DOCSLIB.ORG

6.6.4 Bank Angle and Channel Cross-Section

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
6.6.4 Bank Angle and Channel Cross-Section Section 6 Physical Habitat Characterization— Non-wadeable Rivers by Philip R. Kaufmann In the broad sense, physical habitat in ecology that are likely applicable in rivers as rivers includes all those physical attributes that well. They include: influence or provide sustenance to river or- • Channel Dimensions ganisms. Physical habitat varies naturally, as do biological characteristics; thus expectations • Channel Gradient differ even in the absence of anthropogenic disturbance. Within a given physiographic- • Channel Substrate Size and Type climatic region, river drainage area and chan- • Habitat Complexity and Cover nel gradient are likely to be strong natural determinants of many aspects of river habitat, • Riparian Vegetation Cover and Struc- because of their influence on discharge, flood ture stage, and stream power (the product of dis- charge times gradient). Summarizing the habi- • Anthropogenic Alterations tat results of a workshop conducted by EMAP • Channel-Riparian Interaction on stream monitoring design, Kaufmann (1993) identified seven general physical habi- All of these attributes may be directly or tat attributes important in influencing stream indirectly altered by anthropogenic activities. Nevertheless, their expected values tend to 1U.S. EPA, National Health and Environmental Effects Re- vary systematically with river size (drainage search Laboratory, Western Ecology Division, 200 SW 35th St., Corvallis, OR 97333. area) and overall gradient (as measured from 6-1 topographic maps). The relationships of spe- scales the sampling reach length and resolu- cific physical habitat measurements described tion in proportion to stream size. It also al- in this EMAP-SW field manual to these seven lows statistical and series analyses of the data attributes are discussed by Kaufmann (1993). that are not possible under other designs. We Aquatic macrophytes, riparian vegetation, and strive to make the protocol objective and re- large woody debris are included in this and peatable by using easily learned, repeatable other physical habitat assessments because of measures of physical habitat in place of esti- their role in modifying habitat structure and mation techniques wherever possible. Where light inputs, even though they are actually bio- estimation is employed, we direct the sam- logical measures. The field physical habitat pling crew to estimate attributes that are oth- measurements from this field habitat charac- erwise measurable, rather than estimating the terization are used in the context of water quality or importance of the attribute to biota chemistry, temperature, and other data sources or its importance as an indicator of distur- (e.g., remote sensing of basin land use and bance. We have included the more traditional land cover). The combined data analyses will visual classification of channel unit scale habi- more comprehensively describe additional tat types because they have been useful in habitat attributes and larger scales of physical past studies and enhance comparability with habitat or human disturbance than are evalu- other work. ated by the field assessment alone. The time commitment to gain repeatabil- This protocol is intended for evaluating ity and precision is greater than that required physical habitat in non-wadeable streams and for more qualitative methods. In our field tri- rivers. Kaufmann and Robison (1998) de- als, two people typically complete the speci- scribe other methods for use in smaller, wade- fied channel, riparian, and discharge measure- able streams. Like the methods for wadeable ments in about three hours of field time. streams, these methods are most efficient dur- However, the time required can vary consid- ing low flow conditions and when leaves are erably with channel characteristics, flow con- on terrestrial vegetation, but may be applied ditions, and the location of boat launching during other seasons and higher flows except areas. as limited by safety considerations. It is de- The protocol defines the length of each signed for monitoring applications where ro- sampling reach proportional to river wetted bust, quantitative descriptions of reach-scale width and then systematically places measure- habitat are desired, but time is limited. ments to statistically represent the entire reach. Like the wadeable streams protocol Stream thalweg depth measurements, habitat (Kaufmann and Robison 1998) this habitat classification, and mid-channel substrate ob- characterization approach employs a random- servations are made at very tightly spaced in- ized, systematic spatial sampling design to tervals; whereas channel "littoral" and ripar- minimize bias in the placement and position- ian stations for measuring or observing ing of measurements. Measures are taken over substrate, fish cover, large woody debris, bank defined channel areas and these sampling ar- characteristics and riparian vegetation struc- eas or points are placed systematically at spac- ture are spaced further apart. The tightly ings that are proportional to baseflow chan- spaced depth measures allow calculation of nel width. This systematic sampling design indices of channel structural complexity, ob- 6-2 jective classification of channel units such as Mid-channel habitat measurements and pools, and quantification of residual pool observations are recorded on multiple pages depth, pool volume, and total stream volume. of the Thalweg Profile Form (Figure 6-3). Instructions for these mid-channel procedures 6.1 Components of the are given in section 6.5. Measurements made Field Habitat while anchored or tied up to the 11 littoral/ riparian plot stations ("transects") are recorded Assessment on 11 copies of the two sided Channel/Ri- parian Transect