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Hydrogeology Geology Dept, Anna University Elango, L 1 AG 9131 Hydrogeology AG 9131 Hydrogeology L. Elango L. Elango Professor Department of Geology Anna University, Chennai [email protected] www.elango.5u.com Reference text: Hydrogeology Groundwater - Freeze, R.A and Cherry, J.A, Groundwater Hydrology – David Keith Todd Groundwater -- H.M. Raghunath Weightage for Grading Weightage for Grading Attendance : 5% Tests (best 2 from 3) : 45% Final Exam : 50% Dept. of Geology Anna Uiversity
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Page 1: Hydrogeology Chp 1

Hydrogeology Geology Dept, Anna University

Elango, L 1

AG 9131 HydrogeologyAG 9131 Hydrogeology

L. ElangoL. ElangoProfessor

Department of GeologyAnna University, Chennai

[email protected]

Reference text:

Hydrogeology

Groundwater - Freeze, R.A and Cherry, J.A, Groundwater Hydrology – David Keith ToddGroundwater -- H.M. Raghunath

Weightage for GradingWeightage for GradingAttendance : 5%Tests (best 2 from 3) : 45%Final Exam : 50%

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Page 2: Hydrogeology Chp 1

Hydrogeology Geology Dept, Anna University

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SyllabusSyllabusIntroduction

Hydrologic cycle – groundwater in various geological formations – role of geological structures - groundwater and geologic processes

Groundwater flowDarcy’s law – hydraulic conductivity – estimation in lab and by tracer techniques

Estimation of aquifer parametersGroundwater resources evaluation groundwater modelsGroundwater resources evaluation – groundwater models

Groundwater abstraction techniquesConstruction of wells – shallow and deep wells

Groundwater quality

Hydrology is the f

Hydrology

Hydrology and Hydrogeology

science of occurrence, movement and transport of water

H drogeologHydrogeology deals with the occurrence, distribution, movement of water and its constituents (quality of water) beneath the Earth's surface- that is groundwater

Hydrogeology

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Page 3: Hydrogeology Chp 1

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Hydrogeology is an Hydrogeology is an interdisciplinary subjectinterdisciplinary subject

►►InvolvingInvolvingGeologyGeology

►►To answer To answer questions posedquestions posedGeologyGeology

HydrologyHydrologyChemistryChemistryMathematicsMathematicsPhysicsPhysicsComputingComputing

questions posed questions posed byby

EngineersEngineersPlannersPlannersEcologistsEcologistsManagersManagersComputingComputing

EngineeringEngineeringAgricultureAgriculture

ManagersManagersEtc.Etc.

Importance Importance

►►Virtually every activity in the earth Virtually every activity in the earth i i k l d fi i k l d f

Life on earth is possible Life on earth is possible primarily because of the primarily because of the availability of water on it. The availability of water on it. The first form of life originated in first form of life originated in water.water.

sciences requires some knowledge of sciences requires some knowledge of groundwatergroundwater

►►Until the 1900 Until the 1900 –– focus on groundwater focus on groundwater as a resource as a resource –– (Still it is the important (Still it is the important

))resource)resource)►►In the past century In the past century –– Engineering and Engineering and

Environmental aspects Environmental aspects –– also become also become importantimportant

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Page 4: Hydrogeology Chp 1

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Scope of HydrogeologyScope of Hydrogeology

►► Important resourceImportant resource

AgricultureAgriculture

IndustryIndustry

DomesticDomestic

Water Balance of the Earth Water Balance of the Earth Distribution of Water Volume

rtan

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ant

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urce

Impo

rIm

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UNESCO, 2000

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Page 5: Hydrogeology Chp 1

Hydrogeology Geology Dept, Anna University

Elango, L 5

Global Distribution of Water

Oceans

Ocean water: 97.2%Ocean water: 97.2%

Fresh water: 2 8%Fresh water: 2 8%

Groundwater – An important resourcert

ant

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Fresh Water

Distribution of Fresh Water

Ice/Glaciers

Fresh water: 2.8%Fresh water: 2.8%

Ice: 2.14%Ice: 2.14%

Groundwater: 0.61%Groundwater: 0.61%

Impo

rIm

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Groundwater

Surface Water

Soil Moisture

Atmosphere

Surface water: 0.009%Surface water: 0.009%

Surface Moisture: 0.005%Surface Moisture: 0.005%

Atmosphere: 0.001%Atmosphere: 0.001%

Need for waterNeed for water

rtan

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cert

ant

reso

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Impo

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USEPA 1987

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rtan

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-GW is significantly less costly to develop than surface water.

