Urban areas in India have been experiencing unprecedented population and economic growth in the last decade. As cities grow and incomes rise, a new challenge has arisen: that of supplying domestic water reliably, and of reasonable quality, to this rapidly growing urban population, while ensuring that the well-being of future generations is not jeopardised.

The implications of this unprecedented urbanisation on water resources are only beginning to be understood. The story of the Arkavathy sub-basin, on the outskirts of Bengaluru city, offers rich insights into the complex interactions between urbanising areas and their surrounding hinterlands. A semi-arid catchment with an average annual rainfall of 830 mm, it overlaps with the western portion of the rapidly growing metropolis of Bengaluru. The main tributary of the Arkavathy river has its headwaters in the Nandi Hills, north of Bengaluru, and is joined by its first major tributary, the Kumudavathy river at Thippagondanahalli (TG Halli) village. At this confluence, the TG Halli reservoir, with a catchment area of 1447 km2, was constructed in 1933. The reservoir’s current storage capacity can supply 149 MLD (million litres per day) to Bengaluru city. An older reservoir, Hesaraghatta, constructed in 1896 to supply 36 MLD to Bengaluru, is located further upstream on the Arkavathy river1 (see Figure 1). THE CHANGING WATERSCAPE Historical development The original scrub forest of the Arkavathy catchment was gradually cleared to make way for cultivation as early settlers moved in, 1 Lele, S., V. Srinivasan, P. Jamwal, BK. Thomas, M. Eswar, and TMd. Zuhail. 2013. Water management in Arkavathy basin: a situation analysis. Environment and Development Discussion Paper No.1. Bengaluru: Ashoka Trust for Research in Ecology and the Environment. probably several thousand years ago. The rulers between the 10th and 17th centuries constructed a series of small earthen bunds on the tributaries to store runoff in small water bodies or ‘tanks’ to create sources of water for irrigation and other domestic water uses. The catchment has an estimated 617 such tanks. These tanks would capture part of the surface flows in the stream, and the overflow would cascade to the next tank in the chain. In effect, this system of small, cascading tanks captured some of the streamflow for providing irrigation to the local community while also allowing significant flow to downstream communities.