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Out of 103 rivers in Sri Lanka the 3
rd largest major river is Kaluganga,which
hasthe highest volume of discharge as a percent (%) of precipitation per year out of the
Sri Lankan rivers. It originates 2243m above mean sea level (Sripada), is 118km in
lengthand opens to the sea at Kalutara.
The lower reaches of Kaluganga is a densely populated zone where the
inhabitants are highly dependent on sand mining activities, which adversely affect the
qualityof the water in the river.
In this study to assess the extent of mining effects, six sites were selected. Out
of those sites, water samples were collected from one site for monitoring purposes, the
location of the Kethhena water intake. In the other five sites heavy sand mining
activities are going on. To compare the variation of chemical, physical & biological
parameters in water, samples were collected from each site and analyzed weekly for
two months.
The physical parameters measured include - temperature, turbidity, suspended
solids and electrical conductivity. Chemical parameters assessed include pH, dissolved
oxygen, BODs (biochemical oxygen demand), alkalinity, water hardness, [Cl] and
COD (chemical oxygen demand).
The data were analyzed by T-Test of Mean using GLM procedure of MINITAB
for comparison with inland water quality standards in Sri Lanka. The data were
analyzed by TWO WAY ANOVA using GLM procedure of MINITAB. Followed ONE
WAY ANOVA with Tukey's pair wise comparison. Microscopic and macroscopic
identification of biological parameters were carried out According to the results obtained, the value of pH, temperature and dissolved oxygen
were in the desirable level. But some values like conductivity, suspended solids,
turbidity, alkalinity, [Cn, [Fe], phosphates as P20S were higher than the desired range.
BOD5 was low, which means low level of free organisms and organic matter in the
river water because of habitat destruction by mining. [Cn along the river indicates that
salt-water intrusion was directly effected by mining activities, lowering the riverbed.
COD, DO, pH, Nitrogen, and water hardness were lower than the standards. Anabena
spp., Nostoc spp., Microcystis spp., Closterium spp., Cosmarium spp., Occilatoria spp.,
Spirogyra spp., Spirulina Spps. were found as biological indicators in the water at
mining sites but was low in abundance. At the site of water intake, few species were
identified but abundance was higher than in other sites. These include, Occilatoria spp.,
Closterium spp., and,Cosmarium spp., Spirogira spps..
According to the above results it can be concluded that water quality at the
selected sand mining locations of the lower reaches of Kaluganga are adversely
affected and that sand mining activities may be a contributory factor.
