Effect of meteorological forcing and Effect of meteorological forcing and stratification variability in three stratification variability in three

morphometrically different urban lakes in morphometrically different urban lakes in Kolkata metro cityKolkata metro city

Dr Nihar R SamalDr Nihar R SamalDr.Nihar R. SamalDr.Nihar R. SamalWater Resources and Environmental Engineering SectionWater Resources and Environmental Engineering Section

Department of Civil EngineeringDepartment of Civil EngineeringDepartment of Civil EngineeringDepartment of Civil EngineeringNational Institute of Technology Durgapur National Institute of Technology Durgapur

(Deemed University)(Deemed University)(Deemed University)(Deemed University)M.G.Avenue, DurgapurM.G.Avenue, Durgapur--713 209, West Bengal, INDIA713 209, West Bengal, INDIA

E-mail: nihar samal@nitdgp ac inE mail: nihar.samal@nitdgp.ac.innihar_samal@yahoo.co.in

OBJECTIVE OF THE STUDY:OBJECTIVE OF THE STUDY:In the present study, extensive continuoushourly thermal profiles indicating thehydrodynamical events such as stratification aswell as mixing over 2249 Julian days ispredicted with the help of a one dimensionalmodel and the changes in stratification in threemorphometrically different lakes.

Effect of meteorological forcing on the Hydrodynamical eventsHydrodynamical events

Temperature (°C)

How do lakes stratify?

5 10 15 20 25 30

Temperature ( C)

1

2

3

Epilimnion

3

4

5th (m

) MetalimnionThermocline5

6

7

Dep

t Thermocline

7

8

9

Hypolimnion

10

How do lakes stratify?Temperature (°C)

A ili i l5 10 15 20 25 30

1

As epilimnion cools, reduce density difference between layers

1

2

3

y

Eventually, get “Fall 3

4

5(m)

y, gTurnover”

6

7

Dep

th (

Turnover returns oxygen to

8

9

the deep water and nutrients to the surface water

10

THERMALLY STRATIFIED WATER LAYERTHERMALLY STRATIFIED WATER LAYER

ThermalThermal stratificationstratification inin thethe waterwater columncolumn isis ananimportantimportant physicalphysical featurefeature inin manymany temperatetemperateandand tropicaltropical lakeslakes andand anan importantimportant regulatorregulator ofofthethe overalloverall metabolismmetabolism ofof aa lakelake..

EpilimnionEpilimnion-- warmerwarmer layer,layer, lessless densedense

HypolimnionHypolimnion-- ColderColder layer,layer, higherhigher densedense

MetalimnionMetalimnion,, alsoalso calledcalled ThermoclineThermocline --strongstrongverticalvertical differencesdifferences (gradients)(gradients) ininverticalvertical differencesdifferences (gradients)(gradients) inintemperaturetemperature whichwhich resultsresults fromfrom densitydensity changeschangeswithwith temperature,temperature, hashas aa strongstrong influenceinfluence onon thetheratesrates biologicalbiological andand chemicalchemical processesprocesses inin lakeslakes..

WIND INDUCED MIXINGWIND INDUCED MIXING

Turbulent MixingTurbulent Mixing

TurbulenceTurbulence isis causedcaused byby aa varietyvariety ofof processesprocessesincludingincluding windwind stressesstresses andand buoyancybuoyancy fluxesfluxes atatthethe airair--waterwater interface,interface, breakingbreaking internalinternal waveswavesinin thethe interior,interior, andand dragdrag atat thethe waterwater--sedimentsedimentboundaryboundaryboundaryboundary..

Illustration of physical processes affecting the thermal Illustration of physical processes affecting the thermal structure of a lakestructure of a lake

TurbulenceTurbulence -- transportstransports heat,heat, momentummomentum andand aa hosthost ofof otherother tracerstracers (e(e..gg..,,nutrients,nutrients, dissolveddissolved andand particulateparticulate organicorganic material,material, sediments,sediments,contaminants)contaminants) throughoutthroughout thethe waterwater columncolumn..

TurbulentTurbulent mixingmixing affectsaffects thethe physicalphysical dynamics,dynamics, forfor example,example, byby transportingtransporting heatheatfromfrom thethe surfacesurface intointo thethe deeperdeeper layerslayers andand byby modifyingmodifying thethe largerlarger--scalescale circulationcirculation..MixingMixing affectsaffects thethe biogeochemicalbiogeochemical dynamicsdynamics asas wellwellMixingMixing affectsaffects thethe biogeochemicalbiogeochemical dynamicsdynamics asas wellwell..

