This report of the Working Group to advise Water Quality Assessment Authority (WQAA) on the minimum flows in the rivers outlines the principles behind environmental flow assessments, provides a description of methods that have been used to assist with such assessments, and highlights the features that will increase the chance of successful implementation of environmental flows.
The four components that constitute the minimum flows are low flows, flushing flows, special purpose flows and maintenance of impoundment levels. However, for the purpose of present study, only requirements for low flushing flows are specific to a particular reach and not a general requirement.
The main difficulties in quantifying the minimum flows are absence of an acceptable definition of ecological needs and, also, the absence of an agreement on the priority of Environmental Flow Releases (EFR). Moreover, while the domestic and agriculture requirements are easily quantified, it is difficult to decide as to what comprises the legitimate ecological needs.
A methodology similar to Tennant method needs to be adopted wherein certain percentages of the annual flows are prescribed as minimum flows as well as flushing flows during the monsoon. Certain studies are undertaken for Indian conditions and recommendations of the Working Group are based on the results thereof. The recommendations are as under –
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