tsunami impact on shallow groundwater in the ampara district in eastern sri lanka: conductivity...

Tsunami impact on shallow groundwater in the Ampara districtin Eastern Sri Lanka: Conductivity measurements and

qualitative interpretations

Jean-Pierre Leclerca*, Christophe Bergera, Anthony Foulonb, Remi Sarrauteb,Lauriane Gabetb

aLaboratory of Chemical Engineering Science, LSGC-CNRS-ENSIC, 1 rue Grandville,B.P. 451, 54001 Nancy Cedex, France

Tel. +33 (3) 83 17 50 66; Fax: +33 (3) 83 32 73 08; email: [email protected]és, Villa Souchet, 105 Avenue Gambetta, 75020 Paris, France

Received 3 July 2006; Accepted 3 May 2007

Abstract

On 26 December 2004 a massive earthquake registering 9.0 on the Richter scale struck off the coastof Sumatra, Indonesia. This was followed by one of the most important tsunamis in history, with an impact onthe coastal area of nearly 15 countries. In Sri Lanka several thousand shallow wells were damaged and polluted bysalt. The east coast of Sri Lanka was strongly affected during the tsunami. Many wells were damaged because of theintrusion of salt water. In order to determine the boundaries of the well area affected by salt and the long-termevolution of the salt concentration in the aquifer, an experimental study of conductivity was carried out. The mappingof the conductivity wells shows that conductivity is high only in the area directly affected by the wave. Data analysisshows that there is a slow natural recovery process, reducing conductivity. The process is a combination of thedownward gravity flow of salt water combined with a lateral fresh water flow toward the sea, but this remains a localphenomenon with different behavior of wells in apparently similar situations.

Keywords: Tsunami; Shallow wells; Conductivity; Salt

1. Introduction

On 26 December 2004 a massive earthquake

*Corresponding author.

coast of Sumatra, Indonesia. This was followedby one of the most important tsunamis in historythat radiated through the Bay of Bengal at a rateof more than 500 km/h, directly impacting thecoastal area of Bangladesh, India, Indonesia,Kenya, Malaysia, Maldives, Mauritius, Myanmar,

Desalination 219 (2008) 126–136

0011-9164/08/$– See front matter © 2008 Published by Elsevier B.V.

registering 9.0 on the Richter scale struck off the

doi:10.1016/j.desal.2007.05.011

J.-P. LeClerc et al. / Desalination 219 (2008) 126–136 127

Reunion, Seychelles, Somalia, Sri Lanka, Tan-zania and Thailand [1]. Sri Lanka was one of themost affected countries in addition to Indonesia:32,000 people lost their lives, about 100,000houses were destroyed and nearly 50,000 housessuffered damages. The number of wells that hadbeen damaged was not determined precisely andthe value varied from one source to another —from 12,000 to a pessimistic number of 100,000wells damaged [2]. This situation is dramatic forthe population in Sri Lanka since 80% of the ruraldomestic water supply is provided from dug wellsand tube wells.

In the Ampara district where the present studywas conducted, 97.4% of the domestic water isprovided from surface water. The wells have beenpolluted by dead bodies, hazardous solid waste,debris and salt from seawater. Even if all the solidmaterial inside the well could be manuallyremoved and pathogens destroyed by chlorinetreatment, the salt in the water remains a moredifficult problem to evaluate and to solve.

First of all, it was not clear where the boun-daries of the area affected by salt are located. Inparticular, strong geysers located behind the limitof the wave impact have been described by seve-ral witnesses. This can be due to an undergroundpressure that could be a strong change of theaquifer behind the impact.

The second point is the expected time of thenatural recovery state of the costal aquifer. Theorder of magnitude varied from 3 months toseveral years from one “specialist” to another.These orders of magnitude have been claimedwithout strong scientific support or under strongassumptions due to the complexity of thephenomena.

The main objective of this study is to presentexperimental results which can be useful for thescientific community working on these twoquestions and to give some clues to the humani-tarian organizations and the local authorities tomake decisions for water projects. A modestqualitative interpretation has been carried out for

a better understanding of the mechanism of theaquifer contamination after the tsunami and toforecast evolution of groundwater conductivitywith time. It should be mentioned that this workis complementary to the remarkable report fromthe International Water Management Institute [3].

2. Groundwater aquifers and analysis of thepossible impact

Six main types of groundwater aquifers havebeen identified and characterized in Sri Lanka[4]:C shallow karstic aquifersC shallow coastal sand aquifersC deep confined aquifersC alluvial aquifersC shallow Regolith aquifersC Lateritic (Cabook) aquifers

The impact of the tsunami mainly concerns theshallow coastal sand aquifers. They are mainlyre-charged during the 3 or 4 months of the rainy(“maha”) season. The water in these aquifers iscollected in the form of a fresh water “lens”floating above the high-density saline water. Thevolume of the fresh water increases during therainy season and decreases during the dry seasonwith fluctuating brackish and saline boundaries.If the extraction of the fresh water is too high,this may result in the entering of brackish waterinto the fresh water.

