Application of hydrologic and hydraulic methods to calculate the environmental flow requirements of the Chaliyar river.

River flow is closely linked to survival of human cultures, the economies providing sustainable livelihoods, and the general well-being of the society. The concept of environmental flows has been globally accepted and efforts are being made worldwide to restore and maintain riverine ecosystems. Assessment of environmental flow requirement of rivers is in an infancy stage in India; this has not been done for most of the rivers including those flowing west to the Western Ghats. In this study, the environmental flow (EF) requirements of the Chaliyar River, a major river flowing westwards of the Western Ghats (WG) in Kerala, India, were estimated using hydrologic and hydraulic methods. This was done using the Indicators of Hydrologic Alterations (IHA), and the Wetted Perimeter (WP) methods. Three major sub-basins of the Chaliyar namely, Chaliyar Main Stream, Punnapuzha, and Karimpuzha were considered in this study. This study concentrated on the low flow periods. Environmental Flow Components (EFC), and Flow Duration Curve (FDC) from the IHA, and Critical Minimum Flow (CMF) from the wetted perimeter method were compared in this study. The environmental flow requirements for the low flow season for the three streams, namely, Chaliyar Main, Punnapuzha, and Karimpuzha, computed using the IHA are 1.32, 1.33, and 0.59 m³/s respectively. The corresponding values obtained by the wetted perimeter method are 1.37, 1.25, and 0.75 m³/s respectively. This indicates that the results obtained using these two methods are in good agreement with each other. [ABSTRACT FROM AUTHOR]