WASH Cluster – Groundwater Development and Drilling
GWD2
Handout
GWD2 – Characteristics of Groundwater Systems
Case Study 1: Impacts of the Asian Tsunami
on groundwater in Sri Lanka
Summary
The Indian Ocean Tsunami impacted coastal sandy aquifers were affected on the eastern side of
SriLanka by causing inflow of salt water into wells.
These aquifers contain a lens of fresh water sitting on top of the denser saline sea water. Recharge to these
aquifers is typically rainfall infiltration.
The Tsunami caused physical damage to many of the wells in the coastal areas, including filling
with rubbish and even removal of well lining from the groundwater.
When the tsunami struck salt water permeated into the entire aquifer, and thus all of the water supply being
highly contaminated by salt.
Immediately after the tsunami wells in the area were extensively pumped in the area by NGOs, civilians
and armed forces as it was believed that this would clean the wells.
Pumping on the wells led to increased EC. The groundwater wells often experienced an upconing effect when
being ‘pumped clean’ after the tsunami.
Many I/NGOs were attempting to pump out the salt water, however due to the increase in the size of the salt
water wedge and excessive pumping resulted in the salt water being drawn up from the salt water wedge and
increasing the salt water concentration at the borehole location
Figure 23 - Groundwater Flow Pre-Tsunami (Lytton, 2008)
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- Groundwater Flow
Post-Tsunami (Lytton, 2008)
Emergency Situation
On the 26th of December 2004 a tsunami was triggered by a 9.0 magnitude earthquake off the coast of Sumatra.
The wave caused destruction to many countries around the Indian Ocean. The tsunami struck the east and
southern coast of Sri Lanka killing 40,000 people, and destroying numerous houses and water supply wells. Up
to 450,000 people were displaced in Sri Lanka (Tamil Information Centre, 2006).
This case study is prepared to outline some of the impacts of the Tsunami on the groundwater resource in
coastal settings
Aquifers in Sri Lanka:
Aquifers in Sri Lanka are described by Panebokke and Perera ( 2005)
The geological basement in much of Sri Lanka consists of high grade metamorphic rocks. The metamorphic
rocks are low permeability crystalline materials although weathered material (regolith) on the upper exposed
outcrop areas forms aquifers in some areas.
Deep confined aquifers are located in the northwest of the island and Miocene limestone that occurs in the north
of the country comprise karstic aquifers.
The coastal zone on the eastern side of the country has extensive shallow coastal sand and alluvial aquifers that
are highly permeable. These are the aquifers of greatest interest in this case study.
Groundwater is highly utilised in many coastal areas from the coastal sand and alluvial aquifers. The majority of
users are undocumented as they are private dug wells.
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Aquifers in SriLanka (after Panabokke and Perera, 2005)
Coastal Sand Aquifers
Along most of the coastline there are shallow aquifers located on the coastal sands. Groundwater recovered
from these aquifers support agriculture (chilli and onions), domestic use by the local population and the tourist
industry (Panabokke & Perera, 2005).
These aquifers contain a lens of fresh water sitting on top of the denser saline sea water. Recharge to these
aquifers is typically rainfall infiltration, which falls during the maha season (October – January). Due to the
varying rainfall patterns the fresh and brackish water boundary expands and contacts over time (Panabokke &
Perera, 2005).
Over-extraction of the aquifers can cause a cone of upwards intrusion into the aquifer, resulting in a saline bore
which can no longer be used (Cooray, 1967; Panabokke & Perera, 2005).
Alluvial Aquifers
Alluvial aquifers are located in or around current and old river beds, and vary in depth, extent and yield (Cooray,
1967; Panabokke & Perera, 2005). These aquifers are generally alluvial sediments, sands, clayey sands, and
gravels which have been deposited, and then overlain with finer sediments. The beds extend several hundred
meters either side of a river and up to 35m deep (Panabokke & Perera, 2005). Thus the water supplies to these
aquifers are quickly recharged, and can support high extraction rates to varying degrees without significant
drawdown effects.
Types of Wells
There are two key types of wells in Sri Lanka: tube and dug wells. Dug wells are generally shallow, water table
aquifers which use the resources unconfined aquifers, often they are not more than 5 - 7m in depth and
approximately 1-1.5m wide and have concrete casing. These are the most common types of wells in Sri Lanka,
and are used for domestic water supply (Panabokke & Perera, 2005). The location and number of dug wells is
not recorded in Sri Lanka.
