Abstract:
The Physical properties of Kotmale, Victoria and Randenigala reservoirs
were studied since 1987 upto now and this paper presents the data obtained during
1987.
The transparency values changed with the reservoir and the season. The
highest frequency percentage of Secchi depth observed at each reservoir were.
Victoria 1.21-1.61m, Randenigala 2.51-3. Olm and Kotmale 2.10-2.30m, indicating
highest values at Randenigala and lowest values at Victoria. Accordingly the
mean euphotic limits were 5.00m at Victoria, 6.25m at Randenigaia and 5.lOm
at Kotmale. The highest differences in temperature gradients were observed
from surface to about 25m depths in all three reservoirs, in the deeper layers the
temperature gradient is distinctly low. The highest conductivity values were
observed closer to the dams of all three reservoirs indicating the accumulation of
dissolved ions towards the dams. Range of 30-87pslcm at Kotmale, 85-139
pslcm at Victoria and 110-188 pslcm at Randenigala. The highest values were
recordedfrom Randenigala. The highest conductivity values were correlated with
the water rentenion levels of the reservoirs. Fluctuations in pH values with the
seasons follow a similar pattern in all three reservoirs. The mean pH values of
the three reservoirs were in between 6.0 and 8.7. In all three reservoirs, the pH
gradient was higher above 10m depth whereas below this depth it remained more
or less constant.
The high dissolved Oxygen concentrations were closely linked with the
euphotic zones of the three reservoirs. The mean Oxygen concentration calculated
during 1987 investigation period from surface to 5m depth were 4.75-7.50
mg]; at Kotmale, 4.70-6.60 mgjl at Victoria and 4.70-6.65 mgfl at Randenigala
reservoirs. Dissolved concentrations were very low below the depth of 20m
in all three reservoirs. However there was no evidencefor the presence of deoxy
genated layers in all three reservoirs.
