Abstract:
A combined approach was used to assess the interaction between surface water
from irrigation canals and an aquifer system in the Uda Walawe .irrigation scheme,
southern Sri Lanka. Surface water in reservoirs arid irrigation canals and
groundwater from shallow and deep wells were sampled and analyzed for chloride,
fluoride and water stable isotopes (oxygen 18, 0180 and deuterium, olH). The
investigation of water stable isotopes provided conclusive evidence for the
contribution of irrigation water to the upper parts ofthe aquifer, with implications
for freshwater quality and availability in the region. The stable isotope chemistry
also showed additional evidence for strong evaporation influencing both surface
water and shallow groundwater, as well as the effects of dilution in affecting
fluoride concentrations. The degree of interaction between the surface water from
irrigation canals and the shallow groundwater, expected to be derived from the
stable isotope study, could not be quantified, most probably due to limitations in the
field approach.
