ for various values of z _____ __- 15 U Tg 10. KT versus _ relation for various sands from U* flume data_____________________________________-_ 17 11-13. Comparison of the estimated and measured total bed- material discharge for 11. Flumedata_ r _____________________---_----_ 19 12. River data. __________ _____ _ _____ _ _ 20 13. Both flume and river data __ __________-__-- 21 m SYMBOLS Symbol Definition Dimension AI Integration constant-_____-_____--_____--.__---_-__-----_ _______ A3 Volume constant of particle__.________---____--_________ _______ a Thickness of contact-bed-material layer____________________ L b e Apparent thickness of contact-bed-material layer (only static L force is considered)_---_-___-_--______--_____-_---_-_-_ L Ca Concentration at distance a from the bed.__________________ F/L3 Cm Mean concentration of contact-bed-material layer ___________ F/L3 c Concentration in dry weight per unit volume at distance y from the bed__________________________________________ F/L3 Cft Weight of contact bed material in a unit volume of the water- bed-material mixture__ _______________________________ F/L3 c, Weight of suspended bed material in a unit volume of the water- bed-material mixture_________________________________ F/L3 D Depth of flow_-----_-__---____---__-----------_-----_--_ L d Bed-material diameter. ___-_-___-____-__--_------__-----_ L de Equivalent diameter (definition in the text, p. I 14) _________ L d50 Median diameter______________________-___-__-----__-_-_ L e Porosity of bed material_______________-_---___-__-----_ _______ f Vector notation of force acting on particle__-_____---__--___ F g Gravitational acceleration. _____--______--____----____--__ L/T2 /i Integral value__-___-_-_________--___-__----_--____----__ _______ /2 Integral value_____-_-_________-_--_-----_---------_----_ _______ j Experimental coefficient, j=a/6c_-_____-_---_--_-_-----_--_ _______ #6 M-tf5e____________-_________-______.________ ___________ _______ Kbe Contact-bed-material coefficient--------------------------- _______ KT Total bed-material discharge coefficient__-___-___-_-__--_-_ _______ I Mixing length______________________----_--_-__-------- L M Coefficient M= Mr Af.___..__________________________ _______ MI Sediment-discharge distribution coefficient--.--------------- ------- M2 Ratio of concentrations between contact-bed-material layer and bed material in stationary bed- _________________________ _______ N Number of particles. ____________________________________ ------- n Number of moving layers in contact-bed-material layer ___ _______ p Percentage by weight of the bed material with diameter d_ ___ _______ pt Total percentage by weight of the bed material- _________ _______ Qb Contact-bed-material discharge per unit width of channel _ F/TL QD Contact-bed-material discharge per unit area._______________ Ff TL2 Q, Suspended-bed-material discharge per unit width of channel.__ F/TL QT Total bed-material discharge per unit width of channel_______ F/TL Rs Ratio of suspended-bed-to contact-bed-material discharge.__ _______ re Ratio of the velocity at £=£<, to the mean velocity of the fluid. _ _______ *S Slope of channel-_______________---_--_------_----_------ --__-__ U Mean velocity of flow.________-_--___-------_----.-------- L/T t/5 Mean velocity of contact-bed-material layer,_______________ L/T IV SYMBOLS Symbol Definition Dimension Um Velocity at water surface_____--_---_-_-----__------------ L/T U* Shear velocity__--_..-________-_.__________L___-.-_ L/T u Velocity at distance y from the bed________________________ L/T u' Fluctuating component of velocity in the x direction.________ L/T Ub Actual velocity of the contact bed material.________________ L/T us Actual velocity of the suspended Bed material.______________ L/T T7 Vector notation of the relative velocity between particle and fluid._-_-_-------_----_---------------_------------_- L/T v' Fluctuating component of velocity in the y direction. ________ L/T W Work done by the relative motion between particle and fluid. _ FL Wb Work done by bed material.______________________________ FL Wf Work done by fluid_._...-______-_-_--_--_-_----.___-_--- FL y Distance from the bed surface___________________________ L 2 Exponent for suspended-bed-material distribution ___________ _______ a Slope of bed (angle)--____________-__----__________---_-_- _______ 6 Ratio of the sediment transfer coefficient to the diffusion co­ efficient of fluid._____________---_-_-_-_____-------_-_- _______ 7 Specific weight of fluid._________-_-___---_____-_-_-__-_-_ F/L3 ys Specific weight of bed material.