Nature-based solutions a must for flood control mitigation

New Delhi
Mainstreaming nature-based solutions (NBS) for flood mitigation can help reduce flood stress by integrating conventional solutions with open areas, experts said, against the backdrop of an allocation of ₹2,500 crore for such projects under the 15th Finance Commission in July for seven most-populated cities of the country.
The National Disaster Management Agency (NDMA), which has approved the plans, will result in urban local bodies incorporating NBS projects among non-structural interventions, alongside conventional engineering solutions. Three of the largest cities, Chennai, Mumbai and Kolkata, will receive ₹500 crore each, and four other cities, Hyderabad, Pune, Bengaluru and Ahmedabad, will get ₹250 crore each.
Governments, especially at the municipality level, often lack the technical know-how and human resources to implement these solutions. Officials also said that standards for executing these NBS projects have yet to be set. “It is not that NBS alone will solve all flooding woes of our cities. Depending on the location, specific effective integration with hard infrastructure can make the entire system much more efficient,” said Krishna S Vatsa, an NDMA member involved in the approval process.
Vatsa said that with this push, the adoption of NBS will be further mainstreamed and state governments will be more forthcoming.
Besides the ₹2,500 crore corpus — officials say this may be insufficient — funding from central government schemes, such as Namami Gange Programme, Atal Mission for Rejuvenation and Urban Transformation (AMRUT), state government schemes and other sources should be explored for NBS projects, officials said.
‘Need of the hour’
Experts have advocated integrating conventional solutions, such as concrete drains, with open green areas, lakes and wetlands to reduce flood stress and reap co-benefits of groundwater recharge and reduction in urban heat island effects, simultaneously reducing overall costs and carbon footprint. However, the implementation of such nature-based projects has been majorly funded by non-governmental entities over the years.
Many nations in the global south vulnerable to climate change ramifications have made significant investments in such projects.
In China, in response to the July 2012 flash floods, the national government launched the Sponge City Programme for more than 650 cities. A study by the University of Leeds found that such a plan for Wuhan city was cheaper than a grey infrastructure-based solution by $600 million. Similarly, in Singapore detention ponds and a network of connected parks trap water during excess rainfall.
Amit Prothi, director general, Coalition for Disaster Resilient Infrastructure, said countries are now integrating NBS into their national climate strategies to enhance flood protection and derive additional environmental and social benefits. “In India, advancing data-driven decision making, integrated planning, robust governance and capacity building are key to scaling up NBS implementation. Given the pressing need for effective flood risk management, it is vital to explore how NBS can offer benefits to both people and nature.”
Lubaina Rangwala, programme head, urban development and resilience at WRI India, said recent floods that are not occurring in historically flood-prone regions can be attributed to poor urban planning that involved increased concretisation of natural ecosystems.
“It is great to see the importance of nature-based solutions being acknowledged by the NDMA. With this, we can hope that there is a greater realisation at state government and municipal levels,” she said.
“The next challenge will be how we can transition from small-scale interventions to bigger ecosystem-level restorations, be it for mangrove ecosystems, wetlands or rivers. Because, sometimes, the larger adaptation potential is lost while operating only at small scale of city or even smaller,” she said.
Sakthivel Beemaraja, a hydrologist developing drainage master plans for multiple Indian cities, said NBS were historically used and worked well until they were disrupted by unplanned urbanisation over the past few decades.
Citing the instance of Chennai, which has only recently adopted the concept of sponge city by having adequate open spaces and structures to trap water, he said: “However, there is a necessity to train officials at all levels so that they can double down on these efforts and there is adequate funding provided for these projects.”
Major works
Under plans approved by the NDMA, the Kolkata Municipal Corporation will create 8.65 hectares of blue zone (water body) and restore multiple existing water bodies to create a water storage capacity of 346 million litres.
Santanu Kumar Ghosh, director general of the sewage and drainage department, KMC said the civic body will dig ponds in multiple wards on the periphery of the city and a large pond will be created in the city core, near the Ballygunge pumping station. He said that a total of 13-14 pre-existing canals that are longer than 100 kilometres will be rejuvenated primarily in the southwestern fringe areas, such as Joka.
“The ponds that we will dig will have multi-purpose usage,” he said.
During excess rain, they will collect water to reduce the run-off and a buffer area will be planned, as an area of recreation. Throughout the year, ponds will also be used for pisciculture to generate employment and ensure upkeep of the pond, and further, 54 eco-block percolation wells will be set up in the city that can recharge groundwater during excess rainfall by decreasing the run-off, he said.
In Bengaluru, municipal commissioner Tushar Girinath said NDMA approved plans to reclaim encroached land surrounding lakes to increase their buffer zone and work on linking and desilting the lakes for easy water transfer among them. He said the civic body will implement recommendations from experts at the Indian Institute of Science (IISc) and Indian Institute of Technology (IIT) Madras to make the lake network more resilient.
TV Ramachandra, coordinator at Centre for Ecological Sciences, IISc, said NBS is the only hope. “The solution to flooding is to re-establish interconnectivity among lakes and make the entire network of lakes and stormwater drains free of encroachments,” he said.
The flooding problem has compounded in recent years as the civic body concretised stormwater drains, which did not allow groundwater seepage and led to increased run-off “against the principle of nature”, he said.
In Mumbai, the local body is rejuvenating the Mithi River — over the past few decades, it turned into a sewer — by creating a holding pond in Dadar. So far, 95% of the widening and deepening of the Mithi has been done, and 85% of the retaining wall constructed.
In Chennai, two such sponge parks at Mathur and Tiruvottiyur will be set up with the funds in line with 50 such planned facilities by the Greater Chennai Corporation. These funds will also be used to dredge the Korattur surplus channel and rejuvenate water bodies, such as Manali, Sathangadu and Madhavaram in the northern periphery of the city, officials said.
Ahmedabad, similarly, is working on implementing a similar exercise at the community level, by setting up “Khambati Kua” — traditional percolation wells — on empty and government plots, prioritising low-lying areas.
“Our target is to eliminate waterlogging by interlinking lakes across the city. So, if one lake fills up, it automatically gets transferred to the other lake so that a balance is maintained,” Ahmedabad Municipal Corporation deputy municipal commissioner Mirant Jatin Parikh said.