Assessing riverine transformations impacted by barrages and dams in the Mahanadi Basin

The relationship between human-engineered structures and natural river systems is critical in shaping regional hydrology and land morphology. This study examines the effects of newly constructed water-retaining structures along the Mahanadi River in Chhattisgarh, India, between the Shivrinarayan and Kalam Barrages. Spanning approximately 74 km, this section has been modified with barrages, dams, and stop dams. Using Landsat 8 satellite imagery, the study tracked changes in water availability, river transformation, and Channel-to-Bank Width Ratio (CBWR) over a decade (2013–2023). Pre-monsoon (March to May) and post-monsoon (October to December) water occurrence maps were developed using the Normalized Difference Water Index (NDWI) to distinguish water from other land cover types. Thresholding and pixel removal further refined the analysis to improve the accuracy of water area calculations. Our findings reveal a significant increase in pre-monsoon water-covered areas over the study period, corresponding reduction in exposed sandbars or riverbeds. This demonstrates that these structures have increased water storage during the premonsoon period. A notable spike in water coverage in 2017 coincided with the completion of major construction, emphasizing their immediate influence on the river’s hydrological and physical features. Water occurrence maps highlight both the increased water retention due to these structures and the reduction in exposed riverbeds. This dynamic shift underscores the dual nature of these interventions: enhancing water availability while altering riverine landscapes. Additionally, the CBWR analysis revealed substantial upstream channel widening post-construction, with downstream sections showing moderate changes. However, reduced riverbed exposure has complex ecological and sediment transport implications that require thorough investigation. A local area analysis is vital to understand how increased water availability during the premonsoon period has affected neighboring regions. Insights from this study into water-retaining structures can inform sustainable river management, focusing on ecological impacts, long-term monitoring, and adaptive strategies.