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Erosion is the process of detachment and transport of soil particles by the erosive agents of
raindrop impact and surface runoff from rainfall.
Erosivity is an expression of the capacity of rainfall to detach particles from a soil surface and
initiate the erosion process; it should not be confused with erodibility, which expresses the
susceptibility of soil, sediment, or rock to erosion processes. Research has demonstrated that
the erosivity (of rainfall) for an individual storm approximates the product of the energy of the
storm and its maximum 30-minute intensity.
Estuary, as a geomorphic feature, is the funnel-shaped river-valley reach where the river
debouches into a marine environment. Most estuaries are continental-margin stream valleys
that were formed by typical fluvial processes at a time, generally glacial, of lowered sea level.
Owing to glacial retreat and rise in sea level, the valley of the formerly free-flowing near-coast
river became flooded as an estuary of a mixture of fresh river water and saline marine water. 20 Eutrophication is the process by which water, generally ponded or stagnant, becomes enriched
in dissolved nutrients and deficient in dissolved oxygen; typically, the process occurs when
runoff from fertilized fields transports phosphates into the water body, thereby causing algal
blooms and a consequent depletion of dissolved oxygen.
Evaporation, as applied to hydrology, is the conversion of water to a gaseous or vapor state.
Evapotranspiration is the loss of water from any surface by the combined processes of
evaporation and transpiration; actual evapotranspiration, the actual rate of water loss to the
atmosphere is a concept often used by hydrologists for water-balance studies, whereas
potential evapotranspiration, a threoretical water loss under conditions of continuous
saturation, is used especially by climatologists.
Exceedance probability is the probability, or likelihood, that the peak discharge of a designated
flood event will exceed a specified discharge within some standard period of time, generally a
Exchangeable sodium percentage is the percent of the cation exchange capacity of soil or
sediment that is due to sodium.
Expansion reach of a stream or channel is a length of the stream or channel in which the width
increases to the degree that flow spreads over the widened section of channel bed, causing a
corresponding increase in cross-sectional area of the flow and reductions in flow depth and
velocity. Owing to lowered velocity as a stream enters an expansion reach, the ability of flow to
transport coarse sediment is diminished and deposition as bars or other in-channel features
occurs. For this reason, channel islands commonly form in expansion reaches. F
Felsenmeer is a type of block field, a continuous surface cover of large angular to subangular
rocks derived from an underlying source of well jointed bedrock; the blocks are generally
dislodged by frost action and form a layer greater than one or two clast thicknesses (as opposed
to a rock veneer, which has a thickness no greater than two clast thicknesses).
Flood is any climatically controlled, relatively high streamflow that overtops the natural or
artificial banks in any reach of a stream, thereby being of geomorphic significance; where a
flood plain exists, a flood is any flow that spreads over or inundates the flood plain.
Flood-frequency curve is a graph showing recurrence intervals of floods plotted as the abscissa
and the magnitudes of the floods plotted as the ordinate.
Flood plain is a strip of relatively smooth land bordering a stream incision, built of sediment
carried by the stream and dropped in slackwater beyond the influence of the swift current of
the channel; the level of the flood plain is generally about the stage of the mean annual flood,
and therefore one and only one flood-plain level can occur in a limited reach of bottomland.
Flow duration refers to the percentage of time that a specified discharge is equaled or
exceeded. 21 Flow-duration curve is a cumulative-frequency curve that shows the percentage of time that
specified discharges are equaled or exceeded.
Fluvial, from the Latin word, fluvius, for river, refers to or pertains to streams; included are
stream processes (fluvial processes), fluvial landforms, such as fluvial islands and bars, and
biota living in and near stream channels. Common usage is often extended by
geomorphologists to hydrologic processes on hillslopes.
Fluvial, or channel, island is a landform that rises above and is surrounded by stream
passageways and which persists a sufficient time so that persistent vegetation can develop if
adequate moisture is available.
Fluvial system, after Schumm (1973), is an idealized representation of a watershed into zones
of (1) erosion and sediment entrainment, (2) transfer of sediment, and (3) deposition of
Freeze-thaw cycle, as applied to rock and soil weathering, is the process by which capillary
water occupies the pores, fractures, joints, or crevices of near-surface rocks or rock fragments
and freezes upon lowered air temperature; owing to expansion as water turns to ice, pressure
is exerted on the pore, fracture, joint, or crevice sides, pushing them apart and causing a form
of physical weathering.
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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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