River Discharge, Major Ion Chemistry and Sediment Transport of the Bharathapuzha River, Southwest India: Implications on Catchment Erosion

The present study deals with the discharge characteristics, major ion chemistry as well as particulate and dissolved sediment transport of the Bharathapuzha river flowing across the Western Ghats through the Palghat gap - a prominent break in the Western Ghats that acts as a climate corridor in the region. While the western part of the basin in Kerala exhibits a wetter/humid climate, the eastern part in Tamil Nadu experiences a semi-arid climate. This peculiar climatic condition together with human interventions has a decisive role on the discharge characteristics as well as catchment erosion of the river basin. The dissolved and particulate contents of the river waters were found to be directly related to the geo-environmental settings of the river catchments. An intercomparison of elemental loading in the river waters in different seasons reveals notable decrease in monsoon compared to nonmonsoon seasons, which is attributed mainly to dilution of the solute contents by monsoon precipitation. The bivariate plots of Na/(Na+Ca) vs Total Dissolved Solids (TDS) and Cl/(Cl+HCO3) vs TDS spread generally in the rock dominance sector of Gibb's model indicating the role of chemical weathering in contributing to the major ion chemistry of the Bharathapuzha river. The intensity of weathering varied significantly among the different sub-basins of the Bharathapuzha river basin. The higher particulate load by dissolved load ratio of the Thuthapuzha and Gayathripuzha tributaries draining the humid areas compared to the Chitturpuzha tributary draining the semi-arid zones of the basin indicates the predominance of physical weathering in the former two sub-basins than the latter.