Stormwater drains: Do we even know where they are?

by A Special Correspondent

It seems that the British left us not only the railways, the postal system, education syllabi, jurisprudence and democracy but also, for Chennai, an 800-km underground stormwater drain of a unique arch design built of brick and mortar that has stood the test for over a hundred years.

The appalling part of the story is that we have not been able to maintain this gift in good repair because we do not – yes, believe it or not – we do not know how it functions and flows nor do we have any map or record of its network. Locations of this drain is known only “anecdotally, passed on from one generation of Corporation employees to the next”. Repair and restoration is carried out only when damage is located accidentally.

In the underground of this vast City, as in many others, there is a complicated network of a variety of pipelines, cables and installations comprising stormwater drains, sewage pipelines, water supply lines, power supply cables and telecom cables. Added to these we now have the underground portions of the Metro network. There being no central agency to coordinate and ensure proper positioning of different underground installations, there is a rash of damages to these vital lines from installation or repair work of one service provider or the other. A related consequence is that in trying to get the clearance of different service agencies, many essential construction projects like roads, flyovers etc. get unduly delayed. The delay of Phase I of the Metro alone has led to over-run of cost and time that may render its originally envisaged scale inadequate by the time it is completed.

Interruption to services, inter-mixing of water and sewage lines, flooding in times of even moderate rains, disease-causing water-logged conditions, and delays of public utility projects are characteristic of metropolitan Chennai. The longer this goes on the more complex becomes the problem, the more time and money it takes to correct it, the more intrusive becomes the corrective action and, finally, the more reluctant the authorities become to touch a problem that has become too large and complicated. The Chennai city rainwater drain project has now reached this ultimate state.

There are several disturbing symptoms in the stormwater drain problem. It is said that there is no map of this ancient installation to be able to undertake periodic preventive maintenance. That it has been allowed to remain this way is poor reflection of successive administrations. It is difficult to believe that there is no way to, by employing scientific devices and test excavations at different points, guess its layout nearly accurately.

A degree of helplessness is evident when it is said that telecom and electric lines criss-cross the drains and civic body engineers in charge of maintenance of the drains are “unable to regulate these projects”. Would not a central coordinating authority be able to facilitate time-bound clearance of repair and installation projects duly secured against any collateral damage?

The British arch model of the underground drain lines has shown tremendous resistance to time- and flood-related assaults. Yet, we are told, it is advisable to replace them, whenever damage occurs to the arch, with specially designed RCC structures. Designing the RCC structure, adapting the arch feature, is unlikely to be beyond the capability of our structural engineers. The RCC components should be such that they are modular and replaceable as spare parts. This work should be completed on high priority before the next flood fury strikes us as it does predictably every North-East Monsoon.

Without proper configuration of the stormwater drain lines and, more importantly, of critical junctions and major inlet and outlet points, planned development and preventive maintenance work is not possible. Also of concern is the citing of instances of repairs carried out by unscrupulous contractors, probably abetted by supervising officials, where they are known to merely plaster the damaged arch top and place a flat RCC slab on top of it to give an appearance of repair/replacement. To overcome this problem, the RCC modular components to be designed should be amenable to periodic inspection.

If only 22 damaged stretches of the current drain line need as much as Rs. 3000 crores, we can be excused for inferring that the damage is serious and that major expansion and renovation cannot brook delay. The work calls for large investment and could be quite invasive of public convenience. Fund availability is reported to be the problem. Funding through multi-lateral agencies and/or through issue of bonds are within reach and, therefore, it is political will and cooperation among succeeding political dispositions of government that is the problem.

Unlike the old times when open soil was of a much higher proportion to paved areas in the city, today the emergence of large buildings and paved areas leaves very little surface area for flood water to seep down, causing it to swell above. Fortunately, in Chennai there are still large open areas to allow rainwater to percolate into the soil. However, indiscriminate constructions and settlements, sometimes with official connivance, in areas covered by lake, ponds and river-sides create artificial flooding. Stormwater management ponds are recommended to be artificially created in cities as a flood control measure. We have abandoned even our natural stormwater ponds. Settlements occupying water-holding areas must be reversed and the original water-containing bodies restored with proper dredging.

A holistic and systemic approach is needed to control flood situations. It is not just the extent of drain network and coverage that is critical but also the strategic location of collection points and identification of canals and rivers as outlets into the sea or to other natural water bodies or artificially created stormwater management ponds. The outlet canals and rivers may need large scale desilting to be able to convey the stormwater into the sea. Several methods are used in cities elsewhere in the world, to cope with large downpour. Simple, cost-effective practices have been adopted to reduce the load on the drain system. Open areas and rain gardens allow stormwater to seep directly into the earth. Permeable pavements in driveways, parking lots and pedestrian walks allow stormwater to infiltrate into the ground. Stormwater pipelines are designed “to be leaky” to support groundwater recharge. Infiltration chambers within the system enable buried pipes to hold back stormwater and release it into the ground. All this calls for seeking knowledge on how similar problems are solved in advanced countries through technology and innovative practices.

A basic question remains. If 800 km of stormwater drain was meant for a population of about 5,00,000 including allowance for a growing population and expanding city over a future 20-30 years, how is 1894 km enough for a population of 9,00,000 spread today over 426 square km and not overlooking future growth? In 2010-11, the Ministry of Urban Development surveyed stormwater drains in the country and found average coverage was below 50 per cent – a level, according to the Ministry, that called for “immediate action for improvement”. Revamping the stormwater drains in Chennai could be a major undertaking, stretching over more than a single electoral term. This task should be tackled at the earliest by successive governments rising above political differences.

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