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Unformatted text preview: lied to hydrology and fluvial geomorphology, is a measure of the amount of
water that can pass through a stream-channel section without spilling onto higher surfaces as
flood flow. 13 Corrosion refers to the water-related chemical erosion of rocks and inorganic soil material by
dissolution and similar weathering processes including oxidation, hydrolysis, carbonation, and
hydration; the older, less specific term, corrasion, is loosely synonymous.
Creep, as applied to geomorphology, is a process of mass movement by which soil and rock
gradually and slowly move by deformation caused by gravitational stress; the process is
continuous, or nearly so, and irreversible, resulting in the movement of sediment and rock
fragments to lower sites on the landscape and the availability of the sediment and rock
fragments for addition to fluvial-sediment loads. Creep also includes glacial processes of
deformation of snow and ice.
Creosote-bush (Larrea tridentate), an indicator species, is a shrub of southwestern North
America extending northward into Oregon, Idaho, and Wyoming; creosote-bush is indicative of
bajadas and related low-relief landforms of semiarid deserts, well drained conditions, and
calcareous soil that commonly has near-surface pedogenic calcrete.
Critical flow in open channels occurs when, for a specified flow rate, that flow rate is at a
maximum for the energy (d + v2/2g, in which d is water depth, v is water velocity, and g is the
acceleration due to gravity) of the water; critical flow occurs only when the Froude number is
Critical shear stress, relative to fluvial geomorphology and hydraulics, is the lowest required
value of shear stress applied by flowing water to initiate motion of individual particles of
specified size (diameter) along the bed of a stream.
Curve number is an index of the runoff potential on a land surface in response to rainfall; as
applied to the USDA-NRCS Curve Number Method, it is 1000/(10+S), in which S (in inches), is
the maximum possible difference between the effective rainfall and the direct storm runoff
depths. Curve numbers range from 0 (no runoff under any condition) to 100 (all rainfall of any
event results in runoff).
Current meter is a device to measure velocity at a point within the flow field of a stream of
water; the device, typically a Price AA or pigmy meter, consists of a vertical rod with attached
cups that are free to rotate at a rate corresponding to the water velocity. 14 D
Darcy-Weisbach formula is a widely used equation of hydraulic engineering to compute head
loss or pressure loss due to frictional losses by water flowing through a pipe or similar conduit.
For use in open-channel flow of natural stream channels, it states that head loss varies with the
surface roughness times channel length divided by hydraulic radius times the velocity head.
Datum is any point or surface to which other landscape points can be related, both horizontally
and vertically, to locate the points on the earth’s surface, typically for purposes of topographic
mapping. The official vertical datum of the United States government is the North American
Vertical Datum of 1988, and the horizontal datum is the North American Datum of 1983 (NAD
Debris flow is the downslope mass movement, by either inertial or viscous processes at
velocities greater than those of creep or solifluction, of a non-Newtonian slurry of a plastic
mixture of water and generally coarse, poorly sorted sediment; debris-flow slurries, depending
on the particle-size distribution of the sediment, typically vary from 50 to 80 percent sediment
Deflation, a form of erosion, is the entrainment and transport of fine (mostly clay, silt, fine
sand), dry, generally unconsolidated, sediment from a source deposit by the action of wind
turbulence; the re-deposited sediment may be concentrated as eolian dunes (sand) or loess
(clay, silt, and very fine sand).
Degradation is the lowering of a bottomland surface through the process of erosion;
conceptually it is the opposite of the vertical component of aggradation and is most frequently
applied to sediment removed from a channel bed or other low-lying parts of a stream channel.
Delta is a fan-shaped landform of fluvial sediment deposited at and beyond the mouth of a
stream, usually a river, as it debouches into a body of standing or low-velocity water, generally
an ocean or lake, or some other water body of reduced or stagnant flow. As a delta continues
to form and grow outward from the mouth of the stream into the standing water, channel
gradient is minimized and the stream typically separates into a complex of relatively straight
channel distributaries that are poorly capable of carrying the coarser fractions of their total
sediment loads to the distal edge of the delta.
Dendrochronology, from the Greek words for tree, time, and study, is the dating of past events,
including climate fluctuations, through the counting of annual tree rings and analysis of the
sizes and structure of the rings; the application of dendrochronology to geomorphology,
sometimes termed dendrogeomophology, is the use of dendrochronological techniques to
interpret and date earth-surface processes and resulting landforms.
Denudation is the s...
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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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