Assessment of River Ecosystems and Environmental Flows: Role of Flow Regimes and Physical Habitat Variables

Globally, rivers are under tremendous anthropogenic stress caused by flow fragmentation, land use changes and regulation. Floodplains had been cut out from rivers by embankments due to urban extension and most of the riparian lands in the river basin are under intensive agriculture. There was also widespread water quality degradation due to the industries and municipal wastewater causing a steep decline in the freshwater biodiversity across the world. It was recognised in the literature that the integrity of flowing water systems depended largely on their natural dynamic character which in turn maintained the habitat. Habitat characteristics and presence and absence of particular species suggests that most fishes of flowing water streams are habitat specialists and physical habitat variables including flow regimes played critical roles in the maintenance of their richness. This paper integrated broad environmental flow concepts and defined a new framework for e-flow assessment and implementation based on a review of supportive understanding of variable flow regimes and their benefits to river ecosystems. The main purpose of the framework was to stimulate the emerging discussion on environmental flows prospects in India and other parts of the world. The paper provided an example of the framework applied to River Ganga in India. We end by examining research needs and gaps in our understanding of the role of variable flow regimes and physical habitat variables and their ecological effects on river ecosystems.