Located in Southern India, Bangalore is the capital city of the state of Karnataka. The city’s population has seen rapid growth in the recent decades. India’s 2011 Census registered 8.5 million people, which at the time was a million more residents than the local water authority was planning for. A UN report in 2016 estimated 10.45 million residents in Bangalore. The population has since continued to grow rapidly, with some unofficial sources estimating the current population to be close to 12 million. Bangalore is the fifth largest metropolis and one of the fastest growing cities in India. The city has experienced an unprecedented expansion of urban area from 226 square km in 1995 to 741 square km in 2010 – a 220% increase over 15 years. This rapid urbanization has put immensense pressure on the city’s resources including its water supply, groundwater issues and lakes.
Water Supply: Bangalore has no proximal river of its own, and as a megacity of over 10 million people, it is unique in this regard. The city’s water needs are met by pumping water from the Krishna Raja Sagar Dam, built on the Cauvery river. Water is pumped for over 140 km before it reaches Bangalore. This source contributes 80% of the city’s water needs. The other 20% comes from the Arkavathy river, which is a tributary of the Cauvery river. This river is heavily disputed between the states of Karnataka and Tamil Nadu as is supplies water to the biggest cities and it is the main water source for agricultural purposes. To give some context about how the city’s water needs have grown – in 2007 Bangalore used to draw 900 million liters a day from the Cauvery river, whereas currently it draws 1400 million liters per day.
Rainfall: The mean annual total rainfall is about 800 mm with about 60 rainy days a year. This has been the average over the last 10 years. There are two peaks in the monsoons – one in May and the other in September-October.
Watersheds: Situated 3,000 ft above sea level in the rain shadow of the Western Ghats, which are a range of mountains that run along the western edge of the subcontinent, Bangalore is part of an ancient wetland system. Bangalore is located on a ridge and forms three watersheds as stormwater runoff flows in three directions along the valleys. Under the administrative boundary of Greater Bengaluru, K&C valley is the largest encompassing an area of 255 square kilometers.
Reservoirs: With few perennial rivers in the area, historically, farming settlements have for many centuries relied on man-made reservoirs created by damming streams to store water from monsoon rains. These were linked in series that in turn connected into a larger system of lakes and streams. Maintained lakes recharged groundwater, supported irrigation, fishing, cattle grazing, cultural and recreational activities, and also served as habitat for migratory birds and other species.
Watersheds with reservoirs and streams that connect them. Source: author.
Almost all the data that I looked into refers to these water bodies as ‘lakes’ so in this blog post I use the terms lake and reservoir interchangeably. Bangalore was once aptly known as ‘city of lakes’ in the local language, due to the presence of large number of reservoirs. There were close to about 285 lakes back in the 18th Century. Today only 81 remain, as recognized by the local government, with only 34 ‘live lakes’.
Infrastructure: When the reservoirs were constructed, they were interconnected with canals/drains (kaluveys’s) to enable transferring excess water from one lake to the next. Many of these canals have been concreted on three sides and now act as the city’s main storm water drains that carry runoff into lakes. This essentially acts as a combined sewer overflow system as storm water and sewage water enter the same drains.
Other infrastructure in the city includes a number of sewage treatment plants. 20 have already been built, the largest having a capacity of 180 MLD. The city has total treatment capacity of 721 MLD, but only 520 MLD gets treated on average. 23 new sewage treatment plants are proposed to be built in the near future.
Challenges of the near future
Groundwater: A major challenge that the city is facing is unchecked groundwater extraction. According to a national government report in 2017, Bangalore was said to run out of groundwater by 2020. But this report has subsequently been dismissed by many experts and even by city officials. While the city may not run out of ground water in the next 2 years, there is some data that has shown the ground water table has lowered in some parts, particularly the east of the city. In a constant search for water, city dwellers and developers have been sinking innumerable wells to extract groundwater for domestic purposes.
Pollution: All over the city, lake beds have collected rubbish and sewage from increasingly polluted streams, and the storm-water channels connecting them are regularly filled with construction material and in many cases are overgrown with weeds. Water quality has severely deteriorated, and local residents say that the biodiversity has nearly disappeared.
Storm water drains are constantly being paved all across the city. Additionally, they are clogged with garbage that gets dumped into them. Losing lakes and the increase in paved surfaces means less infiltration, where rainwater would filter down through the soils or from the lakes themselves into the groundwater table to recharge it. Instead, storm water run-off currently flows into drains, mixes with untreated sewage, and flows into lakes. This in turn is polluting the groundwater.
Vulnerabilities: Some of the vulnerabilities as discussed previously include untreated sewage flowing into reservoirs thereby polluting them and killing any biodiversity. Paving or concreting SWD, a depleting groundwater table, drying up lakes, and unchecked groundwater extraction are other issues that affect the reservoirs severely. This has in turn affected the livelihoods of families who live around the reservoirs and biodiversity that once thrived in many of them.
Despite the above mentioned problems, the city has an amazing network of water bodies that, if protected, can have a cascading effect of positive externalities some of which are – replenishing the ground water table, bringing back biodiversity, and providing recreational spaces for residents.
I will be focusing on the issue of polluted water entering these reservoirs.
These images show you the present scenario with regard to storm water drains. Huge amounts of solid waste including plastics and food waste gets dumped into them. Along with this, untreated sewage is a major contributor of pollution.
This leads to the proposed solution – waste management, water treatment, and phytoremediation as a three pronged solution to tackle this issue.
The first step would be to install filtration mechanisms at identified locations. These could be trash traps or floating barriers that can collect materials like plastic that float along the surface. As there are many locations that have small bridges that span across the stormwater drain, filters could be installed at these locations too for convenience. This waste material will have to collected periodically so it doesn’t clog the storm water drain. Once collected, there is a possibility that the waste could be used to generate power to operate the next step of the process: water treatment.
The city is proposing 23 new sewage treatment plants. This is a huge opportunity in that if these treatment facilities are located strategically, a huge amount of the city’s waste water can be treated. Currently, 20 sewage treatment plants treat nearly a third of the city’s waste water. The new plants could have the potential to treat over 60% of the city’s waste water – that could then be let into the reservoirs. As mentioned earlier, the city could leverage the waste it generates to power these treatment plants. Apart from keeping waste from going to landfills, this method could also have monetary benefits.
The final step would be to introduce constructed wetlands to capture and treat water before it enters into a reservoir. Constructed wetlands are engineered systems that use natural functions of vegetation, soil, and organisms to treat different water streams. These usually consist of a series of shallow ponds with vegetation that can breakdown organic matter or other sediments that are present in waste water.
Taking a site in Bangalore where this can be applied is the Bellandur lake – the largest water body in the city – which covers an area of 900 acres. It is so polluted that in January of last year caught fire and extinguished after it burned for 30 hours. Nearly 40 % of the city’s untreated sewage flows in to the lake. The water is a potent mix of domestic and industrial waste which causes frothing and fuels fires.
The blue arrows that you see are the storm water drain that bring effluent into the lake. As you can see there are three major inlets. There already is a sewage treatment plant on the northern side, but this plant does not function to its full capacity. Waste filters can be installed at strategic locations before water reaches the sewage treatment plant or constructed wetlands. The wetlands are located at inlets to trap waste water and treat it before it enters into the lake.
The issue of waste management is one of the biggest that Bangalore needs to tackle on a city-wide scale. This proposed solution depends heavily on managing and hopefully restriction waste that gets dumped into the storm water drains. Without this, it may not be possible to save Bangalore’s lakes using simple feasible solutions.