PRELIMINARY STUDIES ON THE GEOCHEMISTRY OF THE MAHANADI RIVER BASIN, INDIA

Water, and suspended and bed sediments were collected during 1986/1987 for the two seasons and analysed to study the geochemistry of the Mahanadi River basin, which is one of the eight major drainage systems in India. The water chemistry reflects the control exercised on weathering by the most abundant lithology, namely the carbonates in the basin. Water composition is in equilibrium with dolomite, kaolinite and chlorite. XRD studies in suspended and bed sediments show the presence of dolomite, kaolinite, chlorite and minor quantities of montmorillonite. The Mahanadi annually delivers 15.74·106t of sediments to the Bay of Bengal, which is high compared to its basin size. The dissolved load dominates over physical load by a factor of 4, with 95% of the transport taking place in the monsoon season. The basin is characterised by an erosion rate of 138.24 t km-2 yr.-1, with a lowering rate of 0.31 mm yr.-1. Textural studies indicate that the bed sediments are relatively coarser grained than the suspended sediments. Due to reworking, the sediments are finer downstream. Fe, Mn, Cu, Zn and Pb concentrations in the sediments are higher compared to the other peninsular Indian rivers. Eventhough, Mahanadi transports annually to the Bay of Bengal < 10% of the total load by other Indian rivers, and its weathering in a complex geological terrain with rich mineral deposits controls to a larger extent the chemistry of the sediments in the Bay of Bengal. © 1990.