Here’s how NASA scientists study the Padma river

The Padma—a lifeline for thousands of people but also a force for change with far-reaching effects on those who live along its banks, flows through the centre of Bangladesh. Its flowing form has shaped and reshaped the terrain it passes through for decades, defying permanence. 

Now, satellite imagery from NASA's Earth Observatory research lab reveals the Padma's dynamic nature, illustrating its growth, meanders, and shifting course over the past 30 years. In a recent blog post, NASA Earth Observatory revealed that Landsat images from 1944-2018 help scientists measure erosion on the Padma river and note differences in the river's width, depth, shape, and overall appearance. "Like parents measuring a child's height, scientists measure erosion on the Padma River by noting differences in its width, depth, shape, and overall appearance," read the blog post.  

Landsat satellites, specifically the Thematic Mapper on Landsat 5, the Enhanced Thematic Mapper Plus on Landsat 7, and the Operational Land Imager on Landsat 8, were used for capturing the photos. To emphasise the distinctions between land and water, they use a mix of visible light, near infrared, and shortwave infrared light.

The river's constant evolution poses challenges for those who depend on it for transport and agriculture. Erosion along its 130-kilometre shoreline has claimed swathes of land, displacing communities and altering the region's geography. Since 1967, over 66,000 hectares (256 square miles) of land have eroded and have fallen into the Padma river, according to Earth Observatory which shares information from NASA research.

Sedimentation is one of the main reasons behind the change in water flow. One theory suggests that sedimentation, triggered by seismic events like the 1950 earthquake, has highly influenced its course. 

Over the last thirty years, the river has changed its shape a lot. It used to be narrow and straight, but now it meanders, braids, and then goes back to being straight again. The biggest change happened near the Harirampur upazila area, where there was a lot of erosion. In 1998, a big flood made this erosion worse, especially because India's Farakka barrage (dam) released more water into Bangladesh, according to Earth Observatory.

Researchers are also interested in the Char Janajat area, where the Padma Bridge was constructed. Near Char Janajat, the river made bends and eroded the land. The bends were most extreme from 1995 to 1996. They started forming in 1992, decreased by 2002, and now they're gone.