Already available and newly collected data sets on water chemistry
of twenty reservoirs located in seven river basins in Sri Lanka were analyzed
to determine the status and trends in irrigation related water quality
characteristics. pH of irrigation water varied within a wide range but the
upper limit did not exceed the proposed level suitable for irrigation water.
Salinity was found beyond the threshold level (1.250 g
l
$^{-1}$
) only in two reservoirs located downstream of the
Malwathu Oya basin and the electrical conductivity had never reached above 1 mS
cm
$^{-1}$
. Sodium absorption ratio (SAR) was well below the
threshold value of 6 meq l
$^{-1}$
in the study reservoirs.
Least square regression model showed that electrical conductivity was a good
predictor of salinity and SAR. Time series data showed no marked changes in
irrigation water quality of the reservoirs located in the Mahaweli river basin
over the last forty three years with respect to EC levels but the EC of those
proximate reservoirs receiving additional transfer water from the trunk stream
of the Mahaweli river showed a progressive decrease following the trans basin
diversion.
