dr. ahmet dogan develop simulation and optimization models for a coastal aquifer: characterize the...

Dr. Ahmet Dogan

Develop simulation and optimization models for a coastal aquifer:

• Characterize the hydrogeology of the Goksu Delta;

• Model three-dimensional variable-density groundwater flow and seawater intrusion using SEAWAT;

• Use groundwater simulation model to develop response matrices for heads and chlorides for the optimization model;

• Maximize groundwater pumping subject to drawdown and chloride constraints, water demands, and pumping constraints; and

• Relate chloride concentrations and maximum pumping rates using GAMS (General Algebraic Modeling System).

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Dr. Ahmet Dogan

Definition of Salt water intrusion

Salt water intrusion is the migration of saltwater into freshwater aquifers under the influence of groundwater development. (Freeze and Cherry, 1979).

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Dr. Ahmet Dogan

Generally, Salinisation process is a result of human activities.

In addition, a relative sea level rise of 0.5 m per century will intensify the salinisation process in all low-lying areas of the world.

Saltwater intrusion is a problem for every coastal region.

Therefore, we should be very careful to protect freshwater resources all over the world!!!

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Wedge

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Seawater intrusion due to over pomping

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Upconing Due to Pumping

Pumping causes water table drawdown...

…and seawater intrudes into well due to upconing.

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Dr. Ahmet Dogan

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SYSTEMInputsExcitationCause

OutputsResponseEffect

Undesirable

Desirable

Uncontrollable

Controllable

Detection Identification Prediction

1 2

Uncontrollable Inputs:◦ Natural Recharge from

precipitation◦ Evapotranspiration

Controllable Inputs: Pumping and injection

schedules Artificial recharge

Desirable Outputs:◦ Reduction in

Subsurface Outflow

Undesirable Outputs:◦ Drying of a wetland◦ Seawater Intrusion

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Dr. Ahmet Dogan

1-Detection problemDetermination of some of the unknown input parameters using both the responses of the system and the system outputs, e.g. (Recharge and leakage estimations)

2-The identification (Calibration) problem Determining the aquifer parameters, e.g. transmissivity and the storage coefficient. Identification is an extremely important problem in groundwater hydraulics.

3-The prediction problemSolving the prediction (forecasting) problem means solving a model in order to obtain the future responses of an aquifer to an anticipated natural replenishment or to any planned schedule of future pumping and artificial recharge in a proposed management scheme.

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Dr. Ahmet Dogan

• Area: 15 000 ha (land) , 7 615 ha (water)• Population: 30 112• Precipitation : 55 cm/yr• Evapotranspiration : 56.3 cm/yr• Irrigation from River:

Area Irrigated: 5565 ha

Irrigation Rate: 1.84 m/yr

Irrigation Volume : 102 x 106 m3/yr

Goksu River: Q = 110 m3/sec (3.47 x 109 m3/yr)

• Groundwater Pumpage: 69 920 m3/day (25.5 x 106 m3/yr)

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A

A

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0

300

600

900

1200

1500

1800

0 500 1000 1500 2000 2500 3000 3500 4000

TDS, mg/l

Cl,

mg/

l

Örnek Adedi = 344Korelasyon katsayısı (r) = 0.987

Ortalama TDS = 759 mg/lOrtalama Cl = 210 mg/l

n= 344r 2=0.987

Average TDS= 759 mg/lAverage Cl=210mg/l

Dr. Ahmet Dogan

July 2008 Chloride Concentration vs Na/Cl ratios

Temmuz 2008

0.0

0.5

1.0

1.5

2.0

2.5

0 200 400 600 800 1000 Cl

Na/

Cl

0.557

Four wells near the coast line have saltwater intrusion whereas two of them are under risk.

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Dr. Ahmet Dogan

Mg/Cl ratio of 0.05 and over indicates saltwater intrusion.

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July 2008 Chloride Concentration vs Mg/Cl ratios

Temmuz 2008

0.0

0.2

0.4

0.6

0.8

0 200 400 600 800 1000 Cl

Mg/

Cl

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Dr. Ahmet Dogan

• Variable-Density Groundwater Flow Equation:

• Solute Transport Equation:

• Darcy’s Equation:

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• Groundwater Velocity:

• Concentration and Density:

• Five Equations, Five Unknowns:

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• Head in aquifer:

• Equivalent Freshwater Head:

• Conversion Between Model Results and Field Data:

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SEAWAT is based on the concept of equivalent freshwater head in a saline ground-water environment

Piezometer A contains freshwater

Piezometer B contains water identical to that present in the saline aquifer

The height of the water level in piezometer A is the freshwater head

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• Combines MODFLOW and MT3DMS.

• Solves Coupled Flow and Solute-Transport Equation

Implictly ( and C from same time step) Explicitly (calculated using C from

previous time step)

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MT3DMS Packages:Basic TransportAdvectionDispersionSource/Sink MixingReactionGeneralized Conjugate Gradient Solver

MODFLOW Packages:BasicBlock-Centered FlowWellDrainRiverEvapotranspirationGeneral-Head BoundaryRechargeSolversTime-Variant Constant Head

•Link Package: LKMT3D

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Distribution of Observation Wells in the Basin

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Recharge zones in Layer 1

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Observed vs Calculated HeadsObserved vs Calculated Heads Observed vs Calculated TDSObserved vs Calculated TDS

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0.0

1.0

2.0

3.0

0.0 1.0 2.0 3.0

Observed head (m, msl)

Sim

ulat

ed h

ead

(m, m

sl) .

