WFM 5103
Hydrogeology and Groundwater
Lectures 3-4
WFM 5103
Hydrogeology and Groundwater
Subsurface environment
Water bearing properties of rocks and soils
Principles of groundwater movement
Recharge
Groundwater withdrawal
Groundwater Quality
Groundwater in Coastal zones
Hydrogeological mapping
Groundwater management
Conjunctive use
Groundwater Models
Groundwater development in Bangladesh
Groundwater Movement
RECAP
Observation well
piezometer
Aquifer properties/parameters
Water transmitting parameter
Permeability or
Hydraulic Conductivity
kg kg
K



Mean pore velocity:
v
vp 
ne
Pores, Porosity and Permeability
Pores: The spaces between particles within
geological material (rock or sediment)
occupied by water and/or air.
Porosity: is defined as the
ratio of the volume of voids
to the volume of aquifer
material. It refers to the
degree to which the aquifer
material possesses pores or
cavities which contain air or
water.
Permeability: The capacity of a porous rock, sediment, or soil to transmit
ground water. It is a measure of the inter-connectedness of a material's
pore spaces and the relative ease of fluid flow under unequal pressure.
Perched Aquifers
An aquifer in which a ground water body is separated from the main ground water below
it by an impermeable layer (which is relatively small laterally) and an unsaturated zone.
Water moving downward through the unsaturated zone will be intercepted and
accumulate on top of the lens before it moves laterally to the edge of the lens and seeps
downward to the regional water table or forms a spring on the side of a hillslope.
Specific yield
Specific retention
-Water that will drain under
the influence of gravity
-Water that is retained as a film on rock surfaces and
in very small openings. The physical forces that
control specific retention are the same forces
involved in the thickness and moisture content of
capillary fringe
Vr
Vd
Sy 
Vt
Sr 
Vt
Groundwater withdrawal
exploration
Groundwater
Geologic
methods
exploration
Geologic methods
Relation between K and grain-size distribution
Water transmitting
Parameter….contd.
(a) General relationship
Cd 2 g
k  Cd 2
K

(b) Empirical formulas
(i) Hazen K  A (d10 ) 2
A = 1.0 for K in [cm/sec] and d10 in [mm]
(ii) Krumbein and Monk k  760(d g ) 2 e
1.31 g
  84 5  95
 g  16

