Impacts of the 2004 tsunami on groundwater resources in Sri Lanka

Abstract

[1] The 26 December 2004 tsunami caused widespread destruction and contamination of coastal aquifers across southern Asia. Seawater filled domestic open dug wells and also entered the aquifers via direct infiltration during the first flooding waves and later as ponded seawater infiltrated through the permeable sands that are typical of coastal aquifers. In Sri Lanka alone, it is estimated that over 40,000 drinking water wells were either destroyed or contaminated. From February through September 2005, a team of United States, Sri Lankan, and Danish water resource scientists and engineers surveyed the coastal groundwater resources of Sri Lanka to develop an understanding of the impacts of the tsunami and to provide recommendations for the future of coastal water resources in south Asia. In the tsunami-affected areas, seawater was found to have infiltrated and mixed with fresh groundwater lenses as indicated by the elevated groundwater salinity levels. Seawater infiltrated through the shallow vadose zone as well as entered aquifers directly through flooded open wells. Our preliminary transport analysis demonstrates that the intruded seawater has vertically mixed in the aquifers because of both forced and free convection. Widespread pumping of wells to remove seawater was effective in some areas, but overpumping has led to upconing of the saltwater interface and rising salinity. We estimate that groundwater recharge from several monsoon seasons will reduce salinity of many sandy Sri Lankan coastal aquifers. However, the continued sustainability of these small and fragile aquifers for potable water will be difficult because of the rapid growth of human activities that results in more intensive groundwater pumping and increased pollution. Long-term sustainability of coastal aquifers is also impacted by the decrease in sand replenishment of the beaches due to sand mining and erosion.

From days to decades: numerical modelling of freshwater lens response to climate change stressors on small low-lying islands

“…In addition, salt water trapped within a borehole, or other direct pathway into the aquifer, may lead to prolonged release of salt water into the surrounding aquifer over time (Illangasekare et al, 2006). These features may delay recovery of the aquifer and, therefore, are an important component to include in modelling studies of storm surge impacts (Chui and Terry, 2013).…”

“…Following a storm surge event when the trenches are filled with salt water, a common remedial action is to drain out the trenches to remove the captured salt water (Illangasekare et al, 2006;Terry and Falkand, 2010;Chui and Terry, 2012). Draining, or pumping out the trenches, is meant to improve the recovery time and assist with removal of the salt water from the system.…”

“…Projected changes in the frequency of hurricanes and tropical storms are uncertain (IPCC -Intergovernmental Panel on Climate Change, 2014); however, there is evidence to suggest that storms may become more intense, increasing the likelihood of storm surge occurrence (Biasutti et al, 2012). Storm surge overwash can lead to salt contamination of the freshwater lens and a temporary loss of freshwater (Anderson, 2002;Illangasekare et al, 2006;Terry and Falkland, 2010). Due to topography, low-lying islands are more susceptible to saltwater inundation from sea level rise and storm surge overwash.…”

Impacts of soil and groundwater salinization on tree crop performance in post-tsunami Aceh Barat, Indonesia

“…The deeper parts of these groundwater aquifers, originating in the hills, were tapped for new wells installed after the tsunami. Alternatively, a model developed by Illangasekare et al (2006) for Sri Lanka, assumes that tsunami seawater infiltrated a freshwater lens situated above a seawater wedge. The mixed water body would then be subject to seasonal oscillations of the groundwater table.…”

Simulations of freshwater lens recharge and salt/freshwater interfaces using the HYDRUS and SWI2 packages for MODFLOW

“…In particular, in view of possible climate change, increased water demands and sea level rise, the development of freshwater lenses supplied with infiltrated rainwater on top of saline aquifers is a subject of intense research (e.g., Werner et al, 2013). A large number of contributions have focused on freshwater lenses in deltaic regions, as well as on islands, peninsulas, or sandbars located in tropical, arid, and temperate climatic zones (e.g., Comte et al, 2014;Contractor and Jenson, 2000;Chang et al, 2016;De Louw et al, 2011;Eeman et al, 2017;Holding and Allen, 2015;Houben and Post, 2016;Illangasekare et al, 2006;Jocson et al, 2002;Mahmoodzadeh et al, 2014;Sadurski et al, 1987;Sinclair et al, 2016;Stuyfzand, 2016;Sulzbacher et al, 2012).…”