Solving India’s Urban Flooding Crisis Isn't Just A Pipe Dream

Designing better storm water drain systems is critical to stop urban flooding.
Pipe and chamber drain systems have several advantages over box drains. Adopting the former will result in a robust network that reduces flooding and ‘ponding’ on roads, prevents potholes and contamination of storm water, reduces maintenance costs, and increases ground water percolation at source.
The views in the commentary are that of the authors.

Once a sporadic occurrence, urban flooding is now a continuous pandemic — from the Mumbai floods of 2005 to the 2015 Chennai floods, to the annual floods in Bengaluru, Hyderabad, Delhi, and other cities. A critical component to stop the flooding of roads, and preventing them from turning into rivers, and allowing for daily life to continue unhindered, is to completely overhaul the design of storm water drains.

A storm water drain across Hayes Road at Richmond Road, Bengaluru, which was redeveloped as a Tender S.U.R.E. road and has not been dug up since 2017 (Image courtesy of Jana Urban Space Foundation)

The current design of concrete ‘box drains’ is a failure on multiple counts and simply not fit for purpose. What we need instead is a ‘pipe and chamber’ system which can overcome all the shortcomings of the widely prevalent yet antiquated box drain. The pipe and chamber system is a modern global standard that is overdue for adoption by India’s cities, in policy and practice.

There are five challenges with box drains. First, it is difficult to maintain sufficient gradient of the drain, and it cannot be rectified once constructed. This creates either back flow or stagnation.

Second, box drains contribute hugely to the flooding of roads because water is expected to reach the drain on its own or horizontal pipes with insufficient gradients are expected to carry water from the road to the drain. These pipes often get clogged with silt and garbage and there is no way to clean them. The ‘ponding’ on roads further results in potholes and repairs, leading to cyclical expenditure. Bengaluru spent over Rs. 7,000 crores on pothole repairs between 2019 and 2022.

Third, box drains are almost always covered by loose slabs. Over time, some of these get removed, making them convenient spots for dumping and life threatening for pedestrians. Removal of garbage and accumulated silt involves cleaning the entire network every year, for which the state has no capacity or competence. More importantly, it is avoidable.

Fourth, properties adjacent to the drains often discharge their wastewater into the drains. Domestic and commercial wastewater is contaminated with faecal matter, detergents, oils, and chemicals that end up in our waterbodies. This is against public health and urban planning norms. Properties should harvest rainwater within their premises and connect their wastewater to either networked sewage or septic tanks within the premises.

Fifth, box drains do not provide for in-situ recharge of ground water.

On the other hand, the pipe and chamber system, which is part of Tender S.U.R.E. roads in Bengaluru, surmounts all these disadvantages. The system is designed to allow for easy maintenance of gradients, as precast pipes are fixed at slopes from chamber to chamber, minimising human error. The system is also designed at the road edge and not the property edge. The road is sloped towards the drain, evacuating water more speedily through catch pits with gratings, reducing ‘ponding’ and flooding. This then reduces the occurrence of potholes, negating the need for frequent repairs.

By design, it eliminates garbage almost completely as the system is not open. Inlets provided at every chamber have metal gratings that filter solid waste. Each chamber has a silt trap that can be cleaned every few years with far less effort than cleaning entire drains. A completely closed drain below the footpath is also safer for pedestrians as opposed to a partially or completely open drain. The system enables separation of storm water and wastewater, thereby reducing downstream contamination of water bodies. Moving the storm water pipe to the road edge also means the property connections do not go through the drain, allowing for ease of maintenance and reducing chances of leakage and contamination.

Finally, each chamber has provision for in-situ recharge with percolation pipes discharging a certain quantity of storm water into the ground.

This has precedence. More than 100 kilometres of Tender S.U.R.E. roads in Bengaluru use this system and do not flood during the monsoons. A recent monitoring and evaluation study on completed Tender S.U.R.E. roads showed that they did not ‘pond’ or flood during moderate to heavy rainfall. With no ‘ponding’, Tender S.U.R.E roads remain pothole-free, saving money and lives.

Back-of-the-envelope costing indicates a 30% higher capital expenditure for pipe and chamber systems. This is more than sufficiently compensated by savings in operation and maintenance of desilting and pothole repairs.

India’s cities can definitely solve the problem of flooding on urban roads in the next five to 10 years by enforcing mandatory adoption of the pipe and chamber system. Every new drain and all drains requiring major repairs must transition to this system, one by one. When all types of roads in all cities and towns of the country adopt this, it will result in a robust network that reduces flooding and ‘ponding’ on roads, prevents potholes and contamination of storm water, reduces maintenance costs, and increases ground water percolation at source and safety. The pipe and manhole, a seemingly innocuous innovation, could be transformational for India’s cities.

(Published under Creative Commons from Mongabay-India. Read the original article here)