Assessment of optimal dam release for anadromous fish migration in estuary.

• Novel methodology for optimum releases from dams to minimize negative impact on fish migration in downstream estuaries. • Identifies requirement of freshwater flow into estuaries based on fish migration velocity. • Effectively uses The Tennant method and T-FDC approaches for estimating Environmental Flow Requirement (EFR) • Uses hydrodynamic models to find the combined effect of river discharge and tidal conditions on flow state in estuary. • Applicability of methodology is illustrated through a case study in India. Dams play a crucial role in meeting growing water demands, generating energy, and flood protection. However, the controlled water release from dams can significantly impact the ecosystem of downstream areas, especially estuaries. This study investigated the effects of Sardar Sarovar Dam (SSD) on downstream flow and estimated the flow requirements necessary to support anadromous fish (in this study Tenualosa ilisha) migration in the Narmada River estuary. The study used hydrodynamic modeling and environmental flow requirement analysis methods to arrive at conclusions. The results indicated that the SSD significantly altered the downstream flow patterns, particularly during the monsoon season. A reduced freshwater flow resulted in increased tidal influence. The study found that the optimal discharge rates for fish migration range from 1500 to 2250 m3/s, and the minimum flow required to prevent tidal dominance in the estuary is 500 m3/s. The study underscores the importance of appropriate freshwater release from dams to preserve downstream ecology, support fish migration, and avoid adverse effects on fishing communities. [ABSTRACT FROM AUTHOR]