Rivers move: char-lands and the riverine border
Along the Brahmaputra and the Ganga, the river redraws its banks every monsoon. The legal boundary does not move with it. What satellite records show about land lost and gained since 1984, and why it matters to the people who live on the chars and the crews who patrol them.
- Across eleven border river reaches, 957 km long in all, satellite records show 1,087 km² of land that became water and 318 km² of water that became land between the first observed year and 2020.
- The Brahmaputra between Dhubri and South Salmara accounts for 57% of the land lost to water: 618 km², against 110 km² gained.
- After the 2017–18 monsoon, chars covered about a third of the Brahmaputra's area in Assam, and many settled in the 1990s have since eroded away.
- The 1974 Land Boundary Agreement drew river lines mid-stream "at the time of demarcation" and called them fixed. When the river moves, the line stays.
- 34.6 km of Assam's border with Bangladesh is unfenced because it is river, 30.37 km of it in Dhubri district.
What the satellites saw
The JRC Global Surface Water dataset maps, at 30 m, where water was present each month from 1984 to 2020, and classifies how each pixel changed between its first well-observed year and 2020 (Pekel et al., Nature, 2016). Our product Nadi sums those transitions over eleven reaches where rivers form or cross the border with Bangladesh or Pakistan.
| Reach | Land to water, km² | Water to land, km² | Ever water, km² |
|---|---|---|---|
| Brahmaputra, Dhubri to South Salmara | 617.8 | 109.7 | 1,221.2 |
| Ganga-Padma, Farakka to Jalangi | 273.9 | 129.8 | 804.0 |
| Teesta, Mekhliganj | 80.3 | 19.5 | 193.9 |
| Sutlej, Ferozepur to Fazilka | 34.9 | 27.3 | 114.7 |
| Torsa, Cooch Behar | 27.8 | 8.2 | 73.8 |
| Raimangal, Sundarbans estuary | 19.4 | 1.8 | 354.4 |
| Ravi, Dera Baba Nanak | 17.4 | 15.1 | 76.3 |
| Ichamati, Basirhat to Hingalganj | 11.9 | 1.6 | 37.0 |
| Mahananda, Malda | 2.1 | 2.5 | 23.9 |
| Kushiyara, Karimganj | 1.0 | 2.2 | 12.9 |
| Feni, Sabroom | 0.5 | 0.6 | 2.6 |
| All eleven reaches | 1,087.1 | 318.3 |
Read these as change in where water sits, not as erosion alone: "land to water" includes fields that now flood each season as well as banks that collapsed. The permanent part is smaller but clearer. On the Brahmaputra reach, 124.8 km² of land became permanent water and 36.2 km² of permanent water became land. Nadi's largest erosion hotspot covers 10.7 km² about 11 km south of Dhubri town (Nadi hotspots).
Chars: land that comes and goes
Chars are the sand and silt islands of braided rivers. After the 2017–18 monsoon they covered about 33% of the Brahmaputra's area in Assam. Researchers at the North Eastern Space Applications Centre found new chars forming faster than the river was widening, and many islands that had settlements in the 1990s eroding away (NASA, 11 Dec 2018).
Downstream in Bangladesh the scale is larger. From 1973 to 2025 the Jamuna, Ganges and Padma eroded about 1,584 km², and only about 433 km² came back as new chars. In 2025 the Ganges was the biggest eroder, taking 5.93 km² (The Daily Star, reporting CEGIS, 6 Sep 2026).
For families on a char, this means fields and homes that may not exist after the next flood. For a patrol, it means a map that is wrong by the next season.
The line does not move
Where the India–Bangladesh boundary follows a river, the 1974 Land Boundary Agreement often ties it to the river as it was surveyed. For the Muhuri: "The boundary in this area should be demarcated along the mid-stream of the course of Muhuri River at the time of demarcation. This boundary will be a fixed boundary." The Feni sector uses the same words (1974 agreement, as gazetted). The 2011 protocol, given effect in India by the Constitution (100th Amendment) Act of 2015, fixed several further stretches by reference to old river courses or the river's edge in 2011 (PRS India).
So when a channel shifts, land can end up on the far side of the water from the people who farm it, while the line stays where it was surveyed. Nadi shows how the river moved. It does not, and is not allowed to, imply any change to an international boundary.
Fences cannot follow a river
Assam's 267.5 km border with Bangladesh has 228.5 km of fence. Of the rest, 34.6 km is unfenced because it is river, 30.37 km of it in Dhubri district, and 4.35 km is held up by objections from Border Guard Bangladesh, the state told its assembly on 6 July 2026 (Assam Tribune). In the Sundarbans the BSF works from 96 boats and 8 floating border outposts (SSBCrack, Jun 2025). These stretches need equipment that floats, survives silt and runs on sunlight, which is the brief for Prahari.
Where the rivers are today
On 21 October 2026, all 18 of Varuna's border river points were at normal levels. The Brahmaputra at Dhubri was running at about 7,690 m³/s, lower than on 98% of the same dates since 1997, while the Ganga at Farakka was at about 17,820 m³/s, above 81% of them. These are model discharges from GloFAS compared with the same model's 1997 to 2025 record, not gauge readings or CWC danger levels (Varuna; flood advisory).
What helps
- A yearly picture of where banks are retreating fastest and which posts, roads and villages are next in line (Nadi).
- River levels against each point's own history, with safer boat-crossing windows (Varuna).
- Shared, neutral numbers on dry-season flow for the Ganges treaty talks (Sandhi).
- Sensors for the stretches no fence can hold (Prahari).
Advisory only. For erosion, flood and displacement decisions follow the state disaster management authority, the district administration, the Central Water Commission and the Survey of India.
Method
Nadi reads JRC Global Surface Water v1.3 (March 1984 to December 2020) through Microsoft Planetary Computer, clips each reach to a river corridor, and sums exact pixel areas on the WGS84 ellipsoid. "Land to water" counts new permanent and new seasonal water; "water to land" counts lost permanent and lost seasonal water. Figures are in Nadi's public file segments.json.
Sources
- Pekel, J.-F., Cottam, A., Gorelick, N., Belward, A. S. (2016), "High-resolution mapping of global surface water and its long-term changes", Nature 540, 418–422; data via Microsoft Planetary Computer (EC JRC/Google). doi.org/10.1038/nature20584
- NASA Earth Observatory / Landsat, "Watching river islands grow on the Brahmaputra", 11 Dec 2018. science.nasa.gov
- The Daily Star, "Rivers devoured five Dhaka cities over 50 years", 6 Sep 2026, reporting CEGIS. thedailystar.net
- Agreement between India and Bangladesh concerning the demarcation of the land boundary (1974), Bangladesh Gazette Extraordinary, 28 Nov 1974. almendron.com
- The Constitution (One Hundredth Amendment) Act, 2015. prsindia.org
- The Assam Tribune, "Bangladesh objections leave 4.35 km of Assam border unfenced, govt tells House", 6 Jul 2026. assamtribune.com
- SSBCrack, "BSF seeks DRDO tech to monitor 113 km Bangladesh border in Sundarbans", Jun 2025. ssbcrack.com
- Trinetra Nadi segment statistics and hotspots; Varuna river board, both generated 21 Oct 2026. segments.json, board.json