A Crash Course on Recharging the Water Table
- ameliedixon
- May 1, 2022
- 3 min read
The groundwater table in India is decreasing at an alarming rate. There are many factors contributing to this problem. India’s increasing population is resulting in an increasing demand for water. Additionally, climate change and groundwater pollution (from over-exploitation of groundwater sources) poses a great threat to the security of water in India. Erratic weather in India means unpredictable periods of rainfall and drought.
One of the ways to address the water security and sanitation in India is through percolation pits or wells. There will be a variety of definitions that we will cover.
We’ll start with groundwater. Groundwater is water found between cracks and spaces in soil and rocks underground. They are normally found in aquifers, which are really deep underground. India is the largest user of groundwater, and it’s reported that the watertable is depleting one to two metres every year.
Moving onto borewells. Borewells are one of, if not the most, common source of water in India. They were introduced by UNICEF in 1970 as a way to combat the water crisis. They typically draw water from confined and deep aquifers, which would be inaccessible by a well. This helped increase the supply of water, as deeper sources of groundwater can be reached and used. However, the seemingly perfect solution came with many problems that would be greatly evident towards the future.
Borewells are has introduced ‘a culture of exploitation of water’. Aquifers are not able to recharge, as they are constantly having water drawn. As aquifers are so deep, it is difficult to monitor the amount of water there and so, water is being extracted without consideration. As previously stated, the water demand is only increasing in India, so deeper borewells are dug to access more aquifers. There are more problems that come with this.
Deeper borewells introduce a risk of chemical contamination. Water deep underground has a higher salt content, so its unfit for drinking and irrigation. Saline water decreases the crop yield and percentage of germination, which can threaten the supply of grown food in India. But, recharging aquifers can help reduce the salinity.
Introducing percolation pits. Percolation, by definition, means the process of liquid slowly passing through a filter. These are one of the ways to recharge the groundwater table artificially. They allow rainwater, or excess water, permeate through soil strata to recharge the aquifers.
There are four main components of percolation pits: the water inlet, the pit, RCC rings and fillers.
Water Inlet
The water inlet is the input of water, and it’s usually water from excess flow after exhausting the water storage of rainwater. The runoff water is used as the water that will be recharging the aquifer.
The Pit
Rainwater needs to be filtered before entering the aquifer, to avoid chemical contamination and keeping the water source clean and safe. The pit uses rain filters, which mostly consists of heavy duty HDPE filters. These work on a centrifugal force to filter the water, so no power is required. Keeping operating and maintenance costs low.
RCC Rings
After filtration, the water can now pass through pipes which lead to storage tanks or underground sumps. These will pass through the fillers to further filter and finally reach its destination.
Fillers
The pit is filled with sand, gravel and other materials. These materials help percolate the water, as the water streams down slowly.
The advantages of percolation pits seem obvious: they help recharge the ground watertable. However, there is more to percolation pits. They are an easy and inexpensive solution for rural areas to recharge aquifers. They only use natural materials: so maintenance and building costs are kept low. There aren’t much requirements to the site. The site only needs to be relatively close to borewells. But, well suited sites would have a large and sufficiently clean catchment area (area for collecting rainwater), the location should permit fast infiltration of percolation of water. The overall quality of the water would increase and it is reported that it increases the water output by three to six times.
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Disclaimer:
Blog posts are prone to error as well as bias.
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