Abstract:
'Kalu Ganga' is one of the main suppliers of river sand (113,360
cubes per year) in the country. Due to the continuation of sand mining, salt water
intrusion has been increased over the years. The focus of the current research is to
understand impacts of salt water intrusion on river sand and to understand whether
the absolute chloride content of mined sand is within permissible level (0.075% Cl-)
for the construction purposes. Two surveys were conducted along 'Kalu Ganga'
estuary (10 km from river mouth) in predetermined intervals to measure depth,
conductivity profiles and to collect sediments samples. Survey dates (16/12/2008
and 12/03/2009) were selected considering the maximum difference of tide and rain
fall. The sand samples were ana lysed for Ct- content. Results showed significant salt
water intrusion even during dry season ("'2300 IlS/ cm). All measured conductivity
values were similar to the conductivity levels observed at the sea mouth. But du:ring
dry season the CI- content of sediments is relatively high at river mouth. However,
during rainy season, measured salt water intrusion levels were dropped down
remarkably ("'200 IlS/ cm) and even at the sea mouth, sediment samples showed
significant low values of absolute Cl- content (0.0176%). Therefore, it is
recommended to extract sand from O.5km from the sea mouth only during rainy
season. This will also control the flooding in Kaluthara area. However, further
studies are necessary for understanding other environmental effects of river sand
mining near the sea mouth.
