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Nanopatterning Hexagonal Boron Nitride with Helium Ion Milling: Towards Atomically-Thin, Nanostructured Insulators
- S. Matt Gilbert, Stanley Liu, Gabe Schumm, Alex Zettl
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- MRS Advances / Volume 3 / Issue 6-7 / 2018
- Published online by Cambridge University Press:
- 01 February 2018, pp. 327-331
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- 2018
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In this report, we demonstrate the use of helium ion milling for the controllable fabrication of nanostructures in few-layer hexagonal boron nitride (h-BN). Using the direct-write lithographic capabilities of a scanning helium ion microscope (HIM), nanopores with diameters as small as 4 nm and nanoribbons with widths of 3 – 10 nm are etched from suspended h-BN sheets. This ability to pattern h-BN sheets with high-throughput and sub-10 nm precision paves the way for future studies that make use of atomically-thin, nanostructured insulators such as those needed for nanopore sequencing and patterned van der Waals heterostructures.
Gradational Thresholds and Landform Singularity: Significance for Quaternary Studies
- Ze'ev B. Begin, Stanley A. Schumm
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- Quaternary Research / Volume 21 / Issue 3 / May 1984
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- 20 January 2017, pp. 267-274
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Geomorphic threshold conditions have been identifed at which stream patterns change and gully initiation occurs. For both, the threshold conditions are defined by the parameter of “relative shear stress” which is a measure of the energy state of the system and is based on known values of stream slope and mean annual discharge (for patterns) or drainage area (for gullies). The probability of passing from a stream pattern to another, or from stable to gullied valley floors, is a smooth function of relative shear stress and so the thresholds separating the different states of the geomorphic systems are gradational. The singularity of landforms prevents the identification of a sharp threshold, and as a result landform sensitivity will differ within the same area and under the same conditions. Therefore, geomorphic predictions and postdictions will be uncertain, and Quaternary correlations will lack precision.
Ephemeral-Stream Processes: Implications for Studies of Quaternary Valley Fills
- Peter C. Patton, Stanley A. Schumm
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- Quaternary Research / Volume 15 / Issue 1 / January 1981
- Published online by Cambridge University Press:
- 20 January 2017, pp. 24-43
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Three unstable ephemeral-stream channels (arroyos), which drain source areas that have high sediment yields ranging from predominantly sand (Arroyo Calabasas) to a mixture of sand, silt, and clay (Sand Creek) to largely silt and clay (Sage Creek), were resurveyed to provide data on the rates and mechanics of erosion and sedimentation processes during periods ranging from 14 to 22 yr. Channel morphology changed significantly. Erosion occurred through nickpoint recession and bank collapse, but erosional reaches are separated by aggrading or stable-channel reaches. In general, sediment that is eroded, as the nickpoint recedes upstream, is trapped in the widened channel downstream. In this manner sediment is transported episodically out of these basins during a series of cut-and-fill cycles. The manner by which the channels aggrade and the morphology of the aggraded stable channels are controlled by the sediment type. The wide and shallow channel of Arroyo Calabasas is filled by vertical accretion of sand-size sediment. The narrow and deep channels of Sage Creek and Sand Creek are created by the lateral accretion of cohesive fine-grained sediment. The channel modification and the cut-and-fill episodes are dependent on high sediment yields, and therefore they are independent of subtle climatic shifts. Cut-and-fill deposits that have been created in this manner should not be equivalent in age from basin to basin, and therefore channel trenching and filling in the semiarid western United States during the Holocene need not be synchronous.
