Research Article| February 01, 1988 Bedload sheets in heterogeneous sediment Peter J. Whiting; Peter J. Whiting 1Department of Geology and Geophysics, University of California, Berkeley, California 94720 Search for other works by this author on: GSW Google Scholar William E. Dietrich; William E. Dietrich 1Department of Geology and Geophysics, University of California, Berkeley, California 94720 Search for other works by this author on: GSW Google Scholar Luna B. Leopold; Luna B. Leopold 1Department of Geology and Geophysics, University of California, Berkeley, California 94720 Search for other works by this author on: GSW Google Scholar Thomas G. Drake; Thomas G. Drake 2Department of Earth and Space Sciences, University of California, Los Angeles, California 90024 Search for other works by this author on: GSW Google Scholar Ronald L. Shreve Ronald L. Shreve 2Department of Earth and Space Sciences, University of California, Los Angeles, California 90024 Search for other works by this author on: GSW Google Scholar Author and Article Information Peter J. Whiting 1Department of Geology and Geophysics, University of California, Berkeley, California 94720 William E. Dietrich 1Department of Geology and Geophysics, University of California, Berkeley, California 94720 Luna B. Leopold 1Department of Geology and Geophysics, University of California, Berkeley, California 94720 Thomas G. Drake 2Department of Earth and Space Sciences, University of California, Los Angeles, California 90024 Ronald L. Shreve 2Department of Earth and Space Sciences, University of California, Los Angeles, California 90024 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1988) 16 (2): 105–108. https://doi.org/10.1130/0091-7613(1988)016<0105:BSIHS>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Peter J. Whiting, William E. Dietrich, Luna B. Leopold, Thomas G. Drake, Ronald L. Shreve; Bedload sheets in heterogeneous sediment. Geology 1988;; 16 (2): 105–108. doi: https://doi.org/10.1130/0091-7613(1988)016<0105:BSIHS>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Field observations in streams with beds of coarse sand and fine gravel have revealed that bedload moves primarily as thin, migrating accumulations of sediment, and coarse grains cluster at their leading edge. These accumulations are one or two coarse grains high and are much longer (0.2-0.6 m long in sand; 0.5-2.0 m in fine gravel) than their height. We propose the term "bedload sheet" for these features, and we argue that they result from an instability inherent to bedload movement of moderately and poorly sorted sediment. In essence, coarse particles in the bedload slow or stop each other, trap finer particles in their interstices, and thus cause the coarse particles to become mobile again. Bedload sheets develop on the stoss side of dunes, causing the dune to advance incrementally with the arrival of each sheet. Successive deposition of coarse sediment from the leading edge followed by fine sediment may generate the grain-size sorting that distinguishes cross-bedding. Available flume experiments and field observations indicate that bedload sheets are a common, but generally unrecognized, feature of heterogeneous sediment transport. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
This book reviews many of the problems which currently confront the environmental planner - problems which promise to become even more signifcant in the near future. Water resources are examined essentially from a physical standpoint, although throughout the text the emphasis is on the application of basic hydrologic principles in problem solving. The stated aim of the authors is to make all those concerned with planning more aware of the opportunities and constraints of natural processes in maintaining or reclaiming environmental quality. They are successful in outlining the significant role of water in many environmental issues. The book provides a comprehensive review of the current literature associated with water resources, but perhaps more importantly can also be used as an introductory working document in dealing with particular environmental problems. Several chapters for instance include working examples to illustrate specific problem-solving techniques. The book is divided into four sections, the first of which describes six case studies and exemplifies many of the problems facing the environmental planner today. The remaining three sections discuss basic hydrologic principles, fluvial geomorphology and water quality, stressing the value of such studies for improved environmental management. The text is supplemented by bibliographies, photographs, tables, and diagrams.