Form (Figures 6-4 and 6-5). Field data collection for the physical Instructions for these transect or littoral/ripar- habitat assessment is accomplished in a single ian assessment activities are discussed in sub- float down each river sample reach. Depend- section 6.6. ing on the survey region, river sample reach lengths are defined as either 40 or 100 times 6.2 Habitat Sampling the wetted width in the vicinity of the point of entry (Figure 6-1). In addition to physical Locations On The Study habitat assessment, the 2-person habitat team of the field crew collects chemical, Reach macroinvertebrate, and periphyton samples (if Measurements are made at two scales of applicable). They may also recon the chan- resolution along the mid-channel length of the nel if they precede the electrofishing boat down reach; the results are later aggregated and ex- the river. To characterize mid-channel habitat pressed for the entire reach, a third level of (Table 6-1), they measure a longitudinal thal- resolution (Figure 6-1). We want to assess weg (or mid-channel) depth profile, tally habitat and other river indices over river reach snags, classify channel habitat types, charac- lengths that are long enough to incorporate terize mid-channel substrate, and locate the the habitat variability due to river meander- 11 systematic transect locations for littoral/ri- ing and pool-riffle structure. To accommodate parian sampling and other habitat observations habitat variability in a way that adjusts for (Figures 6-1 and 6-2). At each of the 11 varying sizes of rivers, EMAP protocols marked reach transect locations (A-K), they specify sample reach lengths that are a mul- measure channel wetted width, bankfull chan- tiple of their average wetted width (40 or 100 nel dimensions, incision, channel constraint, Channel-Widths). Water velocity, habitat bearing and gradient; then assess near-shore, complexity, fish abundance, and species rich- shoreline, and riparian physical habitat char- ness may also affect capture efficiency and acteristics by measuring or observing littoral consequently the required sample reach depths, riparian canopy cover, substrate, large length. In the Oregon river pilot, it was found woody debris, fish cover, bank characteris- that 85 channel widths is adequate for Oregon tics, riparian vegetation, and evidence of hu- rivers (Hughes et al. In Review). In the Mid- man activities (Table 6-1). They also collect Atlantic region, river reaches of 40 channel benthic macroinvertebrates (Section 9), take widths long were used in order to make this benthic algal samples (if applicable), and aspect of field methods consistent between measure conductivity and water temperature wadeable and non-wadeable streams. For this using procedures described in section 5. field manual, we discuss the methods used to 6-3 Figure 6-1. River reach sample layout. 6-4 Table 6-1. Components of River Physical Habitat Protocol. 1. Thalweg Profile: At 10 equally spaced intervals between each of 11 channel cross-sections (100 along entire reach): * Classify habitat type, record presence of backwater and off-channel habitats. (10 between cross sections, 100 total) * Determine dominant substrate visually or using sounding rod. (10 between cross-sections, 100 total) At 20 equally spaced intervals (for 100 ChW reach) or 10 equally spaced intervals (for 40 ChW reach) between each of 11 channel cross-sections: * Tally mid-channel snags - 10 (or 20) between cross-sections, 100(or 200) total. * Measure thalweg (maximum) depth using Sonar or rod - 10 (or 20) between cross-sections, 100(or 200) total. 2. Littoral/Riparian Cross-Sections: @ 11 stops ("transects") at equal intervals along reach length: Measure/estimate from one chosen bank on 11 channel cross-sections: * Gradient (clinometer or Abney level) between
Load more

Recommended publications
  • 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]
  • 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]
  • 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]
  • Channel Aggradation by Beaver Dams on a Small Agricultural Stream in Eastern Nebraska
    University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln U.S. Department of Agriculture: Agricultural Publications from USDA-ARS / UNL Faculty Research Service, Lincoln, Nebraska 9-12-2004 Channel Aggradation by Beaver Dams on a Small Agricultural Stream in Eastern Nebraska M. C. McCullough University of Nebraska-Lincoln J. L. Harper University of Nebraska-Lincoln D. E. Eisenhauer University of Nebraska-Lincoln, [email protected] M. G. Dosskey USDA National Agroforestry Center, Lincoln, Nebraska, [email protected] Follow this and additional works at: https://digitalcommons.unl.edu/usdaarsfacpub Part of the Agricultural Science Commons McCullough, M. C.; Harper, J. L.; Eisenhauer, D. E.; and Dosskey, M. G., "Channel Aggradation by Beaver Dams on a Small Agricultural Stream in Eastern Nebraska" (2004). Publications from USDA-ARS / UNL Faculty. 147. https://digitalcommons.unl.edu/usdaarsfacpub/147 This Article is brought to you for free and open access by the U.S. Department of Agriculture: Agricultural Research Service, Lincoln, Nebraska at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Publications from USDA-ARS / UNL Faculty by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. This is not a peer-reviewed article. Self-Sustaining Solutions for Streams, Wetlands, and Watersheds, Proceedings of the 12-15 September 2004 Conference (St. Paul, Minnesota USA) Publication Date 12 September 2004 ASAE Publication Number 701P0904. Ed. J. L. D'Ambrosio Channel Aggradation by Beaver Dams on a Small Agricultural Stream in Eastern Nebraska M. C. McCullough1, J. L. Harper2, D.E. Eisenhauer3, M. G. Dosskey4 ABSTRACT We assessed the effect of beaver dams on channel gradation of an incised stream in an agricultural area of eastern Nebraska.
