Aquifer

An aquifer is an underground layer of water-bearing rock. Water-bearing rocks are permeable, meaning that they have openings that liquids and gases can pass through. Sedimentary rock such as sandstone, as well as sand and gravel, are examples of water-bearing rock.

1. Aquifer & types of aquifer

2. aquifer An aquifer is an underground layer of water-bearing rock. Water-bearing rocks are permeable, meaning that they have openings that liquids and gases can pass through. Sedimentary rock such as sandstone, as well as sand and gravel, are examples of water-bearing rock. OR The geological formation which contain & yields sufficient amount of water. An aquifer easily supplies water to well, installed in the formation. The formation composed of sand & fine gravels are the good aquifers.

3. Types of aquifer Confined Aquifer Unconfined Aquifer Semi Confined Aquifer Perched Aquifer

4. Confined aquifer It is one which is covered by impervious layer from its top & bottom , both the sides. In other words “it lies b/w two impermeable layers”. OR One in which groundwater is confined under pressure greater than atmospheric by overlying impermeable strata. It is also known as artesian or pressure aquifer

5. Unconfined aquifer This aquifer is not covered from the upper side with impervious formation , while essentially covered by an impervious layer from its bottom side .Water table is the upper surface of this aquifer sometime it I also referred as water table aquifer. OR One in which a water table serves as the upper surface of the zone of saturation. It is also known as a free, phreatic or non-artesian aquifer.

6. Semi confined aquifer In this aquifer the upper or lower layer which confine the aquifer is in semipermeable nature. Semi confined aquifers are also called leaky aquifers, as there is leakage of water from semi pervious layer . OR An aquifer partially confined by soil layers of low permeability through which recharge and discharge can still occur.

7. PERCHED AQUIFER It is a special type of unconfined aquifer , in which water is stored to a limited areal extent. OR An impermeable saucer shaped stratum of a small areal extent occurring in the zone of aeration may retain & hold some amount of water.

8. Aquifer terms related with hydrological properties

9. porosity Groundwater occurs in voids, or pores of geologic formations. Porosity term is defined as : = W/V where W is the volume of water required to saturate all voids or volume of all pores and V is the total volume of the rock (soil).

10. SPECIFIC RETENTION Specific Retention ( Sr ): When groundwater is pumped or drained, some water is retained by molecular and surface tension forces. Specific retention is therefore expressed as: Sr = Wr /V (usually expressed in %). Wr is the volume of water retained and V is the total volume of rock (soil).

11. SPECIFIC YIELD Specific Yield ( Sy ) : The water removed by the force of gravity is the specific yield or effective porosity. It is defined as: Sy = Wy /V (usually expressed in %). Wy is the volume of water drained while V is the total volume of rock(soil). Since total volume, W = Wy + Wr Porosity, : = Sr + Sy .

12. STORATIVITY Storage Coefficient ( Storativity , S): It is the volume of water which an aquifer releases from or takes into storage per unit surface area per unit change in head. Units = L 3 = [ ] ie . dimensionless ie . has no units. (L 2 ) (L) For the unconfined aquifer, S = Sr

13. transmissivity Transmissivity (T): It is a measure of the ease of water movement in the soil. It is the hydraulic conductivity (K) multiplied by aquifer thickness (b). ie . T = K x b m 2 /d m/d x m

14. permeability Permeability is the property of rocks that is an indication of the ability for fluids (gas or liquid) to flow through rocks. OR Permeability is essentially related to the quantity of pores & other entities in a rock.

15. Hydraulic conductivity The ability of a porous material to transmit a fluid. In darcy law , the hydraulic conductivity is a proportionality factor which essentially expresses an interaction between the porous media (soil) & flowing fluid (water).

16. Hydraulic Conductivity Depends Upon The: Soil matrix Properties of water flowing through the soil

17. Hydraulic conductivity of different aquifer materials

18. Thank you