Morphometric analysis of knickpoints and basin disequilibrium in the Cauvery river basin: implications for the transient nature of landscape evolution in Southern India

The changes in the channel steepness along the longitudinal river profile, identified as knickpoints or knickzones, provide insights into factors that affect landscape evolution. Identifying locations, quantifying magnitudes and understanding the spatial distribution of knickpoints in a basin are essential for interpreting the process-response of a transient landscape as it reveals erosional patterns, bedrock incision rates and drainage divide migration trends. Despite their geomorphic importance, knickpoints are understudied in many tropical river basins, with existing analyses often constrained by the use of coarse-resolution topographic data that affect channel extraction and concavity estimation. Prompted by these gaps and challenges, we employed a data-driven approach using open-source LSDTopoTools to extract knickpoints across 14 tributary basins of the Cauvery River using 30 m resolution topographic data. Unlike traditional slope–area–based approaches that are prone to topographic noise, this study adopts a χ-based morphometry method for more reliable concavity index estimation. The spatial distribution of major knickpoints, concavity index, normalised channel steepness, and the collinearity of channels in the χ–elevation profile were examined in relation to lithological, topographic, and tectonic factors to infer the fluvial adjustments in a transient landscape. Palar, Bhavani, Kabini and Chinnar basins exhibit deviation from linear trends in the χ–elevation profile, indicating transient geomorphic responses or active tectonics despite draining similar lithological units. This is further supported by a pronounced knickpoint concentration in the middle Cauvery region, validated by field surveys and using high-resolution images in Google Earth Pro. The Bhavani basin records the highest number of knickpoints, while clustered slope-break knickpoints in the headwaters of Moyar in Nilgiris and its tributaries draining the Biligirirangan range indicate headward erosion and an actively propagating erosional wave driving fluvial incision. This study underscores the potential of knickpoints and their analysis as a robust diagnostic framework for interpreting geomorphic responses to litho-tectonic and climatic perturbations in fluvial landscapes of tropics. The protocol evolved in the study can be used to better understand the fluvial adjustments in a transient landscape, analogous elsewhere.