- Urban Flooding
- Sustainable solutions
- Global Examples
- Indian scenario
- Lack of Innovative solutions
- URDPFI guidelines
Urban Flood Management
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Urban flooding is a common experience in most of the cities around the world. In India, it becomes more pronounced on the onset of monsoons and hampers the daily activities of the huge urban population. To prevent flooding there is a need for efficient urban water management systems, especially in cities, which are largely based on traditional engineering approaches till date.
- Urban flooding is the inundation of land or property in a built environment, particularly in more densely populated areas, caused by rainfall overwhelming the capacity of drainage systems, such as storm sewers.
- It can be sometimes triggered by events such as flash flooding or snowmelt, urban flooding is a condition, characterized by its repetitive and systemic impacts on communities.
- Aside from potential overflow of rivers and lakes, snowmelt, stormwater or water released from damaged water mains may accumulate on property and in public rights-of-way, seep through building walls and floors, or backup into buildings through sewer pipes, toilets and sinks.
- In urban areas, flood effects can be worsened by existing paved streets and roads, which increase the speed of flowing water.
- Concrete surfaces prevent rainfall from infiltrating into the ground, thereby causing a higher surface run-off that may be in excess of local drainage capacity.
- In the last few decades with an increase in frequency of extreme weather events such as high-intensity rainfall, water-related research has gained traction.
- Pluvial flooding — rain-driven flooding that results from the excess of natural or engineered drainage capacity — has emerged as a critical issue in urban water management.
- Many contemporary cities are vulnerable to pluvial flooding and associated risks are projected to increase with global climate changes and urban populations growth.
- To address the concern, the concept of slow, spread, sink and store runoff has been adopted by many cities to cater to high rainfall events and avoid urban surfaces turning into water-logged areas.
- Several cities have opted for bioswales, rooftop gardens, retention ponds and permeable pavements, which can reduce runoff to at least half.
- The efforts are known as water-sensitive urban design, low-impact development and sustainable urban drainage systems.
- These concepts generally represent more holistic approaches with more attention on urban planning, ecological quality and local conditions.
- Heavy rainfall in July 2011 prompted the city of Copenhagen to develop a Cloudburst Management Plan in 2012 to prepare the city for one of the biggest climate change challenges — extreme rainfall and pluvial flooding.
- The plan contains site identification, developing stormwater roads and pipes that transport water towards lakes and harbour, detention areas to store large volumes of water, green roads to detain and hold back water in smaller side streets.
- The Netherlands is dotted with ponds, lakes, seaside parking garages and city plazas that double up as water storage ponds during flooding events.
- To address the urban flooding issue, China’s sponge city initiative set an ambitious goal — by 2020, 80 percent of urban areas should absorb and re-use at least 70 percent of rainwater.
- The initiative seeks to reduce the intensity of rainwater runoff by enhancing and distributing absorption capacities more evenly across targeted areas.
- The resulting groundwater replenishment increases availability of water for various uses.
- Monsoons are a great asset for India, provided Indians take advantage of this bounty of nature.
- But layout of urban drains along roads is the only method followed to manage stormwater in cities.
- Stormwater runoff has historically been addressed by way of engineered systems with a standard technique being drain/channel conveyance.
- Drains as conveyance helps move water to a specific discharge point through drains on roads.
- Drainage channel conveyance systems, unfortunately, are singular in function and do not provide any additional ecological benefits.
- They do little to prevent stormwater runoff from occurring in the first place.
- Even though the National Mission on Sustainable Habitat suggests that 2-5 percent of municipal area should be reserved for water bodies, there is no legal protection for city lakes, catchment and drainage systems.
- Hence many urban water bodies and their catchment have been encroached upon or taken away for housing and other buildings.
Lack of Innovative solutions:
- Although clearly identified pluvial flooding as a major issue in cities during monsoon, the authorities responsible in Indian cities often lack the knowledge and tools required to deal with stormwater management.
- Development authorities often make use of conventional approaches implemented in developed countries during the 20th century, which aims to evacuate the runoff from the city as quickly as possible rather than endeavour to store and reuse it.
- Alternative and additional measures (storage /infiltration/delayed surface runoff) remain relatively unknown or unused in cities.
- It is imperative that we realise the risks of not addressing stormwater management in the early stages of planning and design causes constraints to new development or (re)development, missed opportunities for cost saving, poor quality of urban environment and overall unsustainable urban development.
- The need is for more integrated land and stormwater management from early stages to reduce the incidences of urban floods.
- It is high time that public open spaces in Indian cities are analysed and designed to give space for runoff to avoid flooding in cities
- This can be in the form of waterbodies /ponds, parks and other green areas, which can be used for recreational activities for the rest of the year as well.
- According to guidelines from the Urban and Regional Development Plans Formulation & Implementation (URDPFI), 2016, the maximum percentage of land is allotted to residential areas in different sizes of urban centres — metropolises to small towns.
- Residential clusters, which occupy the largest share (35 to 45 per cent, apart from recreational areas of 18 to 20 per cent) of land use in cities and towns, comprise building rooftops, sidewalks, paved parking spaces and previous areas that could be gardens or just open land and accessible roads.
- According to the guidelines, the average built-up area for an urban area is 24 per cent, while for an open space, it is 76 per cent.
- The standards and guidelines provide enough open areas to design such stormwater management projects.
- The 2019 manual on storm water drainage systems, prepared by Central Public Health and Environmental Engineering Organisation, included a chapter on innovative stormwater management practices.
- It talked about integrating smart practices such as water sensitive urban design.
- However, it is a herculean task to be incorporated at city level.
There is a need to include public open spaces within urban fabric in the form of storm management infrastructure, which could help our cities transform into water-sensitive cities.
It requires effective policy implementation, addressing technical integration problems, legislative constraints, social equity, and community acceptance for Urban management of flooding.