Tsunami-induced groundwater salinization in southeastern India

On 26 December 2004, a northern Indonesia earthquake generated a tsunami that devastated coastal Indian Ocean regions. The impact of the tsunami on groundwater quality was unexpected as inundation and retreat of the tsunami wave lasted just 5 min. We report data showing salinization of the regionally extensive “Dune aquifer” in southeastern India. We present evidence that tsunami inundation resulted in contamination of groundwater supplies by locally raising salinity from potable levels up to 13,000 μS/cm, which is approximately one quarter the salinity of seawater. Peak salinity occurred within 1 month as the saline water infiltrated. Salinization persisted for more than 10 months in the contaminated coastal region delimited by half of the run-up distance of the tsunami. Then, during the subsequent monsoon season, a second salinity peak was recorded. The timing and extent of natural attenuation of the saline groundwater is greatly influenced by recharge occurring from semiannual monsoons. Given the tsunami damage, our results highlight the fragile nature of water resources in this subsistence-level environment, which is densely populated within 500 m of the coast. We suggest guidelines for future protection of vulnerable coastal groundwater resources based on the tsunami experience. India has at least 750 km of coast bordered by the sand-dune aquifer that was flooded by the tsunami.