SuDS: India's answer to clogged and closed box drains
Cities have had a turbulent engagement with water throughout history. Our greatest urban centers owe their very existence to the harbors, rivers, and drinking water sources that provided inspiration for development and the means for economic prosperity. Yet, despite our instinctive attraction to water, we have all too often exploited the relationship by confining it, degrading it, and largely ignoring it.
Cities can’t go on being concrete jungles, in conflict with nature. To flourish, cities need to work ‘in tune’ with nature. They need to learn quickly how to deploy nature-based solutions that bring far wider benefits than traditional engineered ‘grey’ infrastructure and contribute positively to biodiversity and carbon reduction.
A critical resource issue:
With either too much or too little of it, water is undoubtedly one of the most critical resource issues we face this century, and cities are likely to be where we experience its dramatic impact. In our eagerness to develop close-by water courses, we effectively paved over natural drainage systems and found ourselves discharging wastes into the same water sources we rely upon for our health and well-being. The effects are obvious. Urban flooding attracts headlines every year and securing potable water supply for our water-hungry urban populations has overstretched local resources and forced us to rely on carbon-intensive water supplies pumped in from distant catchments. And to make matters worse, climate change will only intensify flood risk and water scarcity.
Causes of urban flooding:
- Storm drainage systems are currently designed in India for rainfall intensities of once in one year to once in two years return periods. In case, rainfall records are not available; rainfall intensity is usually adopted in the range of 12 mm/hr – 20 mm/hr. Therefore, ‘Accommodation & Transportation’ capacities of such hydraulically configured drainage facilities are easily overwhelmed, whenever rainstorms of higher frequencies are experienced.
- Unplanned urbanization causes a considerable increase in impervious areas, thereby leading to enhanced surface runoff and frequent flooding.
- The absence of a drainage scheme: a systematic approach to formulating and implementing a holistic stormwater drainage scheme within a specified planning horizon has turned urban areas and cities so vulnerable now that even rain of light and medium intensity causes urban flooding.
- The problem of illegal disposal of Construction and Demolition waste, municipal solid waste, and plastic waste coupled with poor maintenance of existing drainage systems often obstructs the storm runoff causing localized flooding in the areas.
Make the most of nature’s drainage:
- Cost-effective, safe, and attractive alternatives to pipes and drains.
- Retain natural channels and incorporate them into public open space.
- Retain and restore riparian vegetation to improve water quality through biofiltration
- Create rifles and pools to improve water quality and provide refuge for local flora and fauna. Protect valuable natural ecosystems.
- Minimize the use of artificial drainage systems.
Sustainable drainage systems aim towards maintaining or restoring a more natural hydrological regime, such that the impact of urbanization on downstream flooding and water quality is minimized.
SUDS involve a change in our way of managing urban run-off from solely looking at volume control to an integrated multi-disciplinary approach that addresses water quality, water quantity, amenity, and habitat. These are referred to as the four pillars of SUDS design.
Different techniques of SUDS include the following:
- Detention Ponds: These are small, excavated storage spaces or can be constructed in natural depressions. These are dry during low flow time. This type of pond provides temporary storage of stormwater runoff.
- Wet Ponds: also called storm water ponds or retention ponds, typically look just like ordinary ponds, with the exception that they are specifically designed to manage stormwater and have a standardized design.
- Infiltration Trenches: Design On-site infiltration trenches to collect the water from the perimeter drainage system and roof and return it to the ground. The infiltrated water recharges the water table and provides base flows for streams.
- Roadside Infiltration Trenches: Design of Roadside infiltration trenches to collect runoff from the road. Design of an underground trench on the ground where water can be slowly infiltrated into the soil to recharge the water table and provide base flows for streams.
- Infiltration basins are designed so that stormwater eventually soaks into the ground, imitating natural conditions and recharging groundwater supplies.
- Bioswales: Swales carry water-like pipes and are designed as shallow, open, planted channels to convey runoff and remove pollutants. They are an alternative to a piped drainage system where space and grade is available. Water moves horizontally along the surface or in subsurface layers. Swales slow water flow and trap sediments to improve the water quality.
- Roof Rainwater harvesting and collecting the same through the collection tank not only reduces the stormwater runoff but also helps in reducing the potable water demand.
- Green roofs provide a considerable reduction in the volume of stormwater leaving a developed site and they reduce the peak rates of runoff.
- These systems receive runoff during flood events. Their implementation increases stormwater storage capacity and infiltration volumes while reducing the volume of water reaching the sewer system and eventually the treatment plants. Within the urban hydrologic cycle, these systems may significantly contribute to integrated urban water management and provide the ability to recycle the stored water volume.
Increase the Pervious Cover:
- Previous Cover: The use of permeable materials for pathways instead of concrete and impermeable materials reduces the runoff and helps in rainwater recharge.
Sustainable urban drainage systems should be considered during the site selection process. Different management strategies may be required for different parts of a site, and flows from roofs should also be considered.
Sustainable urban drainage systems are likely to become even more important as the population increases, water resources are put under increasing pressure, and the impact of climate change is felt.