Simulation of 3 -D Groundwater Flow and Seawater

Simulation of 3 -D Groundwater Flow and Seawater Intrusion Along the Mediterranean Coast of Turkey

Investigation 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). Dr. Ahmet Dogan 2

Definition of Salt water intrusion is the migration of saltwater into freshwater aquifers under the influence of groundwater development. (Freeze and Cherry, 1979). Dr. Ahmet Dogan 3

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!!! Dr. Ahmet Dogan 4

Natural Occurance of Seawater Intrusion Dr. Ahmet Dogan 5

Wedge Dr. Ahmet Dogan 6

Seawater intrusion due to over pomping Dr. Ahmet Dogan 7

Dr. Ahmet Dogan 8

Upconing Due to Pumping causes water table drawdown. . . …and seawater intrudes into well due to upconing. Dr. Ahmet Dogan 9

Dr. Ahmet Dogan 10

Groundwater System Uncontrollable SYSTEM Detection Controllable Inputs Excitation Cause Identification 1 Uncontrollable Inputs: ◦ Natural Recharge from precipitation ◦ Evapotranspiration Controllable Inputs: Pumping and injection schedules Artificial recharge Outputs Response Effect Undesirable Desirable Prediction 2 3 Desirable Outputs: Undesirable Outputs: ◦ Reduction in Subsurface Outflow ◦ Drying of a wetland ◦ Seawater Intrusion Dr. Ahmet Dogan 11

Groundwater Systems and Three Unique Problems 1 -Detection problem Determination 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 problem Solving 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. Dr. Ahmet Dogan 12

Goksu Delta Setting • • • 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 m 3/yr Goksu River: Q = 110 m 3/sec (3. 47 x 109 m 3/yr) • Groundwater Pumpage: 69 920 m 3/day (25. 5 x 106 m 3/yr) Dr. Ahmet Dogan 13

A A Dr. Ahmet Dogan 14

Hydrogeologic Section A-A’ Dr. Ahmet Dogan 15

Piezometric Surface in Goksu Delta Aquifer in July 2008 Dr. Ahmet Dogan 16

Chloride versus TDS Concentrations in Water from Deep Wells n= 344 r 2=0. 987 Average TDS= 759 mg/l Average Cl=210 mg/l Dr. Ahmet Dogan 17

July 2008 Chloride Concentration vs Na/Cl ratios 0. 557 Four wells near the coast line have saltwater intrusion whereas two of them are under risk. Dr. Ahmet Dogan 18

July 2008 Chloride Concentration vs Mg/Cl ratios 0. 14 0. 05 Mg/Cl ratio of 0. 05 and over indicates saltwater intrusion. Dr. Ahmet Dogan 19

Observed TDS Concentrations in Section A-A’ Dr. Ahmet Dogan 20

Observed TDS Concentrations at -45 m, msl (Layer 5) Dr. Ahmet Dogan 21

Equivalent Freshwater Heads in the Surficial Aquifer Dr. Ahmet Dogan 22

TDS Concentrations in the Surficial Aquifer Dr. Ahmet Dogan 23

Advection-Dispersion Equations for Heterogeneous Flow • Variable-Density Groundwater Flow Equation: • Solute Transport Equation: • Darcy’s Equation: Dr. Ahmet Dogan 24

Advection-Dispersion Equations for Heterogeneous Flow • Groundwater Velocity: • Concentration and Density: • Five Equations, Five Unknowns: Dr. Ahmet Dogan 25

Equivalent Freshwater Head • • Head in aquifer: • Conversion Between Model Results and Field Data: Equivalent Freshwater Head: Dr. Ahmet Dogan 26

Freshwater Head 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 Dr. Ahmet Dogan 27

SEAWAT • • Combines MODFLOW and MT 3 DMS. Solves Coupled Flow and Solute-Transport Equation Implictly ( and C from same time step) Explicitly ( calculated using C from previous time step) MODFLOW Packages: Basic Block-Centered Flow Well • Link Package: Drain LKMT 3 D River Evapotranspiration General-Head Boundary Recharge Solvers Time-Variant Constant Head MT 3 DMS Packages: Basic Transport Advection Dispersion Source/Sink Mixing Reaction Generalized Conjugate Gradient Solver Dr. Ahmet Dogan 28

Conceptual Hydrologic Cross-Section Dr. Ahmet Dogan 29

Discretization and Boundary Packages in Layer 1 Dr. Ahmet Dogan 30

Distribution of Observation Wells in the Basin Dr. Ahmet Dogan 31

Recharge zones in Layer 1 Dr. Ahmet Dogan 32 32

Discretization and Boundary Packages in Column 23 Dr. Ahmet Dogan 33

Observed vs Calculated Heads Observed vs Calculated TDS Dr. Ahmet Dogan 34

Simulated Heads in Layer 5 (-45 m, msl) Dr. Ahmet Dogan 35

Simulated TDS Concentration in Column 23 Dr. Ahmet Dogan 36

Simulated TDS Concentrations in Layer 5 (-45 m, msl) Dr. Ahmet Dogan 37

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. Dr. Ahmet Dogan 38

In the last century average temperature of the earth rose 0. 6 C. (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. 8 C due to green house effect. Dr. Ahmet Dogan 39

Scenarios About the Expected Climate Change Temp. Sea Level Recharge Rise Scenarios Increase mm/d m C -0. 00005 B 1 (avrg) 1. 8* 0. 25* (%17) B 1 (max) -0. 00012 and 4. 0* 0. 38* (%45) A 1 FI (avrg) -0. 00021 A 1 FI (max) 6. 4* 0. 59* (%97. 4) * IPCC, 2007. Climate Change 2007: The Physical Science Basis. Summary for Policymakers. WGI Dr. Ahmet Dogan 40

CLIMATE CHANGE AND SALTWATER INTRUSION? Change of saltwater/freshwater interface caused by sea level rise (Liu, 2003). Dr. Ahmet Dogan 41

RESULTS 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. Dr. Ahmet Dogan 42

HOW CAN SALTWATER INTRUSION BE AVOIDED? WHAT TO DO? NOT TO DO? Dr. Ahmet Dogan

Seawater Intrusion Coastal Aquifer - No Pumping Water Table Equilibrium Sea Level Ocean Fresh Water Brackish Water Dr. Ahmet Dogan

Seawater Intrusion Coastal Aquifer - With Pumping Water Table Sea Level Ocean Fresh Water Brackish Water Dr. Ahmet Dogan

Seawater Intrusion Coastal Aquifer - Intrusion Advancing Water Table Sea Level Ocean Brackish Water Fresh Water Dr. Ahmet Dogan

Seawater Intrusion Coastal Aquifer - Pumping and Injection Water Table Sea Level Ocean Brackish Water Fresh Water Dr. Ahmet Dogan

Seawater Intrusion Coastal Aquifer - Pumping and Injection Water Table Sea Level Ocean Brackish Water Fresh Water Dr. Ahmet Dogan Stranded Brackish Water (Saline Water Plume)

Artificial Recharge Helps to Stop Saltwater Intrusion Dr. Ahmet Dogan 49

Conclusions / Recommendations 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 Dr. Ahmet Dogan 50

Acknowledgments • 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 Dr. Ahmet Dogan 51

THANK YOU Dr. Ahmet Dogan 52