Supreme Court asking Tamil Nadu to use groundwater wont' work, says expert

CHENNAI: The Supreme Court’s suggestion in its recent final verdict in the Cauvery appeals case by the basin states that, given the 20 tmcft of groundwater potential, Tamil Nadu could “safely” use 10 tmcft of groundwater for irrigation in the Cauvery delta areas along with the surface flows in the river, is completely unfeasible, says the well known hydrologist, Dr P M Natarajan.

Sharing his thoughts on the apex court verdict with DC, Dr Natarajan, a former member of the State level expert committee, Government of Tamil Nadu, and who was also a member of the UNDP team that assessed the groundwater potential of the Cauvery delta in the early 1970s’, said that the ‘ground realities are so complicated’ in both the states that the suggestion would simply not work.

Dr Natarajan said that the upper riparian Karnataka and the lower riparian state of Tamil Nadu in the Cauvery basin have “completely different geological, geomorphologic, hydrological, environmental and weather settings including origin of rocks, their composition and age” that the absorption capacity of water even in a normal monsoon year was vastly different.

In the delta areas in Tamil Nadu, without assured flows in the river, the renewable groundwater recharge is uncertain even in normal monsoon years, he said. This limitation in the groundwater potential was explained by water experts when the Cauvery Waters Disputes Tribunal headed by Mr Justice Chittatosh Mukherjee had first gone around the entire area, he said. 

The Tribunal, even in its final award given in 2007, had not taken groundwater into account.

Dr Natarajan explained because of this different natural settings in both the states, “even for the same quantum of rain in a unit area”, the renewable water resources, “due to inherent behaviour of the aquifers” were different in quantity. During normal monsoons, while the renewable groundwater potential “will be recharged to the maximum extent in the aquifers” in the basin’s upper part in Karnataka, in the delta areas in Tamil Nadu, the recharge will be far less, he said. The hydrocarbon explorations in the delta, is further complicating this dynamics.

Even the global practice is that in water-sharing agreements, groundwater is not taken into account, “since without precipitation there is no recharge,” he stressed. Hence, in handing down such awards courts should not consider including “undependable groundwater”, Dr Natarajan contended.

Another key factor is that after the December 2004 Tsunami, particularly in the coastal tail end areas of Cauvery delta, sea water intrusion had turned into saline about three tmcft of ground and surface water, he pointed out.

Already, in Thanjavur district, there has been a huge decline in groundwater levels from 50 feet in 1998 to over 250 feet now, Dr Natarajan said.

Even if there is no reduction in groundwater potential in future, the groundwater quality will “change to unacceptable standards”, he added to drive home why the Apex court’s verdict on this aspect in the Cauvery case was unworkable.