Contributors
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- By Mitchell Aboulafia, Frederick Adams, Marilyn McCord Adams, Robert M. Adams, Laird Addis, James W. Allard, David Allison, William P. Alston, Karl Ameriks, C. Anthony Anderson, David Leech Anderson, Lanier Anderson, Roger Ariew, David Armstrong, Denis G. Arnold, E. J. Ashworth, Margaret Atherton, Robin Attfield, Bruce Aune, Edward Wilson Averill, Jody Azzouni, Kent Bach, Andrew Bailey, Lynne Rudder Baker, Thomas R. Baldwin, Jon Barwise, George Bealer, William Bechtel, Lawrence C. Becker, Mark A. Bedau, Ernst Behler, José A. Benardete, Ermanno Bencivenga, Jan Berg, Michael Bergmann, Robert L. Bernasconi, Sven Bernecker, Bernard Berofsky, Rod Bertolet, Charles J. Beyer, Christian Beyer, Joseph Bien, Joseph Bien, Peg Birmingham, Ivan Boh, James Bohman, Daniel Bonevac, Laurence BonJour, William J. Bouwsma, Raymond D. Bradley, Myles Brand, Richard B. Brandt, Michael E. Bratman, Stephen E. Braude, Daniel Breazeale, Angela Breitenbach, Jason Bridges, David O. Brink, Gordon G. Brittan, Justin Broackes, Dan W. Brock, Aaron Bronfman, Jeffrey E. Brower, Bartosz Brozek, Anthony Brueckner, Jeffrey Bub, Lara Buchak, Otavio Bueno, Ann E. Bumpus, Robert W. Burch, John Burgess, Arthur W. Burks, Panayot Butchvarov, Robert E. Butts, Marina Bykova, Patrick Byrne, David Carr, Noël Carroll, Edward S. Casey, Victor Caston, Victor Caston, Albert Casullo, Robert L. Causey, Alan K. L. Chan, Ruth Chang, Deen K. Chatterjee, Andrew Chignell, Roderick M. Chisholm, Kelly J. Clark, E. J. Coffman, Robin Collins, Brian P. Copenhaver, John Corcoran, John Cottingham, Roger Crisp, Frederick J. Crosson, Antonio S. Cua, Phillip D. Cummins, Martin Curd, Adam Cureton, Andrew Cutrofello, Stephen Darwall, Paul Sheldon Davies, Wayne A. Davis, Timothy Joseph Day, Claudio de Almeida, Mario De Caro, Mario De Caro, John Deigh, C. F. Delaney, Daniel C. Dennett, Michael R. DePaul, Michael Detlefsen, Daniel Trent Devereux, Philip E. Devine, John M. Dillon, Martin C. Dillon, Robert DiSalle, Mary Domski, Alan Donagan, Paul Draper, Fred Dretske, Mircea Dumitru, Wilhelm Dupré, Gerald Dworkin, John Earman, Ellery Eells, Catherine Z. Elgin, Berent Enç, Ronald P. Endicott, Edward Erwin, John Etchemendy, C. Stephen Evans, Susan L. Feagin, Solomon Feferman, Richard Feldman, Arthur Fine, Maurice A. Finocchiaro, William FitzPatrick, Richard E. Flathman, Gvozden Flego, Richard Foley, Graeme Forbes, Rainer Forst, Malcolm R. Forster, Daniel Fouke, Patrick Francken, Samuel Freeman, Elizabeth Fricker, Miranda Fricker, Michael Friedman, Michael Fuerstein, Richard A. Fumerton, Alan Gabbey, Pieranna Garavaso, Daniel Garber, Jorge L. A. Garcia, Robert K. Garcia, Don Garrett, Philip Gasper, Gerald Gaus, Berys Gaut, Bernard Gert, Roger F. Gibson, Cody Gilmore, Carl Ginet, Alan H. Goldman, Alvin I. Goldman, Alfonso Gömez-Lobo, Lenn E. Goodman, Robert M. Gordon, Stefan Gosepath, Jorge J. E. Gracia, Daniel W. Graham, George A. Graham, Peter J. Graham, Richard E. Grandy, I. Grattan-Guinness, John Greco, Philip T. Grier, Nicholas Griffin, Nicholas Griffin, David A. Griffiths, Paul J. Griffiths, Stephen R. Grimm, Charles L. Griswold, Charles B. Guignon, Pete A. Y. Gunter, Dimitri Gutas, Gary Gutting, Paul Guyer, Kwame Gyekye, Oscar A. Haac, Raul Hakli, Raul Hakli, Michael Hallett, Edward