Most of the wells in this area are shallowwells, dug and cased with concrete casings of 1 to1.5 m diameter with a depth variable from 3 to7 m. They are mainly private wells used fordrinking, bathing, washing or any household use.After the tsunami, it was observed that thesalinity of the water inside the well was veryhigh. As a consequence, the population stoppedusing it, resulting in an increase of the utilizationof the unaffected wells.

Fig. 1 illustrates the possible processes ofinfiltration of salt in the fresh water. The tsunami

J.-P. LeClerc et al. / Desalination 219 (2008) 126–136128

Fig. 1. Schematics of the possible processes of infiltration of salt in the fresh water.

run-up of the order of 8–10 m was observed inthis area. Thus, most of the water came directlyfrom the wave in the open shallow wells becausethe land was inundated during a non-negligibleperiod. After, when the seawater returned, the saltcame indirectly by infiltration into the soil. Thisinfiltration was certainly rapid due to the natureof the soil. The flooded area has been properlydetermined on maps.

The second possible infiltration can be due tothe strength of the wave underground. It is notknown if the pressure of the wave were strongenough to modify the aquifer configuration and tostrongly modify the salt water/fresh waterequilibrium.

Another slower process in the Ampara area is

due to the lagoon or empty pocket that were filledwith seawater: the salt may diffuse progressivelyto the fresh water. It should be also pointed outthat the important need for fresh water during thecrisis may lead to a displacement of the transitionzone between fresh water and salt water but thisa reversible and short-term consequence.

Some programs have been conducted to cleanthe wells consisting of manually removing thesolid hazardous wastes and to kill the pathogensby chlorine treatment. Finally a control pumpingshould be done carefully [5]. If it is not doneproperly, this last step may lead to aspiration andmixing of salt water in the fresh water.

Finally it was expected that rainfall will favorthe decreasing of the salinity.


3. Experimental

To answer to the two questions stated in theintroduction, two measurements programs havebeen carried out. The first one was to measure theconductivity of the wells in a given area at agiven time to determine the boundaries of theaffected area. The second one is to record theconductivity of some wells during a long-termperiod to evaluate the kinetics of desalinization.

The conductivity measurement is not difficultsince most of the detectors included the com-pensation of temperature variation. Due to thepossible gradient of salt concentration, precau-tions needed to be taken into account for themeasurements. Salinity was measured on thesame day for several wells selected in a chosenarea from one side and another of the limit ofextension of the wave. Wells were located with aGPS. Conductivity was measured with the sameconductivity meter. Taking into account that adifference of density between salt and sweetwater may lead to a salt concentration gradient inthe well, caution was exercised when measuringthe conductivity at different levels. Some differ-ences were observed during the first days butquickly the conductivity was constant inside theaccessible volume of the well. Three measure-ments were made each time per well to insurereproducibility of the experiment and reliabilityof the results.

4. Results

4.1. Determination of the wells area affected bysalt

Due to the process of salt infiltration into thefresh water, it was not clear after the tsunamiwhat was the zone where the fresh water had beenpolluted with the salt. Moreover, several wit-nesses described strong geysers of water behindthe impact of the wave. These observations led tosuspicions that the fresh water would have been

affected by the salt behind the impact boundary.The first step was to determine if this area cor-responded to the affected area by the wave.

Two areas were selected: A first set of dataconcerning 20 wells was tested on 4 February2005 in Karaitivu. In this area, the density ofpopulation is large and several wells are concen-trated in a small area. The second area is larger;the objective is to confirm the observation atdifferent scales.

Fig. 2 illustrates the conductivity of 20 wellsin the Karaitivu area. The conductivity in thewells located in the flooded area is higher thanthe wells situated behind it. It should be pointedout that the boundary of the flooded area was notaccurately determined because it was based onwitnesses that were sometimes contradictory andfrom visual observation of the degradation of thehouses. The conductivity differed greatly fromone well to another one, even wells very close,without any logical geographical spreading.These observations seem to prove that the impacthad varied strongly from well to well. Never-theless, the conductivities were lower behind theboundary of the impact, suggesting that the mainorigin was due to direct inundation.

The second set of data was from 17 wellswhich were tested on 19 February 2005 in Peri-yaneelavanai, Maruthamunai and Pandiruppu.This area is larger. These results (see Fig. 3)confirm the conclusion derived from analysis ofthe first set of data. Still again, strong geo-graphical heterogeneity for underground watersalinity was observed.