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-GW is less susceptible to contamination than surface water

- quite often requires little or no treatment to be used as drinking water.

GeotechnicalGeotechnicalE

W

Flow DirectionSeptember 2006

May 2007

Groundwater flow velocity (m/d) at FRFCF site

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Page 7: Hydrogeology Chp 1

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Landsides Landsides (Land subsidence)(Land subsidence)

Management strategyManagement strategy

Fig.1. Location of area considered for groundwater modeling.

Fig. 8. Simulated of groundwater head in the beach well

Fig. 4. Simulated of groundwater head in the beach well pumping at the rate of 5000m3/d.

Fig.12. Simulated of groundwater head in the beach well pumping at the rate of 15600m3/d.

g gpumping at the rate of 7800m3/d.

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Page 8: Hydrogeology Chp 1

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MiningMining►Neiveli Lignite Corporation►Groundwater occurs below

the entire lignite bed, exerting an upwardexerting an upward pressure of 6 to 8 kg/cm2.

► Pumping to depressurise the water pressure to the safe mining condition.

Colorado School of Mines

Contaminant migrationContaminant migrationMODEL RESULTSMODEL RESULTS

OBSERVED OBSERVED -- SIMULATED NITROGEN (NSIMULATED NITROGEN (N--NONO ) CONCENTRATION IN THE) CONCENTRATION IN THE

2017

0

2

4

6

N (m

g/kg

) ObservedSimulated

0

5

10

N (m

g/Kg

)

10

20

mg/

kg)

NONO33) CONCENTRATION IN THE ) CONCENTRATION IN THE UNSATURATED ZONEUNSATURATED ZONE

0N (

0

5

10

N (m

g/Kg

)

1.001.001.001.00

16 22 28 38 48 96Days after Transplantation

N (m

g/Kg

)

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►► Love canal in Niagra FallsLove canal in Niagra Falls►► Dug in 1890 for shipping/hydropower Dug in 1890 for shipping/hydropower

but not completedbut not completed►► Hooker chemical co dumped wastes (organicHooker chemical co dumped wastes (organic

Contaminant migration ...contd

►► Hooker chemical co. dumped wastes (organic Hooker chemical co. dumped wastes (organic chemicals, pesticides etc.,) from 1942 to 1953chemicals, pesticides etc.,) from 1942 to 1953

►► Covered with soil and soldCovered with soil and sold►► High rainfall in 1975High rainfall in 1975--76 eroded soil cover76 eroded soil cover►► Liquid wastes contaminated groundwaterLiquid wastes contaminated groundwater►► As wastes denser than As wastes denser than

water it could not water it could not penetrate soft claypenetrate soft clay

►► Health risks and source of contamination known Health risks and source of contamination known in 1978in 1978

Contaminant migration ...contd

in 1978in 1978►► Declared as federal emergencyDeclared as federal emergency►► School and homes evacuated School and homes evacuated ►► Cleaning up Cleaning up –– perimeter drain and groundwater perimeter drain and groundwater

intercepted, onsite treatment plant installedintercepted, onsite treatment plant installedThi i d h i l di iThi i d h i l di i►►This improved the environmental conditionThis improved the environmental condition

►► A clear A clear hydrogeologicalhydrogeological problem!problem!

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Leaking Gas TanksLeaking Gas TanksLNAPLLNAPL

Contaminant migration ...contd

Geological work of groundwaterGeological work of groundwater

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Water/Earth InteractionsWater/Earth InteractionsWater/Earth InteractionsWater/Earth Interactions

Interactions go both waysInteractions go both ways•• Groundwater controls Groundwater controls

geologic processesgeologic processes•• Geology controls flow Geology controls flow

and availability of and availability of yygroundwatergroundwater

Water/Earth InteractionsWater/Earth InteractionsWater/Earth InteractionsWater/Earth InteractionsGeology controls groundwater flowGeology controls groundwater flow

Permeable pathways are controlled by distributions Permeable pathways are controlled by distributions of geological materials of geological materials

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Water/Earth InteractionsWater/Earth InteractionsWater/Earth InteractionsWater/Earth InteractionsGeology controls groundwater flowGeology controls groundwater flow