___________________________ F/L3 Ay Submerged specific weight of bed material._________________ _______ e Efficiency.-_ ____________________________________________ _______ e0 Diffusion coefficient of the fluid.__________________________ _______ f, Sediment transfer coefficient._____________________________ _______ « von Karman's coefficient--------------------------------- ____--_ M Dynamic viscosity of fluid.________--_---______-__-__----- FT/L2 v Kinematic viscosity of fluid.____________-__________--_---- L2/T STUDIES OF FLOW IN ALLUVIAL CHANNELS TOTAL BED-MATERIAL DISCHARGE IN ALLUVIAL CHANNELS By F. M. CHANG, D. B. SIMONS, and E. V. KICHAKDSON ABSTRACT This is a study of total bed-material discharge (wash load excluded) in alluvial channels, based partly on existing theories. The contact-bed-material discharge was obtained by utilizing the energy-work relation of the fluid and the bed material. An equation for velocity distribution was obtained by integrating the Reynolds equation through use of the Prandtl's hypothesis of mixing length. Through application of the basic equation for the distribution of suspended bed material by M. P. O'Brien, the suspended-bed-material discharge was in­ vestigated in terms of contact-bed-material discharge. Then, the total bed- material discharge was obtained simply by adding the contact-bed-material discharge and the suspended-bed-material discharge. The results were checked with available la boratory and field data and appeared to be mutually consistent and satisfactory. INTRODUCTION SCOPE No purely theoretical approach to the general principles of sediment discharge in alluvial channels seems possible at present because of insufficient quantitative knowledge of fluid turbulence and its effect on sediment within the fluid. Hence, the approach used in this report is semitheoretical and is based on existing theory of turbulent flow and on general ideas derived from observation and reasonable speculation. This study concerns itself principally with 1. The classification of the graded sands which comprise the bed material of natural alluvial channels. 2. The development of the velocity distribution, which includes consideration of the body force of the flow. 3. The subdivision of the total bed-material discharge into com­ ponents based upon significant forces to which the particles are subjected. 4. Relations for estimating suspended-bed-material discharge, contact- bed-material discharge, and hence, total bed-material discharge. I l 12 STUDIES OF FLOW IN ALLUVIAL CHANNELS 5. Evaluation of the formula on total bed-material discharge by use of laboratory and field data. The flume data (Simons, 1961b) used for the investigation were collected by the U.S. Geological
Load more

Recommended publications
  • Measurement of Bedload Transport in Sand-Bed Rivers: a Look at Two Indirect Sampling Methods
    Published online in 2010 as part of U.S. Geological Survey Scientific Investigations Report 2010-5091. Measurement of Bedload Transport in Sand-Bed Rivers: A Look at Two Indirect Sampling Methods Robert R. Holmes, Jr. U.S. Geological Survey, Rolla, Missouri, United States. Abstract Sand-bed rivers present unique challenges to accurate measurement of the bedload transport rate using the traditional direct sampling methods of direct traps (for example the Helley-Smith bedload sampler). The two major issues are: 1) over sampling of sand transport caused by “mining” of sand due to the flow disturbance induced by the presence of the sampler and 2) clogging of the mesh bag with sand particles reducing the hydraulic efficiency of the sampler. Indirect measurement methods hold promise in that unlike direct methods, no transport-altering flow disturbance near the bed occurs. The bedform velocimetry method utilizes a measure of the bedform geometry and the speed of bedform translation to estimate the bedload transport through mass balance. The bedform velocimetry method is readily applied for the estimation of bedload transport in large sand-bed rivers so long as prominent bedforms are present and the streamflow discharge is steady for long enough to provide sufficient bedform translation between the successive bathymetric data sets. Bedform velocimetry in small sand- bed rivers is often problematic due to rapid variation within the hydrograph. The bottom-track bias feature of the acoustic Doppler current profiler (ADCP) has been utilized to accurately estimate the virtual velocities of sand-bed rivers. Coupling measurement of the virtual velocity with an accurate determination of the active depth of the streambed sediment movement is another method to measure bedload transport, which will be termed the “virtual velocity” method.
