Geomorphic Variability and Sediment Connectivity in a Transitional Himalayan - Cratonic River Basin

Sediment connectivity governs sediment dynamics in large river basins by linking erosion sources to delivery sinks, yet remains underexplored across Himalayan–orogenic to cratonic transitions where upstream pulses encounter downstream impedance. This study analyzes spatiotemporal connectivity and hotspot dynamics in the Yamuna basin’s transitional hinterlands, integrating contrasting Himalayan Upper Yamuna and cratonic Chambal ravine–badland sub-basins using a modified Index of Connectivity (IC) that combines structural (topographic slope, NDVI roughness) and functional (rainfall) controls for annual and monsoonal (June–October) conditions over 1999–2005. The Upper Yamuna exhibits the highest, most coherent connectivity (annual mean IC ≈ −8.64 versus −8.68 in Chambal), due to higher slopes and rainfall intensity, with persisting hotspots occupying ~20% of the basin and concentrated in the upper–middle Himalayan reaches. However, the ~750 km reach of the Yamuna River between the SubHimalaya to its confluence with the Chambal River is largely coldspot dominated, so sediment released from upland persisting hotspots experiences prolonged routing and storage, and only a modest fraction reaches the outlet. In contrast, the Chambal ravine–badland basin has slightly lower, more fragmented connectivity but far more dynamic hotspots, with new and sporadic classes occurring at ~10× the frequency seen in the Upper Yamuna and total hotspot–coldspot area ~50% larger. Persisting hotspots in the ~550 km long Chambal valley form a nearly continuous belt, spreading ~20–100 km from the trunk stream. These proximal, highly connected badland patches drastically shorten travel distances and reduce buffering, so monsoonal erosion pulses are efficiently transmitted to the gauge, with mean discharge about three times and mean sediment load about nine times higher than at the Upper Yamuna station, despite the lower basin-averaged IC of the Chambal basin. Together, these patterns show that the location, persistence, and river-parallel extent of connectivity hotspots relative to outlets can outweigh basin-averaged connectivity in controlling measured sediment loads, highlighting cratonic ravines as intermittent sediment sources that can rival or exceed Himalayan contributions. These findings also underpin a scalable structural–functional IC framework for tailored sediment management in Himalayan - cratonic river systems and analogous anthropogenically altered rivers worldwide.