Guwahati: A first-of-its-kind space-based flood study has revealed how sudden water releases from key hydropower projects — Ranganadi in Arunachal Pradesh, Doyang in Nagaland, and Kurichhu in Bhutan — could amplify flood risks across Assam’s river basins.
Conducted jointly by the North Eastern Space Applications Centre (NESAC) and the Assam State Disaster Management Authority (ASDMA), the study marks a new era in scientific flood forecasting and management for the Northeast.
The report, titled “Flooding Scenario Generation and Discharge-Based Downstream Impact Study in Assam for Ranganadi, Doyang & Kurichhu Hydro Power Projects,” combines satellite-based remote sensing, digital elevation models (DEM), and 2D hydrodynamic simulations to map how varying dam discharge scenarios can reshape downstream flood patterns across Assam.
Researchers generated detailed “flooding scenario maps” that visualize the spread, depth, and velocity of water during controlled and uncontrolled releases.
While dams are designed for electricity generation and irrigation, the study underscores their dual role in intensifying floods when water is suddenly released during heavy rainfall.
The report points out that transboundary hydropower projects on tributaries of the Brahmaputra — including Ranganadi, Doyang, and Kurichhu — alter natural river flows, increase sedimentation, and elevate flood risk downstream in Assam.
Keshab Mahanta, Assam’s Minister for Revenue, Disaster Management, Information Technology, Science, and Technology, highlighted the state’s vulnerability due to its unique geography.
“The state of Assam is the valley area of two of India’s large river basins — the Brahmaputra and Barak. Surrounded by six hilly Northeastern states and parts of Bhutan, Assam receives major upstream discharges that contribute not only to its abundant water resources but also to severe flood problems,” Mahanta said.
He noted that during monsoon months, natural flows from upper basin areas, coupled with regulated releases from projects such as Ranganadi, Subansiri, and Kurichhu, pose major challenges for flood management.
“The report has generated valuable decision support for managing downstream flooding scenarios caused by peak monsoon releases from these hydroelectric dams,” Mahanta added.
Dr. S.P. Aggarwal, Director of NESAC, says the project develops a robust, decision-ready framework to understand how controlled releases and extreme inflow events translate into downstream flooding.
“These simulations, validated against real flood events from 2017 and 2022, revealed that a sudden peak discharge of 1,000–2,500 cubic meters per second could inundate large parts of downstream villages within hours,” the study noted.
By employing 2D hydrodynamic models (HEC-RAS and MIKE FLOOD), researchers reproduced realistic flood propagation under both normal and extreme scenarios. The simulations — scaled up to 1,200 m³/s for Ranganadi, 800 m³/s for Doyang, and 8,000 m³/s for Kurichhu — produced highly detailed maps of probable flood spreads across Assam’s Lakhimpur, Golaghat, Kokrajhar, and Bongaigaon districts.
The models demonstrated that even moderate rainfall, when combined with dam discharge, could inundate villages within a few hours of release.
The study reveals several previously undocumented dynamics. One key finding is that the timing and rate of discharge from upstream hydropower projects have a far greater influence on downstream flooding than total rainfall volume. Simulations showed that a sudden peak discharge from the Ranganadi dam could inundate areas of North Lakhimpur district within hours, extending flood zones up to 15 kilometres beyond the usual river course.
Similarly, the Doyang project, located in Nagaland’s Wokha district, was found to influence flood behaviour in Golaghat and adjoining areas.
The model indicates that even moderate rainfall, when combined with peak discharge releases, could lead to high inundation in low-lying villages along the Dhansiri River.
In the case of Bhutan’s Kurichhu project, the transboundary implications are striking. The study found that uncoordinated release patterns from the Kurichhu reservoir could intensify downstream floods in Assam’s Kokrajhar and Bongaigaon districts, especially when coupled with local monsoon surges.
The report recommends installing four state-of-the-art discharge measurement stations downstream of the Ranganadi Dam to improve real-time flood monitoring. These data stations will help correlate river flow with dam releases and refine the accuracy of flood forecasts.
The study also highlights the importance of transboundary flood cooperation between India and Bhutan, particularly for the Kurichhu-Beki river system.
By quantifying flood risks from various discharge levels, the project offers a technical framework for cross-border data sharing and real-time coordination between dam operators and disaster authorities.
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