Interaction between canal water and groundwater in the Uda Walawe irrigation system:hydrochemistry and isotopes Mauro Prado, Kevin Hiscock, Lorraine Rajasooriyar, Eline Boelee Universities of East Anglia , Jaffna & International Water Management Institute Presented at Session C "Innovation and Technologies" of International Symposium 2010, Ruhuna University, Sri Lanka November 16, 2010

1. Interaction between canal water and groundwater in the Uda Walawe irrigation system:hydrochemistry and isotopes Mauro Prado, Kevin Hiscock, Lorraine Rajasooriyar, Eline Boelee Universities of East Anglia , Jaffna & International Water Management Institute Presented at Session C “Innovation and Technologies” of International Symposium 2010, Ruhuna University, Sri Lanka November 16, 2010

2. Outline Approach Study area: geology and sampling points Sampling results and analysis Discussion, conclusions and recommendations

3. Approach Isotope study; part of a larger research project Objectives Understand determining factorsof groundwater quality Interactions between surface waters and groundwater Consequences for management Mapping Water infrastructure, geology, land use Results Sampling Analysis

4. Study area: Uda Walawe irrigation system Average Temp 28°C Humidity 77% ETpot 1988 mm Rain 1979 mm Etpot:Potential Evapotranspiration Source: IWMI, 2002

5. Uda Walawe irrigation system < 400 km2 Source: L. Rajasooriyar, 2003

7. Uda Walawe

8. Ridiyagama

9. Three sampling rounds

10. Tube wells / boreholes

11. Shallow dug wells

12. Canals

13. Chemical analysis

14. Ion specific electrodes, ion chromatography, titration, spectrophotometry

15. Isotope analysisSource: MCCM .Prado, 2002

17. Combining with data from hydrochemical study (fluoride)

18. Variation between surface and groundwater in terms of physical and chemical featuresSource: Created by Eline Boelee for the purpose of this presentation

20. More pronounced for deeper groundwaterSource: Created by Eline Boelee for the purpose of this presentation

23. Surface water: increasing evaporation

24. Groundwater:

25. Enrichment in discharge areas close to the sea

26. Lower rainfall in south

27. Influence sea spray

29. Uda Walawe geology A hjhgjkhsjkhg Source: L.Rajasooriyar, 2003 B Geosutur

30. Uda Walawe groundwater flow Source: L.Rajasooriyar, 2003

31. Uda Walawe fluoride Source: L.Rajasooriyar, 2003

32. Uda Walawe fluoride related to canal recharge Source: L.Rajasooriyar, 2003

34. Isotope analysis limited in sample size

35. Results in line with those from hydrochemical analysis

36. Important implications for groundwater quality and drinking water supply

37. No quantification of surface – groundwater interactions

39. Shallow wells are preferred sources of drinking water

40. Recharge = seepage = leakage?

41. Lower irrigation efficiency?

43. Thank you! For more information please visit: University of East Anglia - www.uea.ac.uk University of Jaffna - www.jfn.ac.lk/ IWMI - www.iwmi.org