Researchers from the Indian Institute of Technology Gandhinagar have documented major changes in the Ravi River downstream of the Ranjit Sagar, or Thein, reservoir. The study combined daily discharge records with almost three decades of satellite imagery to examine river flow, surface water, vegetation and human activity across the floodplain.
Published in Next Sustainability, the research compared conditions before and after the reservoir began operating. The team analyzed daily discharge data from 1980 to 2019 and focused on April and May, before the monsoon, to avoid additional reservoir releases.
Median discharge fell from 296 cubic meters per second during 1980–2000 to 221 cubic meters per second between 2001 and 2019. Satellite images also showed that water networks visible across the floodplain in 1992 and 1998 became less prominent in later imagery from 2003, 2009 and 2019.
The estimated mean surface-water area decreased from 17.35 square kilometers to 3.46 square kilometers, representing a fivefold reduction. The study did not directly assess the consequences for agriculture, but the researchers said the decline could affect water availability and floodplain processes.
The researchers also observed increased vegetation in some areas where active water coverage had diminished. They said that less frequent movement of water and sediment may allow vegetation to establish, potentially making parts of the floodplain more stable and less connected to the active river channel.
Reservoir regulation can change the timing and size of high and low flows, while also trapping sediment that would otherwise move downstream. These changes can influence channel shape, erosion and the river's connection with its floodplain. The study also examined sand mining and other human activity, identifying artificial pits and changes in the river pathway through high-resolution imagery.
The researchers said the effects were not uniform across the floodplain and argued that river management should consider flow, sediment transport, land use and sand extraction together. They linked the findings to the need for sustainable management practices, including approaches that preserve connectivity and reduce the effects of sediment loss downstream of dams.
The study places the Ravi within a broader pattern of rivers being altered by dams, sediment extraction, land-use change and climate variability. Its authors said that understanding how these pressures interact can help guide water infrastructure management while maintaining the river processes that support floodplains and ecosystems.
Sources: Phys.org.