Urban flood management in Delhi's changing climate

Evidence on increasing risk should be tipping scale for the government

At the COP21 talks in Paris, Chennai had been brought up as an unfortunate exhibit of the perfect storm triggered by climate change and indiscriminate urban planning. While India is already driving the conversation about the global effort to climate-proofing, hopefully the impact of this latest flood will also force its leadership to sit up and take notice of the urban problems they've put off for far too long. Till such time, the effects of urbanisation and climate change will continue to converge in dangerous ways.

Delhi's urban sprawl, for instance, has been expanding much faster than its drainage infrastructure could catch up. All this is exacerbated by its often impetuous approach to urban planning.

Increased storm frequency and intensity related to climate change are exacerbated by such local factors as the growing occupation of floodplains, increased runoff from hard surfaces, inadequate waste management and silted-up drainage.

Climate scientists too have been warning about rapid unplanned urbanisation - expanding both outwards and upwards, extinction of water bodies, deforestation and growing encroachments on the Yamuna floodplains shaping up to be a tinderbox.

Environment watchdogs say the Capital's vulnerability has to do with both its unplanned development as well as its location. A UN panel report on climate change in April 2014 placed Delhi among three of the world's largest cities that are at high risk of floods; the other two being Tokyo and Shanghai.

The report says river floodplains need to be secured to be able to adapt to extreme weather and recommends setting aside buffer zones along rivers instead of "hard defences" like channelisation or dams. AT A GLANCE

• 1,484 sq km Area cover of Delhi
• 11,297 persons per sq km Average population density
• 4.5 million Slum-dwellers without sewerage system
• 670 mm Average rainfall received, of which 75% is during July, August & September
• 800 Water bodies facing encroachment, dumping of waste
• 8,360 metric tonne Total solid waste generated per day. In addition to this, 500-600 million gallon sewage is generated in the city each day

> Storm-water drainage comprises roadside surface drains of 1,695 km, 22 drains outfalling in River Yamuna

Experts added that floods in Delhi are not nature's doing but invariably the irresponsibility of the authorities. This is clear from the recurring phenomenon of floods in Yamuna and flooding of city's roads from choked drains.

The city has, in the past, witnessed floods of various ferocity in the Yamuna and the Najafgarh drain system. The Yamuna crossed danger level (fixed at 204.83 m) six times since 1978. The peak level of the Yamuna at two and a half metres above danger level was on September 6, 1978. The Yamuna breached its danger level again in 1988, 1995, 1998, 2010 and 2013.

Moreover, Delhi has experienced major floods in 1924, 1947, 1976, 1978, 1988 and 1995. "Delhi has two different but related sources of flooding. One, the floods in the river on which the city stands and the other is urban flooding from the city's inability to harmlessly drain away its flood waters to the river. So, while the river may flood, yet there may be little or no rain in the city, as was seen in 1995. Or, heavy rains in the city might create urban flooding but little or no floods in the river," said Manoj Misra, convener, Yamuna Jiye Abhiyaan.

The flow of the Yamuna within Delhi is, by and large, influenced by discharge from the Hathni Kund barrage in Haryana, 250 km upstream. In the event of heavy rain in the catchment area, excess water is released from Hathni Kund. Depending on the river flow level downstream, it takes 48 hours for the Yamuna level in Delhi to rise. The rise level also cause a backflow effect on the city's drains. The city also experiences floods due to its network of 22 major surface water drains, sadly now sewage drains.

Environmentalists have been raising hackles over rampant land use change of the Yamuna floodplains in Delhi. Construction of the Akshardham Temple and the Commonwealth Games (CWG) Village on the Yamuna riverbed are examples of construction being allowed through land-use change.

Besides, the storm-water drainage network has been compromised through solid waste and sewage dumping, encroachment and concretisation - a clear case of inviting disaster.

Himanshu Thakkar of the South Asia Network on Dams, Rivers & People said there are five main reasons which make Delhi prone to floods - depletion of water bodies, deforestation, increase in concretisation, climate change and encroachment on the Yamuna catchment.

Experts added Delhi used to have a little over 800 water bodies but a majority either vanished or were encroached on. "The way the city has invaded its floodplains in the form of advance bunds and raising of structures like Akshardham, CWG village, Metro and bus depot, a Chennai redux is more than likely," Thakkar added.

Delhi is currently in the process of developing a storm-water drainage master plan, with the assistance of IIT Delhi. The plan is intended to be completed by February next year. Misra said the plan must rethink its entire strategy in the wake of floods in Srinagar in 2014 and Chennai more recently. The government must be willing to implement all the recommendations of the said study, howsoever extreme or unpleasant these might appear.

The National Disaster Management Authority (NDMA) has mapped the city's flood zones. Areas have been classified into 13 zones, based on flooding risk in relation to incremental rise in water level of the Yamuna. These cover a range from 199 m to 212 m level of water in the Yamuna. This map covers parts of north Delhi on the west bank of the Yamuna and almost the entire trans-Yamuna area on the east side. NDMA officials in charge were not available for comment. An official in-charge of maintenance works in the Delhi headquarters of the public works department could also not be reached for comment.

Although the unprotected flood-prone area - 1.7 per cent (or 25 km) towards the south-east and five per cent (or 74-sq. km) in the north-eastern parts of the city - is protected by sand embankments every year, the water level in the Yamuna rises above the danger mark and a large population often has to be evacuated to the top of the bunds.

A significant phenomenon on the rise in recent years is local flooding. Urban areas are characterised by a high area under impervious surfaces (roads, pavements, houses, etc). This results in flash floods in the low-lying areas even after moderate precipitation. Since the river is already flowing at a higher level within its embankment, the water gets choked in the city areas and it takes several days to mechanically flush it out. Similarly, during the past few years, flooding due to the city's 18 major drains has become a recurrent nightmare.

Already under pressure of the city's effluent discharge, these drains experience reverse-flow from the Yamuna in spate, and, as a result, tip their banks, flooding neighbouring colonies.

As the non-absorbent city lives with flood risk, building climate change resilience through bottom-up adaptation to flood risk is the way forward. For that, rapid urbanisation requires the integration of flood risk management into regular urban planning and governance.

UNJUST WATERS: 4 MAJOR FLOODS

• 1977: Najafgarh drain experienced heavy floods due to discharge from the Sahibi River. The drain breached at six places between Dhansa and Karkraula, marooning a number of villages in Najafgarh block. Six human lives were lost due to house collapse. 14 persons died in a boat mishap. Crop damage was estimated at Rs 1 cr
  

AVERAGE RAINFALL: 12.3% above normal

• 1978 (Sept): River Yamuna experienced a devastating flood. Widespread breaches occurred in rural embankments, submerging 43 sq km of agricultural land under 2 m of water, causing total loss of the kharif crop. In addition to this, colonies of north Delhi, namely Model Town, Mukherjee Nagar and Nirankari Colony suffered heavy inundation, causing extensive damage to property. The total damage to crops, houses and public utilities was estimated at Rs 17.61 cr
  AVERAGE RAINFALL: 18.9% above normal
   
• 1988 (Sept): Yamuna experienced floods of very high magnitude, flooding many villages and localities like Mukherjee Nagar, Geeta Colony, Shastri Park, Yamuna Bazaar and Red Fort area, affecting approximately 8,000 families
  

AVERAGE RAINFALL: 23.5% above normal
 

1995 (September): Yamuna experienced floods following heavy runs in the upper catchment area and the resultant release of water from Tajewala (now Hathni Kund) water works. The flood rendered approximately 15,000 families homeless
AVERAGE RAINFALL: 10.6% above normal