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Borewell : A poster (Part 2)

A 2 part poster to detail out borewells

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Borewell : A poster (Part 2)

  1. 1. boreWELLsThe borewell is perhaps the most common source of water in urban India today. Borewells or ‘tube wells’ are manmade wells dug deep into the ground to tap into water-bearing soil or rock layers termed aquifers. They typically draw water from “confined deep aquifers”, i.e., rock layers deep underground, where water is trapped under pressure between the cracks of rocks and are formed over many years, sometimes even centuries, due to water percolating down the rock layers. Did you know India has over 30 million borewells! India is the largest user of groundwater in the world, and much of it is through borewell extraction. This was not always the case. Open wells used to be the norm till around the 1970s when borewell technology arrived in India. This was when UNICEF brought borewell rigs to help deal with water shortage. Borewells source water from deep within the ground, from the deeper aquifers. These rock layers are at great depths and are usually less permeable, and cannot soak up water. Thus water stays trapped in cracks, surrounded by rocks under pressure. All open-wells and bore-wells get their water from “aquifers”. An aquifer is a continuous interconnected space underground within which water resides and moves – this is “groundwater”- this space can be between soil particles or in cracks and fissures of rocks. The open-well gets its water from the shallow unconfined aquifer – groundwater which is shallow and not under pressure. Borewells typically go deep and get their water from aquifers formed by cracks and fissures of rocks where water is under pressure. Aquifers can be local or regional. Aquifers get their water from “recharge” – when rainwater seeps down the earth and fills up all these spaces. HISTORY DIGGING A BOREWELL HOW IT WORKS We can withdraw water from an open-well when the shallow aquifer has water. However, when all the water from the shallow aquifer is pumped out for use, and there is not adequate recharge from the rains, over time the aquifer, and consequently an open-well, will dry up. We can recharge the shallow aquifer by redirecting water into an existing open-well. Alternatively we can build an open-well only to “recharge.” Such a well is called a recharge well. The recharge well can also help us prevent floods. RECHARGE WELLS BOREWELL STORIES top soil WEATHERED ZONE unconfined shallow aquifer LAKE BOREWELLS OPEN WELL RECHARGE WELL STORM WATER DRAIN deep aquifers FRACTURED ZONE BEDROCK SOIL casing borehole water level pump WEATHERED ZONE WEATHERED and fractured ZONE HARD ROCK India’s first borewell rig, brought by UNICEF, is still preserved in Pune. (above) A borewell rig (above) and a borewell (left) And by the late 1970s, borewells started replacing open wells. They became popular in cities because of the perception that borewell water was cleaner and would be available even during summers. They however spurred a culture of exploiting water as borewells make groundwater “invisible”. As borewells dried up, deeper ones were dug. Some even go down to 1800 feet, but as you go deeper, the risks of chemical contamination increase. When a borewell is dug, such water-bearing cracks are struck are various depths, and water juts out at high pressure into the borehole. This causes a sudden rise in water level in the borehole. The level gets stabilised over time; this stable level is called the static water level of the borewell. As the depth increases, the rock becomes even less permeable and the number of cracks decrease reducing the chance of finding water. The vehicle that is used to remove the pump is aligned with the borewell. The delivery pipe is connected to the winch and wound up. The water level in this 1400 ft borewell stabilised at 300 ft, and you can see that a signifant length of the pipe is wet. The new pump is reassembled and the delivery pipe is connected to its first shaft. The entire assembly is reinserted into the borehole. Power cables are attached and the delivery pipe is unwound to its full depth. At this site, the borewell pump developed a problem and had to be removed, refitted and re-inserted.