A Comprehensive Hybrid Framework to Study the Impact of Dams on the Shoreline Evolution in the Downstream Estuarian Region

Abstract The increasing demand for fresh water has led to a proliferation of dams worldwide. While humans benefit from water storage projects, the environment faces growing pressure. Dams significantly impact flow dynamics, reducing freshwater and sediment flow. This alteration in flow results in increased tidal dominance in estuarine areas. The combined effects of changes in water and sediment flow in the river, along with heightened tidal influence, have a significant impact on downstream morpho-dynamics. Understanding the long-term impacts of dam construction on shorelines is crucial as changes in shoreline evolution can have significant ecological, economic, and social implications. The present study proposes a novel hybrid framework, which combines Range of Variability Analysis (RVA) of river discharges, hydrologic modeling for sediment trapping by dams, hydrodynamic modeling of estuaries, and digital shoreline analysis, for gaining insight into shoreline changes triggered by the construction of large dams on rivers, and identifying the factors driving these changes. To illustrate the proposed methodology, it is applied to the Narmada River estuary in central India to study the impacts of the world’s second-largest concrete dam, Sardar Sarovar Dam (SSD). The construction of SSD reduced the magnitude of the flood by more than 40% and the sediment flow by 90%. The rate of shoreline change in the estuary has reduced during the post-construction period although the shoreline length undergoing erosion has significantly increased. The analysis using the hybrid approach suggests that the decreased rate of shoreline change is most likely due to reduced monsoonal flow, while the increased extent of erodible areas can be related to decreased sediment transport.