Environmental flow assessment of Saryu (Himalayan River) through various integrated hydrological approaches

A large number of people depend on Himalayan rivers for a wide range of functions, including biodiversity conservation, irrigation, and domestic water supply. For example, approximately 361,259 people (as per the Census of 2023) rely on the Saryu River in the region of Uttarakhand, India for their short- and long-term needs. To support these functions and ensure their sustainability, it is essential that rivers and streams remain healthy and undergo continuous monitoring and assessment. Therefore, the present study focuses on conducting an Environmental Flow Assessment (EFA) of the Saryu River, a significant Himalayan river located in the Bageshwar district of Uttarakhand. EFA is performed using four different hydrological approaches, and the corresponding results are tabulated to assess environmental benefits. The differences and complementarities of various methods used for environmental flow assessment are also investigated, compared, and discussed. The minimum flow required in the river, i.e., the environmental flow, is evaluated through four desktop methods using data collected at four different gated sites along the Saryu River. Based on the results, it is observed that hydrology-based methods of EFA represent a necessary first step in planning environmental allocations and can be particularly helpful in developing countries. Furthermore, the complementary features of existing environmental flow assessment techniques can prove very useful in arriving at justified estimates of environmental flows, even in conditions with limited basin-specific eco-hydrological knowledge. Finally, a suitable environmental flow schedule for various gauged stations of the river, i.e., the release schedule from the dams, is suggested to mitigate the negative impacts on the riverine ecosystem.