Delineation of palaeochannels using DEM and spectral indices in the Gundar basin of Kadaladi region

The identification and mapping of palaeochannels offer an essential understanding of past fluvial processes and groundwater potential, particularly in arid and semi-arid regions facing severe water stress. This study focuses on the Gundar River Basin within Kadaladi Taluk, Ramanathapuram District, Tamil Nadu, aiming to delineate palaeochannel networks using integrated geospatial techniques. Remotely sensed datasets, including Landsat 9 imagery and ASTER GDEM, were used to generate topographic derivatives such as slope, aspect, curvature, flow accumulation, and Topographic Wetness Index (TWI) along with spectral indices like NDVI, NDWI, and NDMI. False Colour Composites (FCC and SWIR-FCC) were prepared to enhance visual interpretation of buried channel patterns. A fuzzy overlay analysis, using a gamma value (γ = 0.8), synthesized these inputs to classify palaeochannel suitability. Results revealed that nearly 18.3% of the basin, predominantly in the central and southeastern sectors, exhibits high palaeochannel potential. These zones are characterized by gentle slopes (< 3°), concave curvature (<-5), high flow accumulation (> 2000), and TWI values above 15, along with NDVI (0.35-0.50), NDWI (> 0.25), and NDMI (0.30-0.41). These findings align with fluvial orientations from northwest to southeast, consistent with regional drainage patterns that flow towards the Bay of Bengal. Despite the absence of field validation, the results correspond well with previous studies in similar Indian basins. This research provides a robust, non-invasive framework for palaeochannel detection, supporting future groundwater recharge planning and paleohydrological reconstructions in coastal, water-stressed environments, such as Kadaladi Taluk.