    [Show full text]
  • 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.
    [Show full text]
  • Missouri River Floodplain from River Mile (RM) 670 South of Decatur, Nebraska to RM 0 at St
    Hydrogeomorphic Evaluation of Ecosystem Restoration Options For The Missouri River Floodplain From River Mile (RM) 670 South of Decatur, Nebraska to RM 0 at St. Louis, Missouri Prepared For: U. S. Fish and Wildlife Service Region 3 Minneapolis, Minnesota Greenbrier Wetland Services Report 15-02 Mickey E. Heitmeyer Joseph L. Bartletti Josh D. Eash December 2015 HYDROGEOMORPHIC EVALUATION OF ECOSYSTEM RESTORATION OPTIONS FOR THE MISSOURI RIVER FLOODPLAIN FROM RIVER MILE (RM) 670 SOUTH OF DECATUR, NEBRASKA TO RM 0 AT ST. LOUIS, MISSOURI Prepared For: U. S. Fish and Wildlife Service Region 3 Refuges and Wildlife Minneapolis, Minnesota By: Mickey E. Heitmeyer Greenbrier Wetland Services Advance, MO 63730 Joseph L. Bartletti Prairie Engineers of Illinois, P.C. Springfield, IL 62703 And Josh D. Eash U.S. Fish and Wildlife Service, Region 3 Water Resources Branch Bloomington, MN 55437 Greenbrier Wetland Services Report No. 15-02 December 2015 Mickey E. Heitmeyer, PhD Greenbrier Wetland Services Route 2, Box 2735 Advance, MO 63730 www.GreenbrierWetland.com Publication No. 15-02 Suggested citation: Heitmeyer, M. E., J. L. Bartletti, and J. D. Eash. 2015. Hydrogeomorphic evaluation of ecosystem restoration options for the Missouri River Flood- plain from River Mile (RM) 670 south of Decatur, Nebraska to RM 0 at St. Louis, Missouri. Prepared for U. S. Fish and Wildlife Service Region 3, Min- neapolis, MN. Greenbrier Wetland Services Report 15-02, Blue Heron Conservation Design and Print- ing LLC, Bloomfield, MO. Photo credits: USACE; http://statehistoricalsocietyofmissouri.org/; Karen Kyle; USFWS http://digitalmedia.fws.gov/cdm/; Cary Aloia This publication printed on recycled paper by ii Contents EXECUTIVE SUMMARY ....................................................................................
    [Show full text]
  • Sediment in Alluvial Rivers and Channels
    Module 2 The Science of Surface and Ground Water Version 2 CE IIT, Kharagpur Lesson 10 Sediment Dynamics in Alluvial Rivers and Channels Version 2 CE IIT, Kharagpur Instructional Objectives On completion of this lesson, the student shall be able to learn the following: 1. The mechanics of sediment movement in alluvial rivers 2. Different types of bed forms in alluvial rivers 3. Quantitative assessment of sediment transport 4. Resistance equations for flow 5. Bed level changes in alluvial channels due to natural and artificial causes 6. Mathematical modelling of sediment transport 2.10.0 Introduction In Lesson 2.9, we looked into the aspects of sediment generation due to erosion in the upper catchments of a river and their transport by the river towards the sea. On the way, some of this sediment might get deposited, if the stream power is not sufficient enough. It was noted that it is the shear stress at the riverbed that causes the particles near the bed to move provided the shear is greater than the critical shear stress of the particle which is proportional to the particle size. Hence, the same shear generated by a particular flow may be able to move of say, sand particles, but unable to cause movement of gravels. The particles which move due to the average bed shear stress exceeding the critical shear stress of the particle display different ways of movement depending on the flow condition, sediment size, fluid and sediment densities, and the channel conditions. At relatively slow shear stress, the particles roll or slide along the bed.