Permeable pathways are controlled by Permeable pathways are controlled by distributions of geological materialsdistributions of geological materialsWhere groundwater is available as a Where groundwater is available as a resource is controlled by geology resource is controlled by geology

Water/Earth InteractionsWater/Earth InteractionsWater/Earth InteractionsWater/Earth InteractionsGeology controls groundwater flowGeology controls groundwater flow

Permeable pathways are Permeable pathways are controlled by distributions controlled by distributions of geological materialsof geological materialsWhere groundwater is Where groundwater is available as a resource is available as a resource is controlled by geologycontrolled by geology

Geology controls groundwater flowGeology controls groundwater flow

controlled by geologycontrolled by geologyContaminant transport in Contaminant transport in the subsurface is the subsurface is controlled by geology controlled by geology

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Water/Earth InteractionsWater/Earth InteractionsWater/Earth InteractionsWater/Earth InteractionsGroundwater controls geologic processesGroundwater controls geologic processes

►►Volcanic ProcessesVolcanic Processes::Igneous RocksIgneous Rocks: : Groundwater controls water Groundwater controls water content of magmascontent of magmasMetamorphic RocksMetamorphic Rocks: : Groundwater injected by Groundwater injected by j yj ymagmas can metamorphose magmas can metamorphose country rocks country rocks VolcanismVolcanism: Geysers are an : Geysers are an example of volcanic activity example of volcanic activity interacting with groundwaterinteracting with groundwater

Water/Earth InteractionsWater/Earth InteractionsWater/Earth InteractionsWater/Earth InteractionsGroundwater controls geologic processesGroundwater controls geologic processes

EarthquakesEarthquakes: fluids control fracturing and fault : fluids control fracturing and fault movement, lubrication and pressuresmovement, lubrication and pressuresLandslidesLandslides: groundwater controls slope failure: groundwater controls slope failureLandformsLandforms: Valley development and karst : Valley development and karst topographytopography

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Hydrogeologists in ……Hydrogeologists in ……

►► GeotechnicalGeotechnical►► Engineering Geology Engineering Geology -- LandslidesLandslides►► MiningMining►► LandfillsLandfills►► Waste disposalWaste disposal►► Oil IndustryOil Industry►► Insurance and Money lendingInsurance and Money lending►► ……………….……………….

Your CareerYour Career

►► Hydrogeologists’ Exam Hydrogeologists’ Exam -- UPSCUPSC►► ConsultancyConsultancy►► Consultancy Consultancy ►► Oil ExplorationOil Exploration►► MiningMining►► EngineeringEngineering►► EntrepreneurEntrepreneur►► EntrepreneurEntrepreneur►► ……………………►► …….…….

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Hydrologic Cycle

The cyclic movement of water through atmosphere, Hydrosphere BioHydrosphere,Biosphere and Lithosphere

Components of the Water CycleIns

Solar Energy InputPrecipitationCondensationCondensationWell Injection

Irrigation

OutsEvaporation

TranspirationInfiltrationPercolation

RunoffGroundwater FlowSurfacewater Flow

Well Pumping

Powered by the Sun- Solar Power

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PrecipitationPrecipitationTypes of Precipitation

NaturalRainSnow

IceHail

Condensation/ Dew

Man-MadeIrrigation

Wastewater Applications

InterceptionInterceptionInfiltration / PercolationInfiltration / Percolation

Percolation

Infiltration

Canopy Interception

Infiltration- Movement Water Into Soil

Percolation - Water Movement Throughthe Soil

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Evaporation / TranspirationEvaporation / TranspirationEvapotranspirationEvapotranspiration

Evaporation- Driven by Thermal Gradient and Moisture Difference

Stomata

Runoff / Overland FlowRunoff / Overland Flow

When Rainfall Rate Exceeds Infiltration Runoff is Generated

Low Infiltration Causes - Overland Flow- Loss

Organic Material

Uncontrolled RunoffCauses Erosion

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The Water Budget: Law of Mass ConservationThe Water Budget: Law of Mass Conservation

PrecipitationPrecipitation EvapotranspirationEvapotranspiration

PP –– ETET –– RR == ΔΔSS

RunoffRunoff SnowpackSnowpackInfiltrationInfiltration ThroughfallThroughfall

Soil MoistureSoil MoistureStorageStorage

RechargeRecharge

Input Input –– Output = Change in StorageOutput = Change in StorageImportance of spatial and temporal variability

Groundwater & Hydrologic Cycle Groundwater & Hydrologic Cycle

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Page 19: Hydrogeology Chp 1

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Elango, L 19

Surface Water & GroundwaterSurface Water & Groundwaterare Related and Connected !are Related and Connected !

