Devanahalli is a small town located 35 km to the north of Bengaluru. It is known for the Kempegowda International Airport, which accelerated the growth of the town.
The town has an area of 16.63 sq km, 23 wards and a population of ~38,000 and is entirely dependent on groundwater for its needs. The primary source of water has been borewells, whose depths have reached more than 1000 feet now. Since many borewells have stopped yielding, the Town Municipal Corporation had to dig new borewells to meet the increasing water demand. There are around 130 borewells, of which 32 are not yielding anymore. It is estimated that the town has a total demand of around 2.66 MLD (million litres per day) at 70 LPCD (litres per capita per day), according to the standards of the State Water Policy 2002, for its current population. Dependence on water tankers is not only at the private level. In some cases, even the TMC sources water from private water tankers.
As the water supplied by the town has high TDS (total dissolved solids) levels and is salty, people use RO (reverse osmosis) water dispensed in select places paying Rs 5 for 20 litres for their drinking water requirements.
Shallow Aquifer Integration – A Solution
Over the last few years, the Hebbal Nagavara Valley project of the Minor Irrigation Department of the Govt of Karnataka, started pumping treated wastewater into lakes around Bengaluru. When Devanahalli TMC desilted Sihineeru Kere, the possibility of integrating the shallow aquifer through an old open well near the lake into Devanahalli’s water supply became a potential opportunity. Biome facilitated the revival of the well by cleaning and strengthening the structure with the anticipation that the well would start yielding. When the treated wastewater pumping to Sihineeru Kere started, the well started yielding as expected, with a capacity of around 100-150 KL/day. To increase the yield from the shallow aquifer, two filter borewells (shallow borewells with slotted casing pipes) were dug, which increased the total yield to 200 KL/day.
The lake provides a livelihood for a fisherman who rears fish here and is also visited by birds like the cormorant and painted stork.
How it all comes together
Currently, the TMC supplies around 1200 KL (kilolitres) of water per day to households at 32-35 LPCD. A Water Treatment Plant (WTP), including a rapid sand filter, a 140-micron multimedia filter, ultraviolet (UV) disinfection and an online chlorinator, has been set up to treat the well water before it is integrated into the water supply system. The WTP ensures that the treated water is compliant with BIS 10500 standards. It has been set up in the existing pumphouse. After passing through the WTP, the treated water is collected in the sump tank. The sump also receives water from the existing borewells, before it is pumped to the overhead tank, the schematic of which is shown below.
The shallow aquifer water from the well requires much less energy for pumping and is, therefore, cheaper than the deep borewell water. It also has a much lower TDS and is potable.
This project was conceptualised and facilitated by Biome Environmental Trust. However, successful execution happened due to contributions from key partners of the ecosystem - TMC Devanahalli, EFI Foundation, SayTrees, the well-digger community, the Indian Institute of Science, Rotary Club and Carl Zeiss. As part of ITC Mission Sunehra Kal's urban water management which is being implemented in collaboration with Biome in Yelahanka and Devanahalli taluks, Devanahalli TMC members, watermen, plumbers and volunteers received training. This helped people understand the importance of urban water management, and created buy-in for this project.
The Way Forward
To make this ecosystem more robust, the following interventions are being planned in Phase 2
Wetland at the inlet point of Sihineeru Kere to treat the water flowing into the lake
Additional filter borewells to increase shallow aquifer withdrawal
Biodiversity enhancement interventions around the lake
Cleaning of the channel called poshakaluve, from the inlet point of used water to the lake
Lake bund stabilisation, connection of the overflow weir to the nala, roadside planting and seating around the lake
Last and probably the most important is to make this a learning laboratory and a case study that can be used in other towns and villages for reviving and integrating shallow aquifers into the water supply.