Quantification of the Escalating Influence of Anthropogenic Factors in Suspended-Sediment Concentration Regimes

Abstract

River systems act as conveyor belts carrying sediments in huge quantities from upstream to downstream regions of the basins. Suspended sediment (SS) is a vital element in a river system due to its importance in the planning, design, and management of hydraulic structures. Abrupt variations in sediment dynamics have been observed recently, attributing these to both changes in climate and different anthropogenic actions. A proper understanding of the dominance and impact of these anthropogenic and natural factors on sediment dynamics will help to maintain the sediment equilibrium of any basin. In this study, we present a comprehensive analysis of different changed regimes of suspended-sediment concentration (SSC) and quantify the dominant factors during such changed regimes in Indian river basins. Declining trends are evident in the SSC profiles of most of the gauge stations (∼80%) and can be attributed to increasing anthropogenic activities, especially the construction of water retaining structures throughout India. On average, more than a 50% reduction in sediment quantity was recorded at most gauge stations over the past three decades. It is apparent that natural factors such as discharge and rainfall still are the most dominant factors; but quite interestingly, their relative importance is decreasing after each change point, whereas the influence from anthropogenic factors such as changes in the cropland and grassland are increasing. Large river basins show more influence of anthropogenic activities on sediment dynamics when compared with other smaller basins. Also, changes in land use land cover (LULC) have increasing impact on upstream/midstream parts of the river basins. It is evident that the completion/commissioning of water retaining structures brings abrupt changes in the sediment dynamics, but once the system stabilizes, other natural and anthropogenic factors take over as dominant factors until the next structure comes up and changes the system dynamics again.