First and foremost, kudos to the team: they well deserve a heart-felt congratulations on their success and it is hardly surprising that the people's mandate has given them, with Mr Kumar as the leader at the helm of affairs, the opportunity to lead Bihar for the second time.
It's a pleasure to see a dedicated civil engineer in action as the CM of a state so vital to the long-term economic and political future of the country. It's definitely more reassuring than the likes of more medievally oriented and century-old mindsets which managed to bring this once prestigious state on the verge of a meltdown.
I am not a structural or civil engineer but I have read extensively on flood and disaster management: available best practice guidelines and evidence. I would only make a few pertinent comments regarding flood control strategy for the Kosi and other rivers:
The USA implemented policies in 1970s to control flood erosion. It obviously has a significant 'lag time' to achieve the desired effects, say 5-10 years.
To put this in perspective, I think the Kosi action plan team should be looking at not only preventing deforestation along the river, but also actively promoting afforestation activities of fast-growing shrubs, especially close to river banks, canals and other bodies.
On searching for information on drainage into the Kosi from Nepal, there are many feeder rivers that make the Kosi: Hence the name- Saptakoshi. Previous experiments and tests have confirmed that the 'Arun' tributary/feeder into Kosi brings the maximum amount of sediment into the Kosi. This alters the course of the river over years/decades, leading to floods.
Bringing technology to the rescue: Active reforestation measures can be combined with 'Gabion Technology' to shore-up river beds/banks. The whole package of Gabion meshes, reinforced baskets and walls would essentially make our water resources safe for decades to come. This could involve, but not limited to: Dams, Erosion control, Gravity bank protection, Light bank protection with geosynthetic MAC-MAT technology & Natural Combines for environmental restoration, River/stream bank protection, Rockfall netting, Soil conservation.
Reinforced cross-linked polymers or simple jute-based products can also dramatically cut-down the cost of base materials prior to using gabion pre-formed steel meshes (reinforced with locally available rocks to decrease transport costs).
This hopefully will be a long-term solution to the Kosi problem. The meshes will reinforce the banks of the rivulets/river/ and it will have enhanced protection over time as vegetation grows into the wire/rock mesh. It is also more malleable as it only is steel wires/meshes with rock between them (That's Gabion technology in a nutshell!), so it does not have cracks appearing it as may happen with concrete/water seepage into concrete etc. It is a very natural system which takes into account of water seepage and the wall but prevents the soil erosion. Over years, the sediment/erosion will reduce and lead to a more naturalized flow of the river. At this later stage, guessing over 10-20 years construction of a major dam may even be beneficial as the river flow would have become more predictable with a decreased sediment load flowing into the river.
Stopping illegal sand-mining will also help: May be creating registered sand vendors and all construction companies signing up to only source materials from registered vendors.
Cost issues: According to my own research: Rs 75 lakh-Rs 1 crore per kilometer of mesh using gabion technology. The river has a total length of 729 km. This will have to involve meshing in higher catchment areas, especially "Arun" tributary within Nepal as this is where the main bulk of sediments is coming from. So, in essence, a Rs 700-1000 crore investment might bring long-term solution to this problem. Readers may recall that the damage caused by the recent floods were estimated at more than 1000 crores.
And lastly, providing communities with renewable sources of energy to reduce dependence on wood. Heartening to see lot of available ranges of solar operated lanterns, street lights etc. at a nominal cost. This could offer us a cheap and cost-effective solution to empowering standalone families in remote locations with reduced dependence on fossil fuels/cutting trees etc.
Who knows we may prevent another Kosi!