Water is a vital resource for country’s economic and social development. Every city in our country is facing water scarcity and groundwater pollution. Ironically according to global standards, India receives abundant rainfall. So where is this “abundant” water disappearing? Architect Arjun Kamal explains the problem and solutions that can help reclaim this endangered natural resource.
The problem of depleting water resource lies in rainwater getting polluted and hence causing groundwater pollution. Urbanization has led to creation of impermeable surfaces like building rooftops, pavements and roads. Such surfaces don’t allow rainwater to percolate into the ground. During rainfall, water flows from rooftops of buildings and paved areas, washing away dirt, dust and pollutants, thus getting contaminated. This run-off enters stormwater drains. Stormwater drains are often ill maintained and get choked during monsoons because of accumulation of garbage. Rainwater that could have gone through these drains accumulates on roads, resulting in water-logging.
The run-off pollutes natural bodies too, as seen in the rivers like Yamuna and Ganga. The pollutants also enter the ground, thereby polluting our groundwater. We all know that construction of rainwater harvesting pits has become compulsory in all newly constructed buildings having more than 200sqm plot area. It is the initial amount of rainwater that contains pollutants so it can’t be stored in the rainwater recharge pit.
So how do we redeem the situation? The answer lies in developing green infrastructure that uses vegetation, soils, and natural processes to manage water and create healthier urban environments. Examples are rain gardens and bio-swales designed to capture the initial flow of storm water and reduce the accumulation of toxins flowing directly into natural waterways through ground filtration.
A rain garden is a shallow planted depression which captures rainwater and allows it to seep and move into the ground. This water otherwise flows as surface run-off that causes erosion, flooding and reduced groundwater recharge. This water also contains pollutants like pesticides, oil spills, and volatile organic compounds. During rainfall, as captured rainwater seeps in ground, these pollutants are broken down by microbes. This decrease in run-off also brings down the local municipal drainage systems as well as the flooding levels.
Rain gardens use and optimize any rain that falls, reducing the need for irrigation. In addition, they allow a building to deal with excessive rainwater runoff without burdening the public storm water systems. On an individual level, the results may look insignificant, but on a larger scale, the results can contribute a lot to a healthy environment. A raingarden can absorb up to 30% more water than a conventional lawn. Another advantage of raingardens is that they require low maintenance as they consist of native plant species which can withstand long periods of accumulated water, like Doob grass, Sheesham (Dalbergia sissoo) and Kaner (Thevetia neriifolia), Sacred Lotus (Nelumbo nucifera).
• What is the natural course of rainwater drainage?
• Where is the maximum slope?
• Where are the down spouts from your terraces leading to?
• Are there any underground services?
After studying all these factors it will become very easy to locate your rain garden. The components of a rain garden include a layer of crushed stone at the bottom level for drainage; above it is nutrient rich porous soil as a growing medium and between soil and crushed stone, a geotextile fabric to prevent soil choking the airspaces between the stone pieces. Native plants are recommended for rain gardens because they generally do not require fertilizer and attract local wildlife such as native birds. A selection of wildflowers, shrubs and small trees take up excess water flowing into the rain garden.
Rain gardens improve water quality by filtering runoff, provide localized flood control, are aesthetically pleasing as also provide interesting planting opportunities. They also help tie together buildings and their surrounding environments in attractive and environmentally advantageous ways thereby offering a significant natural solutions to groundwater pollution.
Rain gardens differ from retention basins, in that the water will infiltrate the ground within a day or two. This creates the advantage that it does not allow mosquitoes to breed.
Controlling groundwater pollution through vegetation is a strategy being widely used in countries like USA and Germany. It’s high time concerned authorities in India start implementing such methods to save “precious water going down the drain”.
A bioswale is a landscaped element designed to remove silt and pollution from runoff water. It uses highly permeable mediums like gravel or coarse sands. Bioswales work on the same principle as rain but gardens but unlike raingardens which are depressions, bioswales are channels, planted with the same hardy, water-tolerant species as that for rain gardens.
Considerations required when designing a bioswale:
• Location must be in a low-lying area where water tends to collect.
• Flat areas or areas with a slope greater than 5% are not practical for bioswales.
• Do not build a bioswale in an area with a high water table.
• Choose plants that are both flood and drought resistant
The water’s flow path is designed to maximize the time water spends in the swale, which aids the trapping of pollutants and silt. Depending upon the geometry of land available, a bioswale may have a meandering or almost straight channel alignment. They are more suitable for stormwater control on a larger level and can be made along the roadsides so that rainwater from road flows towards them and percolates in the ground. A common application is around parking lots, where substantial automotive pollution is collected by the paving and then flushed by rain.