4
6.6
n  log 2 (d n )
dg= geometric mean grain diameter [mm]; k in [mm];
2
d
(i) Kozeny-Carman k 
m
(1  n ) 2 180
n3
Water transmitting
Parameter….contd.
Transmissivity
T = Kb
Water transmitting
Parameter….contd.
Storage parameter
Unconfined aquifer
Specific yield
-Water that will drain
under the influence of
gravity
Vd
Sy 
Vt
Confined aquifer
Storage coefficient/storativity
-Water that is released or taken
into storage per unit surface area
of aquifer per unit change in head
S  Ss b  S y
Ss  g(n  )
 = bulk modulus of compression of matrix
 = bulk modulus of compression of water
Cone of Depression
Pumping
Decline in
WL in well
Head gradient
From surrounding
aquifer to well
Convergent flow
into the well
Cone of Depression
Unconfined aquifer
-Cone of depression expands very slowly (drainage through gravity)
-Increased drawdown in wells and in aquifer (dewatering of aquifer)
Confined aquifer
-Cone of depression expands very rapidly (why??)
-No dewatering takes place
Mutual interference of expanding cones around adjacent wells
occurs more rapidly in confined aquifers
1. 1 Exploration of groundwater
Objective:
to locate aquifers capable of yielding water of suitable
quality, in economic quantities, for drinking, irrigation,
agricultural and industrial purposes, by employing, as
required, geological, geophysical, drilling and other
techniques.
Assessments of ground water resources range in scope and
complexity from simple, qualitative, and relatively inexpensive
approaches to rigorous, quantitative, and costly assessments.
Tradeoffs must be carefully considered among the competing
influences of the cost of an assessment, the scientific defensibility,
and the amount of acceptable uncertainty in meeting the objectives
of the water-resource decision maker.
Groundwater exploration
Exploration of Groundwater
1.1.1 Surface exploration
- “non-invasive" ways to map the
subsurface.
-less costly than subsurface
investigations
1. Geologic methods
2. Remote Sensing
3. Surface Geophysical Methods
(a) Electric Resistivity Method
(b) Seismic Refraction Method
(c) Seismic Reflection Method
(d) Gravimetric Method
(e) Magnetic Method
(f) Electromagnetic Method
(g) Ground Penetrating Radar
and others
Groundwater exploration
Exploration of Groundwater
1.1.2 Subsurface exploration
1. Test drilling
geologic log
drilling time log
Water level measurement
2. Geophysical logging/borehole
geophysics
Resistivity logging
Spontaneous potential logging
Radiation logging
Temperature logging
Caliper Logging
Fluid Conductivity logging
Fluid velocity logging
3. Tracer tests
and others
Groundwater exploration
Exploration of Groundwater
1.1.1 Surface exploration
- “non-invasive" ways to map the
subsurface.
-less costly than subsurface
investigations
1. Geologic methods
2. Remote Sensing
3. Surface Geophysical Methods
(a) Electric Resistivity Method
(b) Seismic Refraction Method
(c) Seismic Reflection Method
(d) Gravimetric Method
(e) Magnetic Method
(f) Electromagnetic Method
(g) Ground Penetrating Radar
and others
1.1.2 Subsurface exploration
1. Test drilling
geologic log
drilling time log
Water level measurement
2. Geophysical logging/borehole
geophysics
Resistivity logging
Spontaneous potential logging
Radiation logging
Temperature logging
Caliper Logging
Fluid Conductivity logging
Fluid velocity logging
3. Tracer tests
and others
Methods
Surface methods
Name of Organization
1. Geologic methods
2. Remote sensing
3. Surface Geo-physical methods
(a) Electric resistivity method
(b) Seismic refraction method
(c) Seismic reflection method
(d) Electromagnetic method
Subsurface methods 1. Test drilling
2. Geophisical logging/borehole
geophysics
(a) Resistivity logging
(b) SP logging
(c) Gamma logging
(d) Temperature logging
(e) Caliper logging
(f) EM conductivity
3. Tracer tests
GSB, BWDB, DU, BADC,
IWM
SPARSSO, CEGIS
GSB, DU
GSB, DU
DU
GSB, DU
GSB, BWDB, DPHE, WASA,
IWM, DU, BADC, BUET
AEC
AEC
AEC, DU
AEC
AEC
DU
BWDB
Groundwater withdrawal
exploration
1.1.1.1 Geologic Methods
Groundwater
Geologic
methods
exploration
Geologic methods
-
an important first step in any groundwater investigation
-
involves collection, analysis and hydrogeologic interpretation of
existing geologic data/maps, topographic maps, aerial
photographs and other pertinent records.
-
should be supplemented, when possible, by geologic field
reconnaissance and by evaluation of available hydrologic data
on stream flow and springs, well yields, groundwater recharge
and discharge, groundwater levels and quality.
- nature and thickness of overlying beds as well as the dip of water
bearing formations will enable estimates of drilling depths to be
made.
Relationship between
geology and groundwater
Groundwater withdrawal
exploration
Groundwater
Geologic
methods
exploration
Geologic methods
 The type of rock formation will suggest the magnitude of water yield
to be expected.
 it is the perviousness or permeability and not porosity which is
significant in water yielding capacity of rocks.
 Igneous rocks have a porosity of 1% and may yield all water while
some clays have a pososity as high as 50% but are practically
impervious.
 Porosity = f (grainsize, shape, grading, sorting, amount and
distribution of cementing materials)
 Permeability = f (interconnectedness, fissures, joints, bedding
planes, faults, shear zones and cleavages, vesicles )
alluvial aquifers : 90% of all developed
Aquifers are alluvial aquifers, consisting
of unconsolidated alluvial deposits,
chiefly gravels and sands.
Groundwater exploration
Geologic methods
Relationship between
geology and groundwater
Limestone aquifer varies in density, porosity and permeability depending on degree
of consolidation and development of permeable zones after deposition. Original rock
materials offer important aquifers.
Volcanic rock can form highly permeable aquifers. Basalts form a good source of
water; easily susceptible to weathering.
Sandstones are cemented forms of sands and gravels; yields are reduced by the
cements. Some may form good aquifers depending on shape and arrangement of
constituent particles and cementation and compaction.
Igneous and metamorphic rocks, in solid state, are relatively impermeable and
hence serve as poor aquifers. Under weathered conditions, however, the presence of
joints, fractures, cleavages and faults form good water bearing zones, and small wells
may be developed in these zones for domestic water supply.
Selection of site for a well
Factors to be considered are:
(i) Topography: Valley regions are more favorable than the slopes and
the top of the hillocks.