StratificationStratification ,, mixingmixing && internalinternal oscillationoscillation inin lakelake isis importantimportant fromfrom thethe pointpoint ofof viewviewofof stabilitystability && transporttransport ratesrates whichwhich hashas directdirect bearingbearing onon thethe ecologicalecological developmentdevelopment

ff (( ffff ffofof thethe lakelake withwith numerousnumerous practicalpractical applicationsapplications (( ee..gg.. thermalthermal effectseffects onon fishesfishes[Stevens[Stevens && Lawrance,Lawrance,19971997]]

FISH KILL IN SUBHAS SROBAR, MAY 2003FISH KILL IN SUBHAS SROBAR, MAY 20037

RABINDRA SAROBARRABINDRA SAROBAR88 21 88 22

2231

2231

Basin K

Basin L

Basin M

NATIONAL LAKES OF KOLKATAAs seen through IRS 1D LISS III Satellite DataN

EW

S

WEST BENGALMETROPOLITANKOLKATA

(Location of National Lakes)

Bay

of B

enga

l

Arabian Sea

C

hi n aPa ki

sta n

INDIAINDIA

RABINDRA SAROBAR RABINDRA SAROBAR (BASIN (BASIN -- K & BASIN K & BASIN –– N)N)

SUBHASH SAROBARSUBHASH SAROBARLegend

LakeParkIsland

0 100 200 300 400 500 MetersScaleScale

88 2288 2188 24

Basin NLegend

LakeParkIsland

Kolkata

S

No

rt

h

24

P

ar

g

an

a s

Ha

o

r

a

Hu g li R

.

Subhash Sarobar

0 100 200 MetersScaleScale

2234

88 24

2234

LakeParkRiver

District BoundaryLegendLegend

RailwaysMajor Roads

0 1 2 3 4 5 KilometersScaleScale

So

ut h

2 4 P

ar g

a na s

S o u t h 2

4

Pa

rg

an

as

Rabindra Sarobar

N

⌂Meteorological station

●SUBHAS SAROBAR●

⌂

RABINDRA SAROBAR●RABINDRA SAROBAR

●⌂Meteorological station

●⌂ JADAVPUR UNIVERSITY⌂

SUBHASSUBHAS SAROBARSAROBAR

Developed:Developed: Bathymetric map & Bathymetric map &

Hypsographic and Volumetric curveHypsographic and Volumetric curve

For Rabindra Sarobar (Basin –K & N)

For Subhas Sarobar

Main Limnological Parameters of Lakes of Central Calcutta Metro city

Main Limnological Parameters of Lakes of Central Calcutta Metro city

EXPERIMENTATION AND DATA ACQUISITIONEXPERIMENTATION AND DATA ACQUISITION

Sampling and data collectionSampling and data collectionSampling and data collectionSampling and data collection

Temperature, Dissolved Oxygen, Conductivity, Secchi Temperature, Dissolved Oxygen, Conductivity, Secchi depthdepthdepthdepth

Bathymetric dataBathymetric data

Meteorological data: Data Meteorological data: Data -- Alipore Meteo station Alipore Meteo station --Rabindra Sarobar & Data Rabindra Sarobar & Data -- Dum dum Meteo station Dum dum Meteo station --Subhas SarobarSubhas Sarobar

lakes separated by an air distance of about 9 km & stations lakes separated by an air distance of about 9 km & stations are about 17 km apartare about 17 km apart

InstrumentationInstrumentation

Water Sampler WTW DO meter Conductivity meter SecchiWater Sampler WTW DO meter Conductivity meter SecchiWater Sampler, WTW DO meter, Conductivity meter, Secchi Water Sampler, WTW DO meter, Conductivity meter, Secchi depth transparency, Mercury thermometer, Anemometerdepth transparency, Mercury thermometer, Anemometer

THE (K (K –– Є) TURBULENCE MODELЄ) TURBULENCE MODEL

Basic assumptions:Basic assumptions:Basic assumptions:Basic assumptions:

••TheThe effectseffects ofof convectionconvection andand diffusiondiffusion inin horizontalhorizontal directiondirection havehave notnot beenbeen consideredconsideredbeingbeing smallsmall comparedcompared toto thethe otherother effectseffects andand areare thusthus neglectedneglected..

••CertainCertain specificspecific mixingmixing processesprocesses suchsuch asas LangmuirLangmuir circulation,circulation, internalinternal waveswaves andandupwellingupwelling havehave alsoalso beenbeen neglectedneglected..

••TheThe boundaryboundary conditionsconditions havehave toto bebe treatedtreated asas oneone –– dimensionaldimensional inin spacespace.. TheThe effecteffectofof aa horizontalhorizontal distributiondistribution ofof heatheat andand momentummomentum fluxflux atat thethe surfacesurface isis notnot possiblepossible totoincludeinclude andand thereforetherefore neglectedneglected..

••TheThe transporttransport processesprocesses areare associatedassociated withwith thethe turbulenceturbulence andand assumedassumed toto bebedescribeddescribed byby turbulentturbulent exchangeexchange coefficientscoefficients..

••InflowsInflows andand outflowsoutflows withinwithin thethe waterbodywaterbody inin thisthis modelmodel areare notnot consideredconsidered.. ForForsimplicitysimplicity onlyonly variationsvariations inin densitydensity duedue toto temperaturetemperature hashas beenbeen consideredconsidered..