C. Halper, Jean Hampton, R. James Hankinson, K. R. Hanley, Russell Hardin, Robert M. Harnish, William Harper, David Harrah, Kevin Hart, Ali Hasan, William Hasker, John Haugeland, Roger Hausheer, William Heald, Peter Heath, Richard Heck, John F. Heil, Vincent F. Hendricks, Stephen Hetherington, Francis Heylighen, Kathleen Marie Higgins, Risto Hilpinen, Harold T. Hodes, Joshua Hoffman, Alan Holland, Robert L. Holmes, Richard Holton, Brad W. Hooker, Terence E. Horgan, Tamara Horowitz, Paul Horwich, Vittorio Hösle, Paul Hoβfeld, Daniel Howard-Snyder, Frances Howard-Snyder, Anne Hudson, Deal W. Hudson, Carl A. Huffman, David L. Hull, Patricia Huntington, Thomas Hurka, Paul Hurley, Rosalind Hursthouse, Guillermo Hurtado, Ronald E. Hustwit, Sarah Hutton, Jonathan Jenkins Ichikawa, Harry A. Ide, David Ingram, Philip J. Ivanhoe, Alfred L. Ivry, Frank Jackson, Dale Jacquette, Joseph Jedwab, Richard Jeffrey, David Alan Johnson, Edward Johnson, Mark D. Jordan, Richard Joyce, Hwa Yol Jung, Robert Hillary Kane, Tomis Kapitan, Jacquelyn Ann K. Kegley, James A. Keller, Ralph Kennedy, Sergei Khoruzhii, Jaegwon Kim, Yersu Kim, Nathan L. King, Patricia Kitcher, Peter D. Klein, E. D. Klemke, Virginia Klenk, George L. Kline, Christian Klotz, Simo Knuuttila, Joseph J. Kockelmans, Konstantin Kolenda, Sebastian Tomasz Kołodziejczyk, Isaac Kramnick, Richard Kraut, Fred Kroon, Manfred Kuehn, Steven T. Kuhn, Henry E. Kyburg, John Lachs, Jennifer Lackey, Stephen E. Lahey, Andrea Lavazza, Thomas H. Leahey, Joo Heung Lee, Keith Lehrer, Dorothy Leland, Noah M. Lemos, Ernest LePore, Sarah-Jane Leslie, Isaac Levi, Andrew Levine, Alan E. Lewis, Daniel E. Little, Shu-hsien Liu, Shu-hsien Liu, Alan K. L. Chan, Brian Loar, Lawrence B. Lombard, John Longeway, Dominic McIver Lopes, Michael J. Loux, E. J. Lowe, Steven Luper, Eugene C. Luschei, William G. Lycan, David Lyons, David Macarthur, Danielle Macbeth, Scott MacDonald, Jacob L. Mackey, Louis H. Mackey, Penelope Mackie, Edward H. Madden, Penelope Maddy, G. B. Madison, Bernd Magnus, Pekka Mäkelä, Rudolf A. Makkreel, David Manley, William E. Mann (W.E.M.), Vladimir Marchenkov, Peter Markie, Jean-Pierre Marquis, Ausonio Marras, Mike W. Martin, A. P. Martinich, William L. McBride, David McCabe, Storrs McCall, Hugh J. McCann, Robert N. McCauley, John J. McDermott, Sarah McGrath, Ralph McInerny, Daniel J. McKaughan, Thomas McKay, Michael McKinsey, Brian P. McLaughlin, Ernan McMullin, Anthonie Meijers, Jack W. Meiland, William Jason Melanson, Alfred R. Mele, Joseph R. Mendola, Christopher Menzel, Michael J. Meyer, Christian B. Miller, David W. Miller, Peter Millican, Robert N. Minor, Phillip Mitsis, James A. Montmarquet, Michael S. Moore, Tim Moore, Benjamin Morison, Donald R. Morrison, Stephen J. Morse, Paul K. Moser, Alexander P. D. Mourelatos, Ian Mueller, James Bernard Murphy, Mark C. Murphy, Steven Nadler, Jan Narveson, Alan Nelson, Jerome Neu, Samuel Newlands, Kai Nielsen, Ilkka Niiniluoto, Carlos G. Noreña, Calvin G. Normore, David Fate Norton, Nikolaj Nottelmann, Donald Nute, David S. Oderberg, Steve Odin, Michael O’Rourke, Willard G. Oxtoby, Heinz Paetzold, George S. Pappas, Anthony J. Parel, Lydia Patton, R. P. Peerenboom, Francis Jeffry Pelletier, Adriaan T. Peperzak, Derk Pereboom, Jaroslav Peregrin, Glen Pettigrove, Philip Pettit, Edmund L. Pincoffs, Andrew Pinsent, Robert