Acre-foot: The quantity of water required to cover 1 acre to a depth of 1 foot; equal to 43,560 cubic feet or 325,851 gallons. Aquiclude: A formation which, although porous and capable of absorbing water slowly, will not transmit it fast enough to furnish an appreciable supply for a well or spring. Aquifer: A formation, or group of formations, or a part of a formation that is water bearing. Artesian water: The occurrence of ground water under sufficient hydrostatic head to rise above the upper surface of the aquifer. Base flow: Discharge entering stream channels as effluent from the ground-water reservoir; the fair-weather flow of streams. Color: Color, in water analysis, is an expression of the visual appearance of water completely free of suspended material. Color is expressed in units of the platinum-cobalt scale. Concentration: The weight of dissolved solids or sediment per unit weight of solution. Concentration is expressed in parts per million (ppm) a unit weight of a constituent in a million unit weights of solution. For chemical concentrations the computation is based on a million unit weights of clear solution containing water-dissolved solids; for sediment concentration it is based on the mixture of water-dissolved solids and sediment. Cubic feet per second: The discharge of a stream of rectangular cross section, 1 foot wide and 1 foot deep, whose velocity is 1 foot per second; equivalent to 448.8 gallons per minute. Climatic year: The 12-month period from April 1 to March 31. Cone of depression: A conical depression, on a water table or piezometric surface, produced by pumping. Direct runoff: The water that moves over the land surface directly to streams promptly after rainfall or snowmelt. Discharge, ground-water: The process by which water is removed from the zone of saturation ; also, the quantity of water removed. Diversion: The taking of water from a stream or other body of water into a canal, pipe, or other conduit. Evapotranspiration: Water withdrawn from a land area by direct evaporation from water surfaces and moist soil and by plant transpiration. Ground-water reservoir: An aquifer or a group of related aquifers. Ground-water runoff: That part of the streamflow which consists of water discharged into a stream channel by seepage from the ground-water reservoir; same as base flow. Head (hydrostatic head): The height of a vertical column of water, the weight of which, in a unit cross section, is equal to the hydrostatic pressure at a point. Hydraulic gradient: The rate of change of hydrostatic head per unit of distance of flow at a given point and in a given direction. VII VIII GLOSSARY Hydrograph : A graph, showing changes in stage, flow, velocity, or other aspect of water with respect to time. Mean annual flood: The arithmetic average of an infinitely long series of annual peak flows; the flood having a recurrence interval of 2.33 years. Part per million : One milligram of solute in 1 kilogram of solution.Perched ground water: Ground water separated from an underlying body of ground water by u...