About thirty years ago, a report of the Planning Commission on the development of coastal areas in India affected by salinity indicated that the problem of salinity in coastal areas is a national problem and that coastal saline areas need to be identified as: (a) Soil salinity areas where the top soil is saline; (b) Water salinity areas where either the water strata for great depths is saline, or even if top 30 ft. has fresh water where fresh water is entirely by rainfall alone.
The report went on to discuss livelihoods in coastal areas, the issue of crops and fodder varieties that can be grown in coastal lands and that “The present groundwater development in coastal tract is very limited but when the ground water withdrawals are to be increased, the existing saline and fresh water disposition may be disturbed and the process of ingress of saline water may be accelerated. Hence scientific management of the vital ground water resource will require critical evaluation of the changes, brought about consequent to withdrawals and must so regulate the draft as to prevent the ingress of saline water in fresh water bodies”.
Where does groundwater come from?
Groundwater comes from the natural percolation of precipitation and other surface waters down through Earth’s soil and rock, accumulating in aquifers -- cavities and layers of porous rock, gravel, sand, or clay. In some of these subterranean reservoirs, the water may be thousands to millions of years old; in others, water levels decline and rise again naturally each year.
Groundwater levels do not respond to changes in weather as rapidly as lakes, streams, and rivers do. So when groundwater is pumped for irrigation or other uses, recharge to the original levels can take months or years.
Increasing pressures on the coast
The last few decades have seen India’s long coastline under increasing developmental pressures. No more are just cities located along the coast – they are now urban agglomerations – with a city or town serving as a nucleus and surrounded by what were supposed to be satellite townships but are seen to convert the entire coast into an unbroken stretch of habitations and industries. Settlements, industries and agriculture vie to occupy the coast and consequently the demand for water has also been rising.
Over a dozen major rivers, some 44 medium sized and an equal number of minor rivers discharge their waters into the sea in India. This water is just not enough for our growing needs and hence the dependence on groundwater for agriculture, domestic and industrial needs has shot up tremendously and now there are reports of extensive ingress of saline water into the ground water bodies. There is also the threat of rising sea levels which can increase saline intrusion.
Saltwater intrusion or saline intrusion occurs when saltwater is drawn-in from the sea into freshwater aquifers. As it carries more solutes, sea water has a higher density than freshwater. This difference in density causes the pressure under a column of saltwater to be greater than the pressure under a column of the same height of freshwater. If these two columns are connected at the bottom, the pressure difference causes a flow of saltwater column to the freshwater column until the pressure equalizes. The flow of saltwater inland is limited to coastal areas. At the sea-land boundary, freshwater flows out from the highest point of the aquifer, and at the lowest point, saltwater flows in. The saltwater intrusion then forms a wedge. ( Wikipedia
Groundwater in Tamil Nadu
Tamil Nadu is reportedly the most critically affected among the Southern states with over 142 of 385 blocks listed as over exploited according to D.S.C.Thambi, Regional Director, Central Ground Water Board, Chennai (The Hindu, Feb 10, 2011
). Eight to 11 coastal blocks were faced with the problem of saline water.
While sea water intrusion was a problem in Chennai and Puducherry areas, brackish water was a problem in a few blocks in Ramanathapuram. According to the Central Ground Water Board, in Tamil Nadu, nearly 73% of the total area of the State is occupied by a variety of hard & fissured crystalline rocks like charnockite, gneisses and granites. The depth of open wells varies from 6 to 30mbgl (metres below ground level) while the depth of bore wells generally varies from 30-100m.
In the Cauvery delta of Thanjavur district, the artesian pressure head ranges between 4.5 m to 17 magl with free flow up to 270 m3/hr. The yield of wells in the alluvium varies from 27 to 212 m3/hr. The yield of wells in the fissured formations varies from 7 to 35 m3
/hr (State Profile of TN, CGWB
The salinization of groundwater along the coast appears to have happened in relatively recent times according to recent discussions with coastal fishermen who said that about 10-20 years ago, they were able to get fresh potable water even close to the shore whereas now they are dependent on municipal supplies or even tankers bringing them supplies from outside as all their wells have turned saline (FIMSUL Stakeholder & Livelihoods Analysis
Groundwater usage in agriculture
If you travel to some of the interior parts of rural India, you can still see water being pumped from canals or shallow dug wells using various simple technologies that require human/animal power. However, in the last forty or fifty years, there has been a sea-change in the source of water – more and more groundwater is being pumped up using electricity to irrigate fields.