B. Pippin, Alvin Plantinga, Louis P. Pojman, Richard H. Popkin, John F. Post, Carl J. Posy, William J. Prior, Richard Purtill, Michael Quante, Philip L. Quinn, Philip L. Quinn, Elizabeth S. Radcliffe, Diana Raffman, Gerard Raulet, Stephen L. Read, Andrews Reath, Andrew Reisner, Nicholas Rescher, Henry S. Richardson, Robert C. Richardson, Thomas Ricketts, Wayne D. Riggs, Mark Roberts, Robert C. Roberts, Luke Robinson, Alexander Rosenberg, Gary Rosenkranz, Bernice Glatzer Rosenthal, Adina L. Roskies, William L. Rowe, T. M. Rudavsky, Michael Ruse, Bruce Russell, Lilly-Marlene Russow, Dan Ryder, R. M. Sainsbury, Joseph Salerno, Nathan Salmon, Wesley C. Salmon, Constantine Sandis, David H. Sanford, Marco Santambrogio, David Sapire, Ruth A. Saunders, Geoffrey Sayre-McCord, Charles Sayward, James P. Scanlan, Richard Schacht, Tamar Schapiro, Frederick F. Schmitt, Jerome B. Schneewind, Calvin O. Schrag, Alan D. Schrift, George F. Schumm, Jean-Loup Seban, David N. Sedley, Kenneth Seeskin, Krister Segerberg, Charlene Haddock Seigfried, Dennis M. Senchuk, James F. Sennett, William Lad Sessions, Stewart Shapiro, Tommie Shelby, Donald W. Sherburne, Christopher Shields, Roger A. Shiner, Sydney Shoemaker, Robert K. Shope, Kwong-loi Shun, Wilfried Sieg, A. John Simmons, Robert L. Simon, Marcus G. Singer, Georgette Sinkler, Walter Sinnott-Armstrong, Matti T. Sintonen, Lawrence Sklar, Brian Skyrms, Robert C. Sleigh, Michael Anthony Slote, Hans Sluga, Barry Smith, Michael Smith, Robin Smith, Robert Sokolowski, Robert C. Solomon, Marta Soniewicka, Philip Soper, Ernest Sosa, Nicholas Southwood, Paul Vincent Spade, T. L. S. Sprigge, Eric O. Springsted, George J. Stack, Rebecca Stangl, Jason Stanley, Florian Steinberger, Sören Stenlund, Christopher Stephens, James P. Sterba, Josef Stern, Matthias Steup, M. A. Stewart, Leopold Stubenberg, Edith Dudley Sulla, Frederick Suppe, Jere Paul Surber, David George Sussman, Sigrún Svavarsdóttir, Zeno G. Swijtink, Richard Swinburne, Charles C. Taliaferro, Robert B. Talisse, John Tasioulas, Paul Teller, Larry S. Temkin, Mark Textor, H. S. Thayer, Peter Thielke, Alan Thomas, Amie L. Thomasson, Katherine Thomson-Jones, Joshua C. Thurow, Vzalerie Tiberius, Terrence N. Tice, Paul Tidman, Mark C. Timmons, William Tolhurst, James E. Tomberlin, Rosemarie Tong, Lawrence Torcello, Kelly Trogdon, J. D. Trout, Robert E. Tully, Raimo Tuomela, John Turri, Martin M. Tweedale, Thomas Uebel, Jennifer Uleman, James Van Cleve, Harry van der Linden, Peter van Inwagen, Bryan W. Van Norden, René van Woudenberg, Donald Phillip Verene, Samantha Vice, Thomas Vinci, Donald Wayne Viney, Barbara Von Eckardt, Peter B. M. Vranas, Steven J. Wagner, William J. Wainwright, Paul E. Walker, Robert E. Wall, Craig Walton, Douglas Walton, Eric Watkins, Richard A. Watson, Michael V. Wedin, Rudolph H. Weingartner, Paul Weirich, Paul J. Weithman, Carl Wellman, Howard Wettstein, Samuel C. Wheeler, Stephen A. White, Jennifer Whiting, Edward R. Wierenga, Michael Williams, Fred Wilson, W. Kent Wilson, Kenneth P. Winkler, John F. Wippel, Jan Woleński, Allan B. Wolter, Nicholas P. Wolterstorff, Rega Wood, W. Jay Wood, Paul Woodruff, Alison Wylie, Gideon Yaffe, Takashi Yagisawa, Yutaka Yamamoto, Keith E. Yandell, Xiaomei Yang, Dean Zimmerman, Günter Zoller, Catherine Zuckert, Michael Zuckert, Jack A. Zupko (J.A.Z.)
