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Carpet of woe

Stop sewage flow into Sal river to save it from growth of water hyacinth

18th May 2017, 06:47 Hrs

A year ago a stretch of the Sal river from the Khareband bridge to Benaulim was de-silted at a cost of Rs 3.76 crore. This work was undertaken after a thick carpet of weeds had formed on the surface. Today, the weed carpet is back and it looks like Rs 3.76 crore has flowed down the river into the Arabian Sea. This was the second time desilting work was undertaken, the first being in 2002-03. Is there a solution to this problem? Or should the State continue to spend huge sums of money de-silting and de-weeding the river every year without ascertaining why the weed returns?
In the case of the Sal river, as with many rivers and ponds in India and world-wide, the culprit is water hyacinth, which was considered an ornamental plant and imported to West Bengal from Brazil. The plant duplicates itself every nine days and once it took over rivers and ponds in that state it was known as ‘Bengal terror’. In India, the weed has affected irrigation, hydroelectric generation, navigation and flood control. It spreads through river flow, boats and fishing nets and appears in places where it never took growth before. The Pampa river in Kerala is inundated with another type of weed called ‘cabomba’, an aquarium plant which was introduced into the riverine system and wetlands by mistake.
Although the water hyacinth problem was recognised in the Sal last year, a last solution is yet to be found. The weed grows rapidly when nitrate and phosphate levels in the river increase. This happens when untreated sewage is released into the river or water body. This phenomenon is evident in the Sal river. If the carpet of weeds is visible up to Benaulim and not further it is because untreated sewage from Margao is emptied at this point. Also, untreated water from the Sirvodem treatment plant is released here making this stretch of the river a fertile habitat for the growth of water hyacinth.
There are many ways to tackle the weed and the most expensive of them is physical de-weeding and de-silting. Boat cutters are available for such jobs, but the cost is huge and perennial. The State government would find it difficult to spend nearly Rs 4 crore every year to clear the weeds and a more lasting solution would be in the interest of all. It took 7,000 armymen and crores of rupees to clear the Ulsoor lake in Bengaluru, but the weeds returned. Herbicides are used in other parts of the world but until cleared for use in India, a large-scale attack on the weed is not possible. No progress is likely until untreated sewage from the city is stopped from flowing into the river. Without a large waste water treatment plant and steep fines for those who dump untreated water into the river, the water hyacinth problem is not likely to go away.

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