Local Water Divide

Sources of Groundwater

►Meteoric water derived from rainfall►Meteoric water- derived from rainfall►Connate water- fossil interstitial water►Magmatic water or Juvenile water- from hot

molten magma►Plutonic water- very deeper condition

( 5k )(>5km)►Volcanic water- shallow depths (<5km)►Metamorphic water- during metamorphism

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Page 20: Hydrogeology Chp 1

Hydrogeology Geology Dept, Anna University

Elango, L 20

Vertical distribution of WaterVertical distribution of Water

SurfaceWater

SoilSoilMoistureMoisture

GroundwaterGroundwater

Unsaturated Zone – Zone of Aeration

Pores Full of Combination of Air and Water

Zone of Saturation

Pores Full Completely with Water

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Page 21: Hydrogeology Chp 1

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Unsaturated Zone:

Soil and Groundwater ZonesSoil and Groundwater ZonesSoil and Groundwater ZonesSoil and Groundwater Zones

Water in pendular saturation

Water Table: where

Caplillary Fringe: Water is pulled above the water table by capilary suction

Saturated Zone: Where all pores are completely filled with water.

Phreatic Zone: Saturated zone below the water table

fluid pressure is equal to atmospheric pressure

The Water Table

Lies Roughly at theg yInterface Between the Unsaturated

Zone and the Saturated Zone

But How Do WeDefine the

Water Table?

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Capillary FringeCapillary Fringe

Surface tension Surface tension –– sediments retain watersediments retain water

Depends on Surface area:Depends on Surface area:smaller grains smaller grains –– higher surface area higher surface area –– higher surface tensionhigher surface tension

Capillary Fringe

Zone above water table that is effectively saturated

Water Held by Tension

Capillary Rise Related

Capillarity Due to Adhesion of Water to a Surface

Capillary Rise Related to Size of Pores

Smaller the Pore, The Larger the Capillary Rise

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Page 23: Hydrogeology Chp 1

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Soil waterSoil waterDepth up to which the root zone extends

Depth up to which the atmospheric conditions has an influence

Intermediate/Gravitational water – zone between soil water and capillary fringe

AQUIFERSAQUIFERS►Aquifer is derived from the Latin term meaning water

bearer. ►Lithologic unit or collection of units capable of yielding

water to wells

►An aquifer is not:A geological formation,A permeable geologic unitA permeable geologic unit,A porous medium, orA petroleum reservoir

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AQUIFERSAQUIFERS

Consolidated or unconsolidated geologic unit (material, stratum, or formation) or set of connected units that yields a significant (economic) quantity of water of suitable quality to wells in usable amountsto wells in usable amounts.

AQUIFER TypesAQUIFER Types►unconfined (or water-table) - the upper surface

of the aquifer is the water table. Water-table if di tl l i b t t daquifers are directly overlain by an unsaturated

zone or a surface water body. ►Water table separates saturated and

unsaturated zones

hi h bilit lhigh permeability layers near the surface

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AQUIFER TypesAQUIFER Types►confined (or artesian) - an aquifer that is

immediately overlain by a low-permeability it ( fi i l ) A fi d if dunit (confining layer). A confined aquifer does

not have a water table.

overlain by confining layer

Confined AquiferConfined Aquifer►►Artesian conditionArtesian condition

►► Permeable material overlain by Permeable material overlain by relatively impermeable materialrelatively impermeable material

►► Piezometric or potentiometric Piezometric or potentiometric surfacesurface

►►Water level in the piezometer is Water level in the piezometer is a measure of water pressure in a measure of water pressure in the aquiferthe aquifer

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AQUIFER TypesAQUIFER Types►perched - a local, unconfined aquifer at a

higher elevation than the regional unconfined aquifer An unsaturated zone is presentaquifer. An unsaturated zone is present between the two unconfined aquifers.

AQUIFER TypesAQUIFER Types►Leaky or semi confined- an aquifer that

receives recharge via cross-formational flow through confining layersthrough confining layers.