- Edited by Robert Audi, University of Notre Dame, Indiana
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- The Cambridge Dictionary of Philosophy
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- 05 August 2015
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- 27 April 2015, pp ix-xxx
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Chapter 20 - River impact on ancient civilizations: a hypothesis
- Stanley A. Schumm, Colorado State University
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- River Variability and Complexity
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- 05 June 2012
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- 05 May 2005, pp 182-197
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Summary
Rivers comprise only a small part of a landscape, but much of the energy of the landscape is concentrated in the river channel, which often creates hazardous conditions for humans and vast floods along the world's great rivers create creation myths and misery. Rivers form boundaries between riparian properties, between states, and between nations. They shift and create international problems as along the Rio Grande border between the USA and Mexico. They provide routes for exploration, as in the opening of western U.S. The route down the Ohio, up the middle Mississippi, and up the Missouri let Louis and Clark finally reach the Pacific Ocean, after crossing the Bitterroot Mountains and continuing down the Snake and Columbia rivers. Exploration of Africa was primarily along the Nile, Niger, Congo, and Zambezi rivers.
Dwellers along great rivers could hardly not be influenced by behavior that ranged from relatively benign to dynamic. For example, river instability, as discussed in the previous chapters, could create environmental conditions leading to uncertainty for the riparian dweller. Diamond (1999) demonstrates the effect of environmental conditions on diverse human groups, and it may not be too problematic to suggest that river type may in the past have had major impacts on human perspectives. For example, if one river is stable and another subject to shift and avulsion, would not the perceptions of the two populations be different? For example, Macaulay in 1838 (Schama, 1995) commented on supposed affinities between French rivers and people.
Part II - Upstream controls
- Stanley A. Schumm, Colorado State University
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- River Variability and Complexity
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- 05 May 2005, pp 37-38
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Summary
Upstream controls affect the type of river that exists downstream (Figure 1.2). They are the quantity and type of discharge and sediment load that is delivered downstream which, of course, reflects history and determines the morphology and dynamics of the downstream river.
Frontmatter
- Stanley A. Schumm, Colorado State University
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- River Variability and Complexity
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References
- Stanley A. Schumm, Colorado State University
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- River Variability and Complexity
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Chapter 4 - History
- Stanley A. Schumm, Colorado State University
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- River Variability and Complexity
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It may be difficult to view history as an upstream control (Figure 1.2, but changing relief, and climate through time, should have the greatest effect on upstream high relief areas, thereby increasing the impact downstream, as the delivery of water and sediment from upstream causes a downstream channel response.
The Davis cycle of landscape change through time, which is based upon the assumption of rapid uplift and then tectonic stability, can be used to explain the variability of rivers in the context of geomorphic history. Assume an uplifted block with a well-defined drainage divide and base level, and flowing water that will initiate channel incision (Figure 4.1). One can envision a large river incising down the right side of the block with the tributary incising to keep pace. The longitudinal profile of the tributary will change (Figure 4.1), with regime developing only at about stage 7 and extending upstream at stages 8 and 9 (Schumm, 1956; Whipple et al., 2000.
The hypothetical cross-sections in Figure 4.2 reveal how the valley develops through time, and they also show how, with each increment of incision, the valley walls provide a significant yield of sediment to the channel, which probably is subjected to alternate periods of aggradation and degradation.
During stages 1–4 the channel is confined by bedrock valley walls. During stages 5–7 the channel is constrained by bedrock valley walls and terraces of older alluvium. During stages 8 and 9 the channels are in regime.
Part VI - Rivers and humans
- Stanley A. Schumm, Colorado State University
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- River Variability and Complexity
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Summary
The variability of rivers creates significant problems for humans, especially with regard to attempts to modify or control rivers. In addition, unintended consequences of human activities may have unfavorable results. Finally, very diverse rivers may determine the character of riparian civilizations.