A tidal channel in a marsh bordering the Potomac River near Alexandria, Va., was mapped, and current-meter measurements of discharge were made at various locations and at various stages in the tidal cycle. These measurements allowed analysis of the change of width, depth, and velocity with discharge at various cross sections and along the length of the channel.There is also presented a theoretical development of some, of these same relations based on hydraulic principles and on the assumption of a uniform distribution of energy and a minimum rate of work in the system as a whole.The change of width, depth, and velocity with discharge downstream developed from the field data checked closely with the theoretically derived values.The estuarine channel differs from a terrestrial one in that discharge at any section in an estuary varies depending on how the flow shaped the entire length of the channel between the point in question and the main body of tidal water. The result is that a tidal channel changes more rapidly in width and less rapidly in depth as discharge changes downstream than does a terrestrial channel.
Successive surveys of the cross section of ephemeral channels in New Mexico over a period of 15 years 1960–1975, show that arroyos that were actively eroding early in the century have reversed the trend and are alluviating. This appears to be associated with the worldwide cooling trend that began about 1940. If the inference proves to be correct, it is significant hydrologically, for it provides some specific knowledge of the climatic conditions associated with the alternate periods of valley erosion and valley alluviation that created the widespread terraces of the semiarid West.
The Los Angeles area is faced with the problem of planning the mitigation of air pollution. The meteorological factors which determine the distribution of the pollution and the intensity of the nuisance are the height of the prevailing summer subsidence inversion and the local sea‐land breeze regime. Data on details of the wind structure and visibility are presented. These, with the time variations of the inversion, are discussed in relation to the pollution problem.
Motion pictures taken at Duck Creek, a clear stream 6.5 m wide and 35 cm deep near Pinedale, Wyoming, provide detailed, quantitative information on both the modes of motion of individual bedload particles and the collective motions of large numbers of them. Bed shear stress was approximately 6 Pa (60 dynes cm −2 ), which was about twice the threshold for movement of the 4 mm median diameter fine gravel bed material; and transport was almost entirely as bedload. The displacements of individual particles occurred mainly by rolling of the majority of the particles and saltation of the smallest ones, and rarely by brief sliding of large, angular ones. Entrainment was principally by rollover of the larger particles and liftoff of the smaller ones, and infrequently by ejection caused by impacts, whereas distrainment was primarily by diminution of fluid forces in the case of rolling particles and by collisions with larger bed particles in the case of saltating ones. The displacement times averaged about 0.2−0.4 s and generally were much shorter than the intervening repose times. The collective motions of the particles were characterized by frequent, brief, localized, random sweep-transport events of very high rates of entrainment and transport, which in the aggregate transported approximately 70% of the total load moved. These events occurred 9% of the time at any particular point of the bed, lasted 1–2 s, affected areas typically 20–50 cm long by 10–20 cm wide, and involved bedload concentrations approximately 10 times greater than background. The distances travelled during displacements averaged about 15 times the particle diameter. Despite the differences in their dominant modes of movement, the 8–16 mm particles typically travelled only about 30% slower during displacement than the 2–4 mm ones, whose speeds averaged 21 cm s −1 . Particles starting from the same point not only moved intermittently downstream but also dispersed both longitudinally and transversely, with diffusivities of 4.6 and 0.26 cm 2 s −1 , respectively. The bedload transport rates measured from the films were consistent with those determined conventionally with a bedload sampler. The 2–4 mm particles were entrained 6 times faster on finer areas of the bed, where 8–16 mm particles covered 6% of the surface area, than on coarser ones, where they covered 12%, even though 2–4 and 4–8 mm particles covered practically the same percentage areas in both cases. The 4–8 and 8–16 mm particles, in contrast, were entrained at the same rates in both cases. To within the statistical uncertainty, the rates of distrainment balanced the rates of entrainment for all three sizes, and were approximately proportional to the corresponding concentrations of bedload.
An analysis of data on hydraulic parameters collected during a single boat trip down a river system is presented, plotted in form of the hydraulic geometry. A dimensionless rating curve is used to estimate bankfull and average discharge for basins of various sizes. When compared with gaging station data, estimates of bankfull discharge are as consistent and possibly equal in accuracy to estimates made from gaging station data. Estimates of average discharge are less consistent; within the range of drainage areas represented by the gaging stations, er- rors of estimate vary from 0 to 58 percent. Local variations of bed material size along the river are compensated mostly by changes in local channel slope and roughness and do not much affect the progres- sive downstream changes in width, depth, or velocity.
