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Unformatted text preview: is a very small incision eroded into soil or soft rock as a direct-runoff response to
precipitation; it is one of the first and smallest incisions to be formed as a result of erosion by
concentrated flow from upland surfaces and therefore is subject to removal by standard tillage
operations of agriculture. 35 Rill erosion is the development of numerous, minute to small, closely spaced incisions resulting
from the uneven removal of surface soil or soft rock by flowing water that is concentrated in
streamlets of sufficient volume and velocity to generate erosive power; it is an intermediate
process between erosion by overland flow and gully erosion and is the most identifiable
indicator of serious erosion resulting from watershed disturbance. The depth of flow that
causes erosion in rills is typically less than about 30 mm. Rill erosion on lands that have been
treated for rehabilitation or reclamation is considered to be accelerated erosion.
Riparian pertains to the banks of a stream; within ecology the term has been broadened to
refer to biota and other characteristics of alluvial bottomlands.
Riparian zone, as applied to the study of fluvial systems, is an ecological term referring to that
part of the fluvial landscape inundated or saturated by flood flows; it consists of all surfaces of
active fluvial landforms up through the flood plain including channel, bars, shelves, and related
riverine features such as oxbow lakes, oxbow depressions, and natural levees. Particularly in
arid and semiarid (water-deficient) environments, the riparian zone may support plants and
other biota not present on adjacent, drier uplands.
River continuum refers to a biotic gradient, resulting from variations in physical characteristics
along an adjusted stream (in dynamic equilibrium and thus time-independent), that is defined
by a series of biological responses and consistent patterns of loading, transport, use, and
storage of organic matter along the stream length. Because the river-continuum concept
addresses biology, it is more specific than that of the biophysical continuum, which considers
Riverine is that characteristic by which a feature or process pertains to or is formed by a river.
Root flair refers to that part of a plant, generally a tree, at which roots extend laterally from the
base of the trunk, or bole. Where only the uppermost part of the root flair is observable, it is
inferred that normal processes of sedimentation or erosion have occurred; if large roots near
the bole are fully visible it is assumed that erosion has occurred since establishment of the tree,
and if none of the root flair is visible, particularly in a riparian zone, it can be inferred that
sedimentation has occurred since tree establishment.
Rock glacier is a mass of poorly sorted, coarse rock debris that typically occurs in periglacial,
high-relief areas of mountains and that contains interstitial ice subject to deformational
processes of glaciers and therefore downslope movement of the ice and rock as a plastic mass;
a landform that previously was deposited as a rock glacier, but, owing to subsequent melting or
insufficient additions of snow, ice, and water to maintain a matrix of interstitial ice subject to
glacial deformation, is an inactive rock glacier.
Rock veneer, or rock-fragment veneer, is a thin accumulation of rock clasts that partially or fully
cover a surface or hillslope. The concentrations of generally gravel- or cobble-sized rock
fragments develop by a variety of processes, all of which increase slope stability by protecting
underlying fine sediment from erosion. Rock veneers typically extend no deeper than one or
two clast thicknesses, thereby distinguishing them from thicker rock accumulations such as
talus, felsenmeers, or coarse channel sediment. 36 Roughness coefficient is a factor in formulas for computing the average velocity of flow of
water in a conduit or channel that represents the effect of roughness of the confining material
on the energy losses in the flowing water. The most widely used roughness coefficient is “n” of
the Manning equation; other roughness coefficients are the Chézy resistance factor and the
Darcy-Weisbach friction factor.
Runoff (or rainfall excess), that part of precipitation that appears in surface streams (m3 s-1), is
the amount of rainfall input minus hydrologic abstractions, or losses, of interception,
depression storage, infiltration, and evaportranspiration; it is more restricted than streamflow
as it does not include stream channels affected by artificial diversions, storage, or other works
Runon is water on the land surface that moves from upslope sites as overland flow or within
small rills into a specified area of observation; where appropriate, runon should be included in
the I (inflow) factor of a water-balance computation, but frequently it is ignored. S
Salinity is a quantitative expression of the concentration of dissolved solids in water or soil and
is generally measured and represented by the electrical conductivity of a sample of the water
or soil; salinity is an important measure of the tolerance of a plant species to subsist with the
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