Human impact on grain size variations of river gravel bars in the western Himalaya: Insights from a UAV survey

Downstream variation in bed material size was investigated over a stretch of the Yamuna River in the western Himalayan region in India. Data on grain size distribution along rivers are critical for understanding river systems and material transport. Flow regulation caused by dam construction can alter sediment transport mechanisms, generating morphological changes. Using an uncrewed aerial vehicle (UAV), we investigated precise grain size variation along the Yamuna River and its tributaries in the Siwalik region, from Lakhwar Dam to Hathni Kund Barrage. All photos were collected via UAV survey.

On these datasets, grain size variation was observed across dams. The upper Yamuna River's bed-load sediments are becoming finer-grained downstream. Since the dam barrier and low flow energy force large particles to remain above the dam, smaller particles are found downstream of the dam. During the survey, evidence of mining in several locations along the river suggests the influence of anthropogenic activity in the regions. Accordingly, this study sheds light on the potential consequences of dam construction on material transportation. We observed that dams work as a barrier for coarse grain particles, which may have an impact on the dam in the near future. Field evidence and preliminary processed data indicate that the size of the gravel bar along the river course has been modified by many human interventions (hydroelectric dams, barrages, mining).