|
<br />by pumping. (2) The area from which water occurring at a
<br />given point or location on a stream orginates. In such case the
<br />term is synonymous with drainage area and watershed. (3) The
<br />term is also used in a general sense to 3RPly to the flow of all
<br />liquids under the force of gravity. (4) The water features of a
<br />map such as seas, lakes, ponds, streams, and canals.
<br />DRAINAGE, WELL - The removal of surplus or excess surface
<br />or ground water by sinking wells to a {'arous formation in which
<br />the hydrostatic head is lower than that of the water on the
<br />surface to be drained. and carrying off the surface, water through
<br />these wells. When filled with stones, the well 15 called a dry
<br />well.
<br />DRA\VDO\VN - (1) The magnitude of the change in surface
<br />elevation of a body of water as a result of the withdrawal of
<br />water therefrom. (.2) The magnitude of the lowering of the
<br />water surface in a well, and of the water table or piezometric
<br />surface adjacenr to the well, resuhin,g from the withdrawal of
<br />water from the well by pumping. (3) The difference in eleva-
<br />tion between the water surface elevation at a constriction in a
<br />stream or conduit and the elevation that would exist if (he con-
<br />striction were absent.
<br />EVAPORATION, TOTAL - The sum of the water lost from a
<br />given land area during any specific time by transpiration from
<br />vegetation and building of plant tissue; by evaporation from
<br />water surfaces, moist soil grains, and snow; and by interception.
<br />The term is applied primatily to stream drainage basins for the
<br />period of the annual climatic cycle or subdivision of that period.
<br />Total evaporation is essentially precipitation upon the drainage
<br />basin minus runoff, corrected fOT change in storage volume with-
<br />in the basin and for subsurface leakage. It has been variously
<br />called evaporation from land areas, evaporlltion, evapo-transpira-
<br />tion, loss, water losses, and fly off.
<br />FLOOD, PROBABLE, MAXIMUM. The maa;mum flood for
<br />which there is reasonable chance that it will occur on a given
<br />stream at a selected site. It is often assumed to be equal to the
<br />maximum flood observed in areas having the same or similar
<br />physiographic and meteorological characteristics. Such a flood
<br />would \'ery likely be less than the maximum possible flood.
<br />FLO\V, RETURN - Any flow which returns to a stream chan-
<br />nel after di\'ersion for beneficial use or other purposes. 1n irri-
<br />gation, water applied to an area which is not consumed in
<br />evaporation or transpiration, and returns to a surface stream or
<br />ground-water aquifer.
<br />FLO\V, SUBSURFACE - (I) That portion of the water which
<br />infiltrates the soil surface and moves laterally through the upper
<br />soil horizons until its course is intercepted by the channel of
<br />the stream or until it returns to the surface at some (loiot down-
<br />stream of its point of infiltration, (2) The rate of flow or dis-
<br />charge of ground water or subsurface water.
<br />FLUME, RAT1NG - (I) An open conduit built in a channel
<br />to maintain a consistent regimen for the purpose of measuring
<br />the flow and developing the stage-discharge relation. (2) A
<br />flume comaininK still water and used for the purpose of rating
<br />current meters, Pitot tubes, etc.
<br />GAGE, RIVER - A device for measuring river stage, i.e., to in-
<br />dicate the height of the water surface above a specific point.
<br />Types in common use include staff gage, waterstage recorder,
<br />and wire weight gage.
<br />GAGING, STREAl\:1 - The operation of measuring the \:elocity
<br />of a stream of ......ater in a channel or an open conduit, and the
<br />area of cross-section of the water, for the pLlrpose of determining
<br />the discharge. Also called gaging.
<br />GALLERY - (l) An underground structure designed and in-
<br />stalled for the purpose of collecting percolating water. (2) A
<br />passageway in a structure, such as a dam, waler treatment plant.
<br />etc., used for obtaining access to interior parts, or to carry pipes,
<br />
<br />6
<br />
<br />;,
<br />I
<br />
<br />or to house machinery. (3) An underground conduit, or reser-
<br />voir or passa~e.
<br />GATE, HEAD - (I) A gate at the entrance to a cond';lit, such
<br />as a pipe line, penstock, or canal. (2) The gate at the high le\'el
<br />end of a lock. (3) The gale at the entr8nce to an irrigation
<br />ditch.
<br />GRA VITY, SPECIFIC - The ratio of the weight of a given
<br />\'olume of a substance to the weight of an equal volume of
<br />water.
<br />HYDROLOGY - The applied science concerned with the waters
<br />of the earth in all its states - their occurrences, distribution. and
<br />circulation through the unending hydrologiC cycle of: lrecipita-
<br />tion, consequent runoff, stream flow, infiltration, an storage;
<br />eventual evaporation; and reprecipitation. It is concerned with
<br />the physical, chemical, and physiological reactions of water with
<br />the rest of the earth, and its relation to the life of the earth.
<br />HYDROLOGY, GROUND-WATER, The branch of hydrol-
<br />ogy that treats of ground water; its occurrence and movements;
<br />its replenishments and depletion; the propenies of rocks that
<br />control ground-water movement and storage; and the methods of
<br />im'estigation and utilization of ground water.
<br />1MBIBlTION - The process by which plants absorb water from
<br />the soil.
<br />1NFLUENCE, CONE OF - The depression, roughly conical in
<br />shape, produced in a water table, or other piezometric surface,
<br />by the extraction of water from a well at <l gi\'en rate. The
<br />volume of the cone will vary with the rate of withdrawal of
<br />waler, Also called COtle of depression.
<br />1RRIGATION, OVER - The application of more water than is
<br />necessary for the needs of vegetation, resulting in loss of water
<br />through seepage and leaching with the resultant loss of humus,
<br />nitrogen, and other mineral elements of the soil.
<br />IRRIGATION, SUPPLEMENTAL - The watering of crors in
<br />regions where normal rainfall ordinarily supplies most 0 the
<br />moisture. It is used during dry periods to pre\'ent retardation of
<br />growth.
<br />1RRIGATION, WINTER - The irrigation of lands during the
<br />non-growing season in order [Q store water in the soil for sub-
<br />sequent use by plants.
<br />LEACHING - (I) The removal of soluble conSlituents from
<br />soils or other material by percolating liquid. (2) The removal of
<br />salts and alkali from soils by abundant irrigation combined with
<br />drainage. (3) The disposal of a liquid through a nonwatertight
<br />artificial structure, conduit, or porous material bv downward or
<br />lateral drainage, or both, into the surrounding permeable soil.
<br />LE VEE - (1) A dIke or embanJonent, generally constructed on
<br />or parallel to Ihe banks of a stream, lake, Ot other body of water,
<br />for (a) the purpose of protecting the land side from inundation
<br />bv flood waters, or (b) to confine the stream flow to its regular
<br />channel. (2) The construction of a levee.
<br />LEVEL, HYDROSTATIC - The level or elevation to which
<br />the top of a column of water would rise, if afforded opportunity
<br />to do so, from an artesian aquifer, or basin, in an open conduit,
<br />or from a conduit under pressure.
<br />LOG, \VELL - A chronological record of the soil and rock
<br />formations which were encountered in the operarion of sinking
<br />a well, Wilh either their thickness, or the elevation of the top
<br />and bottom of each formation given. It also usually includes
<br />statements as to the lithologic composition and water-bearing
<br />characteristics of each formation.
<br />LOSS, CONVEYANCE - The loss of water from <l conduit due
<br />to leakage, seepage, evaporation, or evapo-transpiration,
<br />MAP, GEOLOGIC - A map which shows the boundaries and
<br />
<br />7
<br />
<br />
|