Impact of the 26-12-04 tsunami on groundwater systems and groundwater based water supplies

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This concept demonstrates the situation when sea water stands in a pond or lake for many weeks to months. Though rainfall will decrease the chloride concentration and thus the density of the surface water, infiltration of saline to brackish water into the subsoil can occur through dense fingers of saline to brackish groundwater (figure 9, see also animation).

Whether or not salt to brackish fingers with higher concentrations intrude a porous medium (called the onset of convection) depends on various aspects. For instance, confining deposits like clayey layers on top significantly retard the salinisation of the groundwater reservoir. Processes in the beginning of the intrusion like the development of a boundary layer and the breaking-up of the fingers are important to determine the rate of salinisation.

Figure 9: Salinisation due to flow caused by density differences only (free convection) in high-permeable sediments

Assumptions:

• salt water has already intruded into the subsoil over a depth of 0.3 m, over a width of 89 m.
• No flow at the boundaries
• Hydraulic conductivity 10.0 m/day
• No anisotropy
• Effective porosity=0.3
• Molecular diffusion=10-9 m2/s
• [No groundwater abstraction]

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