AbstractComprehensive assessment of hydrological alteration due to anthropogenic interventions is a prerequisite for sustaining the native biological profile and integrity of river ecosystems. This paper proposes a novel strategy to measurably evaluate how the dams have modified the natural flow regime at a downstream site. The Bhagirathi Basin, a part of the Himalayan ranges of the Ganga River Basin in India, is studied to comprehend the impact of multiple dams on natural river flow at Devprayag. The methodology for estimating the River Flow Health Index (RFHI) consists of four steps: (1) segregation of the flow data based on preimpact and postimpact periods, (2) identification of important hydrological parameters, (3) assessment of the alterations, and (4) development of an index indicating the health of the river flow during the altered period on a 0–1 scale. Results show that the different components of the flow regime have changed due to construction of dams across the river, and the hydrological alterations could be seen at the downstream site, Devprayag. The RFHI increased after subsequent addition of dams, i.e., 0.328 after commissioning of Maneri Bhali I hydro-electric projects (HEP), 0.374 after Maneri Bhali I HEP, Maneri Bhali II HEP, and Tehri HEP were commissioned, and 0.411 after Koteshwar HEP was commissioned in 2011. Our results may help upgrade the design and implementation of reservoir operation policies that consider downstream hydrological alterations. Further studies can be made to consider the coordination of hydrological alterations with different river ecosystem services important for the sustainable management of water assets.

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