ENVIRONMENTAL FLOW REQUIREMENT FOR A WATER RESOURCES DEVELOPMENT PROJECT

Abstract

Around the world, there is a conflict between water resources managers for allocation of water for different needs. Besides that there is an increased desire to conserve the ecological health and functioning of rivers and their wetlands for human use and biodiversity. To achieve this, many studies have been done around the world for the assessment of a desired flow regime for the sustenance and maintenance of biodiversity of rivers. An environmental flow is the water regime provided within a river ecosystem and their benefits where there are competing water uses and where flows are regulated. Environmental flows provide critical contributions to river health, economic development and poverty alleviation. Area of present study is Ramganga project on Ramganga river at Kalagarh. At the reconnaissance level of present study, it was observed that the concept of environmental flows was not followed at Ramganga project at the time of its planning mainly because this concept was not in vogue at that time. More than 200 methods have been developed to assess environmental flows, but there is no single method or combination of methods that are appropriate for all conditions. In the present study, several methods have been reviewed in detail and three methods, namely Flow Duration Curve Method, Tennant Method and truncated Building Block Methodology have been applied to assess environmental flow requirement for river Ramganga downstream of Kalagarh dam. The results obtained by 'these methods were also checked with outcomes of recommendations of WQAA. A holistic approach has been adopted to collect information on several aspects as desired for the proper implementation of the Building Block Methodology. But time and resources were limited for this study. Therefore, in place of organizing workshop, meetings were arranged with specialists in different fields for better understanding of the subject. An analysis was also done to assess impact on irrigation/hydropower by releasing water for environmental and ecological purposes. An EFR of 4.70 cumec has been recommended to be released in most critical reach of river Ramganga. A flushing flow of 102 cumec, for the maintenance of morphology of river and to clean debris is also recommended to be released in river at least once in a year at 2°d 10-daily period of August for the duration of 48 to 72 hours.