••TheThe validityvalidity ofof thesethese assumptionsassumptions dependsdepends onon thethe physicalphysical naturenature ofof thethe situationsituation••TheThe validityvalidity ofof thesethese assumptionsassumptions dependsdepends onon thethe physicalphysical naturenature ofof thethe situationsituationstudiedstudied..

Model -LAKEoneDPrinciples of the kPrinciples of the k--εε Model:Model:Solution of coupled partial differential equations for:Solution of coupled partial differential equations for:The temperature (balance equation of heat energy)The temperature (balance equation of heat energy)Horzontal flow velocities (balance equation of momentum)Horzontal flow velocities (balance equation of momentum)Small scale turbulence effects(TKE, Turbulent dissipation rates)Small scale turbulence effects(TKE, Turbulent dissipation rates)

ItIt isis drivendriven byby meteorologicalmeteorological fields,fields, namely,namely, airair temperature,temperature, globalglobal irradiance,irradiance,relativerelative humidity,humidity, windwind speedspeed andand cloudiness,cloudiness, andand determinesdetermines temperature,temperature, turbulentturbulentkinetickinetic energyenergy andand turbulentturbulent dissipationdissipation ratesrates onon aa depthdepth gridgrid withwith dzdz == 00..2525 mm andand onontimetime stepssteps ofof 44 minutesminutes..

•Processes:Wind stress: turbulent mixingShortwave radiation

Absorption and heating of water columnLongwave radiation, heat conduction, evaporation

Heat flow across water surface

•Model:Horizontal flow u, vTemperature TTurbulent kinetic energy kTurbulent dissipation rate ε

The equations fortemperature, turbulentkinetic energy and itskinetic energy and itsdissipation together withthe balance equations formomentum in horizontaldirection are solvednumerically using aimplicit time integrationmethod.

Governing Equations of thek- є turbulence model in LakeOneD

(Samal, 2006):

LakeoneDLakeoneD-- I/OI/OMeteorological Input:Meteorological Input:g pg pWind speed, Air Temperature, relative humidityWind speed, Air Temperature, relative humidityGlobal irradiance, Cloud cover: Hourly valuesGlobal irradiance, Cloud cover: Hourly values

Lake morphometry:Lake morphometry:Hypsographic curve (AreaHypsographic curve (Area depth distribution)depth distribution)Hypsographic curve (AreaHypsographic curve (Area--depth distribution)depth distribution)Light Extinction Coefficient: KLight Extinction Coefficient: Kcwcw = 1.7/ Z= 1.7/ ZSecchiSecchi((1.131.13 for Basinfor Basin--K, 1.16 for Basin K, 1.16 for Basin ––N & 1.00 for Subhas SarobarN & 1.00 for Subhas Sarobar))

Results:Results:TemperatureTemperature--depthdepth--distribution T(z,t)distribution T(z,t)TemperatureTemperature depthdepth distribution T(z,t)distribution T(z,t)Turbulent diffusivityTurbulent diffusivity v(z,t)v(z,t)

Successfully been applied for the simulation of temperature stratification of Lake Successfully been applied for the simulation of temperature stratification of Lake y pp py pp pAmmer in Germany and also studying the intermittent mixing in Ammer in Germany and also studying the intermittent mixing in lake Nieuwe lake Nieuwe Meer, Amsterdam which has also been reported for Hoogheemraadscap Rijnland Meer, Amsterdam which has also been reported for Hoogheemraadscap Rijnland using this turbulence model (Huisman, et al., 2004).using this turbulence model (Huisman, et al., 2004).

SCHEMATIC ARRANGEMENT OF THE FLOW CHART TO SOLVE THE (K - ε) TURBULENCE MODEL

K- ε TURBULENCE MODEL (LakeOneD)

INPUT * EXE

12121212

OUTPUTINPUT *.EXE OUTPUT

TEMP DATA

TEMP MATRIX

K- ε - PARAMATER

DIFF MATRIX

HEAT BALANCE PARAMETERHYPSOGRAPHIC DATA

METEOROLOGICAL DATA

HEAT BALANCE PARAMETER

LIGHT EXTINCTION COEFFICIENT

CALIBRATION WITH EXPERIMENTALLY OBSERVED DATA OVER 2249 JULIAN DAYS

MODEL SIMULATION OF THE THERMAL PROFILEMODEL SIMULATION OF THE THERMAL PROFILETheThe modelmodel runrun isis initialisedinitialised byby applyingapplying thethe prescribedprescribed atmosphericatmospheric forcingforcing totoaa stationarystationary waterbodywaterbody atat uniformuniform temperaturetemperature closeclose toto thethe averageaverage airairaa stationarystationary waterbodywaterbody atat uniformuniform temperature,temperature, closeclose toto thethe averageaverage airairtemperaturetemperature..

