lecture 18 19

7/27/2019 Lecture 18 19

1/53

Lectures 18 and 19

Groundwater

Dr. K. Vijaya KumarSchool of Earth Sciences

SRTM University, Nanded

431 606Maharashtra, INDIA

(E-mail: [email protected])

7/27/2019 Lecture 18 19

2/53

Groundwater

Water resources

Geologic Agent

7/27/2019 Lecture 18 19

3/53

Earth materials

Rock

Sediment (Soil)

Fluids (Water)

Geologic processes

Form,

Transform and Distribute (redistribute) Earth materials

Water is a primary agent of many (all?) geologic

processes

Hydrogeology Defined

Water Earth

7/27/2019 Lecture 18 19

4/53

Hydrogeology DefinedWater-Earth Interactions

Interactions go both ways

GeologyGroundwater

Geology controls flow

and availability of

groundwater because

Groundwater flows

through the pore spaces

and/or fractures

Groundwater geologic

processes.

7/27/2019 Lecture 18 19

5/53


Water

Earth InteractionsGeology controls groundwater flow Permeable pathways are controlled by distributions of

geological materials.

E.g., Artesian (confined) aquifer

7/27/2019 Lecture 18 19

6/53


Water



Groundwater availability is controlled by geology.

7/27/2019 Lecture 18 19

7/53


Water



Groundwater availability is controlled by geology.

Subsurface contaminant

transport in is controlled

by geology.

7/27/2019 Lecture 18 19

8/53


Water

Earth InteractionsGroundwater controls geologic processes Igneous Rocks: Groundwater

controls water content of

magmas. Metamorphic Rocks:

Metasomatism (change incomposition) is controlled by

superheated pore fluids.

Volcanism: Geysers are anexample of volcanic activityinteracting with groundwater.

7/27/2019 Lecture 18 19

9/53


Water

Earth InteractionsGroundwater controls geologic processes Landforms: Valley development and karst topography are

examples of groundwater geomorphology.

Landslides: Groundwater controls slope failure. Earthquakes: Fluids control fracturing, fault movement,

lubrication and pressures.

7/27/2019 Lecture 18 19

10/53

Hydrogeology Sub-disciplines Water resource evaluation

What controls how much groundwater is stored and can be

safely extracted? What controls where groundwater comes from and where it

flows?

What controls natural water quality: natural interactions withgeological materials control the chemistry of groundwater?

How can we protect groundwater recharge areas andgroundwater reservoirs from contamination and depletion?

d l b di i li

7/27/2019 Lecture 18 19

11/53

Hydrogeology Sub-disciplines Contaminant Hydrogeology

Anthropogenic effects: degradation of water qualitydue to

human influences (contamination) How fastare dissolved contaminants carried by groundwater?

Transport pathways of contaminants: Where are sources ofcontamination impacting the groundwater, where are the goingand what are the destinations?

Remediation (clean-up) of contaminants dissolved in thegroundwater.

7/27/2019 Lecture 18 19

12/53

Ground Water Zones

Degree of saturation

defines different soil

water zones

7/27/2019 Lecture 18 19

13/53

Unsaturated Zone/zone of

aeration:Atmosphericpressure is more than

fluid pressure

Saturated Zone:

Where all pores are

completely filled with water.

Phreatic Zone: Saturated zone below the water table

Water Table: where fluid

pressure is equal to

atmospheric pressure

Soil and Groundwater Zones

Capillary Fringe: Water ispulled above the water

table by capillary

suction

7/27/2019 Lecture 18 19

14/53

Ground water and

the Water cycle

Infiltration Infiltration capacity

Overland flow

Ground water

recharge GW flow

GW discharge

7/27/2019 Lecture 18 19

15/53

Bedrock Hydrogeology

Hydraulic

Conductivity of

bedrock iscontrolled by

Size of fracture openings

Spacing of fractures

Interconnectedness of fractures

7/27/2019 Lecture 18 19

16/53

Porosity and

Permeability

Porosity: Percent of volume

that is void space.

