Why rivers decide to run away

The Times of India: When the Kosi reverted to its 250-year-old course last month, leaving 30 lakh people homeless in northern Bihar, apparently due to heavy rains in Nepal, the near-Biblical scenes of havoc left many with just one question: Why? Why do rivers change course? What happens to the people they displace? Are these refugees of wayward rivers entitled to compensation for the land they lost? And just how prepared is India to check its surging rivers?

It’s futile to ask ‘why’, says A K Bajaj, chairman of the Central Water Commission because “it’s very natural for a river to keep shifting its course. It’s a part of its natural evolution.” Bajaj explains that fast-flowing rivers are prone to silting up as they surge down the hills and spread out on the plains, allowing sand and suspended matter to deposit in their slower, wider depths. Over time, the deposits create resistance, forcing the river to move to an area of lower resistance. This is called changing course.

Nature’s fury — earthquakes, landslides, hurricanes — can change a river’s course as well. And then there’s man. Environmentalists now say at least some of the blame lies with human activity. Says IPCC chief RK Pachauri, “As a result of climate change, floods are increasing in frequency and intensity. It’s not possible to ascribe a single event such as the current floods in Bihar to human-induced climate change, but the trend is unmistakable. These are likely to get more serious in the future if the emissions of greenhouse gases are not mitigated at the global level.”

Bajaj agrees that “the volume of water in rivers has been on the rise, resulting in greater force of flow. Therefore, even relatively lesser amount of rain during monsoon can lead to a catastrophe”. He adds that “in the next 15-20 years, this phenomenon will continue till most of the glaciers have melted. After that, there will be just minimal flow of water.”

… Officials at the department of hydrology studies say that building dams may be the best way out, as is the case with the Colorado river in the US. It has 30 dams to keep it in check. “In case of the Ganga and the Kosi, the government of Nepal, where both rivers originate, is not allowing construction of dams. So, we shall remain at perpetual risk,” says Bajaj….

The dry river bed of the Niranjana River in Bihar, India -- not too far from the Kosi. Shot by Hyougushi / Hideyuki KAMON from Takarazuka, Hyogo, JAPAN, Wikimedia Commons via Flickr, under Creative Commons Attribution ShareAlike 2.0 License (cc-by-sa-2.0)