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What is a Drainage System and Why are Drains Vital to Recharging Groundwater in Urban Areas

A drainage system not only protects land from potential flooding, but also provides the benefit of harvesting rainfall, allowing water to easily percolate into the aquifers.

Aniruddha Ghosal | News18.com@aniruddhg1

Updated:July 24, 2019, 10:01 PM IST
What is a Drainage System and Why are Drains Vital to Recharging Groundwater in Urban Areas
File photo shows a man bathing under a broken water pipeline next to a drain in Delhi. (Reuters)

New Delhi: The distinction between a drain and a sewer is often one restricted to maps and plans in government offices. But this distinction is vital to preserve and maintain – not just to ensure that cities are not flooded but to also make certain that ground water aquifers are recharged.

What exactly is a drain, how does it restore groundwater, and what happens in case the natural hydrological systems are ignored? News18 explains.

What exactly is a drainage system? Why do they matter for cities?

Simply put, a drainage system is a network of channels, hydraulic control structures or levees that drain land and protect it from potential flooding. They can be man-made or natural. Importantly, they also provide the benefit of harvesting rainfall, allowing water to easily percolate into the aquifers.

A drainage system refers to the network of channels, drains, hydraulic control structures, levees, and pumping mechanisms that drain land or protect it from potential flooding.

Take, for instance, the case of storm-water drains meant for surface water to drain excess rain and ground water from impenetrable surfaces such as paved streets, car parks or footpaths. Rapid urbanisation has disconnected this storm water from its natural hydrological surface.

What is the difference between a drain, a nallah and a sewerage drain?

The world nallah, when used in the case of physical geography, refers to a stream or a drain. In the case of physical infrastructure, a storm-water drain is meant for fresh water. These may be artificial or natural. While sewerage drains or sewer lines are typically underground networks of pipes that carry sewage (waste water and excreta) to treatment facilities or sewage treatment plants (STP).

So what’s wrong in case of cities like Delhi?

When IIT Delhi’s civil engineering department in 2018 finished their report of Delhi’s drainage system, they were aghast. While recommending an urgent overhaul, they asked for storm drains to be treated like “key public assets” to ensure that encroachment is prevented and ensure that natural or artificial drains should carry only storm water of treated sewage. For instance, it chastised the Delhi Jal Board (DJB) for puncturing sewer lines when they were blocked, and draining sewage into storm-water drains.

What happens when these natural systems are disturbed?

The negative impact of urbanisation that treats storm water and drains as nuisances, or blots to be erased in order to preserve the sanctity of cities, is becoming apparent globally, say researchers.

Take for instance, the case of Bengaluru. Amidst the doomsday prediction for the city’s groundwater, researchers flagged the ways in which the 19th century drains carrying rainwater to tanks were ignored by modern planners. As cities grow, the question of how they will quench their thirst becomes more and more important. Drains still hold considerable potential to recharge groundwater and are key for urban spaces.

Manoj Mishra, a river expert and former bureaucrat, summarised, “The basic job of a drain is to carry water to the river. In the case of Delhi, drains are specifically important because of the undulated drain… storm water follows a natural path to the river and these natural paths are these drains.”

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