A new role for water bodies in the city – BangaloreNovember 17, 2012
A New role for tanks in the city
Silt trap – Storm-water drain with silt is separated from the main lake. The silt will need regular removal.
Known as the city of tanks for years Bangalore has seen large scale destruction and encroachment of its surface water bodies over the year. Public outcry, activist groups and the courts have ensured that some efforts are on to save what remains and conserve these water structures for the city.
Built primarily as irrigation structures these tanks have outlived that particular purpose as urbanization has changed land use and converted the ‘atchcuts’ or command areas, where crops used to be grown , into primarily housing but also other sites. These tanks were also not perennial; most of them would go dry during summer. What is therefore a new role for them in a modern city?
NEW ROLE: Tanks could serve many a purpose in the modern urban context. They could be space for bio-diversity, acting as a wetland where many birds and aquatic life could flourish. They could be a recreational space, where such activities as walking, jogging, boating and even swimming could happen. They could be micro-environment moderating space cooling with evaporation and water vapour during the hot summer months. They could hold storm water during heavy rains and act as a water buffer moderating floods. They could be percolating structures recharging the groundwater among many other roles.
The best and most appropriate as well as sustainable role for the water bodies seems to be that of recipients of treated sewage water. The city gets over 1400 million litres per day from the Arkavathy and Cauvery rivers. Waters which are not natural on the city as rain but piped and brought from far to quench the thirst of the city. Of this 80 % or over 1120 million litres per day will flow as waste-water or sewage as commonly known. This water will need to be treated , nutrients and pollutants removed if we have to do justice to the ecosystem. The best way to do this is to locate decentralized and well distributed sewage treatment plants attached to all the remaining tanks of our city.
In addition to the sewage flows over 3000 million litres per day equivalent falls as rain on the city. Over half of this can be picked up in the tanks if they are designed properly to receive the waters from urban catchments.
There are many examples dotting the landscape. The tank at Lalbagh has been refurbished and receives water from the small sewage treatment plant set up upstream of it. Almost 1.5 million litres per day thus becomes perennial flow to the tank keeping it full. This recharges the groundwater and makes it available as open well water and bore-well water to slake the thirst of Lalbagh.
Nagavara tank receives treated waste-water from the Jakkur sewage treatment plant and is always full of water for recreational activities.
Jakkur tank, with a water spread of 50 Hectares, has a 10 million litres per day sewage treatment plant located upstream of the tank. The treated waste-water is let into an artificial wetland for further biological treatment before it reaches the main water body of the tank. This then recharges the groundwater around the water body and fills up the surrounding wells and bore-wells.
In the absence of a legal and institutional framework and a managed groundwater policy a bore-well has been sunk by a private person nearby and the water is being sold in tankers to the nearby residents. The city has invested hugely in both the waste-water treatment plant and the tank itself but the benefits of recharge are being taken by private bore-well owners nearby.
In theory at least 10 million litres per day could be available from the groundwater surrounding the tank if recharge is maintained well and could be supplied to 100,000 people at 100 litres per day.
There is a groundwater act passed recently and a groundwater authority has been created. This board should focus on such opportunities and see how the groundwaters can be brought to augment the city supplies as a public good rather than a private good.
The road ahead: The utilization of tanks to receive treated waste-water and then to pick it up as groundwater has tremendous potential for the city. Institutions and the law should quickly move to make this possible. The water shortage of Bangalore and in fact most cities in the Deccan Plateau can be overcome and the lakes saved if such an approach is adopted. This is truly integrated water management for the city. Are we ready to be water wise?