• acre-foot

    The volume of water necessary to cover one acre to a depth of one foot. Equal to 43,560 cubic feet or 325,851 gallons, or 1,233 cubic meters.

  • alabaster

    A fine-grained massive variety of gypsum that may be white, pink, gray, or even black. It can be polished and made into attractive objects of art.

  • alluvial aquifer

    An aquifer formed by material laid down by physical processes in a river channel or on a floodplain.

  • alluvial plain

    A level, gently sloping, or slightly undulating land surface produced by extensive deposition of alluvium, usually adjacent to a river that periodically overflows its banks.

  • alluvium

    Unconsolidated clay, silt, sand, or gravel deposited during recent geologic time by running water in the bed of a stream or on its floodplain.

  • amphipod

    An invertebrate animal, member of the biologic order Amphipoda. Amphipods are small segmented crustaceans. Some amphipods are nonpigmented cave-adapted species.

  • anastomosis

    A network of tubular passages or holes in a cave or in a solution-sculpted rock. A complex of many irregular and repeatedly connected passages. A labyrinth.

  • anhydrite

    A mineral usually associated with gypsum and of nearly the same chemical composition. Anhydrite is distinguished from gypsum in that it lacks water, as its name implies.

  • aquiclude

    An impermeable layer of rock that does not allow water to move through it. Some shales, for example, have such low permeability that they effectively form an aquiclude.

  • aquifer

    A geologic formation (or one or more geologic formations) that is porous enough and permeable enough to transmit water at a rate sufficient to feed a spring or a well. An aquifer transmits more water than an aquitard. Sandstone beds and the Ogallala Formation are some of the best water-producing layers in Kansas and are used extensively for private and municipal water supplies.

  • aquitard

    A part of a geologic formation (or one or more geologic formations) that is of much lower permeability than an aquifer and will not transmit water at a rate sufficient to feed a spring or for economic extraction by a well.

  • arid

    Said of a climate characterized by dryness, variously defined as rainfall insufficient for plant life; less than 10 inches (254 mm) of annual rainfall.

  • artesian aquifer

    An aquifer in which groundwater is confined under pressure significantly greater than atmospheric pressure. This pressure, called artesian pressure, is generally due to the weight of water at higher levels in the same zone and is sufficient to cause water to rise above the level of the aquifer in a well or natural fissure. An artesian aquifer is bounded above and below by confining beds of less permeable rock. Synonym: confined aquifer.

  • atmosphere

    (1) The gaseous portion of the planet. (2) Standard unit of pressure representing the pressure exerted by a 29.92-inches (760-mm) column of mercury at sea level at 45 degrees latitude and equal to 14.696 pounds per square inch (psi) or 101.325 kilopascals (An).

  • available moisture (or moisture)

    Portion of water in a soil that can be absorbed by plant roots. It is the amount of water released from a wet soil between field capacity and the permanent wilting percentage.