Impacts of hydropower-induced flow alterations on composition and diversity of riparian vegetation in the Western Himalayas: A case study in Uttarakhand, India

The increasing demand for water and energy resources has led to widespread dam construction, particularly in ecologically sensitive regions like the Himalayan Range. This study focuses on the Uttarakhand state in the Western Himalayas, where hydroelectric projects (HEPs) have significantly altered river flow regimes. The research investigates the impact of flow alterations on the composition and structure of riparian vegetation in the Garhwal Himalayas, specifically analysing four rivers regulated by hydroelectric projects. Utilizing the paired-reach comparison method, control (undisturbed), diverted (downstream of barrage/dam), and altered flow conditions (downstream of water outlet) were examined. The research reveals diverse and unique riparian ecosystems, with 89 genera and 113 taxa identified, showcasing the dominance of families like Asteraceae and Lamiaceae. The study unveils the structural importance of key species such as Berberis asiatica and Artemisia nilagirica . The density, diversity, and richness of shrub and herb species vary significantly across flow conditions. Notably, altered flow conditions demonstrate resilience in vegetation structure, while diverted conditions exhibit decreased species richness and density. The study emphasizes the importance of nuanced environmental flow management for mitigating adverse effects on riparian biodiversity in the fragile Himalayan region. These findings contribute to the global discourse on dam impacts and riparian ecology, shedding light on the complexities of this dynamic relationship in a vulnerable ecosystem.