DOCSLIB.ORG

Base Level, Aggradation, and Grade

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Base Level, Aggradation, and Grade BASE LEVEL, AGGRADATION, AND GRADE LUNA B. LEOPOLD AND WILLIAM B. BULL Reprinted from PROCEEDINGSOF THE AMERICANPHILOSOPHICAL SOCIETY, Volume 123, No 2, April 1979 @DINGS of the ical Society Contents of olurne 123, Number 3 Variations in the Sun and Their Effects on Weather and Climate WALTERORR ROBERTS 151 Afro-American Biography : The Case of George Washington Williams JOI-IN HOPEFRANKLIN 160 Cultural and Social Background of the Rapid Modernization of Japan SANICI-IIROMIZUSHIMA 164 Base Level, Aggradation, and Grade LUNAB. LEOPOLD,WILLIAM B. BULL 168 Price for complete number $2.50 AMERICAN PHILOSOPHICAL SOCIETY INDEPENDENCESQUARE PHILADELPHIA, PA. 19106 BASE LEVEL, AGGRADATION, AND GRADE LUNA B. LEOPOLD Professor of Geology, University of California, Berkeley and WILLIAM B. BULL Professor of Geosciences, University of Arizona (Read April 20, 1978) GENERAL STATEMENT there is no long term change in climate or vegetation, and if the basin is not subjected to uplift or other JOHN WESLEYPOWELL introduced the term base eustatic movements, the river tends to attain an equ- level to specify the elevation below which a stream libriuni or graded coliclition characterized by a stable cannot downcut. Fluvial processes cease where a LGngitudinal profile neither raising or lowering in river flows into a large lake or tlie ocean, because the elevation. In each portion of river length that is in hydraulic gradient is reduced to zero and potential such equilibrium, the longitudinal profile of that por- energy is not further transfornied into kinetic energy. tion tends to be concave upward with gradient de- The ocean is regarded as a permanent hase level even creasing in the downstream direction. This flattening though sea level varies. of gradient is influenced by several factors but tht. Local base levels occur between the headwaters of principal cause is the downstream increase in dischargt. a stream and the ocean. For example, a resistant as tributaries enter. The concave upward longitudi- outcrop forms a local base lezwl because the stream nal stream profile is developed upstream from a base is unable to downcut through the outcrop as rapidly level or a local base level. This profile tends toward as through tlie materials upstream and downstream ‘such a shape that there is at each point along Its from it. Thus tlie resistant outcrop forms a relatively length a mutual adjustment among hydraulic factors stable reach to which the upstream portions of the which G. K. Gilbert referred to as “an equilibrium channel system flow until the outcrop is removed of action” (1880: 11. 107). by erosion or is buried by alluvium. Such local base William Morris Davis (1902 : 1). 107) proposed levels are regarded as being temporary when con- that tlie word “graded” be used specifically for the pared to the permanence of the oceans. Even more stream in which equilibrium is maintained and that temporary are the elevations of alluvial reaches of “degrading” and “aggrading” be restricted to cases streams, which also may be regarded as base levels. of the shifting equilibrium. J. Hoover Mackin ( 1948 : Each point along a stream, be it underlain by rock p. 478) stated that “ ‘degrading’ is downcuttitlg ap- or alluvium, is part of a continuum of elevations along proximately at grade” and that “ ‘aggrading’ is up- tlie streambed. Each streambed elevation partly de- building approximately at grade.” Mackin ( 1948 : p. termines the total relief (and therefore tlie slope of 471) defined grade as follows: the stream) for that part of the system upstream from the elevation. The graded stream is one in which, over a period of Elevations of points along a streambed may be years, slope is delicately adjusted to provide, with avail- able discharge and with prevailing channel characteristics, changed by the local base lezd processes of aggrada- just the velocity required for the transportation of the tion, degradation, and tectonic movements (B~ill. load supplied from the drainage basin. The graded 1973; Bull and McFadden, 1977). Variation of stream is a system in equilibrium; its diagnostic char- ocean or lake level is also a base level process. Al- acteristic is that any change in any of the controlling though base level processes nlay change streambed factors will cause a displacement of the equilibrium in a elevations along much of a stream system, base level direction that will tend to absorb the effect of the change. change generally is viewed as being a perturbation If the lower end of such an equilibrium profile is that occurs within a short reach, but which may affect raised or lowered by a rise or fall of the controlling tlie reaches upstream and downstream. Examples base level, it is generally supposed that given time would