1:1 Line

0.0

1.0

2.0

3.0

4.0

0.0 1.0 2.0 3.0 4.0

Observed TDS (g/l)

Sim

ulat

ed T

DS

(g/

l)

1:1 Line

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Dr. Ahmet Dogan

The Ghyben-Herzberg relation states that a one-meter height of freshwater above sea level assures 40 meters of freshwater below sea level.Likewise, a 0.5 m rise in sea level due to climate change would cause a 20 m reduction in the freshwater thickness. That eventually causes more seawater intrusion.

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Dr. Ahmet Dogan

In the last century average temperature of the earth rose 0.6C. (IPCC, 2001).

Last 30 years’ heating trend seems worse than that of last 100 years.

It is estimated that the temperature of the earth will rise about 1.4 to 5.8C due to green house effect.

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Temperature-Recharge Relationship

y = 0.0009-0.000033x

R2 = 0.809

0.0000

0.0001

0.0002

0.0003

0.0004

0.0005

0.0006

0.0007

0.0008

0 5 10 15 20 25 30 35

Temperature, oC

Rec

harg

e, m

m/d

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Dr. Ahmet Dogan

SScenarioscenarios

Temp.Temp.

IncreaseIncrease

CC

Sea Level Sea Level RiseRise

mm

RechargeRecharge

mm/mm/dd

B1 (B1 (avrgavrg)) 1.8*1.8* 0.25*0.25* -0.00005 -0.00005 (%17)(%17)

B1 (max) B1 (max) andand A1FI A1FI ((avrgavrg))

4.0*4.0* 0.38*0.38* -0.00012 -0.00012 (%45)(%45)

A1FI A1FI (max)(max) 6.4*6.4* 0.59*0.59*

-0.00021-0.00021

(%97.4)(%97.4)

Scenarios About the Expected Climate Change

* IPCC, 2007. Climate Change 2007: The Physical Science Basis. Summary for Policymakers. WGI

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Change of saltwater/freshwater interface caused by sea level rise (Liu, 2003).

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CLIMATE CHANGE AND SALTWATER INTRUSION?

Dr. Ahmet Dogan

The SEAWAT model simulated the Göksu Delta succesfully which will help us understanding the hydrogeology of the region accurately. In addition the location of saltwater/freshwater interface was determined by means of the model.

Effects of the probable pumping schemes on saltwater intrusion were succesfully tested by means of the model.

Effects of the climate change on saltwater intrusion mechanism were also investigated by means of the model.

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RESULTS

Dr. Ahmet Dogan

HOW CAN SALTWATER INTRUSION BE AVOIDED?

WHAT TO DO?

WHAT NOT TO DO?

Dr. Ahmet Dogan

Coastal Aquifer - No PumpingCoastal Aquifer - No Pumping

Water TableWater Table

OceanOcean

Sea LevelSea Level

FreshFreshWaterWater

BrackishBrackishWaterWater

EquilibriumEquilibrium

Dr. Ahmet Dogan


OceanOcean


Sea LevelSea Level


Coastal Aquifer - With PumpingCoastal Aquifer - With Pumping

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OceanOcean

Brackish WaterBrackish Water Fresh WaterFresh Water

Sea LevelSea Level



Coastal Aquifer - Intrusion AdvancingCoastal Aquifer - Intrusion Advancing

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OceanOcean


Sea LevelSea Level



Coastal Aquifer - Pumping and InjectionCoastal Aquifer - Pumping and Injection

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OceanOcean


Sea LevelSea Level


Stranded Stranded Brackish Brackish

Water Water (Saline (Saline Plume)Plume)


Coastal Aquifer - Pumping and InjectionCoastal Aquifer - Pumping and Injection

Dr. Ahmet Dogan

Artificial Recharge Helps to Stop Saltwater Intrusion

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Saltwater Intrusion can not be stopped but it can be CONTROLLED.

SEAWAT type of models can be very useful in determining aquifer characteristics and saltwater intrusion mechanism to determine safe yield pumping rates in coastal aquifers.

Luckily, there is a growing awareness of salt water intrusion and upconing but safe yield pumping rate regulations should enforced strickly to assess the potential salinity impacts caused by pumping.

Uncontrolled water pumpage should be prevented by law or local authorities strickly.

Remediation procedures and measures should be implemented based on the type of saltwater intrusion problem at coastal regions immediately

Conclusions / Recommendations

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Dr. Ahmet Dogan

• State Hydraulic Works (DSI), Republic of Turkey

• Scientific and Technical Research Council of Turkey (TUBITAK)

• Research Foundation (No. MMF.2000.13), Cukurova University, Adana, Turkey

• Society for the Protection of Nature (DHKD), Turkey

• Mersin Directorate, Authority for the Protection of Special Areas, Ministry of the Environment

• National Science Foundation, U.S.A.

• University of Florida, Gainesville, Florida, U.S.A.

• Suleyman Demirel University, Isparta, Turkey

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Dr. Ahmet Dogan

THANK YOUTHANK YOU

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dr. ahmet dogan develop simulation and optimization models for a coastal aquifer: characterize the...

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