Impact of Anthropocene on the Fluvial Sediment Supply: The Mahanadi River Basin Perspective

Abstract

The Mahanadi River basin is the third biggest in central India and the longest in the state of Odisha. The peninsular river basin has a significant history of watershed land use changes and human disturbances in the channel. The Mahanadi Delta, located on India’s east coast, is a hybrid delta formed by water, suspended and bed sediments, and minerals from a web of distributaries of the Mahanadi River system. The current state of research on the quantification of river sediment supply and its connection to human catchment disturbances is discussed in this chapter, with an emphasis on the physical characteristics of the river basin. Nonparametric time series assessment methods are used to examine the annual runoff and suspended sediment characteristics of the gauging stations of the basin. The function of various attributes influencing runoff and suspended sediment dynamics of the gauging stations is also investigated. The average correlation between the discharge and suspended sediment load (SSL) is studied using sediment rating curves (SRC). Also, the role of differential supply of sediments from the watershed is characterized using the hysteresis analysis of suspended sediments. The development of the Mahanadi coastline subjected to the regulated sediment supply from the catchment in terms of land loss and gain is evaluated using geospatial data. The statistics of hydrological data reveal a large seasonal variance, with the monsoon being the most dominant. The annual SSL distributions are more irregular and non-normal relative to yearly runoff. The investigation of hysteresis loops revealed that the supply of sediments also significantly affected the transport capacity of all the channels within the basin. A substantial loss in SSL is evident throughout the majority of the stations in comparison to a negligible change in water outflow. Besides, 81% of the stations show a 2-year periodicity in runoff and SSL. Also, the flow of SSL to the ocean has fallen nearly three times more than the annual runoff, which is alarming. It, therefore, shows the strong impact of artificial force relative to natural variations. The statistical estimates for seashore morphological changes on a volumetric basis show that coastal landscapes prone to erosion are susceptible. The rating parameters vary inversely due to intense human-induced activities throughout the catchment. The rise in withdrawal over time for non-monsoon irrigation and hydropower generation is observed from the release of water from the reservoirs. The demand for thermal power stations has increased fourfold in the recent decade, significantly increasing water utilization. Overall, large impoundments, excessive water distribution across multiple business sectors, and varying watershed soil management efforts are highlighted as critical anthropogenic attributes impacting the decline in catchment sediment transport and eventually causing the delta to retreat. Further studies in the basin should focus on the impact of future land use on the sediment budget of the Mahanadi delta. This study aims to shed light on the dynamics of runoff and suspended sediment load over the past five decades and to fill in shortcomings about the evolving nature of rivers in the Mahanadi River basin.