Landsat archives, a key source for disentangling the complex anthropogenic controls of large river changes

Abstract. River form reflects the balance of water and sediment fluxes acting on an inherited geological and climatic template;  where human activity alters that balance, channel and floodplain morphology adjust in response. On large regulated rivers, these pressures rarely act alone: flow regulation, sediment extraction, and urbanization act simultaneously and produce overlapping morphological signatures. Most studies attribute change to a single dominant driver or resolve change along a reach at one point in time, leaving the relative contribution of co-occurring drivers unresolved. Understanding which human drivers dominate that adjustment, and how their imprint varies along a river, is central to managing heavily used systems. This manuscript addresses the gap by integrating the temporal and spatial signatures of individual drivers to separate their contributions. 

This study examines the geomorphic response of the Yamuna River to human activity, focusing on the heavily anthropogenically altered part of the river, spanning 460 km from the mountain front to the downstream of the Delhi megacity, making it an ideal system for disentangling competing controls on river morphology. We extracted the active floodplain from the Global Surface Water maximum-water-extent dataset (1984–2021) and delineated the corridor into 92 reach IDs, each 5 km long. For each reach ID, we quantified riverscape metrics, active channel width (ACW), water width (WW), braiding index (BI), and vegetation width (VGW), from Landsat and Sentinel-2 imagery spanning 1984–2024, and analyzed their change against the timeline of dam construction, sand mining, and urban expansion.

To isolate the effect of individual drivers, we divided the corridor into four segments defined by each driver's location, enabling before–and–after and upstream–downstream comparisons of their impacts. For each segment, we formulated hypotheses predicting expected river-scape changes, then tested and verified them against observed metrics. Human activity has measurably reshaped the riverscape, but the dominant control differs among drivers and along the river. At the segment scale, sediment mining emerges as the primary control on channel form, acting most strongly on active channel width and flow width. This reworking of the active channel decouples water width from discharge: across much of the studied reach, WW is no longer governed by flow but by mining-altered morphology, as reflected in the breakdown of the width–discharge relationship. Dam-driven flow regulation and urban expansion may have imposed secondary imprints superimposed on this mining signal, but they can’t be detected. Together, these results show that, in intensively used alluvial rivers, direct sediment extraction can override hydrology as the first-order control on channel geometry, underscoring the need for informed, place-based management to preserve the ecological and geomorphic integrity of major Himalayan river systems amid intensifying anthropogenic pressure.