Bangalore metropolis is the fastest growing city in India. The city is situated on a high plateau forming part of the gneissic complex with no perennial river source in the vicinity. 65% of its total water consumption of Bangalore city, which is located at an altitude of 3,000 feet above MSL, is from drawn from reservoirs where it has to be pumped up 1000 feet in altitude, over a distance of 100 km. This makes Bangalore’s water the costliest available water in all of India and Asia, costing the government Rs.82/Kilolitre on actual, whereas Delhi’s only Rs.28/Kl (Nilekani, 2014). The naturally undulating terrain of Bangalore City, with hit hills and valleys, lends itself perfectly to the development of more than 200 tanks, which were traditionally rainwater harvesting and collecting systems, used to capture and store rain water for irrigated agriculture. The peripheral areas of the city municipality, where most of the tanks are located is solely dependent on groundwater, which is an open access common property, (upto 1000 MLD; depths upto 450m) leading to over exploitation. The over exploitation of groundwater in and around the city is inturn leading to depletion in water in tanks where untreated sewage gets dumped due to the poor sewerage network in these areas. There are about 60 of these urban tanks/lakes which are a part of 6 lake series(viz. interconnected to each other).
However restoration has been piecemeal – if one lake is treated, but the upstream and downstream lakes remain polluted, and Rajakaluves (Storm water drains) continue to be blocked, so that in a few years the lake returns to its original polluted condition. Hence, Lake restoration is to be taken up based on Lake series and not in isolation, to have better results and impact.
Bangalore requires a transition in its sources of urban water supply, a shift to a more decentralised, closed loop urban water systems through a restoration economy approach to Urban watershed regeneration.Discourse on urban lakes suggests that lakes can simultaneously provide recharge, flood protection, aquatic habitat and ecosystem services. But some of these goals are clearly conflicting. If an urban lake is to be optimized for groundwater recharge, it must be desilted to allow stormwater to seep into the ground. However, this means the lake will be nearly empty in the dry season, which may not serve as an ideal habitat for birds and amphibians. This study will determine the water exchange dynamics at a individual tank/catchment scale and how these exchanges regulate tank performance and catchment water balances.
Parallely, very little is understood about the fractured granitic aquifers that underlie Bangalore and the interpretation of observed levels in these aquifers remains a challenge. There are huge inconsistencies between secondary well data and field observations where even monitored wells (through participatory groundwater monitoring programmes) show water levels are highly heterogeneous in space and time. Studies suggest that there is high density of fractures close to the ground surface but fracture density decreases with depth.