Restoring Environmental Flows for Managing River Ecosystems: Global Scenario with Special Reference to India

Abstract

Most of the major river basins throughout the world are under stress due to cumulative impact of droughts, over-allocation of water resources and water quality deterioration. Various previous and ongoing water resource development projects have caused both short-term and long-term ecological degradation resulting in interrupted fluxes of water, sediment and nutrition and declining river health across all the river basins. It is evident that most of the key manipulations of flow regimes are associated with in-channel large dams that are designed to store water during the wet season and deliver it downstream or off-stream as and when required. A lot of scientific studies are in progress to understand the fragile river ecosystem and to mitigate the adverse ecological impacts. A broad general agreement has emerged from all these scientific discussions, to protect fresh water biodiversity as well as maintain the ecosystem services by maintaining natural flow variability or keeping flow regimes similar to natural flows. The best ecological outcomes in a river basin result from conditions when environmental water passes through rivers and associated wetlands in ways that they mimic natural conditions. With this shift in thinking, a broader ‘riverine ecosystem’ perspective on assessment of instream environment came up, which gradually switched to more inclusive terms such as ‘environmental water allocation’ and ‘environmental flows’. Various studies undertaken to measure and implement environmental flows indicate that key to improving rivers’ health is maintaining more natural and variable flows including good water quality. This paper focuses on three things: firstly, the effects of hydrological alterations on Indian river ecosystems as well as from other countries; secondly, the science and management of environmental flows to sustain the river ecosystems; and thirdly, the need of strong legislature in developing nation’s water framework directives. This study also indicates that there is considerable opportunity for improving the data gathering techniques and the overall methodology for the environmental flow assessment.