Hydrological Modeling for Environmental Flow Estimation under Data- Scarce Condition
DOI:
https://doi.org/10.53550/ijsc.v54.i1.213Keywords:
Environmental flow, EMC, Flow duration curve, GEFC, Sankh river, SWAT modelAbstract
Estimating environmental flows is crucial for mitigating anthropogenic impacts and restoring their ecological functions; however, such assessments remain challenging, particularly in data-scarce and regulated basins. This study addresses this gap by estimating environmental flows for the Sankh River (4,027.4 km²), a regulated and hydrologically data-limited tributary in eastern India, using an integrated Soil and Water Assessment Tool (SWAT)– Global Environmental Flow Calculator (GEFC) modeling framework. Despite its widespread use, the SWAT-GEFC approach is limited in small- to medium-sized Indian basins, especially in ecologically sensitive and undermonitored rivers such as the Sankh. The SWAT model performed satisfactorily in simulating streamflow, as evidenced by the test statistics obtained during calibration and validation (NSE: 0.81 and 0.90; R²: 0.81 and 0.92; RSR: 0.44 and 0.32, respectively). To assess ecological flow requirements, the GEFC was used to derive environmental flow regimes through Flow Duration Curves (FDCs) and Environmental Management Classes (EMCs). Results indicate a systematic decline in Mean Annual Runoff (MAR) allocations from EMC “A” to “F”, with SWAT-simulated values (39.5 to 0.9%) closely matching with the observed trends (47.1 to 1%), thereby supporting the model robustness. Seasonal analysis identified December and January as the most flowstressed months, with a minimum ecological flow threshold of 5.72 m³ s⁻¹ required to sustain riverine health. The findings offer practical benchmarks for integrating environmental flows into reservoir management, regional water allocation, and policy planning, particularly within the framework of India's National Water Policy (2012). Integrating hydrological modeling with ecological considerations can lead to sustainable river management. Future research should integrate habitat simulation models and climate-change-driven flow scenarios to support resilient and adaptive environmental flow management.
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