Visualizing Erosion from Space
Padma river, Bangladesh (credit: NASA/Landsat)
Padma means Sacred Lotus in Sanskrit and symbolizes growth and beauty. However, a river that carries its name is constantly changing in ways that are not at all that blessed for the people who live along its meandering course.
According to NASA, in over 30 years of satellite observations the river has enlarged, shrank, and been transformed in size, shape, and location. Flowing from the Himalayas through India, the Padma joins the Ganges and Jamuna Rivers, and then merges with the Meghna River to finally drain into the Bay of Bengal. The vast river system is used for transportation, irrigation, and housing but residents must constantly adapt to abrupt shoreline changes. Erosion is a constant process with a free-flowing river whose banks are largely made of sand. Huge shoreline chunks regularly collapse plunging everything situated there into the river.
Landsat satellites began photographing the Padma in the late 1960's. Measurements now show an area of riverbank the size of Chicago (250+square miles) has eroded and disappeared. Utilizing a combination of images captured with short wavelength infrared, near infrared, and visible light cameras, to highlight the differences between land and water, changes to the shape of the river between 1988-2018 become obvious. To fully visualize these changes, NASA engineers combined imagery into a photo-animation where each change in the river tells the story of a different erosion event. During the three decade period, the Padma changed from having a relatively narrow, straight line course into a meandering and braided one, and then changed back to a straight flow. In the animation, the greatest changes occurred upstream that showed the most erosion.
Remote sensing is a powerful tool to develop preparedness for environmental disasters. With a river system as changeable of this one, such advanced tools don't offer easy solutions like saying 'move to higher ground' for people living along its course. WHB