Storage capacity and rainfall pattern in the reservoirs in Chennai from 2015 to 2019

In the month of May, June and July, Chennai city usually experiences the searing heat due to the summer season. A decade ago, even though the temperature was as high as 38°C – 45°C (Highest recorded – 45°C in 2003), drinking water supply for the city was not disrupted in the way it experienced in the summer of 2019. The well-known reason is there was more greenery in every 100 to 200 m of vicinity. Hence, there were chances of mild rainfall even in summer. In May and June 2019, the highest temperature recorded was 43°C. This is due to large-scale urban agglomeration and developmental activities. Since the reservoirs’ stock got exhausted and there were no more left even for the survival of aquatic organisms, water was being extracted from quarries and agricultural wells. Several hardships for the general public meant that there was delay in each and every routine activity both in residence and in workplaces.

Based on Oceanic Nino Index (ONI) data, it is evident that 2015-16 is a very strong El Nino year and 2018-19 is weak El Nino year. Also, 2016-17 and 2017-18 are weak La Nina years (Null, 2019). As per the World Meteorological Organization (WMO) report, hotter years are driven by increased emissions of heat-trapping carbon dioxide. The earth’s climate has been warmer and every fraction of a degree of warming makes a difference to human health and access to food and freshwater, to the extinction of animals and plants. Hence 2015-16 experienced heavy rainfall and copious water was stored in all the reservoirs and served for late 2015, throughout 2016.

Water supply woes

As per the Chennai Metro Water Supply and Sewerage Board (CMWSSB) data, the city receives about 985 million liters per day (mld), as against the required amount of 1200 mld. Despite drought and other challenging conditions in summer, the city requires 550 – 600 mld of water till the North East monsoon, which usually sets in during October. After a dry spell of six months starting from December 2018, the city received mild rainfall in the third week of June 2019. The city, as always, was not prepared to handle the situation of water-logging and choking of drains. In spite of repeated insistence for Rain Water Harvesting in the residences and official buildings, there were instances of rain water being wasted in the sea. Also, it can be identified that during summer the reservoirs are almost bone dry to zero in the water level in the reservoirs. This scarcity can be attributed to the lack of steps for desilting of lakes, cleaning of lakes, removal of water hyacinth and debris in water bodies other than these reservoirs. Had the clearing up of choked drains been carried out, the situation of water logging for days together would have been prevented.

2015-16, being a very strong El Nino year, the city experienced heavy rainfall in the first week of November. Throughout November the rainfall recorded was around 350 – 500 mm in and around the city areas. A study from IISc shows that on December 1, clouds were stationary over Chennai due to a phenomenon – ‘upstream blocking’ (Phadtare, 2018). Therefore, they were stationary throughout the day and gave continuous rainfall resulting in massive flooding. This resulted in the swelling up of all the reservoirs and subsequent inundation of all the low lying areas.

Usually in the months of May to August, the storage capacity in all the four reservoirs becomes very negligible and the government authorities rely upon alternate sources such as quarries and wells for water. The following tables show the storage capacity (quantity in mcft) of all the five reservoirs from 2015 to 2019 from May to August, which is a very lean period and from September to December, the period of North East Monsoon. From tables 1 and 2, it is evident that storage of water differs based on the rainfall. Table 3 and 4 shows the rainfall pattern in the city through the aforementioned eight-month period.

Table 1: Storage level of reservoirs from May to August

t1copySource: Chennai Metro water Supply and Sewerage Board website

Table 2: Storage level of reservoirs from September to December

t2

Source: Chennai Metro water Supply and Sewerage Board website

Table 3: Rainfall in the reservoir areas from May to August, from 2015 to 2019 (in mm)

t3
Table 4: Rainfall in the reservoir areas during North East Monsoon period, from 2015 to 2019 (in mm)
t4

The above tables show that there was scanty rainfall during the period of May to August in all the four years. This may be due to heat convection and atmospheric instability.

In 2016, Tamil Nadu experienced three tropical cyclones – Roanu, Vardah and Nada. In case of Roanu and Nada the damages were minimal and there were no fatalities. Cyclone Vardah, which crossed close to Chennai on 12/12/2016 uprooted nearly 1 lakh trees in Chennai and its suburbs and caused extensive damage to electric poles and other infrastructure.  In 2017, although the city experienced a normal monsoon, the southern city of Kanniyakumari bore the brunt of cyclone ‘Ockhi’ causing fatalities and damages to a tune of $ 155 million (Down To Earth, 2017, The New Indian Express, 2/3/18, Deccan Chronicle, 10th and 20th December 2017).

Table 5 shows the storage level during the last week of August in all the reservoirs. It shows that other than Veeranam and Poondi, there is no water in the Cholavaram, Redhills and Chembarambakkam reservoirs.

Table 5: Storage level in the reservoirs in August 2019

t5

As per IMD report, for the period June 1 to July 24, 2019, Chennai received close to 221 mm of rain. Much of it has been wasted as run off through the drains. In many of the buildings, rainwater harvesting system is only a namesake pit dug out, which does not harvest the rainwater properly. Most of these pits form a cesspool and stagnate everywhere leading to breeding place for mosquitoes. Due to the clayey nature in most parts of the city, recharge structures should take the water down to 300 – 400 feet to improve the ground water table (The Times of India, 26/7/19, pg. 6). Though the rainfall received in this period is in short spells, there was good rainfall over the lakes and reservoirs that supply water to the city.

