Quantifying the Suspended Sediment Dynamics and Morphological Impacts due to Sand Mining in the Narmada River, India

ABSTRACT The extraction of sand from alluvial rivers can impact their geomorphology, alter channel bathymetry and sediment transport from local to reach scales. Many of these impacts are currently poorly quantified in alluvial river systems constrained by underlying bedrock geology. In this study, we quantify the impact of sand mining in a bedrock confined alluvial reach of the Narmada River, India, located between two gauge stations, Sandia and Hoshangabad. We analyse the planform dynamics of the river using multi‐temporal satellite images from 2000 to 2020. Further, we use in situ water level, discharge and suspended sediment concentration data from 1987 to 2015 to assess the hydrogeomorphic impacts of sand mining. Despite an increase in sand mining in the study reach, we do not observe any significant changes in the planform morphology of the river. However, we do notice alterations in the water and sediment dynamics. For example, hysteresis values (H‐index) show wider loops until the year 2009 (the year in which sand mining operations intensified), which later become narrower. A specific gauge analysis highlights that post‐2008, the slope of the water level decreased for fixed discharges and . However, for it increases at both stations. Sediment rating curves demonstrate a distinct rise in river discharge at both stations. Yet, suspended sediment concentration appears to decrease at Sandia and increase at Hoshangabad in 2013. We conclude that the accelerated rate of sand mining has led to the degradation and progressive incision of the riverbed, increasing the overall channel area, flow velocity, and conveyance capacity of the river. This likely led to an increase in the erosive power of the river and its discharge, which subsequently contributed to rise in severity and frequency of floods in the study reach.