Today, urban cities have become concrete forests. Our houses are made up of concrete; our roads are made up of impervious asphalt, bitumen, and concrete. Our pathways are made up of cement tiles. All in all, we have done a very nice job in making our cities an impermeable forest through which rainwater cannot permeate into soil and recharge groundwater aquifers. As a result today, handling rainwater runoff has become one of the major problems for many cities. Waterlogging after the rain has become a usual site for many cities like Mumbai, Gurugram, etc.

The traditional approach to address storm-water runoff is to build expensive, well-designed, massive interconnected drainage systems throughout the city but this approach is no longer sustainable. While cities that have a good drainage system, may not face waterlogging but they still end up wasting millions of liters of freshwater as stormwater runoff.

Most of the drainage systems today are old and don’t have the capacity to meet the flow. As a result, massive up-gradation is required. Realizing the shortfall of traditional methods, many cities today have decided to go for a more sustainable option of a decentralized approach using green infrastructure instead of building massive interconnected central drainage systems. This will allow them to treat, and store the stormwater locally within the communities.

What are Green Infrastructures?

Green infrastructure is defined as “the range of measures that use plant or soil systems, permeable pavement or other permeable surfaces or substrates, stormwater harvest, and reuse, or landscaping to store, infiltrate, or evapotranspiration storm-water and reduce flows to sewer systems or to surface waters.” Or in simple words, Green infrastructures are those structures that filter and store rainwater and reduce surface runoff. Examples of green infrastructure include rain-water harvesting, permeable footpaths, etc.

Example of green infrastructure:

• Rain Harvesting system
• Permeable pavements/footpaths
• Green roofs
• Urban tree canopy
• Green streets and alleys
• Rain Gardens

Advantages of the decentralized approach

1. Water-saving:

A green infrastructure focuses on the reuse of water. Be it directly reusing the rainwater harvested or recharging the aquifers, or simply using the water for irrigation. The main aim of green infrastructure is to convert stormwater runoff from a problem to a potential freshwater source by preventing rainwater from running off and being wasted in drains.

2. Cost-effective:

Traditional central drainage systems require large capital investment, as they involve acquiring a large number of lands, construction of vast water conduits; maintenance, etc. while a decentralized approach in the form of green infrastructure is much cheaper. These structures don’t require a large amount of land and detailed design or costly regular maintenance.

3. Less disruption of natural water systems and aquifers:

Traditional drainage systems are designed to carry water directly into the river, disrupting the natural water distribution system of the catchment. It prevents the recharging of aquifers while increasing the water flow of the river.

4. Environment friendly:

The concept of green infrastructure was developed with keeping sustainability in mind. The traditional drainage system has the tendency of disrupting the environment in a lot of ways, be it the excessive carbon footprint associated with the construction of these drains or the fact that runoff of these drains tends to carry a lot of pollutants with them and dispose of them into rivers and polluting them. On the other hand, green infrastructures are constructed in a way that they have a minimum carbon footprint, as well as prevent runoff of pollutants into the river. Most of the green infrastructures also have the added bonus of integrating a lot of greenery in them which further results in cleaner air.

5. More efficient

Centralized drainage systems are massive systems that require regular and intensive maintenance. These systems are prone to leakage, damage, silting, blockage, etc. even a small blockage at the right place has the potential of disrupting the entire system and can cause massive waterlogging (which can be seen frequently in many cities). Moreover, if the system is not well designed, it requires costly changes. But having a decentralized system makes it easier to maintain and the consequence of failure are less severe. Also, since most of the green infrastructures are based on improving natural water storage in plants and increasing permeability within the site, they are much more efficient and robust.

6. More hygienic:

Green infrastructures are designed to keep the rainwater as clean as possible and to prevent waterlogging while on the other hand; most of the traditional drainage system uses a combined drain for rainwater runoff and sewage/greywater. As a result in the case when the traditional system fails, the waterlogged not only contains clean rainwater but also contains a large amount of unhygienic sewage and greywater as well.

7. Reduce flood risk

The traditional drainage system was designed with the goal to collect the maximum amount of run-off water and dispose of them in the river and disrupting the natural water balance. They reduced the surface infiltration and increased the runoff as a result in case of heavy rainfall, more water get send into the river which increases the flood risk. While on the other hand, green infrastructures are constructed to capture the run-off and prevent excessive inflow of water into the river which reduces the risks of flooding.

As we can see that decentralized system enjoys a lot of advantages over a traditional system. This has resulted in the fact that today; decentralized systems are becoming a necessity. Many countries have made it mandatory for large housing societies and industries to install green infrastructure on their campus. The use of these green infrastructures is no more limited to just run-off only, with the rise of ZLD (Zero-liquid discharge) in urban housing society has made them even more popular, as many societies today are using them with treatment systems to absorb their greywater. In the end, it is safe to conclude that, decentralized run-off systems like green infrastructures are a sustainable way to the future.