Environmental Flows (EFs) assessment is a global challenge involving a number of tangible and intangible segments of hydrology, hydraulics, biology, ecology, environment, socio-economics, and several other branches of engineering including the management of water resources. It has consequently led to the development of more than 240 methods available in literature. Required for the longevity of a river, EFs derived from a single method are usually not accepted. In the present study, the EFs variability was assessed using three hydrological methods: (i) Tennant, (ii) Tessman, and (iii) Flow Duration Curve (FDC) for various sub-watersheds of Damodar River Basin (DRB), located in the states of Jharkhand and West Bengal. The minimum and maximum range of magnitude, duration and frequency of flow estimated using these methods are recommended as EFs, which can be used by water resource managers for habitat protection, water supply planning and design, waste load allocation, reservoir design, future water resource and river health assessment in the basin.