A lake rejuvenated

Still waters are deep: Once again Udaisagar Lake experiences aquatic richness. Photo: Abha Sharma  

Known as the city of lakes, Udaipur was adjudged one of the ten best tourist destinations in the world in 2009. It is also a favourite hotspot for big fat weddings and its scenic beauty has lured many a movie makers from both Bollywood and Hollywood.

Udaipur owes its beauty to lakes. If it loses its beauty, it means loss of tourists, loss of business and perhaps its identity too. For years, these lakes have been facing the problem of water hyacinth but lately contamination has been a greater menace. But thanks to the concerted efforts of a section of citizens and the use of the innovative Green Bridge technology, the city lakes have got a fresh lease of life.

There are about hundred small lakes in Udaipur but the main ones are Pichhola, Fatehsagar and Udaisagar. The Ahar river, that feeds the Udaisagar, is experiencing the burden of urbanisation with the entire domestic and industrial waste of Udaipur, about 100 to150 million litre per day, flowing into it, including almost 10 per cent untreated industrial effluents.

The high BOD (biochemical oxygen demand) values, COD (chemical oxygen demand) and alkalinity in Ahar, in turn, badly affected the ecology of Udaisagar Lake. Deforestation, catchment area degradation, over-exploitation of ground water and eutrophication added to the woes. Low oxygen concentration in lake water led to anaerobic conditions, resulting in foul smell and loss of aquatic life. The lake, which earlier harboured nearly 40 species of fish, has been left with only 17 now. It also resulted in ground water contamination all along its 21-km-stretch. The non-perennial Ahar was nothing short of a sewer drain for almost eight months in a year and had water in the monsoon, only if the catchment area received good rainfall.

The Green Bridge technology, however, proved a life saving measure. It was initiated by Jheel Sanrakshan Samiti (Lake Conservation Society), working for past two decades in collaboration with International Lake Environment Committee Foundation, Japan, and active participation of all stakeholders — Udaipur Chamber of Commerce & Industry, civil society groups, village councils, industrial organizations and government agencies — in 2009. Shrishti Eco-Research Institute, Pune, provided technological inputs. The project was completed in June 2010.

“For Green Bridge, the energy sources are sun and air which synthesise their own chemicals and assimilate. While a mechanical clean-up would require an expenditure of Rs. one crore per MLD (million litre), the cost would be almost nil in Green Bridge,” said Anil Mehta, joint secretary of Jheel Sanrakshan Samiti.

This technology is most economical and there is zero necessity of electricity. There is no recurring expenditure and one doesn't need any skilled maintenance force. Unlike conventional mechanical process of cleaning up a river, the process is bio-degradable and bio-absorbing, Mr. Mehta explained.

It uses filtration and purification power of biologically originated cellulosic/fibrous materials in combination with root system of plants, sand and gravel. The fibrous materials like coconut coir or dried water hyacinth or aquatic grasses are woven to form a porous wall-like structure or bridge. It is further strengthened with sand and stones. Thus turbidity of flowing water is substantially reduced. Planting of shrubs and grass helps in absorption of soluble substances, including heavy metals and helps in regeneration of aquatic life.

The installation of Green Bridge was done at one end of Ahar river, the point where the river enters the Udaisagar Lake. Six bridges of varying length from 12 to 14 metre were installed. Having a trapezoidal shape, the three limbs have a loose stone wall of 4 metre width at the base and two metre at the top. Two screens made up of mild steel with anti-corrosive paint were installed to prevent floating objects. All floatable and suspended solids like cans, bottles and other wastes were trapped in this biological bridge.

Plants have had a very effective role in the eco-restoration work. Lemon grass, barley grass and small variety of bamboo were used. In addition, local shrubs like Guggal (Commifora wightee), kanna jhadi (ephedra) and trees like drum stick, peepal, tamarind, amaltas (cassia) and Arandi (castor) were also planted for their anti-bacterial and anti-turbidity properties.

Once the water hyacinth and floating materials like plastic were removed, sun rays and air could penetrate the water surface. Thanks to the bio-culture of green bridges, the muck deposited at the bottom of the river started releasing gases like methane and carbon-dioxide. The muck, totally devoid of oxygen initially, became oxygenated and erupted on the surface. The change became visible within one month of the installation of the green bridges.

The experiment passed the final test during monsoon when Udaipur had a good rainfall last year and the river flowed 15 ft. above the green bridges. There were apprehensions that since green bridges were just a system of loose stone walls, it was destined to be washed away. But it was noticed that but for minor dislocation of some loose stones, the bridges were intact.

One of the main reasons of the success of the project was the involvement of all sections concerned. The Jheel Sanrakshan Samiti in association with other agencies conducted several meetings with different communities, villagers and industries before starting the project. Once this was done, the difficult task of clearing the lakes of water hyacinth and polythene from river bed was taken care of by public groups. The construction of the road to carry construction material at the site was done by Urban Improvement Trust while the seed money for the project was donated by Singhal Foundation. Donations were also collected organisations like Hindustan Zinc and MMCF.

At the project site, there is no foul odour now; the transparency of flowing waste water has increased; cattle has started grazing along the river bank; moor hen, egret, lesser cormorant and wood duck have started converging at the location and aquatic life has regenerated. The success story was presented at the International Lake Conference held in Texas late last year.

Taking inspiration, neighbouring state Punjab has also initiated a similar project in Ludhiana. It was also shortlisted for the National Urban Water Awards last year.

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Printable version | Sep 11, 2021 10:41:03 AM | https://www.thehindu.com/sci-tech/energy-and-environment/a-lake-rejuvenated/article3436472.ece

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