The following table shows the water level in a few areas in Chennai in 2018 and in 2019.

t6


This increasing depth in search of water may be due to rampant drawing of groundwater with larger bores and lack of awareness about the installation of full-fledged rainwater harvesting structures. A few areas such as Valasaravakkam, Virugambakkam, Alwar Thirunagar, Porur and parts of Mylapore have sufficient groundwater. In the recently concluded ‘Water Conclave’ (23rd and 24th August, 2019 in Chennai) organized by ‘The Times of India’, it has been suggested for installation of water meters, crimes and punishments for illegal activities and encroachments in the water bodies, effective methods for rainwater harvesting, use of latest ultrafiltration techniques that minimizes the reject water for every one litre of filtered water etc (The Times of India, 25/8/2019). Also, it has been highlighted that even though there was moderate rainfall in the 2nd and 3rd weeks of August, the groundwater recharge was very low when compared to 2018.

Voluntary initiatives by citizens

There have been instances of residents of particular locality raising money of their own to desilt the nearby waterbodies or to construct a recharge well to make use during summer. For e.g., residents of Vengaivasal near Medavakkam have raised money to construct a recharge well in Periyaeri lake through crowd-funding. The well is now used to supply water to the locality (The Hindu, 27/8/2019). Another report mentions that under the guidance of ‘The Rain Centre’, two apartment complexes in Mandaveli sorted out the problem of salty groundwater and high TDS figures by constructing filter chambers to boost the storage capacity in a cost effective way (The Hindu, 14/7/2019). Another report carried by ‘The New Indian Express’ (13/8/2019) states that residents cleaned nearly 4.5 tonnes of garbage from Velachery lake. The original size of the lake is 255 acres, which has shrunk to 55 acres, which itself is a contaminated waterbody. If this is the fate of Velachery lake then we could imagine the quantum of plastic wastes and construction debris over Pallikaranai wetland, which, once was 14000 acres, which has shrunk to 1500 acres. A gated community on 200 feet Radial Road, has gone green drive by segregating waste, composting and generating manure. In addition, the apartment complex has installed 10 kW solar panels on the rooftop and has been tapping solar energy since 2018 (Citizen Matters, 24/4/2019).

Fig 1

Source: ‘The News Minute’, 25/7/19, online edition

Why there is no groundwater recharge

  • Indiscriminate dumping of plastic, glass and other inert materials everywhere.
  • Lack of knowledge about keeping the city clean, as we do it in the home.
  • Digging deeper in search of water. For e.g. consider what will happen if there are holes for every 100 – 150 m for these reasons – in search of water, for underground sewerage system, for laying underground cables, for metro rail works etc. Unlike Tambaram or any other suburb where, the soil is rocky, most part of the city has clayey soil, which is a bit loose.
  • Rampant drawing of groundwater with broader bores – 10 inches to 12 inches and from 400 feet to 800 feet.
  • Seawater ingress / intrusion have lead to newer and newer bore wells in close vicinity in search of water.

Fig 2

Source: ‘The Times of India’, 8/7/19, pg. 3

The image shows the negligible rise in groundwater level in few parts of city. Also in areas such as Adyar, Royapuram and Perungudi, due to the presence of alluvial soil with mixture of clay, silt and sand helps the water percolate down easily.

Conclusion

The city receives rainfall not only from North East monsoon, but also during summer, of course, sparsely. Yet, due to lack of awareness about conservation of water, bulging population in the suburban areas (city areas are already saturated) and growing demand for construction activities has lead to water scarcity. As per NITI Aayog report, Chennai, along with 21 other prominent cities will run out of groundwater in 2021. ‘Day Zero’ is a term coined for Cape Town, South Africa when it experienced drought induced water scarcity in 2018. If the current trend continues for Chennai, it would be unfortunate that Chennai would witness the same in 2025. Although initiatives by individuals, residents of apartments and volunteers are taken for conservation of water, better co-operation and coordination is the need of the hour. Considering the ballooning population of both urban and rural areas, if the city needs to be maintained well, stricter laws and harsher punishments for encroachments and offenders are enforced.  Hence, it is up to the Chennaiites to realize and spring into action – to save water.

References

  1. Null J (2019). El Nino and La Nina years and Intensities based on Oceanic Nino Index (ONI). Golden Gate Weather Services.
  2. Chennai Metro Water Supply and Sewerage Board (CMWSSB) data of storage levels of lakes on the first day of the month.
  3. Phadtare J (2018). Role of Eastern Ghats Orography and Cold Pool in an extreme rainfall even over Chennai on 1 December 2015. Monthly Weather Review, 146(4), 943 – 965.
  4. https://www.thenewsminute.com/article/has-mushrooming-borewells-caused-chennai-s-groundwater-levels-plummet-106087
  5. Down To Earth – ‘Death toll in cyclone Ockhi touches 22; extremely strong winds lash Lakshadweep’, Dec. 3, 2017.
  6. The New Indian Express. 191 fishermen to be construed dead during Ockhi cyclone in Tamil Nadu, March 2, 2018.
  7. Deccan Chronicle. Cyclone Ockhi damage may run to Rs 1000 crore in Tamil Nadu, Dec. 10, 2017.
  8. Deccan Chronicle. Tamil Nadu government seeks Rs 9302 crore for cyclone Ockhi relief. Dec. 20, 2017.
  9. The Times of India. Showers slow depletion of water table in Chennai, July 8, 2019.
  10. Chennai Metro Water Supply and Sewerage Board website – https://chennaimetrowater.tn.gov.in/
  11. ‘To end crisis, call for action from people’. The Times of India, August 25, 2019.
  12. Pallikaranai apartment shows the way towards greener living. Citizen Matters, April 24, 2019.
  13. ‘Here is how they got rid of ‘salty’ and ‘muddy’’. The Hindu, July 14, 2019.
  14. ‘Voluntary efforts to restore lakes get WRD approval’. The Hindu, August 27, 2019.
  15. ‘Residents remove 4.5 tonnes of garbage from Velachery lake. The New Indian Express, August 13, 2019.

Dr. Srinivasan Gopalakrishnan


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