be the aggradation and degradatioli associated the whole profile will as a result tend to be raised with vertical fault rupture of a streambed, and the creation of natural or human-made dams. by deposition of sediment on the streambed or low- If, over a period of years, hydrologic conditions ered by erosion of the streambed. in other words in a river basin remain essentially constatlt, that is, by aggradation or degradation. VOL. 123, NO. 3, 19791 BASE LEVEL, AGGRADATION, AND GRADE 169 Mackin stated clearly how he conceived base level and the equilibrium profile to be related. A rise in base level is equivalent to the rising of a barrier across the path of the graded stream . the final readjusted profile will tend toward parallelism with the original profile . but because of secondary effects of aggradation . , precise parallelism will usually not be achieved (Mackin, 1948 : p. 496). Lowering of base level is, insofar as the response of the stream is con- cerned, essentially the same as the lowering of a barrier in its path. Downcutting must continue until slope is again completely adjusted to supply just the velocity required to transport all of the debris shed into the stream; as in the last case, and with the same qualifica- tions, the final adjusted profile will tend to parallel the original profile (Mackin, 1948: p. 498). This conclusion is inferred in part from the fact that in many river systems, stratigraphic and morpho- logic evidence shows that when a master stream aggraded, so also did entering tributaries. If a ter- race or level of an abandoned flood plain occurs along the valley sides of a master stream it is usual to see a similar terrace along the sides of tributary valleys and, at the junction of the valleys, the terraces are at the same elevation. FIG. 1. Aerial photograph of the Loop, an abandoned me- Similarly most tributaries enter the master stream ander, showing its relation to the present canyon of the at the elevation of the master stream and are said to San Juan River. be “graded to the master stream.” Only where a tributary is at its mouth traversing a resistant layer dation of valley fill alluvium during periods of un- of rock, or whose elevation’ was determined by some changing local base level. process operating in the past such as glacial action, By the analysis of field examples in which the sepa- does the tributary discharge over a waterfall into the ration of base level from basin changes can be made, master stream. Such “hanging valleys” are seen in we propose to draw some inferences that may clarify glaciated terrain and in deep gorges as in the Grand the relations between local base levels and base-level Canyon system. processes, and between a base-level change and the When a tributary meets the master stream at grade, longitudinal profile upstream. the usual case, it is not possible to say whether the effect of the master stream is felt far upstream or ALLUVIAL HISTORY OF A CHANNEL DURING merely a short distance. A rise or lowering of the SLOWLY LOWERING BASE LEVEL WHEN level of the master stream constitutes a base-level SEPARATED FROM THE MASTER STREAM change for the tributary. Therefore it cannot be The Loop of the San Juan River, Utah ascertained whether the observed change in the tribu- Preliininary remarks tary system was caused by change of base level or Rivers have a heritage but no beginning. Through by a combination of base-level change and concurrent geologic time even the first incipient channel system discharge-sediment relations affecting both tributary appearing on an emerging landmass changes in forin, and master stream simultaneously. The separate ef- drainage network, and gradient as relief increases. fect of such base-level changes cannot be isolated. There is continual modification, but at any stage the existing system is different from that which existed PURPOSE AND SCOPE at a previous state, but has been influenced by that The influence of local base level and the effects of earlier stage. a change of base level can be separated from the in- Therefore there is a special interest attached to any fluence of hydrologic and geomorphic processes within fluvial system that, owing to some geologic accident, the basin under certain conditions. has a definite and known origin. A singular case of These include the following situations : 1) observed this is an abandoned meander loop that becomes iso- changes in the longitudinal profile by aggradation or lated from the river of which it was once a part. degradation when a local base level is lowered or Three examples exist in the canyon country in the raised while the basin conditions remain unchanged. middle reaches of the Colorado River in Utah; the 2) observed changes in aggradation and/or degra- Rincon of the main Colorado River, the Gooseneck in 170 LEOPOLD AND BULL [PROC. AMER. PHIL. SOC. FIG.2. Topographic map of the Loop.
