Response of the groundwater system to a Base Level Drop: The Dead Sea Case

1. Response of the groundwater system to a Base Level Drop: The Dead Sea Case Yael Kiro, Yoseph Yechieli, Vladimir Lyakhovsky, Eyal Shalev, Abraham Starinsky Hebrew University of Jerusalem Geological Survey of Israel

2. The Dead Sea level during the past 70 years Continuous drop gw response Continuous drop TZ response Instantaneous drop gw response Instantaneous drop TZ response Introduction

3. Location map maps.google.com Continuous drop gw response Continuous drop TZ response Instantaneous drop gw response Instantaneous drop TZ response Introduction

4. The rate of the groundwater level drop is smaller than the rate of the DS level drop Groundwater levels in the Tureibe region Yechieli et al., 2004 Continuous drop gw response Continuous drop TZ response Instantaneous drop gw response Instantaneous drop TZ response Introduction

5. Groundwater levels in Wadi Arugot Groundwater levels drop at the same rate as the Dead Sea in all boreholes Continuous drop gw response Continuous drop TZ response Instantaneous drop gw response Instantaneous drop TZ response Introduction

6. The transition zone during the Dead Sea level drop The transition zone drops and widens over time Continuous drop gw response Continuous drop TZ response Instantaneous drop gw response Instantaneous drop TZ response Introduction

7. The response of the groundwater system involves two aspects: • The response of the groundwater level • The response of the transition zone • an instantaneous lake level drop • a continuous lake level drop Continuous drop gw response Continuous drop TZ response Instantaneous drop gw response Instantaneous drop TZ response Introduction

8. Problem settings Dead Sea salinity 340 g/L specified pressure according to the lake level at each time step no flow Constant inflow no flow Continuous drop gw response Continuous drop TZ response Instantaneous drop gw response Instantaneous drop TZ response Introduction

9. An instantaneous lake level drop Bear, 1979 Continuous drop gw response Continuous drop TZ response Instantaneous drop gw response Instantaneous drop TZ response Introduction

10. An instantaneous lake level drop Freshwater discharge Simulations: Continuous drop gw response Continuous drop TZ response Instantaneous drop gw response Instantaneous drop TZ response Introduction

11. The response of the transition zone The response of the transition zone depends on • The response rate of the fresh water (τgw) • The horizontal density gradient • Depends on the transition zone slope • Depends on the hydraulic gradient Continuous drop gw response Continuous drop TZ response Instantaneous drop gw response Instantaneous drop TZ response Introduction

12. The response of the transition zone • Saline water circulates in steady-state • As the lake level drops, the saline water flows towards the lake • When the groundwater reaches a new equilibrium, the saline water circulation reappears Continuous drop gw response Continuous drop TZ response Instantaneous drop gw response Instantaneous drop TZ response Introduction

13. The response of the transition zone Transition zone characteristic time Continuous drop gw response Continuous drop TZ response Instantaneous drop gw response Instantaneous drop TZ response Introduction

14. A continuous lake level drop Continuous drop gw response Continuous drop TZ response Instantaneous drop gw response Instantaneous drop TZ response Introduction

15. A continuous lake level drop A quasi-equilibrium is reached, in which the groundwater level drops but the discharge to the lake and the hydraulic gradient remain constant Continuous drop gw response Continuous drop TZ response Instantaneous drop gw response Instantaneous drop TZ response Introduction

16. Field measurements and simulation results Simulation results and field data both indicate that the hydraulic gradient remained constant during the past few years. The groundwater level maintained a quasi-equilibrium Continuous drop gw response Continuous drop TZ response Instantaneous drop gw response Instantaneous drop TZ response Introduction

17. The response of the transition zone to a continuous lake level drop The saline water circulation reappears during the lake level drop Continuous drop gw response Continuous drop TZ response Instantaneous drop gw response Instantaneous drop TZ response Introduction

18. The effect of bathymetry The transition zone widens when the bathymetry slope is larger Continuous drop gw response Continuous drop TZ response Instantaneous drop gw response Instantaneous drop TZ response Introduction

19. Seasonal changes in the fresh-saline interface Continuous drop gw response Continuous drop TZ response Instantaneous drop gw response Instantaneous drop TZ response Introduction

20. Summary • We defined two characteristic times that describe the groundwater response rate: • A groundwater characteristic time (τgw) which depends on the aquifer diffusivity and its length. • A transition zone characteristic time (τTZ) which depends on τgw, and the hydraulic gradient. • During a continuous lake level drop after a time interval proportional to τgw, the discharge to the lake and the hydraulic gradient attains a constant value. • At this stage, the saline water circulation reappears

21. Thank You

22. A continuous lake level drop Quasi-equilibrium The hydraulic gradient increases until it attains quasi-equilibrium and remains constant Continuous drop gw response Continuous drop TZ response Instantaneous drop gw response Instantaneous drop TZ response Introduction