Sediment: Determined by how

tightly packed and how clean

(silt and clay), (usually

between 20 and 40%)

Rock: Determined by size and

number of fractures (most

often very low,

7/27/2019 Lecture 18 19

17/53

Porosity and

Permeability

Permeability: Ease with

which water will flow through

a porous material

Sediment: Proportional to

sediment size

GravelExcellent

SandGood

SiltModerate

ClayPoor

Rock: Proportional to fracture

size and number. Can be good

to excellent

Excellent

Poor

7/27/2019 Lecture 18 19

18/53

Porosity and

Permeability

Permeability is not

proportional to

porosity.

1%

5%30%

7/27/2019 Lecture 18 19

19/53

Porosity (stores) and Permeability (transmits) k

Define specific yield and specific retention of the Groundwater

Sediments granular rocks from

detrital material matrix flow

Primary porosity (and dual)Fine grained and Coarse grained

eg: shale, sandstone

Crystalline rocks fractures

Secondary porosity with water

only in the fractures fractureflow

Fracture density controls yield

eg: granite, basalt

high low k

low low khigh high k

low high k

7/27/2019 Lecture 18 19

20/53

Porosity, specific yield

and specific retention

7/27/2019 Lecture 18 19

21/53

What controls:

How much groundwater

flows?

How fast groundwater

flows?

Where groundwater flows?

Darcys LawAnswers the fundamental questions of hydrogeology.

D L

7/27/2019 Lecture 18 19

22/53

Darcys Law

Henry Darcys Experiment (Dijon, France 1856)

Darcy investigated ground water flow under controlled conditions. Darcys

law states that the f low o f water through a porous medium is

proportional to hydraulic gradient or coefficient of permeability k

wh ich is characteris t ic of porous media.

7/27/2019 Lecture 18 19

23/53

Darcys Law

7/27/2019 Lecture 18 19

24/53

Water table: the

surface separating

the vadose zone

from the saturated

zone.

Measured using

water level in well

The Water Table

d l

7/27/2019 Lecture 18 19

25/53

Precipitation

Infiltration

Ground-waterrecharge

Ground-water flow

Ground-waterdischarge to

Springs

Streams and

Wells

Ground-Water Flow

d l

7/27/2019 Lecture 18 19

26/53

Velocity is

proportional to

Permeability

Slope of the water

table

Inversely

Proportional to

porosity

Ground-Water Flow

Fast (e.g., cm per day)

Slow (e.g., mm per day)

7/27/2019 Lecture 18 19

27/53

Infiltration

Recharges ground

water

Raises water table

Provides water to

springs, streams and

wells Reduction of

infiltration causes

water table to drop

Natural Water Table Fluctuations

7/27/2019 Lecture 18 19

28/53

Eff f P i

7/27/2019 Lecture 18 19

29/53

Pumping wells

Accelerates flow near

well May reverse ground-

water flow

Causes water tabledrawdown

Forms a cone of

depression

Effects of Pumping

Wells

Eff f P i

7/27/2019 Lecture 18 19

30/53

Pumping wells

Accelerate flow Reverse flow

Cause water table

drawdown

Form cones of

depression Low river

Gaining

Stream

Gaining

Stream

Pumping well

Low well

Low well

Cone of

Depression

Water Table

Drawdown

Dry Spring

Effects of Pumping

Wells

Eff t f

7/27/2019 Lecture 18 19

31/53

Dry river

Dry well

Effects of

Pumping Wells

Dry well

Dry well

Losing

Stream Continued water-

table drawdown

May dry upsprings and wells

May reverse flow

of rivers (and

may contaminateaquifer)

May dry up rivers

and wetlands

7/27/2019 Lecture 18 19

32/53

Ground-Water/

Surface-Water

Interactions

Gaining streams

Humid regions

Wet season

Loosing streams

Humid regions, smaller

streams, dry season

Arid regions

Dry stream bed

G d h / i h

7/27/2019 Lecture 18 19

33/53

Groundwater Recharge / DischargeInteraction between groundwater and surface water

T f W t b i b di

7/27/2019 Lecture 18 19

34/53

Types of Water bearing bodies

Diff t t f W t b i ti

7/27/2019 Lecture 18 19

35/53

Different types of Water-bearing properties

Aquifer: Aquifer is defined as a rock body that is capable of holding ground

water supplies by virtue of its high porosity and permeability. The aquifer yields

water when tapped at good velocity and volume and for longer periods.Gravels, limestone and coarse sandstone make good aquifers. If the velocity of

the ground water flow is low due to relatively smaller pore size and relatively

less permeability, they are called as Aquitards.

