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Unformatted text preview: coefficient (or coefficient of skewness) 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.
Slack water, as applied to fluvial systems, is runoff or streamflow that is prevented in some
manner from maintaining a normal velocity and thereby becomes ponded or nearly so. 40 Slack-water deposit is fine-texured sediment that falls from suspension in a body of slack water
owing to little or no stream velocity; slack-water deposits resemble and in many cases are
nearly the same as deposits of lacustrine sediment.
Slope is any inclined surface of the earth. As a geomorphic measurement, slope is the
inclination, generally measured in degrees departure from horizontal or expressed as a nondimensional number (meters per meter), of any surface of the earth’s landscape (including subaqueous surfaces); for application to models of hillslope soil loss, steepness is often used
synonymously with slope.
Soil, as a product of natural hydrologic and geomorphic processes, is a layered mass of minerals
and, generally, organic matter and rock fragments that differs from the parent material (rocks)
from which it is derived in terms of morphology, physical and chemical characteristics, and
organisms and organic content; the layers, or horizons, that comprise a soil are of variable
thickness (as also are soil bodies), are typically but not always unconsolidated, and differ from
each other in terms of degree of alteration that has occurred during the weathering process of
the underlying parent material. A fundamental classification of soil types includes clay, silt,
sand, gravel, peat, chalk, and loam (having significant amounts of clay, silt, sand, and possibly
Soil association, or soil complex, of an area refers to two or more soils that are closely related,
and are mapped as contiguous features, owing to similar conditions of climate, topography, and
vegetation; if the soils have similar characteristics owing to common parent material from
which they have developed, they represent a catena.
Soil horizon, or soil zone, is a thickness of soil that differs from adjacent strata in terms of
physical properties such as structure, color, or particle-size distribution, or by chemical
composition, especially the amount and alteration of organic matter or the content of clays and
related weathering products; standard designations of the three mostly commonly recognized
mineral horizons of soils are the uppermost, dark-colored A horizon, which is a zone of humicmaterial accumulation, reducing conditions, and leaching, the underlying B horizon, which is
generally lighter or reddish in color owing to oxidizing conditions and is the zone or horizon at
which humus, silicates, and clays typically accumulate, and the lowest C horizon, which
contains little organic material and is formed of partially weathered, unconsolidated rock
material and fragments that are transitional between the developing soil above and bedrock
Soil loss is generalized as that portion of eroded sediment that moves from agricultural fields,
small catchments, or other sites of disturbance or interest; the remainder of eroded sediment is
stored at various sites of microtopography, behind vegetation, or in other small depressions on
the hillslope surface. More precisely, soil loss is the rate of soil eroded from that portion of the
land surface experiencing a net loss of soil mass or volume.
Soil moisture is water held by capillary forces, including adhesion, between soil particles and
organic material and as a film on soil particles in an aerated (unsaturated) soil zone; soil
moisture is lost to the atmosphere by processes of evapotranspiration and is replenished by
precipitation. 41 Soil profile is an assemblage of all soil horizons at a site that in vertical section extends from
the surface to the parent material from which the soil was derived.
Soil science, a composite science, includes the study of soil processes and treats or considers
the formation, properties, classification, and mapping of soils; a synonymous term is pedology
although some soil scientists regard soil science to have two principal sub-disciplines, pedology
Solifluction is a slow (normally at a velocity less than 5 x 10-2 m yr-1) type of mass movement by
viscous processes of a non-Newtonian, generally saturated, mixture of poorly sorted sediment
and related soil material; the term applies in particular to the plastic flow of surficial material, in
areas of high relief and high elevation, that is underlain by frozen ground, thereby preventing
the downward movement of meltwater during episodes of near-surface thawing.
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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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