Part III - Fixed local controls
- Stanley A. Schumm, Colorado State University
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- River Variability and Complexity
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Local controls can be fixed in position (Figure 1.2) by bedrock, resistant alluvium, tributaries and tectonic features.
Contents
- Stanley A. Schumm, Colorado State University
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- River Variability and Complexity
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Part V - Downstream controls
- Stanley A. Schumm, Colorado State University
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- River Variability and Complexity
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Summary
There is really only one downstream variable, and it is gradient change. However, the change occurs in four ways. A rise or a fall of base-level increases or decreases the gradient. The same impact on a channel occurs as the channel lengthens or shortens either naturally or by human influences.
River Variability and Complexity
- Stanley A. Schumm
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- 05 June 2012
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Rivers differ among themselves and through time. An individual river can vary significantly downstream, changing its dimensions and pattern dramatically over a short distance. If hydrology and hydraulics were the primary controls on the morphology and behaviour of large rivers, we would expect long reaches of rivers to maintain characteristic and relatively uniform morphologies. In fact, this is not the case - the variability of large rivers indicates that other important factors are involved. River Variability and Complexity presents an interesting approach to the understanding of river variability. It provides examples of river variability and explains the reasons for them, including fluvial response to human activities. Understanding the mechanisms of variability is important for geomorphologists, geologists, river engineers and sedimentologists as they attempt to interpret ancient fluvial deposits or anticipate river behaviour at different locations and through time. This book provides an excellent background for graduates, researchers and professionals.
Preface
- Stanley A. Schumm, Colorado State University
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- River Variability and Complexity
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The origin of this book was a project involving the geomorphic character of the lower Mississippi River and water-rights litigation between the Forest Service and the State of Colorado. The Mississippi River project revealed to me that large alluvial rivers can vary greatly in morphology downstream, although hydrologic conditions are not greatly different. This suggests that river-control works and activities such as dredging will influence a river differently depending upon channel variability and the diverse character of reaches. The water rights litigation confirmed that generalizations about rivers, such as hydraulic-geometry relations have limits depending upon scale.
It must be recognized that rivers differ among themselves, and through time, and one river can vary significantly in a downstream direction. If the morphology and behavior of large alluvial rivers are determined primarily by hydrology and hydraulics, long reaches of alluvial rivers should maintain a characteristic and relatively uniform morphology. In fact, this is not the case, and the variability of large alluvial rivers is an indication that hydraulics and hydrology are not always the dominant controls. Therefore, the purpose of this book is to present to the fluvial community examples of river variability and the reasons for them. The recognition that marked changes from one type of river or river pattern to another can occur is important for geomorphologists, river engineers, and stratigraphers.
Part IV - Variable local controls
- Stanley A. Schumm, Colorado State University
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- River Variability and Complexity
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Summary
In addition to fixed local controls there are local controls that are variable (Figure 1.2). That is, they shift position through time, as weather conditions generate local floods and vegetation changes. In addition, accidents such as log jams, fires, and landslides can occur at numerous locations within the drainage network.
Chapter 6 - Lithology
- Stanley A. Schumm, Colorado State University
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Lithology obviously affects runoff and sediment yield and therefore, it is an upstream control (Figure 1.2). For a given relief, sound rock will yield less sediment, but shattered rock will cause mass movement and the delivery of large quantities of sediment to the main streams. As considered previously, the type and amount of sediment delivered to a valley can determine the type of channel found there, as well as the variable morphology and behavior of the channel.
Schumm (1960, 1961) argued that, at least for sand-bed rivers, those draining from shale or siltstone areas will have a high percentage of silt and clay in banks and bed, and they will be narrow, deep and sinuous, whereas those draining from sandy and gravel areas will be wider and shallower, and relatively straight. A good example of this is provided by the Kansas River system in Colorado and Kansas.
The Kansas River (Figure 1.3) is formed where the Smoky Hill and Republican Rivers join in central Kansas. The Smoky Hill River in its headwaters drains sandy sediment, as does the Republican River. However, the Smoky Hill River is joined by two large tributaries, the Saline and Solomon Rivers that drain from Cretaceous shales. Moving downstream from a small upstream tributary of the Smoky Hill River (Figure 6.1, Site 32), the channel is very sandy (Sites 32–37) and width increases dramatically, but depth only doubles.