►Leaky confining unit (K is too low to be an aquifer, but great enough to permit significant flow through the layer)

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Other geological formations!Other geological formations!

►Aquitard (flow through the layer is signifcant on a regional scale or over very long (e.g., geologic) time scales) sandy clay

►Aquifuge (no K and no n) massive rock

►Aquiclude (no/very less K) clay►Aquiclude (no/very less K) clay

How water occurs in How water occurs in beneath ground surface?beneath ground surface?

S b lid iS b lid i►► Spaces between solid grains Spaces between solid grains –– PoresPores►► FracturesFractures►► Measure of pore volume Measure of pore volume -- PorosityPorosity►► Measure of water yield Measure of water yield –– Specific YieldSpecific Yield►► Measure of water retention Measure of water retention ––

Specific Retention Specific Retention

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Porosity

%% 100%100%VVVVn% =n% =n% = porosity (expressed as a percentage)n% = porosity (expressed as a percentage)VVVV = volume of the void space= volume of the void spaceVVTT = total volume of the material (void + rock)= total volume of the material (void + rock)

x100%x100%VVVVVVTT

Primary and secondary porosity

Primary PorosityPrimary Porosity Secondary PorositySecondary Porosity

SedimentsSedimentsSedimentary RocksSedimentary Rocks

Igneous RocksIgneous RocksMetamorphic RocksMetamorphic Rocks

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Igneous / Metamorphic RocksIgneous / Metamorphic RocksLow Primary PorosityLow Primary Porosity

Can Have High Secondary PorosityCan Have High Secondary Porosity

Porosity Ranges for SedimentsPorosity Ranges for Sediments

Well Sorted Gravel: 25 – 50%Sand and Gravel Mix: 20 – 35%Glacial Till: 10 20%Glacial Till: 10 – 20%Silt: 35 – 50%Clay: 33 – 60%

Gravel Sand Silt &

FCC BCC Simple cubic26% 32% 47.6%

Non-uniform grain sizes

Limestone karstic& Dolostone

Shale Sandstone Siltstone

Gravel Sand Silt &Clay

0 8 16 24 32 40 48 56 64

Porosity, %

Fractured Basaltcrystallinerocks

Pumice

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Factors controlling porosityFactors controlling porosity

►► Grain sizeGrain sizeG i hG i h►► Grain shapeGrain shape

►► Mode of arrangementMode of arrangement►► SortingSorting►► CementingCementing►► CompactionCompaction►► Solution activitySolution activity

Sorting

WindWindRiverRiverBeachBeachBeachBeach

GlacialGlacial

Better Sorting = Higher PorosityBetter Sorting = Higher Porosity

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Specific YieldSpecific Yield

Drainable Porosity! (under gravity)Drainable Porosity! (under gravity)

Sy= Vy/VSy= Vy/V

Domenico & Schwartz (1990)

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Specific YieldsClayClay 2%2%SiltSilt 18%18%S dS d 26%26%SandSand 26%26%

Smaller the Grain Size Smaller the Grain Size –– Lower the Specific YieldLower the Specific Yield

What about the water that is retained?What about the water that is retained?

Specific Retention (Sr) = Vr/VSpecific Retention (Sr) = Vr/VSpecific Retention (Sr) = Vr/VSpecific Retention (Sr) = Vr/V

n =n = SySy ++ SrSr

Specific Yield (%)

Material Maximum Minimum Average

coarse gravel 26 12 22

medium gravel 26 13 23

fine gravel 35 21 25

gravelly sand 35 20 25

coarse sand 35 20 27

medium sand 32 15 26

fine sand 28 10 21fine sand 28 10 21silt 19 3 18sandy clay 12 3 7clay 5 0 2

(Johnson (1967) as quoted by C.W. Fetter(2000)

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Sediment PropertiesSediment Properties

Storage Coefficient or Storativity (S)

Volume of water that a permeable unit will absorb or expel from storage per unit surface area per unitstorage per unit surface area per unit change in head.