(ii) Climate (annual rainfall, sunlight intensity, max. temperature, humidity):
heavy to moderate rainfall -- more deep percolation – good aquifer.
Intense summer weather -- evaporates and depletes GW through direct
evaporation from shallow depths and
evapotranspiration through plants.
Selection of site for a well
Groundwater exploration
Geologic methods
(iii) Vegetation: can flourish where GW is available at shallow
depths.
Phreatophytes, plants that draw the required water directly from the
zone of saturation indicate large storage of groundwater at shallow
Selection of site for a well
Groundwater exploration
Geologic methods
(iii) Vegetation: can flourish where GW is available at shallow
depths.
Phreatophytes, plants that draw the required water directly from the
zone of saturation indicate large storage of groundwater at shallow
depths.
Xerophytes, plants that exist under arid conditions by absorbing the
soil moisture (intermediate or vadose water), indicate the scarcity of
groundwater at shallow depths.
Selection of site for a well
Groundwater exploration
Geologic methods
(iii) Vegetation: can flourish where GW is available at shallow
depths.
Phreatophytes, plants that draw the required water directly from the
zone of saturation indicate large storage of groundwater at shallow
depths.
Xerophytes, plants that exist under arid conditions by absorbing the
soil moisture (intermediate or vadose water), indicate the scarcity of
groundwater at shallow depths.
Halophytes, plants with a high tolerance of soluble salts, and white
efflorescence of salt at ground surface indicate the presence of
shallow brackish or saline groundwater.
Selection of site for a well
Groundwater exploration
Geologic methods
(iv) Geology of the area: thick soil or alluvium cover, highly
weathered, fractured, jointed or sheared and porous rocks indicate
good storage of groundwater, whereas massive igneous and
metamorphic rocks or impermeable shales indicate paucity of
groundwater.
(v) Porosity, permeability: highly porous, permeable zones of
dense rocks encourage storage of groundwater. Massive rocks do
not permit the water to sink.
(vi) Joints and faults in rocks: Wells sunk into rocks with
interconnected joints, fractures, fissures and cracks yield copious
supply of water.
(vii) Proximity of rivers: Streams and rivers serve as sources of
recharge and water is stored in the pervious layers.
1.1.1.2 Remote sensing
Source
A physical quantity
(screen)
Processor
(records data
and interprets
information)
(light/radiation)
Sensor
signal
(eyes)
Groundwater exploration
Remote sensing
Groundwater exploration
Remote sensing
Remote sensing
- an increasingly valuable tool for understanding GW conditions.
-information on an object on the earth is acquired by remote registration/
sensing from aircraft or satellite at various wavelengths of the
electromagnetic energy reflected and emitted.
-difference in reflectance properties of objects produce varying signatures on
the photos or images, which can be interpreted for a variety of purposes of
which application of hydrogeology is one.
-stereoscopic airphotos (color, black and white, infrared), oblique air photos
and high resolution satellite imageries taken from GMS, APT, NOAA, AVHRR,
SPOT and Landsat, ERS-SAR, RADARSAT, open up new possibilities for the
assessment of groundwater resources.
- observable patterns, colors, and relief makes it possible to distinguish
differences in geology, soils, soil moisture, vegetation and land-use (hence
areas of groundwater recharge and discharge).
Groundwater exploration
Remote sensing
RS applications
forest cover mapping and
monitoring;
land use and land cover
mapping;
 mapping of water
resources;
Others: agriculture;
fisheries; coastal zone;
marine environment.
Identify data needs
Land cover
Dense Cover Conifers
Medium Cover Conifers
Closed Scrub
Open Scrub
Grassland
Croplands
Rock / Bare soil
Stream beds / concrete
Groundwater exploration
Remote sensing
Advantages of remote sensing technique in general:
- speed of operation
- survey of inaccessible areas
- possibility of repetitive coverage of changing landform, land use,
vegetal cover, water spread in reservoirs, soil salinity, water logged
areas, etc.
- permits mapping and preliminary evaluation at lesser cost.
“The remote sensing technique is only an additional tool in the
quest of groundwater and not a substitute for other methods. For a
meaningful interpretation, there should be adequate ground check
in the field”.
Groundwater withdrawal
1.1.1.3. Surface Geophysical
Methods
Groundwater exploration
Surface geophysical methods
- scientific measurement of physical properties and
parameters of the earth’s subsurface formations
and contained fluids by instruments located on the
surface for investigation of mineral deposits or
geologic structure.
-provide only indirect indication of groundwater
-success depends on how best the physical
parameters are interpreted in terms of
hydrogeological language.
- Accurate interpretation requires supplemental
data from subsurface investigations to substantiate
surface findings.
exploration
withdrawal
1.1.1.3 (a) Electric Resistivity Method Groundwater
Surface geophysical
Groundwater
exploration
methods
♦Electrical resistivity is the resistance
of a volume of material to the flow of
electrical current.
♦ current is introduced into the
ground through a pair of current
electrodes
♦ resulting potential difference is
measured between another pair of
potential electrodes
♦ Apparent resistivity is then
calculated as:
V
 a  2a
I
V is the measured Potential difference (in Volts)
and I is the current introduced (in Amperes).
Electric resistivity
Surface
geophysical methods
exploration
1.1.1.3 (a) Electric Resistivity Method Groundwater
Surface geophysical methods
Electric resistivity
Wenner arrangement
V
 a  2a
I
Schlumber configuration
a

L / 2 2  b / 2 2

b
V
I
 The measured potential difference is a
weighted value over a subsurface region
controlled by the shape of the region,
and yields an apparent resistivity over
an unspecified depth.
Vertical electrical Sounding (VES)
Changing the spacing of electrodes
changes the depth of penetration of the
current. So it is possible to obtain field
curve of apparent resistivity vs depth.
For a single homogeneous, isotropic layer of
infinite thickness, resistivity curve will be a
straight line.
True/actual resistivity - if formation
is homogeneous and isotropic.
Apparent resistivity
if formation is anisotropic
consisting of two or more layers of
different materials.
Groundwater exploration
Surface geophysical methods
Electric resistivity