ABSTRACT Graphical abstract titled 'Bridging Sediment Data Gaps in Ungauged Rivers: Field Monitoring and Empirical Model Evaluation in the Mahanadi Basin' contains four main sections. Top left shows Study Area with a topographic map of the Mahanadi Basin in Chhattisgarh state, India, displaying elevation gradients from high (red-orange) in western regions to low (blue-green) in eastern areas, with Sakari Goreghat station marked. Center left displays Methodology flowchart with three sequential steps in blue and green arrows: Data Collection and Processing involving field surveys and sediment sampling from 2021 to 2023; Development of Sediment Rating Curve using Monte Carlo simulation for uncertainty quantification; and Sediment Load Estimation and Model Evaluation using empirical equations with statistical validation. Center shows Key Finds in green box listing: sediment rating curve developed with strong correlation and robust parameters under uncertainty; sediment transport predominantly driven by monsoonal flows; Engelund-Hansen overestimates at high discharge and Karim-Kennedy underestimates at low discharges. Top right Results section contains Stage-Discharge Curve plot showing water level versus discharge with data points from four time periods (2001-2004, 2005-2006, 2007-2014, 2015-2019) represented by different symbols, displaying upward curved relationship. Adjacent Sediment Rating Curve shows log-log plot of suspended sediment load versus discharge with fitted power equation y equals 28.54x to the power 1.0304 and R-squared equals 0.928. Bottom right shows comparison plot of Predicted versus Observed Sediment Load on logarithmic scales ranging from 1 to 1 million tonnes per day, with 1:1 diagonal reference line, Engelund-Hansen (1967) predictions marked with asterisks showing overestimation at higher loads, and Karim-Kennedy (1990) predictions marked with plus signs showing underestimation at lower loads, demonstrating model performance across six orders of magnitude. Sediment transport assessment in ungauged river systems remains a major challenge for sustainable river basin management, particularly in monsoon-dominated regions where sediment flux is highly seasonal and event-driven. This study addresses the sediment data gap at the Sakari Goreghat station in the Mahanadi basin, India, by developing integrated stage–discharge and sediment rating curves supported by three consecutive years (2021–2023) of monsoonal field observations. A Monte Carlo Simulation was employed to quantify uncertainty in rating curve parameters, ensuring robust discharge estimation. The derived sediment rating curve exhibited strong predictive capability (R = 0.83), enabling practical estimation of suspended sediment loads from routinely measured discharge data. To further evaluate total sediment transport, the Engelund and Hansen (1967) and Karim and Kennedy (1990) equations were applied and validated against field observations. Both models demonstrated high correlation (R = 0.97); however, Engelund–Hansen overestimated sediment load at higher discharges, while Karim–Kennedy showed improved performance under flood conditions. The findings highlight the necessity of site-specific calibration of empirical models in monsoonal alluvial rivers. The developed rating relationships offer a cost-effective approach for sediment load estimation and demonstrate how field monitoring combined with uncertainty-aware modelling can improve sediment management in ungauged rivers.
ahmad et al. (Tue,) studied this question.