Abstract

Environmental flow assessment in the regulated tropical river is often constrained by limited data and strong hydropower alteration. Conventional hydrological approaches based on fixed flow indices rarely account for the ecological complexity required for sustainable management. This study develops an extended species-centred environmental flow assessment framework by integrating hydrological analysis, hydraulic simulations, habitat suitability thresholds, and discharge-water quality analysis. The approach was applied to the downstream of Cirata Dam on the Citarum River, Indonesia. Habitat-based modelling identified an optimal discharge of 93.12 m³/s, maintaining 94% of suitable habitat area, while achieving good water quality conditions would require a discharge exceeding 500 m³/s, which is hydrologically unrealistic. The integrated results demonstrate that environmental flow determination in a regulated river must balance ecological and hydrological feasibility. Flow alone cannot ensure recovery with pollution control, illustrating the importance of combined flow regulation and watershed-scale water management policies.