    [Show full text]
  • Seasonal Controls on Meteoric 7Be in Coarse‐Grained River Channels
    HYDROLOGICAL PROCESSES Hydrol. Process. 28, 2738–2748 (2014) Published online 24 April 2013 in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/hyp.9800 Seasonal controls on meteoric 7Be in coarse-grained river channels James M. Kaste,1* Francis J. Magilligan,2 Carl E. Renshaw,2 G. Burch Fisher3 and W. Brian Dade2 1 Geology Department, The College of William & Mary, Williamsburg, VA, 23187, USA 2 Department of Earth Sciences, Dartmouth College, Hanover, NH, 03755, USA 3 Department of Earth Science, University of California, Santa Barbara, CA, 93106, USA Abstract: Cosmogenic 7Be is a natural tracer of short-term hydrological processes, but its distribution in upland fluvial environments over different temporal and spatial scales has not been well described. We measured 7Be in 450 sediment samples collected from perennial channels draining the middle of the Connecticut River Basin, an environment that is predominantly well-sorted sand. By sampling tributaries that have natural and managed fluctuations in discharge, we find that the 7Be activity in thalweg sediments is not necessarily limited by the supply of new or fine-grained sediment, but is controlled seasonally by atmospheric flux variations and the magnitude and frequency of bed mobilizing events. In late winter, 7Be concentrations in transitional bedload are lowest, typically 1 to 3 Bq kgÀ1 as 7Be is lost from watersheds via radioactive decay in the snowpack. In mid- summer, however, 7Be concentrations are at least twice as high because of increased convective storm activity which delivers high 7Be fluxes directly to the fluvial system. A mixed layer of sediment at least 8 cm thick is maintained for months in channels during persistent low rainfall and flow conditions, indicating that stationary sediments can be recharged with 7Be.
    [Show full text]
  • Introduction to Morphodynamics of Sedimentary Patterns
    MORPHODYNAMICS OF SEDIMENTARY PATTERNS Paolo Blondeaux, Marco Colombini, Giovanni Seminara, Giovanna Vittori Introduction to Morphodynamics of Sedimentary Patterns DIDATTICARICERCA RICERCA Genova University Press Monograph Series Morphodynamics of Sedimentary Patterns Editorial Board: Paolo Blondeaux, Marco Colombini Giovanni Seminara, Giovanna Vittori Advisory Board: Sivaramakrishnan Balachandar (University of Florida U.S.A.) Maurizio Brocchini (Università Politecnica delle Marche, Italy) François Charru (Université Paul Sabatier, France) Giovanni Coco (University of Auckland, New Zealand) Enrico Foti (Università di Catania, Italy) Marcelo H. Garcia (University of Illinois, U.S.A.) Suzanne J.M.H. Hulscher (University of Twente, NL) Stefano Lanzoni (Università di Padova, Italy) Miguel A. Losada (University of Granada, Spain) Chris Paola (University of Minnesota, U.S.A.) Gary Parker (University of Illinois U.S.A.) Luca Ridolfi(Politecnico di Torino, Italy) Andrea Rinaldo (École Polytechnique Fédérale de Lausanne, Switzerland) Yasuyuki Shimizu (Hokkaido University, Japan) Marco Tubino (Università di Trento, Italy) Markus Uhlmann (Karlsruhe Institute of Technology, Germany) Introduction to Morphodynamics of Sedimentary Patterns Paolo Blondeaux, Marco Colombini, Giovanni Seminara, Giovanna Vittori Introduction to Morphodynamics of Sedimentary Patterns is the bookmark of the University of Genoa On the cover: The delta of Lena river (Russia). The image was taken on July 27, 2000 by the Landsat 7 satellite operated by the U.S. Geological Survey and NASA (false-color composite image made using shortwave infrared, infrared, and red wavelengths). Image credit: NASA This book has been object of a double peer-review according with UPI rules. Publisher GENOVA UNIVERSITY PRESS Piazza della Nunziata, 6 16124 Genova Tel. 010 20951558 Fax 010 20951552 e-mail: [email protected] e-mail: [email protected] http://gup.unige.it/ The authors are at disposal for any eventual rights about published images.
