In the coastal areas of Eastern Sri Lanka, the majority of the population, which is rural or semi-urban, is relying on groundwater for their domestic and agricultural activities, most predominantly through traditional private shallow open dug wells in the sandy aquifers. As the tsunami destroyed practically all wells within the reach of the flood waves, access to freshwater for these people was suddenly cut off and interim alternatives had to be sought urgently in the form of freshwater trucked in from unaffected areas.
Soon after the tsunami, massive efforts to clean the wells were initiated from a range of different actors in an attempt to rapidly return the water supply to normal conditions, or at least ameliorate the immediate impacts of the salinization of the wells. Based on indications that these efforts were un-coordinated, inadequate, inefficient and at the extreme harmful to the water quality and the well functioning, IWMI set in at various levels to try and guide and coordinate these efforts.
With the aim to assess and document the extent of the damages and the immediate and intermediate term impacts of the tsunami on groundwater and associated water supply, a field monitoring program was initiated in March 2005 (2.5 month after the tsunami) in three areas on the east coast (Kallady, Kaluthavalai, and Oluvil, in Batticaloa and Ampara District). A total of approximately 150 wells were selected within approx. 2 km distance from the coastline covering both affected and non-affected wells. Salinity, groundwater level, and turbidity were monitored on a regular basis, with from 20 to 40 days interval.
In addition, salinity levels in sea and lagoon water were measured. Results indicate that 39 % of the wells had been flooded by the tsunami, with the flooding being more severe in the two most northern sites (49 % in both Kallady and Kaluthavalai), as compared to the last site (21 % in Oluvil). This pattern could be explained by the way the waves had come in and had been received by the land complex.
Salinity levels in flooded wells decreased significantly from the estimated levels at the time of the tsunami (29,400 μS/cm) till the start of the monitoring (3200 μS/cm). This can be explained by the rainfall that occurred shortly after the tsunami and the rapid dissipation and mixing of intruding seawater with pre-tsunami fresh groundwater and potentially the well cleaning effects. As time passed, average salinity levels in flooded wells decreased only slowly, until the end of the study period (middle of July), when the average salinity was 2600 μS/cm. The slower decrease can be attributed to the unset of the dry season and the slower mixing and dissipation mechanisms as concentration gradients decreased. Non-flooded wells showed an opposite trend with salinity levels slightly increasing during the dry season (from 890 to 1090 μS/cm), a generally encountered phenomenon. Hence, seven months after the tsunami, flooded wells had higher average salinity level than background, non-flooded wells, indicating that the groundwater still had not recovered fully from the tsunami, and that at least one more rainy season was required to flush the system and restore the aquifers to pre-tsunami conditions.
Based on a drinking water salinity acceptance threshold derived from the actual use of the wells, it was found that a large fraction of the flooded wells (between 67 and 100 % in the three sites), and even wells not flooded (between 17 and 50 %) were not suitable for drinking at the end of the study period. This indicates that people in the areas had become accustomed to the alternative water sources supplied by various relief organizations, because background, non-flooded wells did not show increased salinity relative to pretsunami conditions and people generally were relying on the well supply for drinking water prior to the tsunami.
Guidelines for well cleaning and groundwater protection and general awareness raising and information sharing was a significant part of the project, and it is believed that the activities involved had an impact on the approach to well cleaning in the affected areas, by drawing attention to the potential problems involved, by linking various actors and by disseminating the knowledge and results generated in the project.