TheThe modelmodel isis calibratedcalibrated byby comparingcomparing thethe resultsresults ofof simulationssimulations withwithmeasurementsmeasurements ofof longlong termterm historicalhistorical temperaturetemperature datadata forfor bothboth thethe lakeslakesmeasurementsmeasurements ofof longlong--termterm historicalhistorical temperaturetemperature datadata forfor bothboth thethe lakeslakes..

SimulationSimulation isis runrun withwith respectrespect toto thethe deepestdeepest pointpoint ofof thethe stationstation inin thethe lakelakeandand aa simplesimple quantificationquantification isis mademade byby minimisingminimising thethe meanmean squaredsquared errorerror..

Simulations and model validationk t b l d l (LAKE D J h k 2000 & S l 2006)•k-e-turbulence model (LAKEoneD, Joehnk 2000 & Samal 2006)

•Simulation using man-made freshwater lakes: “Rabindra Sarobar & subhassarobar”

•Assuming knowledge of hourly meteorological data only

•Meteorological data of Two stations used•Meteorological data of Two stations used

•Model validation using temperature data of different locations within the lakes

Turbulent mixing and stratification in Basin Turbulent mixing and stratification in Basin --K & N of Rabindra SarobarK & N of Rabindra Sarobar

TheThe variationsvariations mainly,mainly, observedobserved betweenbetween thethe measuredmeasured andand estimatedestimatedyytemperaturetemperature atat thethe surfacesurface asas wellwell asas atat thethe bottombottom layerslayers..

TheThe naturenature ofof temperaturetemperature structurestructure inin bothboth simulatedsimulated andand measuredmeasured plots,plots,howeverhowever remainsremains samesame ThisThis stronglystrongly suggestssuggests thatthat thethe possibilitypossibility ofof errorerror ininhowever,however, remainsremains samesame.. ThisThis stronglystrongly suggestssuggests thatthat thethe possibilitypossibility ofof errorerror ininmeasurementmeasurement ofof temperaturetemperature distributiondistribution isis minimumminimum;; andand thethe resultsresults furtherfurthersubstantiatessubstantiates thethe validityvalidity andand usefulnessusefulness ofof thethe modelmodel postulatedpostulated..

TheThe apparentapparent causescauses ofof thethe shiftshift oror differencedifference betweenbetween thethe observedobserved andandTheThe apparentapparent causescauses ofof thethe shiftshift oror differencedifference betweenbetween thethe observedobserved andandsimulatedsimulated temperaturestemperatures areare likelylikely toto bebe linkedlinked withwith meteorologicalmeteorological effectseffects..

TheThe gradualgradual increaseincrease inin simulatedsimulated temperaturetemperature ((55 00C)C) asas comparedcompared toto thethedd t tt t 1212thth JJ 20052005 bb dd tt thth ddddmeasuredmeasured temperaturetemperature onon 1212thth JanuaryJanuary 20052005 maymay bebe duedue toto thethe suddensudden

changechange inin thethe weatherweather whichwhich isis happenedhappened inin 2626thth DecemberDecember 20042004,, duedue totoseveresevere earthquakesearthquakes (e(e..gg.. aboutabout 55..88 inin thethe RichterRichter Scale)Scale) thatthat occurredoccurred inin andandaroundaround KolkataKolkata..aroundaround KolkataKolkata..

TheThe coldcold temperaturetemperature inin thethe hypolimnionhypolimnion ofof thethe temperaturetemperature profilesprofiles takentaken onon2525thth MayMay andand 66thth JuneJune ofof yearyear 20012001 suggestssuggests thatthat therethere isis bottombottom currentcurrentinducedinduced byby thethe internalinternal oscillationoscillation thisthis oscillatingoscillating verticalvertical motionmotion isis notnotinducedinduced byby thethe internalinternal oscillation,oscillation, thisthis oscillatingoscillating verticalvertical motionmotion isis notnotexplicitlyexplicitly includedincluded inin thethe modelmodel postulatedpostulated..

5

4

3

2

1

015 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35

5

4

3

2

1

015 20 25 30 35

Simulated Measured

Dep

th (m

)

•The effect of theanticipated smallincrease in average

6 6

5

4

3

2

1

015 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35

5

4

3

2

1

015 20 25 30 35

06.11.2000 11.12.2000 19.12.2000 13.01.2001 23.01.2001 02.02.2001 23.04.2001 17.05.2001

Dep

th (m

)

hypolimnetic temperature(nearly 2°C) duringwinter period (07thD b 2001) i t 6

5

6

5

4

3

2

1

015 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35

4

3

2

1

015 20 25 30 35

20.05.2001 25.05.2001 06.06.2001 15.06.2001 22.06.2001 26.06.2001 29.06.2001 06.07.2001

Dep

th (m

)

December 2001) is notexpected to besignificant, where theadditional upward

6

5

6

520.07.2001

D27.07.2001 08.08.2001

TemperatureOC) TemperatureOC)

13.08.2001

TemperatureOC)

14.09.2001 20.09.2001 28.09.2001 05.10.2001

2

1

015 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35

2

1

015 20 25 30 35

m)

additional upwardbuoyancy of the deepwarm water iscounterbalanced by the

6

5

4

3

2

6

5

4

3

2

1

015 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35

1

015 20 25 30 35

12.10.2001 29.11.2001 07.12.2001 21.12.2001 28.12.2001 04.01.2002 11.01.2002 18.01.2002

T27540BI 08.03.2002

05.04.2002

02.04.2002

Dep

th (mcounterbalanced by the

increased density fromdissolved salts.

