Thursday, 18th May 2023. It was our fourth day with Biome Environmental Trust and we were to visit a government school at Sonnappanahalli. The school is around 23 kilometers from the center of the city, towards the north. The school has a capacity of 350 students and has a water demand of 5000 liters per day. A rainwater harvesting setup had been executed at this school under the sponsorship of ITC Limited as part of their CSR (Corporate Social Responsibility) initiative. It was an attempt to create a sustainable model of water conservation for the surrounding community to get inspired from.
Government School, Sonnapanahalli
Rainwater from the rooftop run-off runs through a series of 4” diameter pipelines and the initial run-off is let down directly into the ground. A manual valve is used for this purpose. There is a Y-joint that prevents water with roof debris from entering into the filter and is in turn deviated into a reject pipe. Once the terrace is cleared off with the initial run-off water, the rest of the rainwater is collected in a harvesting pit with layered aggregates through the other arm of the Y-joint. The filter is of 3 layers - larger stones, charcoal and smaller aggregates.
The underground sump of this setup has a capacity of 12,000 liters and the recharge well close to the Anganwadi building was 20’ deep and 4’ in diameter. The capacity of the underground sump is calculated and designed keeping in mind the average rainfall the region receives.
The school also has a well at its backyard which supplies 50,000 liters per day after its rejuvenation. However, contaminants from the soak pits of the surrounding neighborhood pollute the well.
Valve that lets initial run-off to the ground, Sonnapanahalli
Recharge well
The Anganwadi buildings were later modified to have a slight slope in the terraces and a small parapet wall was built to prevent rainwater from flowing across the external walls of the building. This measure protects the structure from prolonged exposure to water and also helps in collecting the rainwater. As a measure to regulate usage of this conserved water, taps in the school were also fitted with aerators.
Rainwater harvesting pit filter Aerators fitted to taps
Our next stop was at a lake in Devanahalli, further north of Bengaluru at a distance of 15 kms from Sonnapanahalli. The lake was locally known as Sihineeru Kere, which literally translates to ‘sweetwater lake’. The lake is adjacent to the Devanahalli Fort. The revival of the lake is part of the Hebbal-Nagawara Valley project. The lake is 10 ft to 15 ft deep and is solely meant for the recharge of groundwater and is not directly used for agricultural purposes since it is secondary treated water. Public activity is also restricted in the case of this lake and hence no fishing or grass cutting takes place here unlike the Kaikondrahalli Lake within the city of Bengaluru.
A well and a filter borewell next to the lake are recharged with the water from the lake. The well is 60 ft deep and was earlier dry and had weeds growing in it including a tree. The Town Municipal Corporation (TMC) was about to close down the well. With the efforts of Biome Environmental Trust, this was prevented and the well was revived. The filter borewell is 85 ft deep and taps into the shallow aquifer, which is replenished by the lakewater. During the visit, another filter borewell was being built next to the same lake, which was 100 ft deep. The lakewater if fetched directly is not usable but this changes as it passes through the soil, and gets filtered naturally. Hence, the water that fills up the well and borewell can be used for daily use (except for drinking). Water from this filter borewell then moves to a sump of 50,000 liter capacity. Water from the sump is pumped to a community overhead tank (OHT). The OHT has a capacity of 1 lakh gallons which is roughly 3,78,500 liters and supplies water to all the homes in the nearby village. These homes now receive water 24x7.
We also learnt how a filter borewell is built. On average, it takes 6 days to build one. It takes 2-3 days to drill and another 2-3 days to suck out murky water using an air compressor. The machinery used to drill a filter borewell can only drill to a depth of 200 ft unlike those used to drill a regular borewell which allows drilling till even 1800 ft - 2000 ft. While digging a filter borewell, the drilling is done until they hit stones.
Devanahalli Lake
We met with a father-son duo, C Sendraiyappa and S Saravana Kumar, whose expertise was at installing filter borewells. They were originally from Tamil Nadu and have now been involved in this for the past 22 years drilling borewells in and around Bengaluru.
A filter borewell
After taking a stroll across the banks of the lake, we headed towards three other wells around Sonnapanahalli.
The first two wells we visited were 80 ft and 74 ft deep, there was vegetation growing in them earlier. Biome initiated the cleaning of the well and removal of silt. Potassium permanganate (KMnO4), lime, and alum were added to clean and purify the well. These two wells get water from Hunasamaranahalli Lake, via underground recharge.
The third well we visited was located in a residential layout. Similar to other wells, this one was also dry and had vegetation growing before it was rejuvenated. The area around the well was used for agriculture before the residential plots were developed. 1.5 lakh liters of water is pumped out of the well everyday, out of which the TMC takes 1 lakh liters. The rest of the 50,000 liters is consumed by the residents in the neighborhood. In total, the well’s water is pumped to two apartments, a college, and a hotel via OHTs.
The fourth and fifth wells we visited did not have a pump and water had to be fetched manually. One of these wells with a manual pulley system was considered sacred by the community. The first shower of a newborn baby in the neighborhood had to happen with the water from this well. It was strictly not allowed for anyone to stand or walk around the walls of the well as it was used for drinking and cooking purposes.
The Sacred Well
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