Hydro GroundwaTERMS

The movement of water below the earth’s surface within the subsurface layers or geological formations.

is a significant component of the water cycle, contributing to the overall movement and storage of water in the subsurface environment.

Subsurface Flow

Four Categories

1. Aquifer

2. Aquitard

3. Aquiclude

4. Aquifuge

Is a saturated formation of earth material which not only stores water but yields it in sufficient quantity. An aquifer transmits water relatively easily due to its high permeability.

Aquifer

Is a formation through which only seepage is possible and thus the yield is insignificant compared to an aquifer. It is partly permeable.

Aquitard

Is a geological formation which is essentially impermeable to the flow of water. It may be considered as closed to water movement even though it may contain large amounts of water due to its high porosity.

Aquiclude

Is a geological formation which is neither porous nor permeable. There are no interconnected openings and hence it cannot transmit water.

Aquifuge

TYPES OF AQUIFER

✓An unconfined aquifer is one in which a free water surface

i.e. a water table exists.

✓A confined aquifer, also known as artesian aquifer, is an

aquifer which is confined between two impervious beds

such as aquicludes or aquifuges.

➢A confined aquifer is called a leaky aquifer if either or

both of its confining beds are aquitards.

FACTS ABOUT WATER TABLE

❑A water table is the free water surface in an unconfined aquifer.

❑The static level well penetrating an unconfined aquifer indicates the level of the water table

at that point.

❑The water table is constantly in motion adjusting its surface to achieve a balance between

the recharge and outflow from the subsurface storage.

❑The water table follows the topographic features of the surface.

Sometimes, a lens or localized patch of impervious stratum can occur inside an unconfined aquifer in such a way that it retains a water table above the general water table. Such water table around the impervious material is known as perched water table.

PERCHED WATER TABLE

Also known as a gaining stream, receives water from the surrounding groundwater.

Effluent stream

Losing stream, loses water to the groundwater system.

Influent stream

The amount of pore space per unit volume of the aquifer material

Porosity

The actual volume of water that can be extracted by the force of gravity from a unit volume of aquifer material

Specific Yield (Sy)

The fraction of water held back in the aquifer

Specific Retention (Sr)

French hydraulic engineer, on the basis of his experimental findings proposed a law relating the velocity of flow in a porous medium

Henry Darcy,

Refers to the volumetric flow rate of water passing through a given cross-sectional area of a porous medium per unit time.

Total Discharge

Also known as Darcy Velocity or Darcy Flux, is defined as the discharge per unit area of the porous medium.

Specific Discharge