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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
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
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
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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