1. The Delayed Effects of Variable Density Flow on Flow and Heads in Fresh Groundwater
Frans Schaars
Theo Olsthoorn
Mark Bakker

2. Variable density modeling
Special interest in the movement of the interface
Environmental risk of salinization
This presentation: The effect of the variable density flow on flows and heads in the fresh groundwater zone

3. ? Changing flow patterns equilibrium 1mm/d transition

4. Calculations using Sea Water Intrusion Package
A formulation for seawater intrusion that does not require a vertical discretization of the aquifer
The formulation is intended for regional modeling for periods of up to 100 years
Implemented in a public-domain MODFLOW package

5. The mass balance is replaced by a volume balance (Boussinesq)
Approximations
The resistance to vertical flow within an aquifer is neglected (Dupuit)
The mass balance is replaced by a volume balance (Boussinesq)
Diffusion and dispersion are neglected
Heavier water is not allowed above lighter water

6. Case 1 cross section increased recharge on island
z(m+ msl)
x(m)

7. Case 1 cross section increased recharge on island
Phreatic head(m+msl)
time(y)

8. Case 2 low lying polder area

9. Case 2 low lying polder area

10. Case 2 low lying polder area

11. Case Terschelling Island

12. The magnitude and direction of the effect is time-dependent.
Conclusions
The movement of brackish or salt water can have a considerable impact on the flow and heads in the fresh groundwater zone.
The magnitude and direction of the effect is time-dependent.
For predictions the transmissivity should be adapted to the considered timescale.