Load more

Recommended publications
  • PRELUDE to SEVEN SLOTS: FILLING and SUBSEQUENT MODIFICATION of SEVEN BROAD CANYONS in the NAVAJO SANDSTONE, SOUTH-CENTRAL UTAH by David B
    PRELUDE TO SEVEN SLOTS: FILLING AND SUBSEQUENT MODIFICATION OF SEVEN BROAD CANYONS IN THE NAVAJO SANDSTONE, SOUTH-CENTRAL UTAH by David B. Loope1, Ronald J. Goble1, and Joel P. L. Johnson2 ABSTRACT Within a four square kilometer portion of Grand Staircase-Escalante National Monument, seven distinct slot canyons cut the Jurassic Navajo Sandstone. Four of the slots developed along separate reaches of a trunk stream (Dry Fork of Coyote Gulch), and three (including canyons locally known as “Peekaboo” and “Spooky”) are at the distal ends of south-flowing tributary drainages. All these slot canyons are examples of epigenetic gorges—bedrock channel reaches shifted laterally from previous reach locations. The previous channels became filled with alluvium, allowing active channels to shift laterally in places and to subsequently re-incise through bedrock elsewhere. New evidence, based on optically stimulated luminescence (OSL) ages, indicates that this thick alluvium started to fill broad, pre-existing, bedrock canyons before 55,000 years ago, and that filling continued until at least 48,000 years ago. Streams start to fill their channels when sediment supply increases relative to stream power. The following conditions favored alluviation in the study area: (1) a cooler, wetter climate increased the rate of mass wasting along the Straight Cliffs (the headwaters of Dry Fork) and the rate of weathering of the broad outcrops of Navajo and Entrada Sandstone; (2) windier conditions increased the amount of eolian sand transport, perhaps destabilizing dunes and moving their stored sediment into stream channels; and (3) southward migration of the jet stream dimin- ished the frequency and severity of convective storms.
    [Show full text]
  • A Multivariate Geomorphometric Approach to Prioritize Erosion-Prone Watersheds
    sustainability Article A Multivariate Geomorphometric Approach to Prioritize Erosion-Prone Watersheds Jesús A. Prieto-Amparán 1, Alfredo Pinedo-Alvarez 1 , Griselda Vázquez-Quintero 2, María C. Valles-Aragón 2 , Argelia E. Rascón-Ramos 1, Martin Martinez-Salvador 1 and Federico Villarreal-Guerrero 1,* 1 Facultad de Zootecnia y Ecología, Universidad Autónoma de Chihuahua, Chihuahua 31453, Mexico; [email protected] (J.A.P.-A.); [email protected] (A.P.-A.); [email protected] (A.E.R.-R.); [email protected] (M.M.-S.) 2 Facultad de Ciencias Agrotecnológicas, Universidad Autónoma de Chihuahua, Chihuahua 31350, Mexico; [email protected] (G.V.-Q.); [email protected] (M.C.V.-A.) * Correspondence: [email protected]; Tel.: +52-(614)-434-1448 Received: 15 August 2019; Accepted: 15 September 2019; Published: 19 September 2019 Abstract: Soil erosion is considered one of the main degradation processes in ecosystems located in developing countries. In northern Mexico, one of the most important hydrological regions is the Conchos River Basin (CRB) due to its utilization as a runoff source. However, the CRB is subjected to significant erosion processes due to natural and anthropogenic causes. Thus, classifying the CRB’s watersheds based on their erosion susceptibility is of great importance. This study classified and then prioritized the 31 watersheds composing the CRB. For that, multivariate techniques such as principal component analysis (PCA), group analysis (GA), and the ranking methodology known as compound parameter (Cp) were used. After a correlation analysis, the values of 26 from 33 geomorphometric parameters estimated from each watershed served for the evaluation. The PCA defined linear-type parameters as the main source of variability among the watersheds.
