Environmental flow is a concern for ecologically healthy river, living river and it comprises both water quality and water quantity. This is the process of optimization of river flow for maintenance of its indigenous beneficial flora and fauna, without any allowance for the opportunistic species to reign in the river system. The biotic and abiotic factors dependant on the environmental flow plays the guiding role for this maintenance of river eco system. Hence the need for the assessment of the

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... biotic and abiotic factors for the determination of environmental flow is felt. Integrated Water Resources Management (IWRM) is to balance water allocation keeping in view to the different users and uses among human and other living creatures of the nature. This is because in many cases of the flows of the rivers of this world are increasingly being modified through impoundments such as dams and weirs, abstraction for agriculture and urban water supply, drainage return flow, maintenance of flows for navigation and structure for flood control (Dyson et al, 2003; Postel and Richter, 2003). It is to be noted that in the Hooghly estuary in India, Hilsa fish is the main commercial and most popular and highest profit making product of the river. Hence its abundance (Hilsa catch) along with the abiotic parameter has been considered for the assessment purpose of the environmental flow, by the method of Hydraulic Rating, which consists low cost and rapid to use (i.e. wetted perimeter, river cross section and salinity variation, River Flux Study with time; Table-1) and a befitting water quality status based on Indexing Method. Indexing Method has been applied using additive type for the determination of proper weight in respect of each water quality parameters considered here, as used by National Sanitation Foundation Water Quality Index (NSF WQI) of the U.S.A.