Even moderate rainfall can lead to major flooding in well-planned urban areas despite the presence of storm water drainage system
Indian cities offer new opportunities for development across various urban sectors, but most of these cities suffer from urban flooding during monsoon. This eventually leads to loss of life and property and affects the economic activities and natural eco-system.
Even the most planned Indian cities suffer from this problem. For instance, when Chandigarh, which is famously known as the first planned city of independent India, receives high rainfall, commuters find it difficult to reach their destinations.
In Chennai too, despite there being a well-placed storm water drainage system that’s divided into micro and macro drainage channels, there have been several instances of catastrophic flooding. Another addition to this list is Capital New Delhi, which witnesses its famously planned commercial area — Connaught Place — flood every time during storm showers. The same goes for Mumbai, India’s commercial capital, as it gets stuck just after a few hours of rain.
Hence, arise the questions: Why, in the existence of planning provisions and storm water drainage infrastructure, India still face the problem of urban flooding every now and then? What is missing in the planning approach of our cities? Is it attributed to the negligible amount of importance given to making our cities resilient to impacts of climate change? Or is it just following benchmarks to make concrete drains along roads?
As Indian cities grow, urban areas expand and are characterised by impervious surfaces like roads, pavements and buildings. Rapid development and construction in these areas result in the loss of green spaces. This decreases a city’s capacity to absorb water making it solely dependent on outflow of surface water runoff.
Under such circumstances, even moderate rainfall can lead to major flooding. The changing land use patterns and encroachment of freshwater bodies, which act as natural rainwater retention systems for moderation of high rainfall events, clearly indicates that in our country land is valued more than water. Hence, we suffer from frequent incidences of urban flooding which is mainly caused by excessive runoff in developed areas where the water doesn’t have anywhere to go.
Moreover, apart from storm water, the drain channels in Indian cities carry wastewater (grey water from kitchen and bath room, effluent from OSS, black water in absence of OSS), excreta (in case of open defecation/urination in drains) and solid waste (due to littering and dumping).
Over the years, the planning approach in India focused more on engineering solutions (layout of pipe according to peak hour rainfall), treating storm water as a liability rather than a resource. However, it is essential now to recognise the importance of water-sensitive spaces in creating a naturally-oriented water cycle while contributing to the amenity of the city.
Although the 2019 draft manual on storm water drainage systems, prepared by Central Public Health and Environmental Engineering Organisation (CPHEEO), has included a chapter on ‘Innovative storm water management practices’. It talks about integrating smart practices such as Water Sensitive Urban Design (WSUD), however, there is a huge need and scope of incorporating these alternative approaches at city level.
Service-level benchmarks (SLBs) for urban services developed by the Ministry of Housing and Urban Affairs (MoHUA) provide service-level guidance on storm water drainage to construct drains along the roads. Conventionally, storm water is considered a nuisance and hence, it is conveyed away from urban areas as rapidly as possible. For instance, according to the ministry's Liveability Standards in Cities: “Coverage of storm water drains (Core) defines the efficiency of storm water management which is an extent to which the road network in the city is covered through a storm water drainage network (pucca covered drains).”
However, storm water needs to be considered a resource. It should be attenuated and retained at source allowing it to infiltrate into aquifers and flow gradually into receiving water bodies. Storm water infrastructure should be designed to enhance the urban landscape and provide recreational opportunities.
Hence, apart from coverage of drainage network which comes under infrastructural component, it is essential to assess other components leading to effective drainage which include — resilience, efficiency, quality, and governance.
In a typical urban area, directing more and more runoff into surface water drainage systems is not the solution. It will eventually overload them, causing major floods. In existing spatial planning process, the focus on lakes, floodplains, buffer or green areas for surrounding vulnerable and watershed areas is neglected.
The need of the hour is to recognise the importance of urban green spaces in creating a naturally-oriented water cycle while contributing to the amenity of the city.
To kick-starting this, the following water-sensitive approaches can be adopted to lower hydrological impact of urbanisation and increase carrying capacity of urban areas:
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