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Tube wells are much smaller in diameter, and draw resources from much deeper in the aquifer. They often
screen unconfined aquifers, not reachable by dug wells, and service both domestic, agricultural and industrial
uses. They are often constructed with PVC pipe and fitted with a hand or motorised pump.
Distribution of tube wells in Sri Lanka (from Panabokke and Perera, 2005)
Impact of the Tsunami on Groundwater
Damage to Wells
The Tsunami caused physical damage to many of the wells in the coastal area, including filling with
rubbish and even removal of well lining from the groundwater.
When the tsunami struck salt water permeated into the entire aquifer, and thus all of the water supply being
highly contaminated by salt. In a study by (Saltori & Giusti, 2006) it was noted that in the few day following the
tsunami that the water within local drinking wells was up to 28,000μS/cm, however decreased to 3,000 –
8,000μS/cm in a few weeks.
The Ampara district experienced three methods of salt water intrusion after the tsunami (Lytton, 2008):
 infiltration from sea water,
 the strength and pressure of the wave causing an underground saline wave into the aquifer (indicated by
several witness reports of geysers beyond the wave extent), and
 the lagoons situated behind the dunes of the beach filling with saline water and slowly releasing it into the
groundwater system (Lytton 2008).
Lytton found EC decreased with distance from the coast line. Most wells, even those not inundated by the wave,
still recorded values over that acceptable to the human palate of 1800uS/cm at the time of testing. Bacterial
content of the wells recorded colonies too numerous to count.
Leclerc et al.’s (2007) testing results concluded that the main cause of saline intrusion in the area was from
direct inundation. Their testing regime involved wells in one local area, and then over an extended area, and
comparing wells of similar conditions.
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As a result of the tsunami, large numbers of wells were without water due to well pollution due to saline
intrusion or to pollution related to latrines and burial pits in the vicinity of wells.
Saltori and Giusti also concluded that with the elimination of fish industry immediately after the tsunami that the
agriculture industry increased and that with the electric pumps supplied by aid agencies that the agricultural
industry could be contributing to the salinity problems in the area due to up coning, as well as contamination
from nitrates and pesticides.
Rehabilitation of wells
Immediately after the tsunami wells in the area were extensively pumped in the area by NGOs, civilians and
armed forces as it was believed that this would clean the wells. In addition, many members of the public believed
that pumping need to take place in order to be able to use their well again.
Various studies showed that pumping on the wells led to increases the EC. Well cleaning was taking place in this
area by various organisations, however most did not take readings before or after their activities, and frequently
the extracted water was dumped next to the well, allowing it to permeate back into the aquifer, causing a
contamination loop (Lytton, 2008). It appears that pumping the well only destroys any remaining fresh water
lens within the aquifer by either pumping it to its extent, the pumping causing mixing of fresh and saline water,
or the recycling of the water causing in effect the same situation as another tsunami would do locally.
The research concluded that there was no way to clean and restore the aquifers in the short term.
As a result of the problems being produced in attempts to clean the wells, by the end of 2005 UNICEF produced
guidelines on the cleaning of wells and the processes to be undertaken (UNICEF, 2005). The rain events in this
area seem to have decreased the EC in the wells, however in some cases it caused an increase between events
perhaps as salt stored in the soils leaching into the groundwater system (Piyadasa et al. 2006).
The groundwater wells often experienced an upconing effect when being ‘pumped clean’ after the tsunami. Many
I/NGOs were attempting to pump out the salt water, however due to the increase in the size of the salt water
wedge and excessive pumping resulted in the salt water being drawn up from the salt water wedge and
increasing the salt water concentration at the borehole location (Figure 24). The pumping was not beneficial for
this reason, additionally many organisations when purging the bore let the contaminated water flow straight
onto the ground next to the bore hole, causing recontamination (Lytton, 2008). In alluvial aquifer systems it was
noted that while the salinity decreased over time, in places the salinity spiked after the first rain period. This was
due to a flushing of the salts captured in the soils by the fresh water as it entered into the groundwater stream.
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