Cobble as fluvial sediment is sediment defined to be

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Unformatted text preview: al sediment, is sediment defined to be of particle diameter between 64 and 256 mm in diameter (b-axis). Coefficient of skewness, or skew coefficient, is a numerical measure or index of the lack of symmetry in a frequency distribution; it is a function of the third moment of magnitudes about their mean, a measure of asymmetry. As applied to hydrologic records such as annual floods or a measure of maximum precipitation events, is a quantitative index of the skewness, or asymmetry, of the frequency distribution of a list of measured values; a skewed distribution occurs when computed values of the mode, mean, and arithmetic mean of the list vary, resulting in a bunching of plotted values on one side of the mean as opposed to a tailing away from the mean of plotted values on the opposite side. Cohesiveness is a strength-imparting property of fine-grained sediment, generally clay, by which individual particles cohere or bond together by electrochemical forces of the particle surfaces. Colluvium is a layer, generally less than 3 meters in thickness, of unconsolidated and heterogeneous weathering products (soil material and sediment) and rock fragments deposited following sheet erosion by unconcentrated surface runoff and by gravitational processes, especially soil creep, other types of mass wasting, physical weathering, and bioturbation; colluvium generally occurs as a blanket of poorly sorted sediment and rock fragments on the lower parts of hillslopes underlain by bedrock. Comminution is the process of reducing a mass to small, fine particles by impact, abrasion, or soil dynamics; as a geomorphic or hydrologic process, comminution occurs through particle interaction in flowing water or glacial ice, and in archaeology the term is applied to taphonomic (fossilization) processes in which charcoal, bone, or shell becomes pulverized and disseminated following deposition and burial by physical weathering, mass movement such as creep, bioturbation, and pedogenesis. 12 Commodity water is that portion of the accessible water resource that is viewed by humans, and economists in particular, to be an article of commerce and thus to have a monetary value as an economic good; in contrast, ecosystem-services water is that portion of the total water resource that is essential for ecosystem function and as such has intrinsic value for physical and biotic processes. Competence refers to the ability of a current of water or wind to transport sediment, emphasizing the particle size rather that the amount, measured as the diameter of the largest particle transported; it depends, therefore, on the critical shear stress, which is a function of the hydraulic radius of the stream channel and the energy slope. Complex response, as applied to geomorphology, connotes the tendency of natural drainage systems that receive water and sediment from a complex assortment of landforms (such as hillslopes, terraces, and flood plain) to respond accordingly in complex, often difficult to anticipate, manners following disturbance such as rejuvenation. The concept is based on the recognition that any change modifying a system, whether natural or imposed, induces change elsewhere that may progress sequentially from a landform or process to others. Composite science refers to complex disciplines, including geomorphology, ecology, soil science, hydrology, and archaeology, that are composed of distinct parts of other types of study but which have specific and generally agreed-upon goals requiring various scientific and technological approaches of investigation to meet those objectives. A goal of geomorphology, for example, is a genetic interpretation of landforms, and techniques of physics, chemistry, biology, and engineering ae employed to develop interpretations. Control, as applied to a gaging station (streamgage) is the physical feature(s), either sectional, channel, or flood plain, that directly defines the slope of the stage-discharge relation at the streamgage. The control defines the relative hydraulic stability of a stream bed, channel, or flood plain. At low flows the sectional control is usually at or immediately downstream from the measurement section of the gage; a typical stable natural control is bedrock or consolidated alluvium that is not subject to scour or deposition. Typical unstable natural controls are sand and gravel riffles and point bars, which are subject to shifting both by scour and deposition. Examples of an artificial control are a weir, flume, or low cement dam. At channel and floodplain flows, the control is defined by the shape and roughness of the channel and flood-plain cross-sections. Convergence, when used in a geomorphic context, is a term to acknowledge that some landforms with outwardly similar characteristics developed from a narrow range of similar process sets causing the landforms and thus may have quite different internal or structural characteristics. When used in a hydrologic context, convergence, or convergent flow, refers to a contraction of flow paths as surface runoff traverses a concave slope or as ground water moves from a relatively unrestricted flow path to one of greater restriction. Conveyance, as app...
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This document was uploaded on 02/26/2014 for the course ES 322 at Western Oregon University.

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