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Storage CoefficientThe storage coefficient (S) consists of two components:

water released from compressibility of aquiferpore fluid draining of the aquifer

S = SsbSs = specific storage (1/L)b = saturated thickness (L)S < 0.005

For confined aquifers, there is no draining of the pores, so all storage comes from the compressibility component

For unconfined aquifers, most of the water is from draining, contribution from compressibility is very small

S = Sy + Ssbb = saturated thickness (L) Sy = specific yieldSs = specific storage (1/L) usually, Sy >> Ssb

S ~ Sy S: 0.02 to 0.30

Specific Storage (Ss)

Amount of water per unit volume of a saturated formation that is stored or expelled from storage owing to compressibility of the mineral skeleton and pore

Elastic storage coefficient

compressibility of the mineral skeleton and pore water per unit head change (unit=1/L)

Ss = ρwg(α + nβ)ρw = density of water

α = compressibility of aquifer skeletong = acceleration of gravity

S = Ssb

α compressibility of aquifer skeletonn = porosity

β = compressibility of water

What contributes more to storage, compressibility of water or compressibility of matrix?

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Aquifer Compressibility:

1. Compressibility of Water2. Compressibility of Porous Medium

In the saturated zone the head create pressure which affect the arrangement of mineral grains as well as density of water in the voids

The expansion of mineral skeleton and pressure areThe expansion of mineral skeleton and pressure are directly proportional (elasticity).

The contraction of water in aquifer and the pressure created by head is inversely proportional.

Think of a tyreFilled with air under pressure

When we release itit is still filled with airSystem is elastic

If pressure increasesSkeleton Water

If pressure increases, Mineral skeleton will expand

Water will contract

If pressure drops,

PExpansion of mineral skeleton and pressure -> directly proportional (elasticity). Contraction of water in aquifer and pressure created by head -> inversely proportional.

Expansion of Water

Compaction of the Aquifer Skeleton

p p ,Mineral skeleton will contract

Water will expandP

When PumpingReduce the Pressure

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Clay 10-6 to 10-8

Sand 10-7 to 10-9

Gravel 10-8 to 10-10

Shale 10-9 to 10-10

Compressibility of Geologic Materials (m2 N-1)

asin

g

Shale 10-9 to 10-10

Sandstone 10-10 to 10-11

Limestone 10-10 to 10-11

Igneous/Metamorphic 10-11

Water 4.4 x 10-10

Dec

rea

Discharge of groundwaterfrom a spring in California.

Springs generally emerge atth b f hill l

Springs

the base of a hillslope.Some springs produce water

that has traveled for manykilometers; while others emitwater that has traveled onlya few meters.

Springs represent placeswhere the saturated zone(below the water table)comes in contact with theland surface.(from Keller, 2000, Figure 10.8)

S. Hughes, 2003

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Page 37: Hydrogeology Chp 1

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Groundwater Table and Occurrence

In Arid Areas: Water table flatter

In Humid Areas: Water Table Subdued Replica of Topography

Subdued replica of topographyWater Table Mimics the Topography

Need gradient for flow

Discharge occurs in topographically low sites

Need gradient for flowIf water table flat – no flow occurringSloping Water Table – Flowing Water

Flow from high to low areas

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Page 38: Hydrogeology Chp 1

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Discharge and Recharge Areas

RechargeDownward

Vertical Gradient

DischargeUpward

Vertical Gradient

DischargeTopographically High Areas

Deeper Unsaturated ZoneFlow Lines Diverge

RechargeTopographically Low Areas

Shallow Unsaturated ZoneFlow Lines Converge

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Page 39: Hydrogeology Chp 1

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Unconsolidated formationsUnconsolidated formationsGlaciated terrains

= Würm moraines with

(Munich)Project area

= Northern edge of Alps

Moraines of

former Inn-glacier

(1994).

River alluviumRiver alluvium

►►HeterogeneousHeterogeneous►►Flood plain depositsFlood plain deposits

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Page 40: Hydrogeology Chp 1

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Particle Size Distribution Particle Size Distribution GraphGraph

Tectonic valleys — Intermontane basins

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Page 41: Hydrogeology Chp 1

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Water in Rock MaterialWater in Rock Material

M t f th i d t hi kM t f th i d t hi kMost of the igneous and metamorphic rocks Most of the igneous and metamorphic rocks are very dense with interlocked texture. are very dense with interlocked texture.

The rocks therefore have extremely low The rocks therefore have extremely low permeability and porosity. permeability and porosity.

Some clastic sedimentary rocks, typically Some clastic sedimentary rocks, typically d t b d bld t b d blsandstones, can be porous and permeable. sandstones, can be porous and permeable.

Weathered rocks can also be porous and Weathered rocks can also be porous and permeable.permeable.

