FACULTY OF SCIENCE JAI NARAYAN VYAS UNIVERSITY JODHPUR

DEPARMENT OF GEOLOGY PRESENTATION ON:

TYPES OF AQUIFERS

SUBMITTED TO-DR. S.R. JAKHARASS. PROF. JNVU

SUBMITTED BY-BABLUMSc-semester 3

CONTENTS

• INTRODUCTION ABOUT GROUND WATER• WHAT IS AQUIFER• WATER TABLE• TYPES OF AQUIFERS• EXAMPLES OF AQUIFERS

Water Distribution on Earth

Ground Water• Ground Water lies beneath the ground surface, filling

pores in sediments and sedimentary rocks and fractures in other rock types

• Represents 0.6% of the hydrosphere (35x the water in all lakes and rivers combined)– Resupplied by slow infiltration of precipitation– Cleaner than surface water– Accessed by wells

WHAT IS AQUIFERA saturated ,permeable , geologic unit that can transmit a significant amount of groundwater under an ordinarily gradient. Or

Aquifer is body of saturated rock or sediment through which water can move easily.

Examples: sand stone, conglomerate, well jointed limestone, highly fractured rock etc.

The Water Table

• Subsurface zone in which all rock openings are filled with water is the saturated zone

• Water table, top of the saturated zone– Water level at surface of most

lakes and rivers corresponds to local water table

• Above the water table is an unsaturated region called the vadose zone

TYPES OF AQUIFERS

• AQUIFERS may be classed as Unconfined or Confined depending on the presence or absence of a water table, while a Leaky aquifer represents a combination of the two types

1. UNCONFINED AQUIFER An unconfined aquifer is one in which water table varies in

undulating form and in slope, depending on areas of recharge and discharge pumpage from wells and permeability.

Rises and falls in the water table correspond to changes in the volumes of water in storage within an aquifer.

Unconfined Aquifer

Unconfined Aquifer • An aquifer that is bounded from above by a phreatic surface is

called a phreatic or unconfined, aquifer, or a water table aquifer• Has a water table, and is only partly filled with water.• Rapidly recharged by precipitation infiltrating down to the

saturated zone

AQUITARD-Rock/

sediment that retards

ground water flow due to low porosity

and/or permeability.

e.g.-shale , clay,

unfractured crystalline

rocks

UNCONFINED AQUIFERS

CONFINED AQUIFERS

PERCHED WATER BODIES A special case of an Unconfined aquifer. This occurs wherever a groundwater body is separated from

the main groundwater by a relatively impermeable stratum of small areal extent and by the zone of aeration above the main body of groundwater.

Commonly produced by thin lenses of impermeable rock (e.g. Shales or clays) within permeable ones

Types of Aquifers

Confined aquifer overlain by less permeable materials

Unconfined aquifer open to Earth’s surface and to infiltration

Perched aquifer underlain by low-permeability unit

Artesian aquifer: water rises in pipe (maybe to surface)

17.04.c,d.mtb

• Confined Aquifer – Completely filled with water under pressure (hydrostatic head)– Separated from surface by impermeable confining

layer/aquitard– Very slowly recharged

2. Confined Aquifers

CONFINED AQUIFERS

Confined Aquifers, also known as ‘Artesian’ or Pressure Aquifers.

It occur where groundwater is confined under pressure greater than atmospheric by overlying relatively impermeable strata.

In a well penetrating such an aquifer , the water level will rise above the bottom of the Confining bed , as shown by the Artesian and Flowing wells in figure on next slide.

Water enters a confined aquifer in an area where the confined bed rises to the surface where the confined bed ends underground, the aquifer becomes Unconfined.

ARTESIAN WELL IN CONFINED AQUIFER

The word Artesian is derived from the French artesian, meaning “of or pertaining to Artois ,” the northernmost province of France.

Here the first deep wells to tap confined aquifers were drilled and investigated, from about 1750.

The term referred to a well with freely flowing water, but at present it is applied to any well penetrating a confined aquifer or simply the aquifer itself.

FLOWING WELL IN CONFINED AQUIFERS

• Well - a deep hole dug or drilled into the ground to obtain water from an aquifer– Wells in unconfined aquifers, water

level before pumping is the water table

– Water enters well from pore spaces within the surrounding aquifer creating a cone of depression

– Water table can be lowered by pumping, a process known as drawdown

Insert new Fig. 11.8 here

ARTESIAN AND FLOWING WELL IN CONFINED AQUIFER

Artesian Wells

– Water may rise to a level above the top of a confined aquifer, producing an artesian well

FLOWING WELL AT NACHANA IN WESTERN RAJASTHAN

THE PIEZOMETRICS SURFACE, OR POTENTIOMETRIC SURFACE OF A CONFINED AQUIFER

It is an imaginary surface coinciding with the hydrostatic pressure level of the water in the aquifer.

The water level in a well penetrating a confined aquifer defines the elevation of the piezometric surface at that point.

3.LEAKY AQUIFER A leaky phreatic aquifer is a phreatic aquifer that is bounded

from below by a semipervious layer, which is usually referred to as an aquitard. This is a layer that is much less pervious than the aquifer overlying it and often is also much thin. It thus behaves as a “semi-pervious membrane” through which leakage out of or into the phreatic aquifer from an underlying saturated region is possible.

A leaky confined aquifer is a confined aquifer, except that one or both confining layers are aquitard.

Pumping from a well in a leaky aquifer removes water in two ways: By Horizontal flow within the aquifer and By Vertical flow through the aquitard into the aquifer.

In the figure, two leaky aquifers: The upper one is a phreatic-leaky aquifer, while The Lower one is a confined-leaky aquifer. They are separated by an aquitard. The piezometric surface is of the lower leaky-confined aquifer.

4.IDEALIZED AQUIFERFor mathematical calculations of the storage and

flow of groundwater , aquifers are frequently assumed to be Homogeneous and Isotropic.

A Homogeneous aquifer possesses hydrologic properties that are everywhere identical.

An Isotropic aquifer is one with its properties independent of direction.

EXAMPLES OF AQUIFERS GOOD AQUIFERS POOR AQUIFERSGravel , sand and deposits Solid rock, Granite

Fractured (broken up) Limestone • Rocks with poor permeability (water cannot pass through them

easily)

Limestone and Karst AquifersLimestone dissolves because rain water is slightly acidic. Cracks and faults form in the limestone, and they can grow to be big caves over time.

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