    [Show full text]
  • Explain How Rivers Adjust to a Change in Base Level with Reference to Examples You Have Studied (2013 Q1C)
    Isostasy | A1 Sample answer Explain how rivers adjust to a change in base level with reference to examples you have studied (2013 Q1C) Isostatic uplift is when land rises above sea level because of tectonic activity. This is usually due to a large weight being removed from the land e.g. when an ice cap melts. Eustatic changes are when the sea level drops. This is due to water being locked away somewhere e.g., in a glacier. When it melts, the sea level rises again. The River Nore in Kilkenny has experienced a change in base level. This can be seen since there are knickpoints along it, roughly 150-200m above sea level. A knickpoint can be seen when the sea level drops and a river rejuvenates because the river starts vertically eroding once more. Rejuvenation is the term used to describe a river that starts eroding like a youthful river even when it is in its old age stage. A knickpoint is a spot where the newly eroded river profile meets the old river profile. Sometimes you will find a waterfall here. River terraces are also found where rejuvenation has occurred. This is when a river forms a new floodplain that is lower down than the last. The remnants of the old floodplain are left as steps and are called terraces. If there are terraces on both sides of the river, they are called paired terraces. Terraces can be formed multiple times if the river rejuvenates more than once, appearing as a series of steps down to the river.
    [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]
  • William Morris Davis Brief Life of a Pioneering Geomorphologist: 1850-1934 by Philip S
    VITA William Morris Davis Brief life of a pioneering geomorphologist: 1850-1934 by PhiliP S. Koch Naught looks the same for long… Waters rush on, make valleys where once stood plains; hills wash away to the sea. Marshland dries to sand, while dry land becomes stagnant, marshy pool. From Nature, springs erupt or are sealed; from earthquakes, streams burst forth or vanish. n Metamorphoses, the Roman poet Ovid, echoing Pythagoras, al- ludes to geomorphology: the study of the forms taken by the Iearth’s surface, and what causes them. Almost 19 centuries later, William Morris Davis, S.B. 1869, devised a clear, concise, descrip- tive, and idealized model of landscape evolution that revolutionized and in many ways created this field of study. Born into a prominent Philadelphia Quaker family, Davis studied geology and geography at Harvard’s Lawrence Scientific School and then joined a Harvard-sponsored geographic-exploration party to the Colorado Territory, led by the inaugural Sturgis-Hooper profes- sor of geology, Josiah Dwight Whitney. Wild stories had circulated since soon after the Louisiana Purchase about Rocky Mountain peaks 18,000 feet or higher. The Harvard expedition set out to investigate, and found none, but they did find “’14ers” (14,000-plus feet). Among these, the expedition members surveyed, named, and made two first- river valleys locally decrease the growing recorded summitings in the “Collegiate Peaks,” designating the tall- elevation differences between “uplands” est in the group Mount Harvard (honoring their sponsor), and the and “base-level” caused by uplift. In “Ma- second tallest Mount Yale (honoring Whitney’s alma mater).
    [Show full text]
  • Late Holocene Sea Level Rise in Southwest Florida: Implications for Estuarine Management and Coastal Evolution
    LATE HOLOCENE SEA LEVEL RISE IN SOUTHWEST FLORIDA: IMPLICATIONS FOR ESTUARINE MANAGEMENT AND COASTAL EVOLUTION Dana Derickson, Figure 2 FACULTY Lily Lowery, University of the South Mike Savarese, Florida Gulf Coast University Stephanie Obley, Flroida Gulf Coast University Leonre Tedesco, Indiana University and Purdue Monica Roth, SUNYOneonta University at Indianapolis Ramon Lopez, Vassar College Carol Mankiewcz, Beloit College Lora Shrake, TA, Indiana University and Purdue University at Indianapolis VISITING and PARTNER SCIENTISTS Gary Lytton, Michael Shirley, Judy Haner, STUDENTS Leslie Breland, Dave Liccardi, Chuck Margo Burton, Whitman College McKenna, Steve Theberge, Pat O’Donnell, Heather Stoffel, Melissa Hennig, and Renee Dana Derickson, Trinity University Wilson, Rookery Bay NERR Leda Jackson, Indiana University and Purdue Joe Kakareka, Aswani Volety, and Win University at Indianapolis Everham, Florida Gulf Coast University Chris Kitchen, Whitman College Beth A. Palmer, Consortium Coordinator Nicholas Levsen, Beloit College Emily Lindland, Florida Gulf Coast University LATE HOLOCENE SEA LEVEL RISE IN SOUTHWEST FLORIDA: IMPLICATIONS FOR ESTUARINE MANAGEMENT AND COASTAL EVOLUTION MICHAEL SAVARESE, Florida Gulf Coast University LENORE P. TEDESCO, Indiana/Purdue University at Indianapolis CAROL MANKIEWICZ, Beloit College LORA SHRAKE, TA, Indiana/Purdue University at Indianapolis PROJECT OVERVIEW complicating environmental management are the needs of many federally and state-listed Southwest Florida encompasses one of the endangered species, including the Florida fastest growing regions in the United States. panther and West Indian manatee. Watershed The two southwestern coastal counties, Collier management must also consider these issues and Lee Counties, commonly make it among of environmental health and conservation. the 5 fastest growing population centers on nation- and statewide censuses.
