introduction to groundwater and aquifer

Introduction to Groundwater

and Aquifer

By: Putika Ashfar .K

References

• Heath, Ralph C., 1983, Basic ground-water hydrology: U.S . Geological Survey Water-Supply

• Todd, D.K. and Mays L.W., (2005): Groundwater Hydrology.(3rd Edition). John Wiley & Sons, New York

• Ground water is one of the most valuable natural resources . • Ground-water hydrology is the subdivision of the science of hydrology

that deals with the occurrence, movement, and quality of water beneath the Earth's surface .

Porous Media and Groundwater Flow

1. Water-bearing rocks

2. Voids of rocks

3. Deposits Consolidation

Water bearing rocks

Voids of rocks • Primary openings If the voids were formed at

the same times as the rocks

• Secondary openings The voids were formed after

rock formed

(E.g : granite)

• Both Primary and

Secondary openings (E.g : limestone, sandstone)

Deposits Consolidation

• Unconsolidated deposits Consist of material derived from the disintegration of consolidated

rocks. The material consists, in different types of unconsolidated deposits, of particles of rocks or minerals ranging in size from fractions of a millimeter (clay size) to several meters (boulders).

• Semi-Unconsolidated deposits These are rocks in which openings include both pores and fractures-

in other words, both primary and secondary openings .

• Consolidated deposits consist of mineral particles of different sizes and shapes that have

been welded by heat and pressure or by chemical reactions into a solid mass.

Zones of Groundwater

Unsaturated zone

saturated zone

aquiclude

aquitard

Zones of Groundwater

Unsaturated zone / vadose zone A zone contains of water and air Capillary fringe A zone which is result from water and rocks attraction, usually adjacent with unconfined aquifer Saturated zone Full water zone Water level Level in the saturated zone when hydraulic pressure equal to athmospheric pressure

Soil surface

Water level

Groundwater

Capillary fringe

Unsaturated zone

saturated zone

well

Aquifer

Aquifer Water bearing geological formation that can store and yield usable amount of water

Aquitard A bed of low permeability adjacent to an aquifer and may serve as a stirage unit

Aquiclude A solid and impermeable area overlies the aquifer pressure which cause a confined aquifer zone

Aquifuge Impermeable body of rocks which contains no interconnected openings

Soil surface

Water level

Confined aquifer

Aquitard

aquifuge

Confining unit

Confining unit

Aquifer Properties

• Porosity (n)

• Specific Yield (Sy)

• Specific Retention (Sr)

• Total Head (Ht)

• Hydraulic Gradient

• Hydraulic Conductivity (K)

• Transmittivity (T)

Porosity (n) The ratio of opening voids to total volume of a

soil/ rocks

Vt = total volume of soil/ rocks sample Vv = volume of opening voids

Specific Yield (Sy)

• Water storage in the groundwater that drain under the influence of gravity

• It simply tells how much water available for man use

Vt = total volume of soil/ rocks sample Vr= volume of water retained

Specific Retention (Sr) • Tells how much water is available after drained by

gravity

• The part retained on rock surfaces in a very small openings (capillary fringe indeed)

Vr = volume of water retained

Total Head (Ht) and Hydraulic Gradient

Ht = z + hp

Ht= total head

z = elevation head

Hp = pressure head

Hydraulic gradient • The change head per unit distance in

a given direction • If the direction isnt specified, choose

the direction with maximum rate of decrease of head occurs

hL = head between 2 wells L = horizontal distance between wells

Hydraulic Gradient

hL 18 m

Water line

Soil surface

datum

Bottom of aquifer

hp

hp

15 m

z

z

ht ht

L = 780 m

Hydraulic Conductivity (K)

By its area,aquifer can be classified as : Homogenous area if hydraulic conductivity (K) is same in any area of aquifer Hetergenous area If there is any differences of K in aquifer By moving direction of groundwater flow : Isotropic If hydraulic conductivity (K) is same in all direction Anisotropic Hydraulic conductivity (K) in one flow direction is different

Q = quantity of water per-unit per-time A = cross-sectional area

Transmittivity (T)

The capacity of aquifer to transmit water in kinetic viscocity

T = K.b

K = hydraulic conductivity

b = aquifer thickness

Transmittivity (T)…. (example) Given average daily flow of two wells as below :

Discharge from half-aquifer (Q) = 5616 m3/day

Distance from A to B = 5000 m

Average thickness of aquifer (b) = 50 m

Average slope on water table = 1/2000

Station Average daily flow (m3/s)

A 2485

B 2355

Storage Coefficient (S)

Volume of water that an aquifer release from or take into

storage

for confined aquifer S = 0,00005 – 0,005

for unconfined aquifer S = 0,07 – 0,25

• Thank you