Consolidated Sedimentary Aquifers Consolidated Sedimentary Aquifers ConglomerateConglomerate

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►►conglomerateconglomerate►►High porosity, high permeabilityHigh porosity, high permeability

►►LimestoneLimestone►►high porosity and low permeabilityhigh porosity and low permeability

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Page 43: Hydrogeology Chp 1

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Groundwater as a Geologic Groundwater as a Geologic AgentAgent

Groundwater as a Geologic Groundwater as a Geologic AgentAgent

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Groundwater as a Geologic Groundwater as a Geologic AgentAgent

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Page 45: Hydrogeology Chp 1

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LimestoneLimestone

Igneous rocksIgneous rocks

Groundwater percolates downward through Groundwater percolates downward through the regolith which is a layer of weatheredthe regolith which is a layer of weatheredthe regolith which is a layer of weathered the regolith which is a layer of weathered rock, alluvium, rock, alluvium, colluviumcolluvium and soil to and soil to fractures in underlying bedrock. fractures in underlying bedrock.

http://capp.water.usgs.gov/aquiferBasics/volcan.html

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Page 46: Hydrogeology Chp 1

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Bedrock HydrogeologyBedrock Hydrogeology

►►HydraulicHydraulic►►Hydraulic Hydraulic Conductivity Conductivity of bedrock is of bedrock is controlled bycontrolled by

Size of fracture openingsSize of fracture openingsSpacing of fracturesSpacing of fracturesInterconnectedness of fracturesInterconnectedness of fractures

►► unfractured graniteunfractured granite►► Low porosity, low permeabilityLow porosity, low permeability

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Volcanic rocksVolcanic rocks

Geologic origin of aquifersGeologic origin of aquifers

Todd (1996)Todd (1996)

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is a graph showing changes in the discharge of a river over a period of

Hydrograph

discharge of a river over a period of time.

Unit Hydrograph TheoryUnit Hydrograph Theory

►►The unit hydrograph is the response of the The unit hydrograph is the response of the watershed to 1 unit of excess runoffwatershed to 1 unit of excess runoffwatershed to 1 unit of excess runoff watershed to 1 unit of excess runoff distributed uniformly over the entire distributed uniformly over the entire watershedwatershed

1 inch (English units)1 inch (English units)1 mm (Metric units)1 mm (Metric units)

http://www.tcnj.edu/~horst/classes.htm

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Page 49: Hydrogeology Chp 1

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Elango, L 49

Unit Hydrograph TheoryUnit Hydrograph Theory

Unit Hydrograph vs Storm Hydrographs

100

150

200

250

300

350

400

Flow

0

50

100

0 5 10 15 20 25 30

Time

Significance of Unit HydrographSignificance of Unit Hydrograph

►►Watersheds response to a given amount of Watersheds response to a given amount of excess precipitation is just a multiplier ofexcess precipitation is just a multiplier ofexcess precipitation is just a multiplier of excess precipitation is just a multiplier of the unit hydrographthe unit hydrograph

►►Use unit hydrograph as a basis to determine Use unit hydrograph as a basis to determine the storm hydrograph from any given the storm hydrograph from any given rainfall distributionrainfall distribution

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ExampleExample

►►Given the following rainfall distributionGiven the following rainfall distribution

Time Precipitation

1 0.5

2 3

3 1.5

4 0.2

►►The watershed will respond as followsThe watershed will respond as follows

http://www.tcnj.edu/~horst/classes.htm

ExampleExample

Incremental Storm Hydrographs

200

300

400

500

Flow

Time Precipitation

1 0.5

2 3

3 1.5

4 0.2

0

100

0 5 10 15 20 25 30 35

Time

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ExampleExample

Incremental + Final Storm Hydrograph

00

200

300

400

500

Flow

0

100

0 5 10 15 20 25 30 35

Time

Unit Hydrograph DerivationUnit Hydrograph Derivation►► A unit hydrograph is derived from historical rainfall and A unit hydrograph is derived from historical rainfall and

runoff datarunoff data

►► The volume of water produced by the storm (area under The volume of water produced by the storm (area under the hydrograph curve) divided by the area of the the hydrograph curve) divided by the area of the watershed equals depth of excess precipitationwatershed equals depth of excess precipitation