This situation appears

6

5

4

3

2

6

5

4

3

2

1

015 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35

1

015 20 25 30 35

02.02.2002 22.02.2002 10.05.2002 29.05.2002 21.09.2002 15.12.2002

Dep

th (m

)

29.04.2003

01.04.200410:00 AM

•This situation appearsjust after the post-monsoon and in thebeginning of winter

6

5

4

3

2

6

5

4

3

2

Temperature (OC)

27.02.2003

Dep

th (m

)

22.05.2003

Temperature (OC)

10:00 AM

Temperature (OC)

01.04.200413:00 PM

01.04.200415:00 PM

01.04.200416:00 AM 01.12.2004 12.01.2005

beginning of winterseason.

Basin Basin ––NN

TheThe measuredmeasured andand simulatedsimulatedTemperatureTemperature--DepthDepth (T(T--D)D) profilesprofiles 2

015 20 25 30 3515 20 25 30 3515 20 25 30 35

2

015 20 25 30 35

29.05.2002

)

21.09.2002

21.05.2003

25.03.200409:00

Simulated Measuredpp pp (( )) pp

showshow aa goodgood agreementagreement forfor bothboththethe stations,stations, exceptingexcepting somesomecases,cases, asas forfor example,example, thethe firstfirsttwotwo profilesprofiles inin stationstation ––IIBIIB (TOP)(TOP)

6

4

2

6

4

2

Dep

th (m

)

Station-IIB

pp ( )( )areare notnot inin goodgood agreementagreement..

TheThe diurnaldiurnal TT--DD profilesprofiles measuredmeasuredonon 2525thth MarchMarch 20042004 buildbuild upup dailydaily 4

2

015 20 25 30 3515 20 25 30 3515 20 25 30 3515 20 25 30 35

4

2

015 20 25 30 35

Dep

th (m

)

25.03.200413:00

25.03.200415:00

25.03.200417:00

pp yythermoclinethermocline inin bothboth thethe stationsstations..

TheThe profilesprofiles atat 0909::0000 amam andand1313::0000 hourhour inin stationstation ––IIBIIB (TOP)(TOP)

6 6

Temperature (OC)

12.01.200501.12.2004Temperature (OC)

015 20 25 30 35 15 20 25 30 3515 20 25 30 35

0

15 20 25 30 35

29 05 2002 Simulated

21 09 2002

21 0 2003

25 03 2004

( )( )showsshows aa differencedifference ofof lessless thanthan22..55 00CC ofof coldercolder hypolimentichypolimentictemperature,temperature, -- thethe presencepresence ofofinternalinternal waveswaves andand oscillationsoscillations inin 6

4

2

0

6

4

2

0

Dep

th (m

)

29.05.2002 Simulated Measured21.09.2002

21.05.2003

25.03.200409:00

Station-IB

basinbasin..

AlthoughAlthough thethe simulationsimulation isis mademadewithwith respectrespect toto thethe deepestdeepest pointpoint 2

015 20 25 30 3515 20 25 30 3515 20 25 30 3515 20 25 30 35

2

0

15 20 25 30 35

pth

(m)

25.03.200413:00

25.03.200415:00

25.03.200417:00

pp pp pp(station(station ––IIB)IIB) (TOP)(TOP) ,, thethe stationstation ––IBIB (BOTTOM)(BOTTOM) showsshows betterbettersimulationsimulation resultsresults inin allall thethe datesdates..

6

4

6

4Dep

Temperature (OC) Temperature (OC)

01.12.2004 12.01.2005

Turbulent mixing and stratification in Subhas SarobarTurbulent mixing and stratification in Subhas SarobarTheThe calculatedcalculated andand measuredmeasured temperaturetemperature --depthdepth (TD)(TD) profilesprofiles areare inin goodgoodagreementagreement onon differentdifferent datesdates atat allall thethe stationsstations exceptingexcepting aa fewfew casescasesagreementagreement onon differentdifferent datesdates atat allall thethe stationsstations exceptingexcepting aa fewfew casescases..

