Dredging Issue in River Kosi

Kosi is referred as sorrow of Bihar. In 2008 it breached the embankment in Kushaha (Nepal) and shifted 108 km eastwards.

The recurrent calamities along the banks of Kosi could be due to 1,082 million tonnes of silt that has been deposited in it in the last 54 years. This has come out in a study conducted by department of earth sciences of IIT Kanpur.

Silt leading to floods

• The silt causes the level of riverbed to rise.
• As a result, the natural longitudinal (straight) course of the river is disturbed.
• Therefore the river searches for a lateral path (left or right).
• As a result it changes its course and breaches the embankments on the new path it has created.
• The breach of embankments causes flo­ods.

Hence dredging can aid in river maintaining its usual course without breaching embankments.

Effective management of silting

The most common arguments against dredging are

• Costs involved.
• Silt management: Once the silt is extracted from the river, it is dumped on the river bank itself because technology is yet to find answer to w=what to do with it. Soon it goes back into the river. Thus, the money literally goes down the drain.

The study of department of earth sciences of IIT Kanpur has brought out various uses of silt. The study says “The Kosi silt consists of fine to very fine sand and is dominated by quartz and significant amounts of muscovite mica. Chemically, this is composed of 72-76% of silica followed by aluminum oxide (10-11%), iron oxide (3-4%), potassium oxide, sodium oxide (3-4%), calcium oxide, magnesium oxide (< 2 %) and minor amount of titanium oxide(<1%).”

Hence the silt can be used as

• Backfill material in road construction.
• It can be substituted as a raw material for manufacturing fired bricks for use in construction of buildings.
• As replacement of raw material for manufacturing Portland cement.
• The fine dredged sediments can rejuvenate poor agricultural soils.
• It can be used to supply organic content and nutrients to deficient soils to increase productivity.
• The fine materials also help to hold water and promote retention of soil moisture needed by the crops.
• The silt can also be used for reclaiming the land disturbed and/or contaminated by industrial activities and restoring its natural condition.

The study has brought out various insights about dredging and effective silt management. A pilot project in one of the silt hotspots can be undertaken so that any loopholes can be addressed before undertaking dredging in large scale. DTE