Morphological adjustments of the Yamuna River in the Himalayan foothills in response to natural and anthropogenic stresses

Abstract

AbstractRivers can adjust to natural and anthropogenic stresses through changes in flow regime and sediment dynamics. Flow regulation due to dam construction can modify sediment transport processes, causing morphological adjustments and changes in conveyance capacity. In this study, we explored morphological adjustments along a 46 km segment of the Yamuna River in the Himalayan foothills from Dakpathar Barrage to Hathni Kund Barrage using a combination of remote sensing approaches. The cloud computing platform Google Earth Engine (GEE) was used to analyse multi‐temporal collections of Landsat satellite imagery acquired between 1989 and 2021. Active river channels (including water and exposed sediment) were classified using an MNDWI and NDVI thresholding approach from annually resolved temporal composite images. Declassified CORONA satellite imagery (acquired in 1965, 1973 and 1976) was manually digitized to provide longer‐term insights into channel change. Morphological adjustments were assessed using the RivMAP toolbox, providing quantitative information on the rates of bank erosion and accretion, bank line shifts and changes in active channel width. Results showed a substantial narrowing of the active channel after 2013, which coincided with the construction of the Lakhwar‐Vyasi Dam. We calculated a 67% reduction in mean active channel width, narrowing from ~800 m in 1989 to ~250 m in 2021. During the same period, evidence of sand mining in the active channel indicates a substantial increase in mining activities after 2015. The concept of stasis was explored under different flow regulation scenarios to suggest that the river has undergone a state of inactivity, where the river is doing nothing for much longer durations. We suggest that the combined effects of flow regulation and increased mining activities during the same period have altered river morphology, and further stresses due to a combination of human activities can be damaging for the river regime. This study sheds light on the potential implications of multiple stresses acting on the Yamuna River at the same time, which can inform future sustainable river management activities.