With every urban washout the cry goes up for desilting the drainage system and to implement water harvesting. Desilting does take place but is that really the solution? A closer look is warranted to understand the phenomenon dogging Indian cities and even cities abroad with increasing frequency and intensity.
The list of affected cities is getting longer with Hyderabad in 2000, Ahmedabad in 2001, Chennai in 2004, Mumbai in 2005, Surat in 2006, Kolkata in 2007, Jamshedpur in 2008, Guwahati and Delhi in 2010, Srinagar in 2014 and Chennai in 2015. In 2016, Bengaluru and, to a lesser extent, Gurugram have already been victims. Waterlogging is the order of the day, setting up mind boggling traffic snarls even in modest rains.
The loss of life and property apart, urban areas contain vital infrastructure that can affect regional economic activity, result in epidemics and weaken building foundations as a result of prolonged waterlogging.
Storm water drainage systems in the past were designed for rainfall intensity of 12–20 mm. But the Indian Institute of Tropical Meteorology, which analysed heavy rainfall events during the period 1970-2006, says that there is an increasing trend of heavy rainfall (≥125mm) in Mumbai, Delhi and Chennai.
The flooding does not affect all parts of the city equally. Cities urbanise existing watersheds and hence it is imperative that town planners respect the topography. Does one ever hear of old core towns such as Shahjahanabad or any cantonment or Civil Lines getting flooded — this is due to their prudent siting on easily drained high ground. Look at the old parts of Srinagar or of Chennai — they were not the ones to suffer. When city planners compromise on basic principles and fail to respect the topography and end up serving real estate interests, the flooding problem becomes inbuilt into the city structure.
It is reported that the marshlands of Chennai, spread over more than 5,000 hectares, have been reduced to a 10th of their original size, leading to significant loss of flood moderation capacity. A similar situation affects Srinagar where posh colonies have been built in the flooding zone of Dal and Wular lakes, or Mumbai’s wetlands near Sewri that have been filled as solid waste disposal sites.
The structural problem becomes aggravated with every inch of space being paved over leaving no space for water percolation into the ground. Thus, the surface runoff from hard surfaces increases As a result, flooding occurs quickly due to faster concentration and greater flow.
The National Disaster Management Authority noted in its guidelines for urban flooding laid down in 2010 that “the average rainfall in Indian cities far exceeds the capacity of drainage system. The designed system capacities do not work due to poor maintenance. Encroachments are another big problem in many cities and towns. Consequently, the capacity of the natural drains has decreased, resulting in flooding. Improper disposal of solid waste, including domestic, commercial and industrial waste and dumping of construction debris into the drains also contributes significantly to reducing their capacities”.
The NDMA went on to lay 25 guidelines of which point 15 states that “low-lying areas in cities have to be reserved for parks and other low-impact human activities”. However, these sensible guidelines have found no resonance with the authorities despite repeated events.
The case of Gurugram
The case of Gurugram is instructive. The converse of waterlogging is groundwater recharge. Gurugram is a bowl with the floodwaters having only a single route of exit, which is via Badshahpur Drain and general surface runoff to the Najafgarh Jheel and through Najafgarh Drain to Yamuna. The Najafgarh Drain is an artificial construct of 1865 vintage with a negligible gradient of less than 1 m in a kilometre and thus, if the Yamuna waters are high, as they often are in the monsoons, then the waters of Najafgarh Drain do not flow, and in extreme cases can back flow. Here, the Najafgarh Jheel comes into play and acts as a holding reservoir for flood water of Gurugram.
Unfortunately, Jheels and depressions have been targeted for their real estate value by both the real estate lobby as well as by the cooperative town planning department, which has neglected the basic canons of urban planning. Thus, in Gurugram, the town planning department has earmarked several sectors within the 100-year high flood level (HFL) zone of the Najafgarh Jheel. And these sectors will be subjected to inundation in due course.
The State Environmental Impact Assessment Authority of Haryana [SEIAA] is also to blame in allowing building activity in this area with the injunction that "plinth level be kept out of 100 year HFL of the Najafgarh Jheel". The SEIAA does not bother to state the 100-year HFL while the builders conveniently respond that they would observe the undefined 100-year HFL. The SEIAA may be asked whether by keeping the plinth level out of the 100-year HFL of the Najafgarh Jheel would it be acceptable if buildings and people were marooned, lives endangered, foundations weakened as a result of prolonged waterlogging, expensive equipment and investments and automobiles ruined?
The Central Ground Water Board has noted the Najafgarh Jheel as an excellent groundwater recharge zone. The National Capital Region Planning Board has in a major study earmarked the Jheel as a groundwater recharge zone and in fact the Haryana government has a policy whereby waterlogged farmlands are to be compensated with Rs 20,000 per acre. This would be more than compensated by the 15 MGD water availability for a water-starved so-called smart city. The original Jheel spread was vast during floods, extending 145 to sq km during the 1958 floods, visited by Siberian Cranes — even as this is written the remnant Jheel is being visited by the Greater Flamingos. Can we look beyond land values and towards eco-system services for our own sustenance at retaining a spread of just 4 sq km.
What does Gurugram need to do now? Depressions not only moderate local flooding but also nourish aquifers. To compensate for the loss of depressions, the 'smart' city needs to abandon colonisation of low-lying lands of Sector 36 B and 101 and create large Jheels instead to which the surface runoff can be directed by gravity or pumping. The newly-created Jheels can remain topped up with tertiary level treated effluent for enabling round the year recharge. Najafgarh Jheel needs to be declared a natural conservation zone up to the 100-year HFL. That would mean no construction within the HFL.
All stormwater drains need to have their beds de-concretised so as to enable percolation of surface runoff and quicker clearance of rain waters. Unfortunately, engineering agencies find greater benefits in sealing and lining drains just as Badshahpur Drain is being illogically concretised right up to Najafgarh Jheel. The city also needs to unseal its paved surfaces, both along public streets as well as within private compounds (certainly institutional ones) and replace the same with porous paving to absorb rainwater and reduce waterlogging.
With these measures and three large Jheels (Najafgarh, Sector 36 B and Sector 101), Gurugram would be better prepared for the monsoon as well as for summers and be well on its way to be a truly smart city.
The author is Principal Director, Natural Heritage Division, Intach
First Published On : Aug 16, 2016 13:05 IST