4.2. Time evolution of the salt concentration inthe wells

The next step was to follow the conductivityas a function of time for several wells to forecastwhen underground water in the affected areawould return to pre-tsunami levels in order tounderstand the possible impact of well pumping(well cleaning activity) and to evaluate the impact


Fig. 2. Conductivity of 20 wells in the area of Karaitivu inside and outside the area affected by the tsunami.

Fig. 3. Conductivity of several wells in the area from Pandiruppu to Perianeelawanai.


Table 1General information about the well selected for the conductivity follow-up.

Well no. Flooded bytsunami

Consumption(L)

Type of use Initialconductivity (µs/cm)

Numberof users

Remarks

1 Yes 170–210 WashingBathing

1739 5

2 No 300–350 DrinkingWashingBathing

1170 12

3 Yes 0 Nothing 3660 / 10 m from the beach

4 Yes 0 Nothing 1800 / 30 m from well no. 3

5 Yes 0 Nothing 1611 / 50 m from the beach


2440 8

7 Yes 30–90 Few useonly whensupply stops

4380 7


1090 6 2 m from well no. 7


2090 4 Same area as wells nos.6–8 (less than 30 mbetween each other)

10 No 150–210 DrinkingWashingBathing

700 3

of rainfall recharge on the salt concentration. Tenwells were selected to be representative of thedifferent situations. The main characteristics ofthese wells are given in Table 1.

Wells No. 2 and 10 were not flooded duringthe tsunami. Wells No. 3, 4 and 5 have not beenused since the tsunami. Wells No. 1 and 6–9 arestill used only for washing and bathing purposes.It should be noted that the distance between wellNo. 7 and 8 is only 2 m, whereas the initial con-ductivity is very different.

Table 2 gives the average kinetics of desali-nation during the period of measurement. Thetwo wells which were not flooded during thetsunami present the slower kinetics of desali-nation (Nos. 2 and 10). The conductivity of thewell which was flooded but for which the initial

Table 2Kinetics of desalination

Well no. Average kinetics of desalination

Relative(percentage/day)

Absolute (μS/cm/day)

1 !0.161 !2.82 !0.132 !1.53 !0.166 !6.14 !0.198 !3.65 !0.246 !3.96 !0.197 !4.87 !0.22 !9.68 0.048 +0.59 !0.223 !4.710 !0.047 !3.3


Fig. 4. Conductivity follow-up of three wells in the same area.

conductivity was low increased slowly. For theothers wells flooded by the tsunami, the kineticsof desalination are of the same order of magni-tude — between !0.132 and !0.246% per day.

4.2.1. Wells in the same flooded areaFor wells in a same area, the conductivity

evolution seems to be similar. Indeed, the threewells — Nos. 6, 7 and 9 — are located in thesame area and their salinities similarly decreased(Fig. 4). The average of the relative derivation isabout !0.2% per day for the three wells (Table 2).

4.2.2. Wells in the same non-flooded areaFig. 5 shows the time evolution of the con-

ductivity for the wells located in the unaffectedrea. The initial conductivities are respectively700 µS/cm for well No. 10 and 1170 for wellNo. 2. They remain more or less constant with

some fluctuations around an average value. Thebehaviors of the curves are different since theconductivity of well No. 2 seems to decreasewhen during the same time the conductivity ofwell No. 10 seems to increase reciprocally. Thisshows that conductivity evolution is a local phe-nomenon due to the heterogeneity of the soil andalso the influence of the uses of the well. Never-theless, the global behavior for a longer time(several months) remains similar.

4.2.3. Well cleaningThe positive or negative effect of pumping

was claimed without any experimental resultsconducted on a long enough time scale. In orderto study this problem, three wells were purposelypumped (No. 1 on day 2, No. 5 on day 13 andNo. 4 the day 60) following the protocol providedby UNICEF [5]. Fig. 6 shows the evolution of the


Fig. 5. Conductivity follow-up of two non-flooded wells.

Fig. 6. Conductivity follow-up of two wells in the same area.


Fig. 7. Conductivity follow-up of three pumped wells.

conductivity follow-up of wells Nos. 3 and 4which are located in the same area; well No. 3 hasnot been pumping. Before pumping, the con-ductivity of both wells decreased similarly. Whenwell No. 4 is pumped (day 60), its salinityincreased to reach about 160% of its initial rateand remained rather high. Fig. 7 shows the evolu-tion of the conductivity of wells Nos. 1, 4 and 5.Wells Nos. 1 and 5 need respectively 2 weeks and4 weeks to recover their initial conductivitywhereas well No. 4 was affected by the procedurefor several months.

