The city’s much abused Mithi river is to get a Rs 60 crore, 6-km long environmentally friendly retaining wall by 2011.
Officials believe this wall will stop both encroachments along and pollution into the river. Forty-six months after work on the widening and desilting of the Mithi began, the Mumbai Metropolitan Region Development Authority (MMRDA) has decided to build the retaining wall using the environmentally friendly Gabion wall technique.
The silt-filled Mithi and the hundreds of encroachments on its banks were blamed as the major cause for the devastating flooding the city saw after the deluge of July 26, 2005. Among the Central Water Power Research Station’s post-deluge recommendations to the state were deepening and desilting of the 17.8-km river to improve the flow of flood water out of the city.
The work was divided between the Brihanmumbai Municipal Corporation, which was to handle 11.8-km of the river, and the MMRDA, which was to take the 6-km stretch from Mahim Causeway to CST Bridge, Kalina.
Work on the desilting and widening has been on, but the retaining wall could not be built as the tides and slippery marine soil made its construction a tricky, expensive exercise.
The Gabion wall technique builds a structure consisting of rocks held together with wire mesh, with minimal use of steel, and almost no concrete.
These structures can be constructed offsite, then lowered into the riverbed by a crane.
“Water can pass through these structures easily, making them less likely to tip over due to water pressure,” Mithi River Protection and Development Authority project director Dr Vikas Tondwalkar said.
MMRDA says this wall is less expensive to build than a concrete wall.
“A concrete wall of one cubic metre costs Rs three lakh, a Gabion wall costs Rs 50,000. Also, its strength increases with time as silt accumulates on its surface,” MMRDA’s executive engineer L M Bisen said.
The wall will stretch from CST Causeway to Mahim Causeway and is likely to be completed by 2011.
MMRDA has begun a pilot project on a one-kilometer stretch, which will be completed in the next three months.