Hydrological Dynamics in Giant Tropical Rivers: A Case Study of the Ganga River

Monitoring river flow and its controlling factors in major rivers like the Ganga is essential for freshwater sustainability, ecosystem health, and hydropower efficiency. As one of the world's largest river systems, the Ganga supports over 400 million people in the Indo-Gangetic Plain, playing a crucial role in agriculture, water quality, and ecological balance. This paper discusses the summer water dynamics of the Ganga throughout its course. The study includes estimation of evaporative loss from river channels, groundwater interaction, and the role of aquifer water levels in sustaining river flow. In the middle plain segment of the river (~1200 km), a crucial region for agriculture and industry, evaporative loss is estimated to be approximately 58% of the river's initial water volume at the segment's start. Additionally, this segment exhibits the most significant river–groundwater interaction, with groundwater discharge increasing the river's volume by roughly 120% compared to its initial volume at the segment's beginning. Two decades of in situ data show stable groundwater levels across most of the central Ganga Plain, suggesting that reduced summer flow is driven by other factors such as increased human activities rather than groundwater depletion.