    [Show full text]
  • River Dynamics 101 - Fact Sheet River Management Program Vermont Agency of Natural Resources
    River Dynamics 101 - Fact Sheet River Management Program Vermont Agency of Natural Resources Overview In the discussion of river, or fluvial systems, and the strategies that may be used in the management of fluvial systems, it is important to have a basic understanding of the fundamental principals of how river systems work. This fact sheet will illustrate how sediment moves in the river, and the general response of the fluvial system when changes are imposed on or occur in the watershed, river channel, and the sediment supply. The Working River The complex river network that is an integral component of Vermont’s landscape is created as water flows from higher to lower elevations. There is an inherent supply of potential energy in the river systems created by the change in elevation between the beginning and ending points of the river or within any discrete stream reach. This potential energy is expressed in a variety of ways as the river moves through and shapes the landscape, developing a complex fluvial network, with a variety of channel and valley forms and associated aquatic and riparian habitats. Excess energy is dissipated in many ways: contact with vegetation along the banks, in turbulence at steps and riffles in the river profiles, in erosion at meander bends, in irregularities, or roughness of the channel bed and banks, and in sediment, ice and debris transport (Kondolf, 2002). Sediment Production, Transport, and Storage in the Working River Sediment production is influenced by many factors, including soil type, vegetation type and coverage, land use, climate, and weathering/erosion rates.
    [Show full text]
  • Federal Agency Functional Activities
    Appendix B – Federal Agency Functional Activities Bureau of Indian Affairs (BIA) Point of Contact: Wyeth (Chad) Wallace, (720) 407-0638 The mission of the Bureau of Indian Affairs (BIA) is to enhance the quality of life, to promote economic opportunity, and to carry out the responsibility to protect and improve the trust assets of American Indians, Indian tribes, and Alaska Natives. Divided into regions (see map), the BIA is responsible for the administration and management of 55 million surface acres and 57 million acres of subsurface minerals estates held in trust by the United States for approximately 1.9 million American Indians and Alaska Natives, and 565 federally recognized American Indian tribes. The primary public policy of the Federal government in regards to Native Americans is the return of trust lands management responsibilities to those most affected by decisions on how these American Indian Trust (AIT) lands are to be used and developed. Enhanced elevation data, orthoimagery, and GIS technology are needed to enable tribal organizations to wholly manage significant, profitable and sustainable enterprises as diverse as forestry, water resources, mining, oil and gas, transportation, tourism, agriculture and range land leasing and management, while preserving and protecting natural and cultural resources on AIT lands. Accurate and current elevation data are especially mission-critical for management of forest and water resources. It is the mission of BIA’s Irrigation, Power and Safety of Dams (IPSOD) program to promote self-determination, economic opportunities and public safety through the sound management of irrigation, dam and power facilities owned by the BIA. This program generates revenues for the irrigation and power projects of $80M to $90M annually.
