A Comparative Study on Environmental Flows Assessment Methods in Lower Reach of Mahanadi River

Abstract

Environmental flows assessment is a process which determines the allocated water for maintaining aquatic habitats and ecological processes in a environment. The river system attains zero flow in low flow period due to construction of hydropower generating structures, water retaining structure and withdrawal of water by water users, which possesses a tremendous threat to the environment, ecology & aquatic life. Therefore a need arises to regulate the reservoirs for releasing the adequate water in the river throughout the year as well as a flushing flow once in a year. Thus environmental flows assessment is done in Lower Mahanadi sub-basin and recommended to provide the EFRs on average 33% of MAF with a range of Low flow 110% of mean low flow & High flow 23% of mean high flow to be ensured at any circumstances to avoid any degradation of river ecosystem. In the present study the assessment of the environmental flows on the basis of Tennant method, Tessman method, VMF method, Q90_Q50 method, Smakhtin method, low flow index (7Q10) method and FDC (EMC shifting technique) method using Global Environmental Flow Calculator (GEFC) software have been made.