    [Show full text]
  • Channel Aggradation by Beaver Darns on a Small Agricultural Stream In
    /'/ ,L. 8'-- Channel Aggradation by Beaver Darns on a Small Agricultural Stream in. Eastern Nebraska 41. C. ~e~ullou~h',J. L. 33arperz,D.E. ~isenbauer',41. G.~osske~' MSTUCT We assessed the effect of beaver dams on channel gadation of an incised stream in an agricultural area of eastern Nebraska. A topogaphic survey was conducted of a reach of Little hluddy Creek where beaver are known to have been building dams for twelve years. Results indicate that over this time period the thalweg elevation has aggraded an average of 0.65 m by trapping 1730 t of sediment in the pools behd dams. Beaver may provide a feasible solution to channel depradation problems in this region. =WORDS. Beaver dams, channel aggradation, sediment, agricultural watershed. In eastern Nebraska, most land, which at one time was tallgrass prairie, has been converted to agricultural land use. This conversion has impacted stream channels both directly and indirectly. One major impact of row-crop agriculture is the increase in overland runoff and peak flows in channels. Between 1904 and 19 15 many stream channels in southeastern Hebraska were dredged and straightened (Wahl and Weiss 19881, resulting in shorter and steeper channels. These changes have resulted in severe channel incision and stream bank instability in eastern Nebraska and throughout the deep loess regions of the central Tjniied States (Lohnes 1997). This trend towards continued channel degradation continues to this day (Zellars and Hotc~ss1997), creating environmental and economic concerns. Beaver aEect geomorphology of streams in ways that may counteract channel degrading processes. Beaver dams reduce stream velocities, causing the rate of sediment deposition to increase behind the dam (Naiman et al.
    [Show full text]
  • 3.3 River Morphology
    NATURAL HERITAGE 159 3.3 River Morphology The Ottawa River environment changes constantly. Rivers can be divided into three zones: the headwater stream zone, middle‐order zone and lowland zone. The Ottawa River displays characteristics of each of these zones. Along its path, the river alternates between rapids, lakes, shallow bays, and quiet stretches. More than 80 tributaries contribute their water to the river’s force. As a tributary itself, the Ottawa River meets the St. Lawrence River at its southern end. The numerous dams along the Ottawa River affect the duration, frequency, timing and rate of the natural water flow. 3.3.1 Channel Pattern Because water will always travel in the path of least resistance, a river’s channel pattern, or map view, is a response to the physiographic features of the area. The channel pattern of a river can take many forms. Kellerhals et al (1976) suggest classifying channel patterns into six categories: straight, sinuous, irregular (wandering), irregular meanders, regular meanders, and tortuous meanders. Overall, the Ottawa River is a constrained, straight river that has been highly altered. The river is said to be constrained because it exists within a valley, although a flood plain exists on the Ontario shore of the river and on parts of the Quebec shore. For the most part there is a main river channel lacking the sinuosity generally observed in unconstrained rivers. Figure 3.25 Main River Channel of the Ottawa Source: Christian Voilemont NATURAL HERITAGE 160 Figure 3.26 Ottawa River Watershed Source : Jan Aylsworth 3.3.2 Landforms and Depositional Forms Material that is transported down a river can be deposited temporarily and then reactivated as the channel shifts, creating transient landforms.
