aquifer An aquifer is an underground layer of water-bearing permeable rock, or unconsolidated materials (gravel, sand, silt, or clay) from which groundwater can be usefully extracted using a well (bore). A common misconception is that groundwater exists in underground rivers (e.g. caves where water flows freely underground), while the truth is that the pore spaces of rocks in the subsurface are simply saturated with water, which can be pumped out and used for agricultural, industrial or municipal uses. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology. »» show more information
alluvium Alluvium is soil land deposited by a river or other running water. The structure formed is called an alluvial deposit. »» show more information
B
bedrock Bedrock is the native consolidated rock underlying the Earth's surface. Above the bedrock is usually an area of broken and weathered unconsolidated rock in the basal subsoil. The term implies that the rock lies in beds, or strata. Under any given location on the surface of the planet, rock will be found. The term bedrock may be somewhat misleading, since in many locations, the bedrock may change over a short distance, or the technical bedrock may be a thin stratum overlying quite different rock.
C
capillary fringe The capillary fringe is the subsurface layer in which water molecules seep up from a water table by capillary action to fill pores. Pores at the base of the capillary fringe are filled with water due to tension saturation. This saturated portion of the capillary fringe is less than total capillary rise because of the presence of a mix in pore size. If pore size is small and relatively uniform, it is possible that soils can be completely saturated with water for several feet above the water table. Alternately, the saturated portion will extend only a few inches above the water table when pore size is large or non-uniform. Capillary action supports an unsaturated zone above the saturated base within which water content decreases with distance above the water table. In soils with a wide range in pore size, the unsaturated zone can be several times thicker than the saturated zone.
D
Darcy's law Darcy's Law is a phenomologically derived constituative equation that describes the flow of a fluid through a porous medium (typically water through an aquifer). The law was formulated by Henry Darcy based on the results of 1855 and 1856 experiments on the flow of water through beds of sand. It, along with the conservation of mass, comprises the groundwater flow equation, which is one the basic building relationships of hydrogeology. »» show more information
drawdown drawdown is the change in hydraulic head observed at a well in an aquifer, typically due to pumping a well as part of an aquifer test or well test »» show more information
G
groundwater groundwater is water in a free state within rocks or sediments, held within a space or void. Voids are created by spaces formed within clastic deposits (packing of sediments), physical and chemical weathering of bedrock or movement of rock masses (fractures and faults). »» show more information
H
hydraulic conductivity Hydraulic conductivity, mathematically represented as K, is a property of soil or rock, in the vadose zone or groundwater, that describes the ease with which water can move through pore spaces or fractures. It depends on the intrinsic permeability of the material and on the degree of saturation. Saturated hydraulic conductivity, Ks, describes water movement through saturated media. »» show more information
permeability In geology, permeability is a measure of the ability of a material (typically, a rock or unconsolidated alluvial material) to transmit fluids through it. It is of great importance in determining the flow characteristics of hydrocarbons in oil and gas reservoirs, and of groundwater in aquifers. The usual unit for permeability is the darcy, or more commonly the milli-darcy or md (1 darcy equals cca 10-12m2). »» show more information
porosity Used in geology, building science and hydrogeology, the porosity of a porous medium (such as rock or sediment) is the proportion of the non-solid volume to the total volume of material. Porosity is a fraction between 0 and 1, typically ranging from less than 0.01 for solid granite to more than 0.5 for peat and clay, although it may also be represented in percent terms by multiplying the fraction by 100%. »» show more information
S
salinity Salinity is the "saltiness" or dissolved salt content of a body of water. »» show more information
specific storage Specific storage (Ss) and its depth-integrated equivalent, storativity (S=Ssb), are indirect aquifer properties (they cannot be mesured directly); they indicate of the amount of groundwater released from storage due to a unit depressurization of a confined aquifer. They are fractions between 0 and 1. »» show more information
specific yield Specific yield (Sy) is a ratio between 0 and 1 indicating the volumetric fraction of the bulk aquifer volume that a given an aquifer will yield when all the water is allowed to drain out of it under the forces of gravity. »» show more information
storativity (also storage coefficient) This is a parameter used in groundwater modelling. It is dimensionless (does not have units) and is equal to the product of specific storage and aquifer thickness. Storativity (S) represents the volume of water an aquifer releases from, or takes in storage, per unit surface area of aquifer per unit change in head. It is usually a very low number <0.005 (e.g. for a pumping test in Lockyer gravels a value of S of 0.0016 was determined by Wilson, 2005).
V
vadose zone The vadose zone, also termed the unsaturated zone, is the portion of Earth between the land surface and the water table, and is thus not considered groundwater ("vadose" is Latin for "shallow"). It comprises the unsaturated portion of the soil, regolith or bedrock, as well as the unsaturated portion of the capillary fringe above the water table. The pore spaces in the vadose zone are subject to atmospheric pressure, and so the water is held to the regolith and rock by adhesion (funiculary groundwater), and in pore spaces by capillary action (capillary groundwater). If the vadose zone envelops soil, the water contained therein is termed soil moisture.
W
water content Water content is a ratio used in hydrogeology and soil mechanics to indicate the amount of water a porous medium (aquifer) contains. In fully saturated groundwater aquifers, all the available pore spaces are filled with water. Above the capillary fringe, some of the pore spaces have air in them too. When the porous medium in question is soil, water content is synonymous with soil moisture.
water cycle The water cycle — technically known as the hydrologic cycle — is the circulation of water within the earth's hydrosphere, involving changes in the physical state of water between liquid, solid, and gas phases. The hydrologic cycle refers to the continuous exchange of water between atmosphere, land, surface and subsurface waters, and organisms. »» show more information