TheThe lowlow temperaturetemperature (i(i..ee.. aboutabout 1616..88 00C)C) atat thethe bottombottom layerslayers asas observedobserved inin thethe firstfirstprofileprofile ofof thethe measuredmeasured datadata isis duedue toto somesome exchangeexchange flow,flow, whichwhich mightmight bebe duedue totothethe internalinternal oscillationoscillation inin lakelake (Samal(Samal etet alal.. 20042004)).. -- AnAn indicationindication ofof thethe shiftingshifting ofof thethethethe internalinternal oscillationoscillation inin lakelake (Samal(Samal etet alal.. 20042004)).. AnAn indicationindication ofof thethe shiftingshifting ofof thethethermoclinethermocline..

AgainAgain thethe epilimneticepilimnetic andand hypolimnetichypolimnetic temperaturetemperature ofof thethe diurnaldiurnal profileprofile onon0707thth AprilApril 20042004 areare notnot inin goodgood agreementagreement withwith thethe calculatedcalculated profileprofile0707thth April,April, 20042004 areare notnot inin goodgood agreementagreement withwith thethe calculatedcalculated profileprofile..

AA wellwell--defineddefined thermoclinethermocline belowbelow aboutabout 33 (m)(m) fromfrom thethe lakelake surfacesurface..However,However, thethe temperaturetemperature atat thethe thermoclinethermocline zonezone remainsremains samesame atat bothboth thethe

filfilprofilesprofiles..

DuringDuring 1717thth January,January, 20052005 itit isis observedobserved thatthat bothboth thethe simulatedsimulated andandmeasuredmeasured profileprofile showsshows identicalidentical naturenature withwith surfacesurface waterwater temperaturetemperaturepp ppdifferencedifference ofof aboutabout 22 00CC atat allall thethe stationsstations.. TheThe naturenature ofof temperaturetemperaturestructurestructure inin bothboth simulatedsimulated andand measuredmeasured plots,plots, however,however, remainsremains samesame..

ThisThis stronglystrongly suggestssuggests thatthat thethe possibilitypossibility ofof errorerror inin measurementmeasurement ofofThisThis stronglystrongly suggestssuggests thatthat thethe possibilitypossibility ofof errorerror inin measurementmeasurement ofoftemperaturetemperature distributiondistribution isis minimumminimum;; andand thethe resultsresults furtherfurther substantiatessubstantiates thethevalidityvalidity andand usefulnessusefulness ofof thethe modelmodel postulatedpostulated..

6

4

2

015 20 25 30 3515 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35

6

4

2

015 20 25 30 35

Simulated Measured

D

epth

(m)

10

8

10

8

8

6

4

2

015 20 25 30 3515 20 25 30 35 15 20 25 30 35 15 20 25 30 3515 20 25 30 35 15 20 25 30 35

8

6

4

2

015 20 25 30 35

07.05.2003

D

28.05.2003 12.08.2003 19.09.2003 08.01.200407.04.2004

11:0007.04.2004

13:00

Dep

th (m

)

T46120BI

T51683BI

T51684BI

T51686BI

T51689BI

T51693BI

IBLake ErieLake Erie

10

8

10

8

8

6

4

2

015 20 25 30 35 15 20 25 30 35 15 20 25 30 3515 20 25 30 35 15 20 25 30 35 15 20 25 30 3515 20 25 30 35

8

6

4

2

015 20 25 30 35

07.04.200416:00

D 25.11.200411:00

25.11.200412:00

25.11.200414:00

25.11.200417:00

25.11.200421:00

26.11.200401:00

Dep

th (m

)

T51699BI

T51701BI

T51705BI

T51707BI

T51900BI

T52548BI

T52955BI

T53219BI

10

8

10

826.11.200403:00

D 26.11.200405:00

26.11.200409:00

26.11.200411:00

Temperature (OC) Temperature (OC)Temperature (OC)

04.12.2004 31.12.2004 17.01.2005 28.01.2005

20

15 20 25 30 3515 20 25 30 35 15 20 25 30 35 15 20 25 30 35

2

0

15 20 25 30 35

m)

Simulated Measured

4

2

015 20 25 30 35 15 20 25 30 3515 20 25 30 35

4

2

015 20 25 30 35

Simulated Measured

m)

10864

10

8

6

4

2

0

15 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35

2

0

15 20 25 30 35

07.05.2003

Dep

th (m

Dep

th (m

)

28.05.2003 12.08.2003 19.09.2003 08.01.2004

10

8

6

4

10

8

6

4

2

015 20 25 30 3515 20 25 30 3515 20 25 30 35

2

015 20 25 30 35

07.05.2003 28.05.2003 12.08.2003 19.09.2003

Dep

th (m

IIB IIIB

10

8

6

4

10

8

6

4

2

0

15 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35

2

0

15 20 25 30 35

(m)

07.04.200425.11.2004

15:00 25.11.2004

21:00 26.11.2004

01:00 26.11.2004

06:00

T51901BII

T52549BII

T52956BII

T53220BII

10

8

6

4

10

8

6

4

2

015 20 25 30 35 15 20 25 30 3515 20 25 30 35

2

015 20 25 30 35

08.01.2004m

)D

epth

(m)

07.04.200425.11.2004

16:0026.11.2004

07:00

10

8

6

4

2

10

8

6

4

2

Dep

th (

26.11.200408:00

26.11.200411:00

Temperature (OC) Temperature (OC)Temperature (OC)

04.12.2004 31.12.2004 17.01.2005 28.01.2005

10

8

6

4

10

8

6

4

Dep

th (m

04.12.2004 31.12.2004

Temperature (OC)

17.01.2005 28.01.2005

Temperature distribution: Evident from the contour plots that varies almost linearlywith depth excepting the periods of complete mixing.

