1. Variable Density Flow and Transport in Tsunami Impacted Coastal Aquifers; Laboratory Investigations in Saturated Porous Media
Meththika Vithanage1,2, Tissa Illangesekera3,
Jayantha Obeysekera4, Peter Engesgaard1,
and Karsten H Jensen1
1Department of Geography and Geology, University of Copenhagen, Denmark
2International Water Management Institute, Sri Lanka
3Colorado School of Mines, Golden, Colorado, USA
4South Florida Water Management District,
West Palm Beach, Florida, USA

2. OUTLINE Introduction to mixed convective variable density flow
Evolution of variable density flow concepts
Variable density flow and tsunami in Sri Lanka
Laboratory investigations
Results from intermediate scale experiments
Future work

3. Unstable Density Configuration
Dense fluid
Light fluid
Hydraulically driven forced convection
Buoyancy driven free convection
Unstable
Stable
Instability is influenced by density difference, ambient velocity, heterogeneity and gravity
Spatial scale for mixing are typically larger
Simmons et al., 2001, 2002

4. EVOLUTION Fluid & heat (1900-1940) (Benard 1900, 1901; Rayleigh 1916)
Fluid, porous media & heat (1940’s)
(Lapwood 1948)
Fluid, porous media and solute (1950’s)
(Wooding 1959)
Fluid, porous media, solute and heat (1960’s)
(Wooding 1963, 1969;List 1965)
Groundwater applications (After 1980’s)

5. ON GROUNDWATER…. Scale References 1980’s and 1990’s 2000’s Laboratory
Schincariol and Schwartz (1990)
Simmons et al., (2001)
Oostrom et al., (1992a,b)
Simmons et al., (2002)
Liu and Dane (1996)
Wooding et al., (1997)
Silliman et al., (1998)
Modeling
Paschke and Hoopes (1984)
Diersch and Kolditz (2002)
Koch and Zhang (1992)
Schincariol et al., (1994)
Fan and Kahawita (1994)
Simmons and Narayan (1997)
Schincariol et al., (1997)
Liu and Dane (1997)
Simmons et al., (1999)

6. - the influence of plume density
- and porous medium heterogeneity
on the pattern of spreading of the plume
They observed
- Gravitational instabilities alter the plume shape and plumes are not reproducible
- Lobe shape protuberances formed first along the bottom edge of the plume and later within the plume
- Density as low as g/cu.cm produced instabilities

7. - Plumes are either stable or unstable and three dimensional
- Importance of non-dimensional numbers to predict plume stability

8. - No gravitational instabilities in unsaturated zone
Particular study evaluated plume behavior in unsaturated and saturated conditions with different densities but without horizontal flow
- No gravitational instabilities in unsaturated zone
- Fingering started to occur right at the water table

9. TSUNAMI DECEMBER 26TH 2004

10. TANK EXPERIMENTS OBJECTIVES
Understand the fundamental processes behind unstable density dependant flow problem created by the tsunami
Identify the factors which influence the fate and migration of the tsunami plume through freshwater aquifers

11. TANK EXPERIMENTS

13. HOMOGENEOUS Dense plume experiments Neutral plume experiments
Effect different salt flux rates and times, hydraulic gradients
were examined

14. Heterogeneous I
Heterogeneous II

15. RESULTS

16. Homogeneous Effect of hydraulic gradient
Increase of gradient from % to 0.018%

17. PLUME MIGRATION
Dense plume experiment
Neutral plume experiment

18. Heterogeneous Dense plume experiments ~ 14 hrs ~ 17 hrs ~ 22.5 hrs
Heterogeneous I Heterogeneous II

19. Neutral plume experiments
~ 5.5 hrs
~ 10.4 hrs
~ 28.5 hrs
Heterogeneous I Heterogeneous II

20. MAJOR OBSERVATIONS
All tsunami experiments showed unstable plume behaviour due to high density and low ambient flow
Micro-scale heterogenieties and density difference likely create the instabilities in the homogeneous media
Heterogeneous layers have significant effect on the migration and flushing time of the plume
Neutral plume pushed the dense plume downward but no effect on the horizontal migration
No instabilities or transition zone at the boundary between neutral and dense plume

21. Challange to the modeling experts!!!
FUTURE WORK
Use a variable density flow code to understand and model the behaviour of the tsunami
Challange to the modeling experts!!!

22. Which code ??? Peclet number?? Rayleigh number?? Mixed convection???
Perturbation??
Fingering???
Heterogeneity??
HST3D ???
SEAWAT???
SUTRA???
MOCDENS???
FEFLOW???

23. Thank you!!!