Heavy monsoon flooding in India has claimed close to 1000 lives, and millions more have been displaced. The most dramatic event has been the abrupt change of course of the Kosi River in northern India. The Kosi River flows from the Himalaya Mountains into the Indian state of Bihar. The flood-swollen river has broken through its banks and re-occupied a channel it had abandoned over 200 years ago, resulting in a 60 km shift in its course.
NASA’s Earth Observatory site has two images. The top image shows the new course of the river on August 24th following the channel shift; the bottom image shows the river a few weeks before.
ReliefWeb has a good article on this disaster: Kosi devastates Bihar; 2 million homeless. The first two paragraphs read:
This is India’s Katrina, only the challenges could be bigger. Like the Mississippi breached the levee to drown an unsuspecting New Orleans in the US, the mighty Kosi river in north Bihar has broken its embankment to pick up a channel it had abandoned over 200 years ago, drowning towns, numerous villages and rendering over a million homeless. Many are reported to have died.
Officials here say it’s a catastrophe unlike annual floods. The brimming river has breached its embankment near the Bhimnagar barrage, close to the Nepal border, and is rushing down as a miles-wide stream to the Ganga, over almost 100km south. Unlike floods, this is not calm water but an angry torrent, making relief work very difficult.
In some ways, the situation on the Kosi Plain is similar to the Mississippi River delta in Louisiana. As sediments pile up around the mouth of the Mississippi, it naturally changes its course every few hundred years. The Mississippi is overdue for a channel change, which makes New Orleans increasingly vulnerable to flooding. Likewise, the Kosi River naturally changes its channel, but on a more frequent basis. The map below shows how the Kosi has changed its course numerous times since 1730.
As the Kosi exits the Himalayas, it creates a broad alluvial fan, well over 100 km across. Since the 1730s, the river has migrated from the east (#1 on the map) to the west (#2), and now seems to have taken an abrupt move back to the east.
As Indian officials respond to this crisis, they will need to take geological reality into account, just like planners in Louisiana need to take into account the fact that the Mississippi River would rather take a shorter path to the sea. We humans like things to stay constant. We like sea level to stay the same. We like climate to stay the same. We like rivers to behave and not change course. But the fact of the matter is that all of these things change. At times we can be the masters over nature, but at other times nature will be the master over us. We need the wisdom to know when to conform nature (such as the course of rivers) to our wishes, and when to adapt to the forces of nature that are still greater than us.
Grace and Peace
(Map from Leeder, M.R., 1982, Sedimentology: Process and Product, London: George Allen & Unwin, p. 148)