Aquiclude: Aquiclude is a rock body which may be porous enough to holdsome quantity of water but due to low permeability does not allow good flow of

water through it. A rock with a low specific yield and high specific retention.

Shale and clays are good examples of aquiclude.

Aquifuge: Aquifuge an absolutely impermeable rock through which there is

little possibility of movement of water, even at slower velocities due to very little

porosity. Plutonic igneous rocks are primarily ideal aquifuges; however

presence of secondary porosity (joints, faults, fractures etc.) makes them

aquiferous.

7/27/2019 Lecture 18 19

36/53

7/27/2019 Lecture 18 19

37/53

7/27/2019 Lecture 18 19

38/53

Groundwater Flow in

Confined and Unconfined Aquifers

Aquifer types:

unconfined (free

surface), water-table

aquifer or phreaticaquifer. Specific yield.

Perched aquifer

confined (under

pressure) aquifers are

bounded byimpervious or semi-

pervious layers.

Storage coefficient.

Artesian aquifer

7/27/2019 Lecture 18 19

39/53

Ground-Water Contamination

Dissolved contamination travels with ground water flow

Contamination can be

transported to water

supply aquifers down

flow

Pumping will draw

contamination into

water supply

7/27/2019 Lecture 18 19

40/53

Sources of Groundwater Pollution

7/27/2019 Lecture 18 19

41/53

Sources of Groundwater Pollution

7/27/2019 Lecture 18 19

42/53


Leaking Gasoline Floats on water

table

Dissolves in groundwater

Transported by

ground water

Contaminates

shallow aquifers

7/27/2019 Lecture 18 19

43/53


Dense solvents E.g., dry cleaning

fluid (TCE)

Sinks past water

table Flows down the

slope of animpermeable layer

Contaminatesdeeper portions ofaquifers

7/27/2019 Lecture 18 19

44/53

Ground-Water

Contamination

Effects of pumping

Accelerates ground water flow

toward well

Captures contamination within

cone of depression

May reverse ground water flow

Can draw contamination up hill

Will cause saltwater intrusion

7/27/2019 Lecture 18 19

45/53

Ground Water Action

Ground water chemically

weathers bedrock

E.g., slightly acidic ground

water dissolves limestone

Caves are formed

Permeability is increased

Caves drain Speleothems form

7/27/2019 Lecture 18 19

46/53

Ground Water Action

Karst Topography

Caves

Sink holes

Karst valleys

Disappearing streams

Giant springs

7/27/2019 Lecture 18 19

47/53

Ground Water Action

Stalactites Stalagmites

7/27/2019 Lecture 18 19

48/53

Ground Water Mining

World Groundwater Resources

7/27/2019 Lecture 18 19

49/53

World Groundwater Resources

Indian Groundwater Regimes

7/27/2019 Lecture 18 19

50/53



7/27/2019 Lecture 18 19

51/53


7/27/2019 Lecture 18 19

52/53

Some definitions

7/27/2019 Lecture 18 19

53/53

In summary

Groundwater occurs as a result of specific geological conditions in

combination with specific hydrological conditions. Aquifers exhibit porosity the capacity to store water.

Aquifers exhibit permeability the capacity to transmit water

Groundwater flows down the hydraulic gradient from high head tolow head (m).

Flow occurs as seepage / matrix flow or fracture flow or both.

Groundwater flows from recharge areas to discharge areas.

Aquifers may be unconfined or confined open to atmosphericpressure or sealed by an overlying impermeable layer.

Groundwater chemistry changes naturally due to rock-waterinteractions in the aquifers.

Groundwater management requires reliable aquifer characterization.

lecture 18 19

Documents