"taming the Kosi - a 'lag time' approach."

………………to be very precise on this context, the fundamental to handle the furious Kosi is to increase the ‘lag time’ in its entire catchment area, as rivers with a short lag time are more likely to flood.

Lag time is the time difference between maximum rainfall and peak flow.

The fluvio-geomorphological and meteorological changes and increasing human interventions in the form of:

• global climatic change and the resultant changes in the elements of weather / climate and their pattern
• alterations in the river basin morphology and its characteristic features
• removing woodland and forests, rapid urbanization, straightening river channels, artificially raising the height of river banks, and, so on and so forth, interferes in the factors and processes of the hydrological cycle.

Under normal circumstances the ‘precipitation input’ and ‘stream discharge’ equation goes like this:

The highlighted text in red background and font shows the area where humans negatively interfere into the system, thereby compelling the river to over flow its banks.

The ‘lag time’ can be increased by allowing the basin area to perform more of interception, percolation and storage than any type of flows and the ultimate discharge into the river channel.

Some of these following human activities can increase the ‘lag time’:

• planting more woodlands and forest.
• building dams to store and control discharge.
• diverting the flood water to other basin areas, say through river linking project.
  
• river channel dredging.
• extracting water for industrial and domestic uses.
• maintaining the wetlands as storage tanks.
• more number of percolation pits with the rapid urbanization process, etc.

In short, at macro (like the entire catchment / basin area) as well as micro level (water percolation pits) there need to be long term strategies and follow ups on flood management in the region.

“The swollen Kosi – an erroneous human approach”

Whereas River Damodar (once called as the ‘sorrow of Bihar and West Bengal’) has been tamed under the DVC Project by following the principles and approaches of TVA on river water management, the Kosi River has again dubiously gained the distinction of being called the ‘river of sorrow’. Its flood havocs have killed many hundreds, rendering more than three million homeless and completely uprooting the rural economy.
Fluvio-geomorphologically, Kosi is a part of the Ganges riverine system which comes out from the Himalayas on a steep gradient course. One of the reasons behind its frequent flooding being a break in the river gradient on entering the Plains of Northern Bihar, multiplied by heavy silt load and incessant rain followed by peak discharge in the basin area (particularly in the Himalayan catchments). The aspect of deforestation, filling of the natural and man-made waterholes that were existing in the form of lakes, ponds and marshy lands etc., large scale settlement in the flood plains can also not be ignored.
However, a lack of political will on part of the Central and State government is equally to be blamed for the same. Though in 1950s, the then Prime Minister Pt. Jawaharlal Nehru had directed the Central Water Commission for a long term solution to tame the river, the government has since then settled on interim and temporary arrangements on a barrage at Hanuman Nagar, Birpur (Nepal) and construction of embankments. It is an open fact that these measures have been grossly erroneous as Kosi:

• is a highly meandering river and has drifted more than 150 kms. in past 120 years. In other words, it has a highly unstable channel / course.
• carries heavy silt load, the source being the fragile sedimentary and crystalline rocks of the Himalayas.
  The silt is infertile unlike the alluvial deposits, and therefore, has devastating effects on the agrarian economy of the state.

It seems that the natural tendency of Kosi do not approve of the steady-water equilibrium engineering of those who are at the planning and execution level in managing this furious river.