    [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]
  • 2019 Li, Z., Wu, X., and Gao, P.*, Experimental Study on the Process of Neck Cutoff
    Geomorphology 327 (2019) 215–229 Contents lists available at ScienceDirect Geomorphology journal homepage: www.elsevier.com/locate/geomorph Experimental study on the process of neck cutoff and channel adjustment in a highly sinuous meander under constant discharges Zhiwei Li a,b, Xinyu Wu a,PengGaoc,⁎ a School of Hydraulic Engineering, Changsha University of Science & Technology, Changsha 410114, China b Key Laboratory of Water-Sediment Sciences and Water Disaster Prevention of Hunan Province, Changsha 410114, China c Department of Geography, Syracuse University, Syracuse, NY 13244, USA article info abstract Article history: Neck cutoff is an essential process limiting evolution of meandering rivers, in particular, the highly sinuous ones. Received 29 July 2018 Yet this process is extremely difficult to replicate in laboratory flumes. Here we reproduced this process in a Received in revised form 1 November 2018 laboratory flume by reducing at the 1/2500 scale the current planform of the Qigongling Bend (centerline length Accepted 1 November 2018 13 km, channel width 1.2 km, and neck width 0.55 km) in the middle Yangtze River with geometric similarity. In Available online 07 November 2018 five runs with different constant input discharges, hydraulic parameters (water depth, surface velocity, and slope), bank line changes, and riverbed topography were measured by flow meter and point gauges; and bank Keywords: fl Meandering channel line migration and a neck cutoff process were captured by six overhead cameras mounted atop the ume. By Neck cutoff
    [Show full text]
  • Rivers and Base Level—Cool Stuff Earth Science Essentials by Russ Colson
    Stories of Other Worlds—How to Build a Landscape Rivers and Base Level—Cool Stuff Earth Science Essentials by Russ Colson The River—The state boundary that moves. The migration of rivers has a long and complex history in human politics and war. The problem arises because rivers were commonly used to mark boundaries of adjacent political entities. When the rivers inevitably migrated, as mature streams are wont to do, disagreements arose about who owned the new land formed on the inside bend of the meanders. It seems like a simple solution would be to keep the boundaries fixed, whether the river migrates or not. That way, the land controlled by a particular political entity is not changed by the vagaries of erosion and deposition. However, suppose that the river is an important defensive barrier against attack? Clearly, in that case the border needs to be maintained along the river. Or, what if the river is important for commerce and transportation? Again, keeping the border along the river makes sense, regardless of the gain or loss of land. In his 1715 (edition) book Of the Rights of War and Peace, Hugo Grotius took the view that many rivers are defensive boundaries and ...the river, by gradually altering its course, does also alter the borders of the territory; and whatsoever the river casts up to the opposite side, shall be under his jurisdiction, to whom the augmentation is made Although geologists treat the various processes of river migration (such as erosion, deposition, meander cut offs, etc) as part of a single process, courts have often ruled that they are quite different.
    [Show full text]
  • Preprint 06-041
    SME Annual Meeting Mar. 27-Mar.29, 2006, St. Louis, MO Preprint 06-041 A MEANDER CUTOFF INTO A GRAVEL EXTRACTION POND, CLACKAMAS RIVER, OREGON P. J. Wampler, Grand Valley State Univ., Allendale, MI E. F. Schnitzer, Dept. of Geology and Mineral Industries, Albany, OR D. Cramer, Portland General Electric, Estacada, OR C. Lidstone, Lidstone and Assoc(s)., Fort Collins, CO Abstract Introduction The River Island mining site is located at approximately river mile The River Island site provides a unique opportunity to examine (RM) 15 on the Clackamas River, a large gravel-bed river in northwest the physical changes to a river channel resulting from avulsion into a Oregon. During major flooding in February 1996, rapid channel gravel extraction pond. Data from before and after the meander cutoff change occurred. The natural process of meander cutoff, slowed for allow evaluation of changes to river geometry, sediment transport, several years by dike construction, was accelerated by erosion into temperature, habitat, and channel form. gravel extraction ponds on the inside of a meander bend during the An avulsion is defined as a lateral migration or cutoff of a river. It flood. involves the diversion of water from the primary channel into a new In a matter of hours, the river cut off a meander and began flowing channel that is either created during the event or reoccupied. through a series of gravel pits located on the inside of the meander Avulsions may be rapid or take many years to complete (Slingerland bend. The cutoff resulted in a reduction in reach length of and Smith, 2004).
    [Show full text]