Impacts of salt water intrusion on construction aggregates of 'Kalu Ganga' estuary

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.