URBAN FLOODS – WHAT CAN BE DONE TO MITIGATE THE EFFECTS

Recently, torrential rains that took place in Chennai, Hyderabad and many other cities, have caused massive urban floods. In many Indian cities, urban floods have become a frequent phenomenon in recent years.

          As the incidence of climate variability and extreme weather events increases, urban flooding becomes more and more common. While the untimely heavy rains can be attributed to climate variability, the urban flooding is largely due to unplanned urbanisation.

MAN-MADE DISASTER

          The overburdened drainage systems, unregulated construction, no regard to the natural topography and hydro-geomorphology all make urban floods a man-made disaster. Cities like Hyderabad, Mumbai rely on a century-old drainage system, covering only a small part of the core city.

          In the last 20 years, the Indian cities have grown manifold in their original built-up area. Lasting irreversible damage has been done to the cities by property builders, property owners, and public agencies by flattening terrain and altering natural drainage routes.

          Indian cities are becoming increasingly impervious to water, not just because of the increasing built-up area but also because of the nature of materials used – hard, a non-porous construction material that makes the soil impervious.

          Even with provisions of rainwater harvesting, sustainable urban drainage systems, etc, in regulatory mechanisms like the Environmental Impact Assessment (EIA), adoption at user-end as well as enforcement agencies remains weak. The number of wetlands have been reduced to 123 in 2018 from 644 in 1956. Green cover is only 9 percent, which ideally should have been at least 33 percent.

SOME SOLUTIONS:

–WORK TOGETHER AND IN COORDINATION

          Urban floods of this scale cannot be contained by the municipal authorities alone. Floods cannot be managed without concerted and focused investments of energy and resources. The Metropolitan Development Authorities, National Disaster Management Authority, State revenue and irrigation departments along with municipal corporations, the surrounding state authorities, should be involved in such work together.

–RECOGNISE WATERSCAPES INSTEAD OF LANDSCAPES

          All cities in the subcontinent are waterscapes. They are threaded with rivers, speckled with wetlands and springs, and they rest on invisible aquifers. Yet, driven by a thirst for land, our cities are planned to subjugate water, not live with it. It is this land-centrism that undermines urban drainage. In almost all cities in South Asia, residential properties have been built on stormwater drains.

          We need to move away from land-centric urbanisation and recognise cities as waterscapes. We need to let urban rivers breathe by returning them to their floodplains. One restored lake or one reclaimed waterway, though welcome, is no longer adequate.

–DEVELOPING SPONGE CITIES

          The idea of a sponge city is to make cities more permeable so as to hold and use the water which falls upon them. Sponge cities absorb the rainwater, which is then naturally filtered by the soil and allowed to reach urban aquifers. This allows for the extraction of water from the ground through urban or peri-urban wells. This water can be treated easily and used for city water supply.

          Wetlands and floodplains, by and large, should not be concretised.

–BIOSWALES NEED TO BE MORE OF SOIL THAN CONCRETE

          Bioswales that are made along roadsides so that rainwater from the road flows towards them and percolates into the ground are generally built on concrete or stones.

We need to make the flood water percolate enough for groundwater recharge through perforated pipes. This will require extreme engineering efforts, but if the best of the expertise and energies are put in, we may see the rainwater percolate through the structures made on highways avoiding frequent flooding of urban roads disrupting the economy in long run.

–FLOOD MAPPING AND PREPARING CITIES          

Vulnerability analyses and risk assessments should form part and parcel of city master plans. Allowing natural drainage, rainwater harvesting, urban watershed management need micro ecological drainage systems, shaped by contours of the terrain.

— BY YOGITA KADU

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