Chapter 1 - Introduction
- Stanley A. Schumm, Colorado State University
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Summary
Upon having some astronomical phenomena explained to him, Alfonso X, King of Castile and Leon (1252–84) exclaimed,
If the Lord Almighty had consulted me before embarking upon creation, I should have recommended something simpler
(Mackay, 1991)River engineers and geomorphologists might well have a similar opinion especially when it is recognized how variable a river can be through time and from reach to reach. However, when Leopold and Maddock published US Geological Survey Professional Paper 252 it was a landmark occasion. Geologists and geomorphologists suddenly became aware of order in rivers, although engineers with their regime equations had anticipated these hydraulic geometry relations. The hydraulic geometry relations of width, depth, and velocity were immediately of value in prediction of river characteristics. However, some of us neglected to recognize how variable the relations were and how significant was the scatter about the regression lines. This should have warned us that, yes, in a general sense channel width increased downstream as the 0.5 power of discharge, but a prediction of what the width was around the next bend could be in gross error, and, therefore recognizing this variability could be of considerable practical significance.
River characteristics vary sometimes little and sometimes greatly. Reaches are singular because of the numerous variables acting that prevent a single variable, discharge, from dominating river morphology and behavior. The question to be answered is why is one reach of a river connected to a different type of reach? That is, why can reaches be so different?
Chapter 18 - Applications
- Stanley A. Schumm, Colorado State University
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- River Variability and Complexity
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Summary
The previous discussions of river variability have applications to river management. The important concept is that river reaches vary in both location and through time. For example, an 11-mile (c. 17 km) reach of the Arkansas River (Figure 1.3) near Leadville, Colorado can be divided into eight reaches of different morphology. Gradient in this gravel-bed stream varies from 0.0067 to 0.011, sinuosity from 1.12 to 1.34, width from 60 to 110 feet (c. 18–33 m), calculated bankfull discharge from 330 to 1,060 cfs (c. 9–30 m3/s), and one reach is anastomosing. Any overall river modification or rehabilitation scheme would seem to fail because of the reach to reach variability of the river.
In order to prevent such problems, there are three concerns when undertaking practical work or, in fact, during any river investigation. These concerns are:
An investigation should always consider not only the site of interest, but upstream and downstream river reaches to determine if the reach of concern is representative of the river. That is, an investigator should back away from the specific problem site and view it in a broader context.
Rivers may range in sensitivity from very to not at all. An attempt should be made to evaluate river and reach sensitivity to determine if change is likely (Figure 11.2).
The multiple hypothesis approach should always be considered in an attempt to explain or anticipate river behavior. That is, the most obvious conclusion may be incorrect.
Concern 1: a broader perspective
A good example of Concern 1 was the problems associated with a bridge over the Cimarron River (Figure 1.3) near Perkins, Oklahoma (Keeley, 1971).
Chapter 10 - Tributaries
- Stanley A. Schumm, Colorado State University
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- River Variability and Complexity
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Summary
Tributaries are a natural component of a river system (Figure 1.2). If a tributary is small, its impact upon the main channel is small, perhaps causing some minor widening and deepening. However, if the tributary is steep or large it can have effects ranging from significant widening and deepening to metamorphosis, a complete change of channel character.
When a steep sediment-laden tributary joins a main stream, the impact can be substantial (Knighton, 1987). For example, most major rapids along 450 km of the Colorado River in the Grand Canyon (Dolan et al., 1978), are caused by the sediment discharge of steep tributaries that follow faults, normal to the river. Rice and Church (1998) have identified sedimentary links in Canadian gravel-bed rivers that are the result of tributary sediment contribution. These links are a channel reach between two tributaries. The result is a series of links that repeat as a sediment fining sequence. Each link contains sediment that fines downstream with a resulting decrease of gradient. This produces a concave profile segment resulting in a cuspate longitudinal profile.
Rutherfurd (2001) describes the major impact of tributaries on Glenelg River in Victoria, Australia, which has a drainage area of 12700 km2. The tributaries supply a very large sand load to the river, which may partly block the river at the tributary junctions (Figure 10.1) and form a back-water lake upstream of the obstruction. The reverse can occur when the main channel aggrades forming lakes in the tributaries (Knighton, 1989).