The duration of stratification and vertical mixing varies seasonally and changes with theg y gvariability in meteorological forcings.

4

2

0

m) 26.0

27.7

29.3

31.0

32.7

34.3

36.0

Daily Temperature (0C)(A)

2

1

0

(m) 27.0

28.8

30.7

32.5

34.3

36.2

38.0

Daily Temperature (0C)(A)

10

8

6

Dep

th (m

16.0

17.7

19.3

21.0

22.7

24.3

Feb 2005Jan 2004Jan 2003Jan 2002Jan 2001Jan 2000

Time (Julian day)

Jan 1999

5

4

3

Dep

th (

16.0

17.8

19.7

21.5

23.3

25.2

Feb 2005Jan 2004Jan 2003Jan 2002Jan 2001Jan 2000

Time (Julian day)

Jan 1999

Daily Temperature Distribution in RS (Left) and SS (Right)Daily Temperature Distribution in RS (Left) and SS (Right)

Changes in meteorological and morphometrical conditions and also Secchi disktransparencies are sufficient to reproduce differences in temperature structure from yearto year and from lake to laketo year and from lake to lake.

Basin –K of RS: completely mixed from surface to bottom with no intermittency roughlyfrom mid-June to February next year till the onset of next thermal stratification (ΔΤ = 6.420C to 0 39 0C) which begins in March and continues till mid-June (summer period)C to 0.39 C), which begins in March and continues till mid-June (summer period)showing the nature of A HOLOMICTIC LAKE, while, the basin –N of RS mixes/stratify(ΔΤ = 10.05 0C to 3.04 0C) for about half months of the year and experiences the natureof MONOMICTIC LAKES.

However, the lake SS under different meteorological forcings and different morphometricconditions exhibits longer stratification period (ΔΤ = 12.83 0C to 6.46 0C) and mixes onlyduring the cold period: COLD MONOMICTIC ONE.

TurbulentTurbulent diffusivitydiffusivity:: TheThe lowlow diffusivitydiffusivity valuevalue impliesimplies lowlow mixingmixing eventevent inin thethe lakelake dueduetoto thethe lowlow energyenergy availableavailable fromfrom thethe windwind fieldfield..

AgainAgain thethe mixingmixing havinghaving highhigh turbulentturbulent diffusivitydiffusivity isis mostlymostly duedue toto thethe nightnight--timetimeconvectionconvection andand thethe mixingmixing inin thethe epilimnionepilimnion duringduring dayday timetime isis duedue toto thethe windwind inducedinducedturbulenceturbulence andand convectiveconvective mixingmixing..

0

0 0447

0.180(B) Hourly Turbulent diffusivity (m2/s)

0

0 04470.180

(B) Hourly Turbulent Diffusivity (m2/sec)

5

4

3

2

1

Dep

th (m

)

1.00E-8

4.02E-8

1.62E-7

6.51E-7

2.62E-6

1.05E-5

4.24E-5

1.71E-4

6.87E-4

0.00276

0.0111

0.0447

8

6

4

2

Dep

th (m

)

1.00E-84.02E-81.62E-76.51E-72.62E-61.05E-54.24E-51.71E-46.87E-40.002760.01110.0447

Feb 2005Jan 2004Jan 2003Jan 2002Jan 2001Jan 2000

Time (Julian day)

Jan 199910

Feb 2005Jan 2004Jan 2003Jan 2002Jan 2001Jan 2000

Time (Julian day)

Jan 1999

Hourly turbulent diffusivity during the simulation period (Jan 1999 – Feb 2005) inRabindra Sarobar (Left) & Subhas Sarobar (Right)Rabindra Sarobar (Left) & Subhas Sarobar (Right)

TheThe basinbasin ––KK && NN ofof RabindraRabindra SarobarSarobar doesdoes notnot exhibitexhibit persistentpersistent temperaturetemperaturestratificationstratification becausebecause itit isis effectivelyeffectively suppressedsuppressed byby thethe fullfull--depthdepth solarsolar heatingheating andandstratificationstratification becausebecause itit isis effectivelyeffectively suppressedsuppressed byby thethe fullfull depthdepth solarsolar heatingheating andandwindwind--drivendriven mixing,mixing, leadingleading toto isothermalisothermal conditionsconditions..

