Drainage basin reorganisation in Trivandrum block, Southern Western Ghats, India

Abstract

Drainage basin reorganisation is a fundamental earth surface process with significant implications for landscape evolution, sediment routing, and hydrological regimes. In this study, we investigate the Kallada and Ithikkara rivers in the southern Western Ghats to constrain the timing, mechanisms, and geomorphic consequences of river capture in their upper catchments. Morphometric and sedimentary provenance analyses indicate that the upper Kallada and Ithikkara basins were once part of a single, integrated drainage network. Chi (χ) analysis further reveals that following the river capture event, the Ithikkara basin experienced a substantial reduction in upper catchment area. The chi map geometry suggests that the upper Kallada basin, presently located upstream of a pronounced channel elbow, may originally have drained through the present Ithikkara channel before being captured by the Kallada river. Detrital zircon UPb geochronology from sediments of both rivers exhibits remarkably similar age spectra, with prominent peaks at ~2500 Ma, ~1900 Ma, ~1000 Ma, ~750 Ma, and ~550 Ma, indicating derivation from a shared sediment source. Integration of geomorphic metrics with provenance data supports a scenario in which tectonic or geomorphic processes separated the upper Kallada basin from the main Ithikkara drainage system, resulting in reorganisation of the regional river network. These findings demonstrate the value of combining quantitative geomorphic approaches with sedimentary geochronology to reconstruct past drainage evolution, even in tectonically stable regions, and provide new insights into the links between river capture, sediment provenance, and landscape dynamics in the southern Western Ghats.