Hydraulic Characteristics Of Aquifers
The most important hydraulic properties of aquifers are their ability to store and transmit water. The aquifer’s hydraulic conductivity is a measure of its ability to transmit water. Hydraulic conductivity is dependent on the porosity and permeability of the material as well as on the dynamic characteristics of the fluid (water). Transmission of water through an aquifer requires a driving force (hydraulic gradient). Fluid flow in an aquifer is driven by pressure changes. The change in total pressure over a specific distance or length is termed the hydraulic gradient. A measure of the volume of water that can be transmitted horizontally by the full saturated thickness of an aquifer is referred to as its transmissivity. The transmissivity is the product of the hydraulic conductivity and the saturated thickness of the aquifer. The hydraulic conductivity, hydraulic gradient, and transmissivity are all characteristics of aquifers that are used to describe the flow of water.
The ability of an aquifer to store or release water is quantified by the value of its storage coefficient. The magnitude of the storage coefficient depends upon whether an aquifer is confined or unconfined. The storage coefficient in confined aquifers is small compared to that of unconfined systems. The term storage coefficient is usually associated with the storativity of a confined aquifer, where water release from storage depends upon the elasticity of the aquifer and the compressibility of the fluid. The term specific yield is normally applied to the storativity of an unconfined aquifer. Unconfined aquifers provide water by physical dewatering (via gravity drainage) of the material through which the decline in the water table occurs.