StratificationStratification andand verticalvertical--temperaturetemperature contrastscontrasts inin thisthis shallowshallow lakelake thereforetherefore frequentlyfrequentlyf llf ll thth iblibl f tif ti ff di ldi l dd ll th lith li dd tt thth di ldi lfollowsfollows thethe possiblepossible formationformation ofof diurnaldiurnal andand seasonalseasonal thermoclinesthermoclines duedue toto thethe diurnaldiurnalpatternspatterns ofof solarsolar radiationradiation andand windswinds

CONCLUSIONS

• The prediction by model needs validation by historical data and oncevalidated it could be utilized for prediction with limited data input andthat is why the model has the speciality of depicting the ecohealth withminimum measured input thereby reducing the lake authority's effort( hi h l f d i G /S i G l )(which are rarely found in Govt./Semi Governmental structure) to aminimum as regards to data collection.

The basin –K of Rabindra Sarobar remains completely mixed (about 8th ) f id J t F b till th t t f th lmonths) from mid-June to February till the next onset of thermal

stratification (from March to mid-June: summer period), showing thenature of a holomictic lake, while, the basin –N of RS mixes/stratify (ΔΤ= 10.05 0C to 3.04 0C) for about half months of the year and

i th t f MONOMICTIC LAKESexperiences the nature of MONOMICTIC LAKES.

And the lake Subhas Sarobar under different meteorological forcingsand different morphometric conditions exhibits longer stratification

i d (f F b t O t b b t 9 th ) d i lperiod (from February to October: about 9 months) and mixes onlyduring the cold period, which implies to be cold monomictic lake.

Fish kills have been recorded in the lake Subhas Sarobar, called the ,“summer fish kill” due to the decreased vertical mixing based on the transport of oxygen from the epilimnion.

TheThe lakelake SubhasSubhas SarobarSarobar stronglystrongly experiencesexperiences thethe effecteffect ofof TsunamiTsunami onon 2626ththDecember,December, 20042004,, indicatedindicated byby thethe elevatedelevated waterwater temperaturetemperature andand oxygenoxygen levellevel((77..33 ppmppm average)average) alongalong thethe depth,depth, observedobserved onon 3131stst DecemberDecember 20042004,, whichwhichalsoalso persistspersists tilltill thethe lastlast dayday ofof samplingsampling ((2828thth January,January, 20052005)) inin thethelimnologicallimnological yearyearlimnologicallimnological yearyear..

In particular, the formation of a hypolimnion oxygen minimum is of great In particular, the formation of a hypolimnion oxygen minimum is of great importance for the fishery management.importance for the fishery management.

In tropical climate, lakes (depth > 4.0 m) exhibit thermal stratification.In tropical climate, lakes (depth > 4.0 m) exhibit thermal stratification.

For shallow lake, Subhas Sarobar, mixing period is shorter than stratification For shallow lake, Subhas Sarobar, mixing period is shorter than stratification period and the lakes are seasonally stratified.period and the lakes are seasonally stratified.p yp y

Mixing is mainly due to the nightMixing is mainly due to the night--time convective current.time convective current.

Simulation of thermal stratification and mixing gives an idea for calculating Simulation of thermal stratification and mixing gives an idea for calculating the depletion rate of dissol ed o gen in the lakethe depletion rate of dissol ed o gen in the lakethe depletion rate of dissolved oxygen in the lakethe depletion rate of dissolved oxygen in the lake

The model can able to hindcast the temperature profiles to fill in measurement The model can able to hindcast the temperature profiles to fill in measurement gaps in previous years.Also prediction of temperature development in the lake gaps in previous years.Also prediction of temperature development in the lake based on actual weather conditions is possiblebased on actual weather conditions is possiblebased on actual weather conditions is possible.based on actual weather conditions is possible.

•• Model also forecast lake temperature and mixing conditions in the lake under Model also forecast lake temperature and mixing conditions in the lake under future climate change scenario.future climate change scenario.

•• Further emphasis should consider deployment of no. of thermister chain , for Further emphasis should consider deployment of no. of thermister chain , for indepth study of microstructure temperature measurement and detailed study indepth study of microstructure temperature measurement and detailed study of internal oscillation.of internal oscillation.

InIn situsitu PhysicoPhysico--chemicalchemical measurementmeasurement atat RabindraRabindra sarobarsarobar andand SubhasSubhas sarobarsarobar duringduring yearyear20032003,, Kolkata,Kolkata, IndiaIndia:: TheThe NationalNational lakeslakes

FishFish killkill duedue toto bioticbiotic pressurepressure atat SubhasSubhas Sarobar,Sarobar, Kolkata,Kolkata, IndiaIndia

LimnologicalLimnological studystudy usingusing CTDCTD ProbeProbe andand GPSGPS atat LakeLake KonstanzKonstanz inin GermanyGermany

Thank You ForThank You ForThank You For Thank You For Listening!Listening!Listening!Listening!