WFM 5103

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WFM 5103 Hydrogeology and Groundwater Lectures
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WFM 5103 Hydrogeology and Groundwater
Subsurface environment Water bearing properties
of rocks and soils Principles of groundwater
movement Recharge Groundwater withdrawal Groundwat
er Quality Groundwater in Coastal
zones Hydrogeological mapping Groundwater
management Conjunctive use Groundwater
Models Groundwater development in Bangladesh
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Groundwater Movement
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RECAP
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Aquifer properties/parameters
Water transmitting parameter
Permeability or Hydraulic Conductivity
Mean pore velocity
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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.
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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.
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Specific yield -Water that will drain under the
influence of gravity
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Groundwater exploration Geologic methods
Groundwater withdrawal Groundwater
exploration Geologic methods
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Relation between K and grain-size distribution
Water transmitting Parameter.contd.
(a) General relationship
(b) Empirical formulas
(i) Hazen
A 1.0 for K in cm/sec and d10 in mm
(ii) Krumbein and Monk
dg geometric mean grain diameter mm k in
mm
(i) Kozeny-Carman
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Water transmitting Parameter.contd.
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Transmissivity
Water transmitting Parameter.contd.
T Kb
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Storage parameter
Unconfined aquifer
Specific yield -Water that will drain under the
influence of gravity
Confined aquifer
Storage coefficient/storativity -Water that is
released or taken into storage per unit surface
area of aquifer per unit change in head
? bulk modulus of compression of matrix ?
bulk modulus of compression of water
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Cone of Depression
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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
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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.
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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
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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
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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
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Groundwater exploration Geologic methods
Groundwater withdrawal Groundwater
exploration Geologic methods

• 1.1.1.1 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.

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Groundwater exploration Geologic methods
Groundwater withdrawal Groundwater
exploration Geologic methods
Relationship between geology and groundwater ?
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 )
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Groundwater exploration Geologic methods
alluvial aquifers 90 of all
developed Aquifers are alluvial aquifers,
consisting of unconsolidated alluvial
deposits, chiefly gravels and sands. 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.
Relationship between geology and groundwater
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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.
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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
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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.
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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.
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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.
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Groundwater exploration Remote sensing
1.1.1.2 Remote sensing
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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).

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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.
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Identify data needs
Land cover
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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.
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Groundwater withdrawal Groundwater
exploration Surface geophysical methods

• 1.1.1.3. Surface Geophysical
• Methods
• - scientific measurement of physical properties
  and parameters of the earths 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.

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Groundwater exploration Surface geophysical
methods Electric resistivity
Groundwater withdrawal Groundwater
exploration Surface geophysical methods
1.1.1.3 (a) Electric Resistivity Method
?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 is the measured Potential difference (in Volts)
and I is the current introduced (in Amperes).
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Groundwater exploration Surface geophysical
methods Electric resistivity
1.1.1.3 (a) Electric Resistivity Method
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Groundwater exploration Surface geophysical
methods Electric resistivity
? 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.