►► The ordinates of the storm hydrograph are divided by this The ordinates of the storm hydrograph are divided by this depth to obtain the unit hydrographdepth to obtain the unit hydrographdepth to obtain the unit hydrographdepth to obtain the unit hydrograph

►► Timing must be taken into consideration (STiming must be taken into consideration (S--curve curve technique to adjust timing)technique to adjust timing)

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Page 52: Hydrogeology Chp 1

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Role of Geological Structures on Groundwater Occurrence & Flow

Attitude of formationsAttitude of formations

Joints and Faults

Folds

Igneous intrusions

Attitude of formations

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Page 53: Hydrogeology Chp 1

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Elango, L 53

Artesian AquifersArtesian Aquifers

“artesian”

GW under pressure due to dipping layers

Non-flowing

Free-flowing

A. Although the contaminated water has traveled more than 100 m before reaching Well 1, the water moves too rapidly through the limestone to be purified.

B. As the discharge from the septic tank percolates through the sandstone, it is

ifi d i l ti l h tpurified in a relatively short distance.

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Page 54: Hydrogeology Chp 1

Hydrogeology Geology Dept, Anna University

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Folds Folds

Axis weak zonezoneOasisdesert spring

Joints and Faults

Weak zones

Increase porosity and K

Increase rate of weathering

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Page 56: Hydrogeology Chp 1

Hydrogeology Geology Dept, Anna University

Elango, L 56

±Igneous Intrusives

±

LegendDykes

Igneous Intrusives

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Impact of dykesImpact of dykes

113

Impact of dykesImpact of dykes

114

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Page 58: Hydrogeology Chp 1

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Land subsidence Land subsidence

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http://tigger.uic.edu/~pdoran

KARSTKARSTKarst Topography

A. GW percolates through limestone along joints and bedding planes. Dissolution creates and enlarges caverns at and below the water table.

B Si kh l f h thB. Sinkholes form when the roof of a cavern collapses. Surface streams may disappear down sinkholes and reappear as springs.

C. As time passes, caverns grow larger and the number and size of sinkholes increase. Collapse of caverns and coalescence of sinkholes form larger, flat-floored depressions (solution valleys). Eventually dissolution may remove most of the limestone from the area, leaving only isolated remnants (towers).

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KARSTKARST Guilin CHINA

http://tigger.uic.edu/~pdoran

GW ErosionGW ErosionCaverns form as a result of dissolution of carbonate rocks below the water table

http://tigger.uic.edu/~pdoran

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Near Las VegasEarth Fissures

http://www.mscd.edu/~eas/Janke/ENV_4010/readings/Keller_Ch06.pdf

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SubsidenceSubsidence Subsidence of the ground surface occurs when GW is pumped out faster than it is replenished in some areas (compaction).

S J i V llSan Joaquin ValleyNew Orleans, LAMexico City

http://www.mscd.edu/~eas/Janke/ENV_4010/readings/Keller_Ch06.pdf

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Hydrogeology Geology Dept, Anna University

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Now we can use i f iinterferometric processing of Synthetic Aperture Radar (SAR) data.

Suspected Land Subsidence in Kolkata from 1992-1998

Identifying land subsidence

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Geological Map of IndiaGeological Map of India

►►GangesGanges--BrahmaputraBrahmaputraBrahmaputra Brahmaputra and Himalayan and Himalayan regionsregions

►►six provinces six provinces distinguished in distinguished in ggpeninsular peninsular India. India.

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Hydrogeology of Tamil NaduHydrogeology of Tamil Nadu

Source: TWADSource: TWAD

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Page 66: Hydrogeology Chp 1

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GeologyGeology

Well no. 43

131

Seripalli Well no. 2

Rose diagramRose diagram

60Dykes Statistical graph

Dyke0

10

20

30

40

50

60

No.

of D

ykes

Fracture

100-

500

501-

1000

1001

-150

015

01-2

000

2001

-250

025

01-3

000

3001

-350

035

01-4

000

4001

-450

045

01-5

000

5001

-550

055

01-6

000

6001

-650

070

00-7

500

1000

0-10

500

Length of Dykes in m

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EphemeralEphemeral Stream(influent)(from Keller, 2000, Figure 10.5b)

• Semiarid or arid climate• Flows only during wet periods (flashy runoff)• Recharges groundwater

S. Hughes, 2003

Contours Reflect Gradient and Direction of Flow

Gaining Stream Losing Stream

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