    [Show full text]
  • Alluvial Cover Controlling the Width, Slope and Sinuosity of Bedrock Channels
    Earth Surf. Dynam., 6, 29–48, 2018 https://doi.org/10.5194/esurf-6-29-2018 © Author(s) 2018. This work is distributed under the Creative Commons Attribution 4.0 License. Alluvial cover controlling the width, slope and sinuosity of bedrock channels Jens Martin Turowski Helmholtz-Zentrum Potsdam, German Research Centre for Geosciences GFZ, Telegrafenberg, 14473 Potsdam, Germany Correspondence: Jens Martin Turowski ([email protected]) Received: 17 July 2017 – Discussion started: 31 July 2017 Revised: 16 December 2017 – Accepted: 31 December 2017 – Published: 6 February 2018 Abstract. Bedrock channel slope and width are important parameters for setting bedload transport capacity and for stream-profile inversion to obtain tectonics information. Channel width and slope development are closely related to the problem of bedrock channel sinuosity. It is therefore likely that observations on bedrock channel meandering yields insights into the development of channel width and slope. Active meandering occurs when the bedrock channel walls are eroded, which also drives channel widening. Further, for a given drop in elevation, the more sinuous a channel is, the lower is its channel bed slope in comparison to a straight channel. It can thus be expected that studies of bedrock channel meandering give insights into width and slope adjustment and vice versa. The mechanisms by which bedrock channels actively meander have been debated since the beginning of modern geomorphic research in the 19th century, but a final consensus has not been reached. It has long been argued that whether a bedrock channel meanders actively or not is determined by the availability of sediment relative to transport capacity, a notion that has also been demonstrated in laboratory experiments.
    [Show full text]
  • River Channel Relocation: Problems and Prospects
    water Review River Channel Relocation: Problems and Prospects Alissa Flatley 1,* , Ian D Rutherfurd 1 and Ross Hardie 2 1 School of Geography, University of Melbourne, 221 Bouverie Street, Carlton, VIC 3053, Australia; [email protected] 2 Alluvium Consulting, Level 1, 105–115 Dover Street, Cremorne, VIC 3013, Australia; [email protected] * Correspondence: alissa.fl[email protected]; Tel.: +61-408-708-940 Received: 28 August 2018; Accepted: 26 September 2018; Published: 29 September 2018 Abstract: River relocation is the diversion of a river into an entirely new channel for part of their length (often called river diversions). Relocations have been common through history and have been carried out for a wide range of purposes, but most commonly to construct infrastructure and for mining. However, they have not been considered as a specific category of anthropogenic channel change. Relocated channels present a consistent set of physical and ecological challenges, often related to accelerated erosion and deposition. We present a new classification of river relocation, and present a series of case studies that highlight some of the key issues with river relocation construction and performance. Primary changes to the channel dimensions and materials, alongside changes to flow velocity or channel capacity, can lead to a consistent set of problems, and lead to further secondary and tertiary issues, such as heightened erosion or deposition, hanging tributaries, vegetation loss, water quality issues, and associated ecological impacts. Occasionally, relocated channels can suffer engineering failure, such as overtopping or complete channel collapse during floods. Older river relocation channels were constructed to minimise cost and carry large floods, and were straight and trapezoidal.
    [Show full text]
  • A Cusp Catastrophe Model for Alluvial Channel Pattern and Stability
    water Article A Cusp Catastrophe Model for Alluvial Channel Pattern and Stability Yi Xiao 1,*, Shengfa Yang 1 and Mi Li 2 1 National Inland Waterway Regulation Engineering Research Center, Chongqing Jiaotong University, Chongqing 40074, China; [email protected] 2 Sichuan Energy Industry Investment Group Co.,Ltd., Chengdu 610000, China; [email protected] * Correspondence: [email protected]; Tel.: +86-023-6265-4621 Received: 17 February 2020; Accepted: 9 March 2020; Published: 11 March 2020 Abstract: The self-adjustment of an alluvial channel is a complicated process with various factors influencing the stability and transformation of channel patterns. A cusp catastrophe model for the alluvial channel regime is established by selecting suitable parameters to quantify the channel pattern and stability. The channel patterns can be identified by such a model in a direct way with a quantified index, which is a 2D projection of the cusp catastrophe surface, and the discriminant function is obtained from the model to distinguish the river state. Predictions based on this model are consistent with the field observations involving about 150 natural rivers of small or medium sizes. This new approach enables us to classify the channel pattern and determine a river stability state, and it paves the way toward a better understanding of the regime of natural rivers to assist decision-making in river management. Keywords: fluvial process; channel stability; channel pattern; cusp catastrophe model 1. Introduction The self-adjustment of an alluvial channel is a complicated process with various factors influencing the stability and transformation of channel patterns. Although the formation of alluvial channels has been extensively studied, the problem of the alluvial channel stability still remains to be systematically resolved.