    [Show full text]
  • Chapter 5: Scaling a Supply Limited Sediment System: Grand Canyon Sediment Sources, Processes, and Management
    Chapter 5: Scaling a Supply Limited Sediment System: Grand Canyon Sediment Sources, Processes, and Management Stanford Gibson INTRODUCTION Dams affect fluvial sediment transport in dramatic but complicated ways. They cut off the main stem sediment supply and flatten the flow regime; trading seasonal extreme high and low flows for a pulsing flow regime dominated by moderate magnitude flows (See Burley this volume). River morphology, recreation, and ecology in the Grand Canyon are all directly connected to the sediment response to the Glen Canyon Dam. Sediment retention in the Canyon is also the primary first-order goal of recent controversial (and costly) management experiments (See Burley in this Volume). In order to understand sediment dynamics in this system and how these processes affect the other physical and biological processes represented in this volume it will be helpful to address three big sediment questions: 1. Where does the sediment come from? (the load question) 2. How does sediment move through the system? (the capacity and process question) and 3. How do these considerations affect management decisions and HFEs? (the management question) 1. WHERE DOES THE SEDIMENT COME FROM? The first step in building a conceptual model of a sediment system is to carefully estimate the mass balance (mass inflows, outflows, and internal sinks). Computing a ‘sediment budget’ begins with identifying and quantifying sources (Figure 1). Before the dam approximately 77-82% of the sediment (60-66 MT/y) came from the Colorado River watershed upstream of the dam site and 14 to 16% came from the two major tributaries (about 2.6 MT/y from the Paria1 and ~9.3 T/y from the Little Colorado).
    [Show full text]
  • 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.
    [Show full text]
  • Channel Morphology of the Shag River, North Otago 2
    Channel morphology of the Shag River, North Otago Channel Morphology of the Shag River, North Otago 2 Otago Regional Council Private Bag 1954, Dunedin 9054 70 Stafford Street, Dunedin 9016 Phone 03 474 0827 Fax 03 479 0015 Freephone 0800 474 082 www.orc.govt.nz © Copyright for this publication is held by the Otago Regional Council. This publication may be reproduced in whole or in part provided the source is fully and clearly acknowledged. ISBN: 978-0-478-37692-0 Report writer: Jacob Williams, Natural Hazards Analyst Reviewed by: Michael Goldsmith, Manager Natural Hazards Published September 2014 3 Channel Morphology of the Shag River, North Otago Technical summary Changes in the channel morphology of the Shag River/Waihemo have been assessed using visual inspections, aerial and ground photography, and cross-section data collected in April 2009 and October 2013. This assessment provides an update on changes in channel morphology that have occurred since the last catchment-wide analysis of long term trends in 2009. This report describes the nature of those changes where they have been significant and is intended to inform decisions relating to the management of the Shag River/Waihemo, including gravel extraction, floodwater conveyance, and asset management. Cross-section analysis of the Shag River/Waihemo indicates that between April 2009 and October 2013 there was an overall increase in mean bed level (MBL) at 16 of the 22 surveyed cross-sections (as shown on Figure 5), and a decrease in MBL at 6 cross-sections. This indicates that (in the short term) the Shag River/Waihemo is showing signs of changing from a state of overall degradation (as described in the previous analysis of channel morphology in 2009) to one of aggradation/stability.
    [Show full text]
  • Three Dimensional Mobile Bed Dynamics for Sediment Transport Modeling
    THREE DIMENSIONAL MOBILE BED DYNAMICS FOR SEDIMENT TRANSPORT MODELING DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Sean O’Neil, B.S., M.S. ***** The Ohio State University 2002 Dissertation Committee: Approved by Professor Keith W. Bedford, Adviser Professor Carolyn J. Merry Adviser Professor Diane L. Foster Civil Engineering Graduate Program c Copyright by Sean O’Neil 2002 ABSTRACT The transport and fate of suspended sediments continues to be critical to the understand- ing of environmental water quality issues within surface waters. Many contaminants of environmental concern within marine and freshwater systems are hydrophobic, thus read- ily adsorbed to bed material or suspended particles. Additionally, management strategies for evaluating and remediating the effects of dredging operations or marine construction, as well as legacy pollution from military and industrial processes requires knowledge of sediment-water interactions. The dynamic properties within the bed, the bed-water column inter-exchange and the transport properties of the flowing water is a multi-scale nonlin- ear problem for which the mobile bed dynamics with consolidation (MBDC) model was formulated. A new continuum-based consolidation model for a saturated sediment bed has been developed and verified on a stand-alone basis. The model solves the one-dimensional, vertical, nonlinear Gibson equation describing finite-strain, primary consolidation for satu- rated fine sediments. The consolidation problem is a moving boundary value problem, and has been coupled with a mobile bed model that solves for bed level variations and grain size fraction(s) in time within a thin layer at the bed surface.
    [Show full text]