Monsoon floods displace millions in India each year and have been mounting pressure on the currently vulnerable urban infrastructure. Sure, everyone remembers the 2013 Uttarakhand Floods and 2015 Chennai floods because of the devastation they caused but urban flooding is not a rare occurrence. Just last year, rainwater entered 80% of residential homes in Patna in what was called Bihar Urban Floods. Sustainable drainage systems are inadequate in India and all we have are old and silted sewers that have not been upgraded efficiently. Most cities in India do not have enough storm drains to redirect excess rainwater. Another major reason for flooding is the population density in urban cities. The more, the merrier, the dirtier. Living in a housing society with poor sustainable drainage is a hellish experience come monsoon. People, homes, cars, common utilities, everything is threatened with one big downpour. Societies need to pay utmost attention to stormwater management since it’s the first step that can alleviate urban flooding at macro levels. Let’s explore the subject in depth.
What is stormwater
Stormwater is the water that is the result of rain, hail, snow or ice melt. Stormwater discharge originates from rooftops, streets, pavements, lawns (all impervious surfaces) and gets soaked into the soil/ground or gathers in the form of ponds, puddles, while the excess water that runs off into rivers is called stormwater run-off.
In the pre-urbanized natural landscape, stormwater run-off or discharge was not a matter of concern. But with the rise in population and pollution, uncontrolled and degraded stormwater run-off is considered nonpoint source pollution (resulting from many diffuse sources as opposed to one main source).
When stormwater seeps into the ground, it replenishes the soil, but when it runs off impervious surfaces and passes through the drain and sewers, it becomes polluted and causes more harm than benefits.
Issues with ill-stormwater management
- Urban flooding
- Damage to people, accidents, fatalities
- Destruction of residential property, assets and vehicles
- Streambank erosion
- Destruction of natural habitats
- Damage to public and private infrastructure
- Sinkhole collapse
- Pollution entrance in nearby water bodies due to bacteria, petroleum, plastic, metals and sediment
- Clogging of waterways
- Loss of fish and aquatic species
Stormwater management involves operational and technically engineered actions to control the quality and quantity of stormwater so that the above-mentioned ill effects do not occur.
Residential societies can incorporate stormwater best management practices (BMPs) which can be divided into structural (construction of devices/natural mechanisms) and non-structural (preventive measures).
Structural best practices for stormwater management
1. Infiltration techniques
Residential Infiltration methods include creating temporary catchments in the premises to capture stormwater and processing it through layers so that pollutants may be reduced, peak flow volume can be reduced and groundwater may be recharged.
2. Vegetative swale (Bioswale)
These are V-shaped narrow trenches along the road emptying into the storm drain. They have gentle slopes on both sides and can be planted with native species of plants. Stormwater flows in a more controlled way through a swale and reduces pollutants.
3. Rain garden (Bioretention)
A depressed area on the ground planted with native vegetation and perennials that collects stormwater from streets, lawns, driveway, and rooftops is called a rain garden. –
4. Porous (permeable) pavements
Stormwater can pass through porous asphalt pavements with an underlying stone aggregate layer that provides detention of stormwater run-off.
5. Reduction methods
Societies can deploy different measures so that stormwater doesn’t turn into run-off, to begin with, thus preventing any damages.
6. Green roofs
To reduce the peak run-off rate, societies can construct extensive roofs (3-6 inches of soil depth for shallow vegetation) or intensive green roofs (6-24 inches of soil depth for large vegetation. Rain gets captured and evotranspired back into the atmosphere without overloading the storm sewers.
7. Rainwater harvesting/ rain barrels
Rainwater collected through rooftops and paved pathways can be stored underground in large storage devices and later directed back to the rain garden, infiltration trenches, directly into the soil or can be reused by residents after filtration. Societies can also use cisterns and barrels for reducing stormwater run-off.
8. Sand and organic filters
These are two-chambered self-contained beds filled with sand, peat, tree branches and other organic materials (with underlying inlets and outlets) that provide filtration basins that reduce stormwater impact.
Non-structural (preventive) practices for stormwater management
Green infrastructure inspired better site design follows low impact development approaches while land planning and design. It takes into account conservation of water quality, uses natural and engineered Infiltration and Storage strategy, preventing stormwater run-off by using effectively on-site natural features. More and more builders/developers are realising the market worth of green buildings as the Indian green building market is slated to double by 2022.
Here’s what residential societies can do to contribute towards better stormwater management and reduce pollutants being released into the natural ecosystem.
- Don’t dump any kind of garbage down the storm drains and sewers.
- Make sure no oil, fluids, petrol leaks from your vehicles and spills onto the driveway or on the pavement.
- Use fewer chemicals, pesticides while gardening and use organic fertilizer instead.
- Maintain, inspect and clean your septic tanks/ sewage treatment plants at prescribed times and before the monsoon.
- Make sure your sewers, dry wells and storm drain/culverts are not obstructed by garbage, snags and tree branches.
- Replace your garden lawns with rainwater ponds, native shrubs and plant basins.
- Pick up after your pets.
- Ensure that you compost safely so that the manure doesn’t run off into the waterways.
- Grow more trees within and outside your housing societies.
- Dump your toxic garbage responsibly.
How many of these best practices are you implementing in your community? Every sustainable step taken by accountable communities can cumulatively help solve stormwater mismanagement and strengthen our cities as they grow larger each year.