    [Show full text]
  • Attributes of an Alluvial River and Their Relation to Water Policy and Management
    Attributes of an alluvial river and their relation to water policy and management William J. Trush*†, Scott M. McBain‡, and Luna B. Leopold§ *Institute for River Ecosystems, Fisheries Department, Humboldt State University, Arcata, CA 95521; ‡McBain and Trush, P.O. Box 663, Arcata, CA 95518; and §Department of Geology and Geophysics, University of California Berkeley, 400 Vermont Avenue, Berkeley, CA 94707 Contributed by Luna B. Leopold, August 15, 2000 Rivers around the world are being regulated by dams to accom- imposed on the river ecosystem (e.g., a recommended flow modate the needs of a rapidly growing global population. These release), we should expect a response (e.g., scouring sand from regulatory efforts usually oppose the natural tendency of rivers to a pool). The significance of an impetus will depend on an flood, move sediment, and migrate. Although an economic benefit, appropriate threshold beyond which a specific response is ex- river regulation has come at unforeseen and unevaluated cumu- pected. A process, therefore, is comprised of an impetus and an lative ecological costs. Historic and contemporary approaches to expected response. To use the alluvial river attributes as guide- remedy environmental losses have largely ignored hydrologic, lines for recovering or preserving critical processes, one must geomorphic, and biotic processes that form and maintain healthy consider how the magnitude, duration, frequency, and timing of alluvial river ecosystems. Several commonly known concepts that an impetus will exceed a threshold to produce a desired response. govern how alluvial channels work have been compiled into a set Rarely, however, is a single impetus imposed on a river ecosys- of ‘‘attributes’’ for alluvial river integrity.
    [Show full text]
  • Patterns and Processes of Sediment Sorting in Gravel-Bed Rivers D
    Progress in Physical Geography 22,1 (1998) pp. 1±32 Patterns and processes of sediment sorting in gravel-bed rivers D. Mark Powell Department of Geography, Leicester University, Leicester LE1 7RH, UK Abstract: Sedimentological studies of coarse-grained alluvial rivers reveal patterns of bed material sorting at a variety of spatial scales ranging from downstream fining over the length of the long profile to the vertical segregation of a coarse surface layer at the scale of individual particles. This article reviews the mechanisms that sort bed material by size during sediment entrainment, transport and deposition and discusses some of the inter-relationships that exist between patterns and processes of sediment sorting at different spatial and temporal scales. At initiation of motion, sorting can arise from the preferential entrainment of the finer fractions from the heterogeneous bed sediments. Bedload grain-size distributions are modified during transport as different size fractions are routed along different transport pathways under the influence of nonuniform bed topography and associated flow patterns, and during deposition as the variable pocket geometry of the rough bed surface and turbulence intensity of the flow control the size of the particles that deposit. The review highlights the poor understanding of the many feedback linkages that exist between patterns and processes of sediment sorting at different scales and the need for a greater awareness of the spatial and temporal bounds of these linkages. Key words: sediment sorting, gravel-bed rivers, fluvial sedimentology, bed material, bedload transport. I Introduction Patterns of sediment sorting in coarse-grained alluvial channels result from the segrega- tion of particles with differing physical characteristics during processes of erosion, transport and deposition.