For all of them an important salinity increasewas observed (between 130 and 180% of theirinitial salinity in 1 day or between 1000 and1500 µS/cm in one day), followed by differentevolutions:C No. 1 recovers its salinity after 2 weeks.C No. 5 recovers its salinity after 1 month.C No. 4 does not recover its salinity. It stays at

a high level (+1000 µS/cm 140% after1.5 months).

These are critical results for several reasons:The first one is the initial behavior of the wellthat does not predict the effect of pumpingprocedure. The second one is that a strict protocolis not a sufficient guarantee for a pumpingprocedure. The third is that pumping may resultin a negative effect at a long-term scale.

4.2.4. Influence of the rainThe influence of the rain is not straightforward

and unfortunately seems to be again differentfrom one place to another. However, in manycases an immediate decrease of conductivity withstrong rain is observed:C Nos. 3, 6, 7 and 9, beginning of April (about

days 20–25)C Nos. 3, 5 7, on 27 May (day 75)C Nos. 3, 6, 7 on 14 July (day 123)

Rain seems to decrease the salinity in stages;sometimes the salinity increases between tworainy periods (No. 3 between 9 April (day 27) and4 May (day 52).


Fig. 8. Conductivity follow-up of well No. 8.

4.2.5. Atypical behaviorFig. 8 shows the conductivity follow-up of

well No. 8. It is difficult to explain the atypicalbehavior observed with this well. The con-ductivity increased slowly and continuously dur-ing 70 days, and then it decreased still moreslowly for 200 days increasing again.

This well is located in the flooded area and theinitial conductivity was of the same order of mag-nitude of unflooded wells. This can eventually beexplained by the progressive equilibrium insidethe aquifer since the conductivity of this well waslower than well No. 7 located 2 m away.

5. Conclusions

The east coast of Sri Lanka was stronglyaffected by the tsunami. Many wells weredamaged due to the intrusion of saltwater. Inorder to determine the boundaries of the well area

affected by salt and the long-term evolution of thesalt concentration in the aquifer, an experimentalstudy of the conductivity was carried out.

The mapping of the wells shows that theconductivity is high only in the area directlyaffected by the wave. This observation has beenconfirmed in several places and it is not likelythat the water table was deeply damaged.

Data analysis shows that there is a slownatural recovery process that is reducing con-ductivity. The rain seems to have a beneficialeffect on this process, but the amplitude variedfrom one well to another one. The process is acombination of downward gravity flow of saltywater combined with lateral fresh water flowtowards the sea.

Even with a strict application of the protocolproposed by UNICEF, well pumping may resultin a small increase of conductivity. It should alsobe pointed out that if wells may be classified intoseveral “classes” with a given behavior, the


conductivity evolution remains a local phenome-non since two wells located very close togethermay have different behaviors. Because of this,during the next step, a larger investigation will bedone to extend the study to 200 wells. Thisextended study will help us to understand betterthe atypical behavior.

We are now working on interpretation of thedata in order to predict the long-term effect of thetsunami on the shallow wells and to determine thewater strategy management in the coastal area.

Acknowledgements

This work has been carried out with thefinancial support of Echo, AESN, Fondation deFrance, Agence de Bassin seine Normandie. Wewould like to thank Mr. M.F. Nawas (Chemistryand Chief Executive Officer, Centre for Soil &Water Research, Southern University of SriLanka) for his assistance, Mr Ameer (lecturer,Southern University of Sri Lanka) and Mr.Kanthan Thayalan (water resources engineer,

water quality monitoring program manager, assis-tant solidarités) for the measurements.

References

[1] S. Pilapitiya, C. Vidanaarachchi and S. Yuen, Guesteditorial: Effects of the tsunami on waste manage-ment in Sri Lanka, Waste Management, 26 (2006)107–109.

[2] Asian Development Bank, The Japan Bank forInternational Cooperation and World Bank, Pre-liminary damage and needs assessment. Colombo,Sri Lanka, 2005.

[3] K.G. Villholth, P.H. Amerasinghe, P. Jeyakumar,C.R. Panabokke, M.D. Weerasinghe, N. Amalraj, S.Prathepaan, N. Bürgi, D.M.D. Sarath Lionelrathne,N.G. Indrajith and S.R.H. Pathirana, A post-tsunamirecovery support initiative and assessment of ground-water salinity in three areas of Batticaloa andAmpara district in Eastern Sri Lanka, InternationalWater Management Institute Report, 2005.

[4] C.R. Panabokke amd A.P.G.R.L Perera, Ground-water resources of Sri Lanka, Water Resources,Board Report, 2005.

[5] UNICEF, Guidelines for the rehabilitation of tsunamiaffected wells, 2005.

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