Spatio-temporal Morphodynamics of Himalayan River in consequence of sand mining using satellite and UAV remote sensing

The Himalayan rivers, characterized by high sediment flux and dynamic morphology, are increasingly threatened by intensive in-channel sand mining. This study investigates the spatio-temporal morphodynamic responses of the Gaula River, an ephemeral Himalayan River in northwestern India to anthropogenic disturbances, using a combination of satellite imagery and UAV-based high-resolution data. The study utilized satellite-based morphometric indices and UAV-generated pre- and post-sand mining DEM of Difference (DoD) to assess the impact of sand mining on channel morphology, sediment transport and net sediment aggradation/extraction. The satellite-based study reveals significant channel narrowing, and loss of wet channels and vegetated bars leading to a reduction in geomorphic diversity, particularly in mining-impacted middle reaches. The UAV-based high-resolution data shows notable changes in bed morphology and slope, knickpoint migration and increased stream power, exacerbating geomorphic degradation, triggering downstream adjustments and altering the sediment regime. Analysis of longitudinal and cross profiles reveal the extent of channel incision, sediment depletion, and their cascading effects on geomorphic processes. The DoD results when compared with reported data on sand mining reveal a discrepancy, with extraction rates exceeding reported figures. By integrating remote sensing techniques with geomorphological principles, this research presents a process-response framework to characterize the geomorphic impacts of sand mining revealing that the Gaula River exhibits a positive feedback response to sand mining. The outcomes of this research contribute to a deeper understanding of the impacts of sand mining on the morphodynamics of the Himalayan rivers and emphasize the need for sustainable management strategies.