    [Show full text]
  • Chapter 4 Sediment Transport
    Chapter 4 Sediment Transport 1. Introduction: Some Definitions 2. Modes of Sediment Transport Dissolved Load Suspended-Sediment Load Wash load Intermittently-suspended or saltation load Suspended-sediment rating curves Typical suspended-sediment loads in BC rivers Relation of sediment concentration to sediment load/discharge Bed Load (Traction Load) Bed load equations 3. The Theory of Sediment Entrainment Impelling forces Inertial forces The Shields entrainment function 4. Applications of Critical Threshold Conditions for Sediment Motion Bedload transport equations The threshold (equilibrium) channel 5. Some further reading 6. What’s next? 1. Introduction: Some Definitions Not all channels are formed in sediment and not all rivers transport sediment. Some have been carved into bedrock, usually in headwater reaches of streams located high in the mountains. These streams have channel forms that often are dominated by the nature of the rock (of varying hardness and resistance to mechanical breakdown and of varying joint definition, spacing and pattern) in which the channel has been cut. Such channels often include pools that trap sediment so that long reaches of channel may carry essentially no sediment at all. Such channels, known as non-alluvial channels, will not be examined in any detail here. Instead, we will focus on alluvial channels, the class of river channel forming the vast majority of rivers on the earth’s surface. Alluvial channels are self-formed channels in sediments that the river typically has at one time or another transported downstream in the flow. Sediment transport is critical to understanding how rivers work because it is the set of processes that mediates between the flowing water and the channel boundary.
    [Show full text]
  • Fluvial Processes with Special Emphasis on Glacial Rivers
    Section 3 FLUVIAL PROCESSES WITH SPECIAL EMPHASIS ON GLACIAL RIVERS An Annotated Bibliography Compiled for the Region II FRPA Riparian Management Science & Technical Committee by Jason E.B. Mouw Alaska Department of Fish and Game, Sport Fish Division SUMMARY Glacial rivers are perhaps some of the most physically diverse ecosystems on earth and are characterized by tremendous habitat complexity that shifts in space and time at a wide variety of scales. They are characterized by a highly variable flow regime and extreme suspended sediment concentrations (Milner and Petts, 1994). Glacial rivers typically adopt one or both of two general channel forms: braided or anastomosed. Braiding is typically referred to as the channel state in which splitting channels flow around bars or islands that are contained between dominant floodplain banks. Anastomosis refers to a split channel form in which multiple channels flow around rather permanent vegetated islands that are not flooded at bankfull discharge. Braided rivers are characterized by relatively high stream power (due to a high channel slope), high rates of erosion, deposition, and channel change. Anastomosing rivers are characterized by lower channel slope gradients, and perhaps higher rates of deposition. In general, glacial rivers flow with cold water, yet due to their aquatic habitat complexity they are characterized by high thermal heterogeneity (Malard et al. 2001) that supports a wide variety of fish species and their various life history stages and strategies. This physical habitat complexity is driven by cut and fill alluviation. These fluvial processes are driven by bank erosion and lateral and point bar accretion. Though the cause of channel form in glacial systems is still debated, there are several important factors that contribute.
    [Show full text]
  • A Genetic Classification of Floodplains G C
    University of Wollongong Research Online Faculty of Science, Medicine and Health - Papers Faculty of Science, Medicine and Health 1992 A genetic classification of floodplains G C. Nanson University of Wollongong, [email protected] J C. Croke University of Wollongong Publication Details Nanson, G. C. & Croke, J. C. (1992). A genetic classification of floodplains. Geomorphology, 4 (6), 459-486. Research Online is the open access institutional repository for the University of Wollongong. For further information contact the UOW Library: [email protected] A genetic classification of floodplains Abstract Floodplains are formed by a complex interaction of fluvial processes but their character and evolution is essentially the product of stream power and sediment character. The er lation between a stream's ability to entrain and transport sediment and the erosional resistance of floodplain alluvium that forms the channel boundary provides the basis for a genetic classification of floodplains. Three classes are recognised: (1) high- energy non-cohesive; (2) medium-energy non-cohesive; and (3) low-energy cohesive floodplains. Thirteen derivative orders and suborders, ranging from confined, coarse-grained, non-cohesive floodplains in high- energy environments to unconfined fine-grained cohesive floodplains in low-energy environments, are defined on the basis of nine factors (mostly floodplain forming processes). These factors result in distinctive geomorphological features (such as scroll bars or extensive backswamps) that distinguish each floodplain type in terms of genesis and resulting morphology. Finally, it is proposed that, because floodplains are derivatives of the parent stream system, substantial environmental change will result in the predictable transformation of one floodplain type to another over time.
    [Show full text]