As officials look elsewhere for source of water, construction along ECR has led to a decline in city’s groundwater due to lack of replenishment from rainwater. Intrusion of sea water is increasing and turning water saline. Ashmita Gupta tries to find out why this is dangerous
With the summer setting in, the city is already struggling hard for water. The Metrowater board is looking at sources over a hundred kilometres away from the city. But a recent study by the Anna University has found that the city is fast losing a quality source of water very close to it by allowing constructions in the fragile aquifer zone along the East Coast Road from Adyar to Muttukadu.
This zone along the coast side of the scenic East Coast Road was one of the aquifer zones that the Metrowater board was tapping for decades to meet the city’s water needs. Aquifer means areas having an underground bed or layer yielding good ground water. For this reason, any new building construction was banned since 1980 in much of this region to preserve rain water penetration. But the ban was lifted in 2007 to promote tourism and over the years, the area has witnessed a massive real estate boom.
The research study by the Geology Department of Anna University has found that this has come at a great cost. The built-up area in this aquifer zone along the coast has seen an increase of 15 percent between 2004 and 2016. Correspondingly, the water quality has plunged over the years. The TDS level (Total Dissolved Solid level, that measures the hardness of the water) has increased drastically suggesting intrusion of sea water. For example, at Neelankarai the groundwater had a TDS level of 569.6 in 2009. But it increased to 1504 in 2010 and 2176 in 2016.
“The sandy nature of the area was allowing excellent penetration of rainwater. If there was 100 mm rainfall, 50 percent of that would get deposited as groundwater and the water quality used to be so nice. But due to urbanisation, the inhabitants in the area are drilling more wells and this is having a very bad impact,” said Professor L Elango, head of the Geology Department who guided the research.
When lifting the ban on construction in the zone, policy makers had argued that rainwater conservation in buildings will preserve the groundwater and granted only a nominal floor-space ratio of 0.33 and a height restriction of 9 metres. However, it is an open secret that there was a lot of illegal construction in the stretch. According to estimates, there are more than 15,000 buildings in the area which were built without coastal regulation zone clearance.
S Dhanamadhavan, the research scholar behind the study, says Neelankarai, which saw a lot of construction in recent years, had the worst water quality. “The amount of chloride and sodium is highest in Neelankarai. The quantity of other ions like calcium, magnesium, potassium sulfate and potassium bicarbonate was also high which indicated the intrusion of seawater as the groundwater had depleted,” he said.
Sea water intrusion is the real danger. As sea water is harder than rainwater, it could effectively stop the latter from percolating. Hence salinity levels will only be worsening in the area. The process may become irreversible.
While Neelankarai was worst affected, the impact was evident across the stretch. At Thiruvanmiyur, from a TDS level of 1280 in 2009, it has increased to 2750.2 in 2016. The water quality was better in far-off areas like Muttukadu.
The study estimated that around 2703 new residential units (from apartment flats to villas) are under construction. By this calculation, the residents will consume 470580 m3 of water per day and most of this need will be met by extracted groundwater.
While this means more water will be pumped out, the increased built-up area would mean a reduction in the amount of water percolating into the ground. The built-up area has increased from around 14 km2 in 2004 to almost 20 km2 in 2016. The study concludes that construction to this tune would reduce groundwater recharged in the aquifer zone from 10000000 m3 to 7500000 m3.