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Unformatted text preview: r internal friction, is the property of a substance, a water/sediment mixture when
applied to fluvial systems, to resist flow; viscosity is measured as the coefficient of viscosity, the
ratio of shear-stress rate to the shear-strain rate. W
Wadi is a channel, generally in arid or semiarid areas of southwestern Asia, the Arabian
Peninsula, and northern Africa, in which streamflow occurs inconsistently or infrequently and,
except during periods of streamflow, is directly underlain by unsaturated alluvium; wadis
typically have a rectangular to steeply sided trapezoidal cross section, banks a meter or more in
height formed of fine-grained, poorly consolidated over-bank sediment, and a nearly flat, sandy
bed. Synonyms are ephemeral-stream channel, dry wash, and arroyo (northern Mexico and
southwestern United States).
Wash load is the part of the total sediment load of a stream that is usually supplied from bank
erosion or from upland sources by overland flow. It is the finest part of the load (that part
which typically can be held in suspension at even very low stream velocity) that can be easily
carried in large quantities (it is “supply-limited”, not “transport-limited”); it is generally
determined by assuming that suspended sediment in transport that is finer than 0.062 mm is
the wash load.
Water balance is an accounting of the volumes of water entering, leaving, and stored in a
hydrologic area or unit, typically a drainage basin or aquifer, during a specified time period in
which the amount of water entering the area or unit equals the amount leaving; in equation
form, the water balance, or hydrologic budget, for a drainage basin is expressed as P = O + ET –
I + ΔS, in which P is precipitation, O is outflow, as streamflow, ET is water lost through
evapotranspiration and sublimation (including loss of intercepted precipitation), I is inflow, as
streamflow and runon, and ΔS is change in stored water, including ground water, soil moisture,
and imposed additions or extractions.
Watershed is a drainage divide or a “water parting”, but commonly usage of the term has been
altered to signify a drainage-basin area contributing water to a network of stream channels, a
lake, or other topographic lows where water can collect. 47 Watershed management is, through the application of scientific principles and knowledge of
drainage-basin characteristics, the administration and regulation of water and related natural
resources of land, soil, and biota of the watershed for the beneficial use and conservation of
those resources; included are the management of water and plant resources and the control of
fluvial processes (especially erosion and sediment deposition).
Water table is a lay term to describe the surface defined by the top of the zone of saturation in
a non-confined, often alluvial, aquifer.
Water year is the period October 1 through September 30; in most mid-latitude areas of the
northern hemisphere, the general time of October 1 is one of low flow, hence the selection of
October 1 as break date.
Weathering is the destruction or alteration, through chemical and biochemical processes, of
near-surface rock and sediment; weathering leads to the removal of waste products as
dissolved loads in water but results in little or no transport of solids (erosion) that are released
or modified by the weathering process.
Wetland is a bottomland or low-lying area, including ephemeral-lake floors, at which water
either is shallowly ponded on the surface or has a persistent (weeks or longer) near-surface
condition of ground-water saturation adequate to support hydrophytic vegetation.
Wetted perimeter of a channel section is the length of which water is in contact with the
channel bed and banks; wetted perimeter is a hydraulic parameter in the computation of
streamflow from physical properties of the channel.
Winnowing is the preferential entrainment and transport of fine particles from those of the
coarse fraction of a sediment deposit by fluid motion; the term is applied especially to the
transport of fine sediment sizes from a poorly sorted reservoir of sediment by wind, but the
winnowing process occurs also by the action of water moving on hillslopes, in rills and gullies, in
stream channels, and along beaches and other parts of lakes or oceanic tidal zones. X
Xeric refers to an environment (habitat) that is characterized by deficient moisture.
Xerophyte is a plant that is adapted to a habitat of low moisture availability. Y
Yardang is a sharp-crested landform, of relatively soft, generally fine-grained sedimentary or
volcanic rocks, that is typically oriented parallel to the dominant wind direction an arid region
or desert and has surfaces sculpted by processes of abrasion by wind-entrained sediment
(mostly sand and silt). 48 Z
Zone of aeration, or zone of vadose water, is the typically moist but unsaturated subsurface
zone between the land surface and the top of the zone of saturation (water table).
Zone of saturation is that part of the subsurface in which the interstices of porous and
permeable rocks are saturated with water under pressure equal to or greater than atmospheric
pressure. Major sources of information:
ASTM Subcommittee D19.07, 1999, D4410-98, Terminology for fluvial sediment: American
Society for Testing and Materials, West Conshohocken, PA, USA, 6 p. Fairbridge, R. W. (ed.),
1968, The Encyclopedia of Geomorphology: Reinhold Book Corp., New York, 1296 p.
Goudie, Andrew (ed.), 1994, The Encyclopedic Dictionary of Physical Geography: Blackwell
Publishing, Oxford, UK, 544 p. Goudie, Andrew (ed.), 2003, The Encyclopedia of
Geomorphology: Routledge, London, UK, 1200 p.
Interagency Advisory Committee on Water Data, 1982, Flood Flow Frequency: Bulletin 17B,
Hydrology Subcommittee, U. S. Geological Survey, Reston, VA, USA, 28 p.
Langbein, W. B., and Iseri, K. T., 1960, General introduction and hydrologic definitions: U. S.
Geological Survey Water-Supply Paper 1541-A, 21 p.
MacArthur, R. C., and Hall, B. R., 2008, Appendix E, Limited Glossary of Selected Terms, In
García, M. H. (ed.), Sedimentation Engineering: American Society of Civil Engineers Manuals
and Reports on Engineering Practice no. 110, 1132 p.
Monkhouse, F. J., and Small, John, 1978, A Dictionary of the Natural Environment: John Wiley
& Sons, New York, 320 p.
Neuendorf, Klaus K. E., Mehl, J. P., and Jackson, J. A. (eds.), 2005, Glossary of Geology, 5th
Edition: American Geological Institute, Alexandria, VA, USA, 779 p.
Phreatophyte Subcommittee PSIAC, 1962, Glossary of terms relating to the phreatophyte
problem: Pacific Southwest Inter-Agency Committee, Menlo Park, CA, USA, 7p. Schumm, S.
A., 1977, The Fluvial System: John Wiley and Sons, New York.
U. S. Geological Survey, 2007, Glossary of the National Water-Quality Assessment (NAWQA)
Program: NAWQA, http://water.usgs.gov/nawqa/glos.html, 19 p.. 49...
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