#RainWaterChallenge is a Tamil Nadu govt initiative to encourage rain water harvesting in buildings
#RainWaterChallenge is a Tamil Nadu govt initiative to encourage rain water harvesting in buildings

Rain Water Harvesting Challenge In TN: Will It Work? 

As the Chief Minister and other ministers call for residents to conserve water, experts say the model is flawed 

Cibe Chakravarthy

Cibe Chakravarthy

Tamil Nadu Chief Minister Edappadi K Palaniswamy might be feeling rather cool about the Rain Water Harvesting (RWH) Challenge that he issued as a video on Thursday. But experts feel otherwise.

His colleague, SP Velumani, Minister for Municipal Administration and Water Supplies, did the same earlier this week.

Velumani said that even a house with a roof area of 200 square feet can help a family harvest enough rain water for use throughout the year.

Experts though feel the idea is not that cool after all. Rain water harvesting, they say, is not about the rooftops, but about the ground beneath the buildings.

But first, here is a look at the numerous drives launched by the state government to promote water conservation at home.

Conserving Water

Tamil Nadu is in the fourth year of severe drought with Chennai city suffering more than the other districts.

The south west monsoon will be over by next month and the state has so far received brief spells due to depressions in the Bay of Bengal. In recent days, the western part of the state has witnessed heavy rains due to the revival of the south west monsoon.

It is at this juncture that the state has launched the RWH drive keeping in mind the north east monsoon due in October.

A website has been launched by the state government to guide residents on how to complete the RWH challenge through self-education.

The Chennai Corporation also launched Project Nimbus last month to ensure that two lakh buildings across the city were rain ready with proper RWH structures in place.

Project Nimbus has a target to ensure RWH in 2 lakh houses before September
Project Nimbus has a target to ensure RWH in 2 lakh houses before September

Is RWH The Responsibility Of Every Individual?

“Every citizen should implement the (RWH) scheme to ensure water availability for the next generation,” said Chief Minister Palaniswamy in the video.

The state-wide drive seeks to inspire every household to invest in RWH structures making water conservation the responsibility of the individual.

The messaging is that the key cause for water scarcity is the lack of the citizen’s attempt to construct and maintain rainwater harvesting structures.

But is that true?

Let us say, for instance, if Chennai city’s households take up the challenge and build RWH structures, will it recharge the aquifers of the city?

Academics and field experts do not agree.

Professor L Elango who is with the Geology department of Anna University stated in a conference last week - “We are blessed with gondwana or cretaceous shale formation which is not really favourable for recharge.”

Cretaceous shale is a type of soil that is not conducive for recharge of the ground water table. Water percolates very slowly and most of the annual rainfall does not reach the water table.

Elango said that RWH structures such as recharge pits or drains are not one-stop solutions for all water woes.

“If you want to plan for rain water harvesting it has to be done by real experts like KRG. If you go by the mandatory norms of the government, it will not meet the purpose and would only exist on paper,” he added.

KRG is a research institute in Gujarat. They are an internationally recognised technical team who design RWH models.

Experts recommend such institutes rather than referring to self-help websites.

TN Water Wise, the website claims to debunk several myths associated with RWH. One myth among them that RWH is expensive and hard to maintain.

TN Water Wise says that RWH is cost effective and easy to maintain
TN Water Wise says that RWH is cost effective and easy to maintain

But maintaining RWH structures is not a cheap affair.

“Geologically speaking, Chennai city is not favourable for ground water recharge. It can be done but it needs great care and money,” said Elango.

But why is it expensive to maintain the RWH structure?

Percolation pits and shafts get clogged as silt enters the structure. As a result, recharge decreases year after year.

The recharge efficiency would reduce by 20% after the first year, 50% after the second year to become defunct the next year.

“During heavy rains, water would be gushing out of the recharge pit and that is a hard fact,” said Elango, referring to the percolation pit and shaft model that is propagated as the common RWH structure in Project Nimbus of the Chennai Corporation.

The Lede had earlier reported that harvesting rainwater does not add to the borewell but to the aquifer, and technical reports are clear that ground water recharge occurs differently in different terrains.

Alluvial soils found along the coast are porous in nature, while clayey soils found in the central and southern parts are sticky and nonporous.

As a result, the coastal area can absorb and store more water compared to inland areas.

So RWH cannot be adopted as easily as it is projected to be. It is clearly a hydro-geological issue and demands expertise.

The state though prefers to simplify the equation by recommending RWH as a single solution to address the water woes of every household.

There Was Never A Single Solution

Individual attempts definitely must be to direct storage of rain water in the household.

From a small storage tank to an underground sump, there are a number of individual choices which can preserve water for future use.

The state on the other hand has a responsibility to increase the water storage capacity of the city.

The Geology Department at Anna University has been studying the Chennai basins over the past decade to arrive at a feasible model to bridge the demand–supply gap in water resources.

The team found that recharge structures such as percolation ponds and check dams along the major rivers Araniyar, Kosasthalaiyar, Cooum and Adayar would contribute to ground water recharge in a big way.

Percolation ponds are water harvesting structures built across rivers to facilitate infiltration of water into the soil.

However, a 2017 Central Ground Water Board report on Aquifer Mapping and Ground water Management has recommended construction of 23 check dams, 166 nala bands, 372 recharge shafts and 273 ponds in the Over Exploited and Critical firkas of the Chennai aquifer system.

Map showing city’s central and southern part less favourable to recharge. Map includes Chennai, Tiruvallur, Kanchipuram and Vellore
Map showing city’s central and southern part less favourable to recharge. Map includes Chennai, Tiruvallur, Kanchipuram and Vellore

As per the 2013 Ground water Status report, of the 109 firkas in the Chennai basin, 38 firkas are in over exploited and critical units. This amounts to over 2000 sq km out of the total area of 6300 sq km.

The report states that there is a threat of sea water intrusion, decline in ground water level and quality due to urbanisation which has created greater demand for ground water.

The Lede had earlier reported that how ground water resources are prone to over exploitation due to old methodology.

A study conducted by Anna University, five years ago in the Minjur-Panchetti area, revealed a that sea water intrusion has extended up to 15 kilometres inland.

Extent of sea water intrusion marked in red 
Extent of sea water intrusion marked in red 

Recommending different models for different issues, Elango notes that linking Araniyar and Kosasthalaiyar, parallelly along the coast, building check dams and percolation ponds along the four rivers and proper ground water regulations can push back the sea water ingress in a period of 15 years.

However it is across the same basin that Adani’s Marine Infrastructure Developer Private Limited (MIDPL) is coming up.

The project proposal mentions that it is proposed to be on non-agricultural and highly saline barren lands available for development.

Anna University has come up with a hydro-geological model to study the city’s water supply and management. It is projected that there will always be a deficit of 20 to 25% during summers throughout the next decade even if the city builds a new storage reservoir.

And this status would continue even by the end of 2030 when the proposed the fourth desalination plant is ready with 400 MLD water output.

Unless the city resorts to waste water treatment, Elango said, the city cannot meet the demand even with all the recharge models and additional supply from desalination plants.

DEWATS (Decentralised Wastewater Treatment Systems) can reduce our direct dependence on fresh water by 30%.

Experts feel that integrated water management is the need of the hour and without multiple approaches, the water crisis would pass on to the next generation.

The state has to focus on challenges in balancing the city’s water demand and supply gap with proper water conservation & management plans or else major water crisis await in the next decade.

The Lede