The mass wasting of the Himalaya is still going on. This makes the Kosi the river with one of the heaviest sediment loads in the world. More than 100 million cubic metres of silt are deposited every year in Nepal and Bihar when the river slows down after breaking through the mountains.
This is why the river is constantly trying to find new channels to the sea. The problem now is that the fertile banks of the Kosi are densely populated, and governments are under pressure to control the floods by straitjacketing the river with embankments.
When the Kosi Barrage was built in 1956, the lifespan of the embankments was 20 years. Today, the Kosi in Nepal flows three metres above the surrounding land. It was only a question of time before it breached the levee. The embankment started collapsing on 15 August, locals warned the authorities, but no action as taken.
Things would have been worse if the Kosi had been in spate. The river could have permanently reverted to the Kosi's 1731 channel, obliterating Sunsari and half of Bihar.
So, what is to be done? The government belatedly realised the seriousness of the crisis and dispatched two ministers to Sunsari. They need to plan alternative routes to rejoin eastern Nepal to the rest of the country, plug the breach, coordinate relief, and resettle 60,000 people.
On Thursday, Indian prime minister Manmohan Singh toured northern Bihar, where 3 million people have been displaced. There are already renewed calls in Bihar to build the Kosi High Dam, which will create a reservoir stretching from Sunsari to Ramechhap.
The dam would be a solution if India and Nepal had a good record in large infrastructure projects, in spreading benefits and taking care of the displaced. But the Kosi dam will be plagued with the same problem that made the barrage unworkable: siltation.
We shouldn't try to correct one mistake by making an even bigger one. India and Nepal must be prepared for the day when the Kosi makes a catastrophic course change, an event that will make this week's disaster look like a picnic. But we do that by making it easy for the Kosi and other Nepali rivers to flow down to the sea. The more obstructions we create in their path, the more destructive future floods will be.
This is what the two countries should be working on, not getting worked up about whether the prime minister should have gone to China first or not.