Unformatted text preview: altation is the process by which sediment, generally of sand size and coarser, bounces along
the stream bed by the impact of the flow of water or of other moving particles; saltation can
also occur by the movement of wind .
Salt water is water on or beneath a land (or water) surface that accumulates as a result of
natural processes of precipitation and which contains concentrations of dissolved solids (mostly
salts) typical of normal sea water or of other small water bodies such as the Dead Sea or the
Great Salt Lake; the concentration of dissolved solids in salt water is sufficient to cause
deleterious effects by ingestion of living organisms adapted to a dependency on fresh water or
Sample, relative to the needs and activities of the natural sciences, is a small part or quantity
that is randomly obtained to represent the whole of a larger mass, volume, group, or
population; it is limited in size to be easily analyzed, studied, characterized, and stored, large
enough to be typical of the larger feature, element, or landscape process, and has a degree of
permanence. In general, a sample (such as a small volume of sand from a selected part of a
dune field) has properties that allow it or a derivative (such as a known volume of water, snow,
or ice that is evaporated but all solid residue is retained) to be preserved without employing
measures that are destructive to the properties that characterize the sample as representative.
Relative to statistical measures of hydrology, a sample is a value or element within a larger
population of values; as an example, an annual flood discharge from a gage site is a sample of
the entire list of floods for an annual series.
Sand, as fluvial sediment, is sediment defined to be of particle diameter between 0.062 and 2.0
mm in diameter (b-axis). 37 Sand splay is a low ridge or rounded length of deposits of sand to fine gravel on a flood plain or
low terrace; sand splays typically are flood sediment extending from the lee, or downstream,
side of an obstacle (most typically large trees) to the flood flow.
Sapping, or ground-water sapping, is a process of steady sediment removal by the laminar flow
to and release of ground water as seepage at the saturated base of an escarpment, arroyo, or
similar erosional feature, above which the soil, subsoil, alluvium, or bedrock is unsaturated.
Sapping results in the separation at the seepage site of sand and silt particles from the rock or
sediment through which the ground-water movement occurs; coupled with sediment-particle
separation due to evaporation and precipitation of salts, the process causes erosion,
undercutting, over-steepening of slope at the base of the landform, and eventually slope failure
and cliff retreat.
Sawyer, a channel snag, is a tree extending from the bed of a stream and having branches that
project above the water surface; the term may be the source of the name for the Mark Twain
novel, Tom Sawyer.
Schmutzdecke is a German term meaning dirty cover, or filth cover; as applied to stream beds,
it is a gelatinous complex, formed in the uppermost few centimeters of the channel alluvium, of
variable proportions of bacteria, fungi, protozoa, rotifera, and aquatic insect lavae. For influent
(loosing) streams, schmutzdecke reduces the potential for transmission loss of discharge by
acting as an interstitial seal in the sand and gravel of the bed material, thereby minimizing the
ability of water to flow through the schmutzdecke layer to underlying horizons of the
Sediment is detached fragmental material that originates from either chemical or physical
weathering of rocks and minerals and is transported by, suspended in, or deposited by water or
air or is accumulated in beds by other natural agencies.
Sedimentation is the process by which sediment is mechanically deposited from suspension
within a fluid, generally water, or ice, thereby accumulating as layers of sediment that are
segregated owing to differences in size, shape, and composition of the sediment particles.
Sediment budget is an accounting, or inventory, of sediment-transport rate, generally as
components based on particle-size ranges entering and leaving a specified area or stream
reach; when the fluxes of sediment that enter and leave are unequal, the assumption follows
that the differences signify the net amounts of sediment that are stored or taken from storage
within the area or reach.
Sediment concentration of streamflow is the amount of sediment, generally as a dry weight,
that is entrained in a specified volume of water; sediment concentration is typically expressed
in milligrams of sediment per liter of the water/sediment mixture.
Sediment delivery is the sum of hydrologic and geomorphic processes resulting in the
availability of sediment for transport in a stream network; sediment-delivery processes range
from entrainment in overland flow to rapid mobilization by bank failure to much slower
movement as soil creep. 38 Sediment-delivery ratio is the ratio, expressed as a percent, of sediment yield of a drainage
basin to the total amount of sediment moved downslope by denudational processes during a
specified period of time; over long time periods, mass balance must be maintained and the
mean sediment-delivery ratio must approach 1.0.
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