As cities get crowded, buildings are built haphazardly without much regard to planning, open, fertile, green, and wooded areas are replaced by impervious land cover like roads, concrete pavements, buildings, the risk of floods in urban areas has increased. Flooding events in Chennai in 2015, Mumbai, Bengaluru and even smaller cities like Belagavi and Dharwad in 2019 are a testament to that. It is estimated that by 2021 around 44 crore Indians will be living in urban areas.
As the urban population increases, so does the pressure on natural hydrological systems. Lakes and rivers are encroached upon and turned into apartment complexes, transit centers and sport stadiums. â€śDevelopmentâ€ť in Bengaluru is a prime example for that. Shockingly, even new development, both in Bengaluru and elsewhere in the country, is taking place on encroached land. Though new projects present us with an opportunity to learn from our past mistakes, it appears as if no lessons have been learned. For example, the Amaravati Capital City project, to build a new capital city for Andhra Pradesh will allegedly encroach upon the floodplains of the Krishna river.
How is urban flooding different?
In addition to flood risks from water bodies, urban areas face the risk of flooding when drainage systems get overwhelmed and water backs up onto the streets. Since urban areas have high percentages of impermeable surfaces, runoff generated is upto six times higher than that with a natural land cover. The flood â€śpeakâ€ť is also higher as shown in figure 1. Therefore, properties not in the vicinity of a waterbody are also at a risk of flooding.
Fig 1: Diagram illustrating how source control reduces runoff, thus lowering the peak discharge in the receiving waterbody. Source: Urban flood risk management, WMO/GWP Associated Programme on Flood Management, 2008.
What is being done?
The Central government has taken various initiatives for flood management, beginning with the National Program of Flood Management in 1954. Since then, a number of initiatives have been taken by the Government of India to address flood risks, the most important being the High Level Committee on Floods (1957), the Ministers Committee on Flood Control (1964), the Rashtriya Barh Ayog (1980) and the Task Force on Flood Management/Erosion control (2004). These initiatives mainly focused on riverine floods and described structural methods of flood control, like dams, embankments, and drainage channels. It was only in 2010 that the issue of urban floods was de-linked from the broader topic of flood control and management, and the National Disaster Management Authority (NDMA) issued guidelines for the management of urban floods. However, several recommendations are yet to be implemented.
Fig 2: Influence of urbanisation on the water cycle. Source: Urban flood risk management, WMO/GWP Associated Programme on Flood Management, 2008.
As per the constitutional provisions, flood management is a state subject and therefore the primary responsibility of flood management lies with the state governments. While some states have taken initiatives, they are limited in both geographic and techno-economic scope. For example, in Karnataka, the responsibility falls under the authority of Karnataka State Natural Disaster Monitoring Center (KSNDMC). While there is a system in place to forecast and monitor flooding in Bengaluru, there are hardly any systems on such scale for other cities in the state. Although forecasting is an indispensable part of flood management and preventing loss of life, investment is necessary to map flood risk zones so that damage to immovable property and infrastructure can be minimized. Flood hazard mapping at the outset may seem expensive. However, lessons from western countries have taught us that investing in risk mitigation costs far less than taking no action and rebuilding in the aftermath of a disaster.
What needs to be done?
The most proactive way of mitigating flood risk is to build away from the floodplain and high flood hazard zones. It might be challenging, in cities, to identify bodies of water that were once free flowing. In such cases, geospatial analysis can be used to find the â€ślostâ€ť urban streams. New construction in floodplains should be strictly regulated and in areas where the floodplain has already been encroached, structural flood control measures, like increasing the stormwater drainage capacity must be taken. The Smart Cities mission and Atal Mission for Rejuvenation and Urban Transformation (AMRUT) are great opportunities for several urban local bodies to plan the cities taking flood risks into account and put risk mitigation measures in place. Residential and commercial building owners could be incentivized to install green infrastructure options like rainwater harvesting systems, rain gardens, green roofs, permeable pavement so that impervious areas are reduced and rainwater will be able to infiltrate the ground easily. In addition to reducing flood risks, these systems store water for drier seasons and help in recharging groundwater. It is only prudent to invest in making our cities resilient so that when disaster strikes, we can bounce back to normal with minimum loss of life and property.
Along with the steps taken by government bodies, the general public will also have to keep themselves informed and avoid buying property in low lying areas and floodplains and increase permeable areas on their properties. Although it is acknowledged that risk can never truly be zero, the goal should be to minimize it as much as possible.
Mahima Rao is a certified floodplain manager and works as a water resources engineer in the US. Views are author's own.