In fact, according to the State of the Environment
report for Tamil Nadu, wells have become the predominant source of irrigation accounting for nearly half the irrigated area. The switch to crops or varieties that are water-hungry demanding extensive irrigation with the availability of cheap power to run motors has been steadily draining our underground reservoirs.
Thus, while the number of open wells and dry wells energised was only 42.4 per cent in 1970-71, it increased to 91.1 per cent in 1999-2000, due to the free supply of electricity to farmers. A recent Planning Commission report
says that electric supply is not metered and a flat tariff is charged depending on the horsepower of the pump. This makes the marginal cost of power zero and provides farmers with little incentive to use power or water more efficiently.
A study by BEDROC
saw farmers in Ramanathapuram candidly agreeing that they had over-exploited their groundwater resources for sugarcane cultivation and this had resulted in their groundwater sources, located not too far from the coast, saline. They also pin-pointed the sixties as the beginning of this water stress, when, with the introduction of electricity in their villages and supportive schemes from the Government popularising motors for pumping up of water, over exploitation of ground water sources started in earnest without adequate recharging measures.
The situation is a little different in the district of Nagapattinam which lies in the tail end of the Cauvery delta. Canal irrigation dominates here with channels drawn from the Cauvery and its distributaries. However, these canals do not contain water for over half the year. Water is released from the Mettur dam in June/July and subsequently, there is rain due to the north-east monsoon between September and December. With almost no gradient, these canals are vulnerable to the backwaters from the sea surging landwards salinizing the fields. The marine water ingress has increased over the years, salinizing more and more of the adjoining agricultural lands and water sources.
Pressures from Industry and domestic demand
What are the other pressures on groundwater? The SoE report says that increased withdrawal of water for domestic and industrial use and increased use of chemicals in agriculture have resulted in the deteriorating quality of groundwater. In coastal areas, there is salinity intrusion. There is extensive withdrawal of water by industries such as leather, textiles, breweries etc which withdraw enormous amounts of water from the ground. Manali industrial area has been studied by the CGWB
and showed that all surface water sources are highly polluted.
Bedroc’s study showed up that effluents from the Pharmaceuticals, Neyveli Lignite Power Plant, fertilizer production companies and other manufacturing companies have been flowing unchecked into the surface water bodies and leading to large scale pollution. Apart from this, is the huge overdraft of ground water consumed by these commercial institutions, either for the domestic purposes of the townships that they have set up or for their industrial purposes. 10 of the 14 blocks have already been classified by the CGWB as semi-critical blocks, in terms of water stress, in the districts of Nagapattinam and Cuddalore.
Shrimp farm effluents have contaminated many coastal areas as well. But what is the remedy? Is it only when a community gets together and fights that such issues are even recognised or any attempts made at resolving them?
Thus Plachimada and the Coca Cola company in Kerala or the closure of dyeing units in Tiruppur or the Narmada Bachao Andolan. Is this the only way out -- to fight as bitter adversaries when the issue is that of a basic right to a life with dignity?
Yes, there are plenty of laws on siting of industries and pollution control. For example, the Tamil Nadu Ground Water Authority has been set up to direct and regulate the development and management of the ground water resources of the State. The Authority has the power to notify areas for regulation. Every use in the notified area will have to obtain the permission of the Authority to extract ground water. Wells cannot be sunk and transport of groundwater by lorries, tankers, etc. cannot be done in a notified area without obtaining a permit. Electricity cannot be provided for energising wells which are in contravention of the Act. But are all these really honoured?
Come midsummer when the water supplies start dwindling, one can see long lines of tankers topping up “illegally” from wells near river beds, or even agricultural fields. On top of all these is the burgeoning increase in built up spaces for housing and habitation, decreasing the natural recharge potential even further, thereby allowing for ingress of saline water especially in coastal areas where most of the freshwater zones are floating lenses over saline water zones.
Another threat to groundwater is from climate change. Groundwater is the world’s largest accessible store of freshwater, the primary source of almost half the world’s drinking water supply but as the IAH Commission on Groundwater and Climate Change (IAH-CGCC) points out, there is very little research on the potential effects of climate change on groundwater. A major problem is the slow recharge of groundwater supplies as well as problems due to sea level rise. Increased temperatures due to global warming are likely to affect soil moisture and are also expected to result in lowered rainfall, less number of rainy days though of higher intensity (short bouts of high intensity rain). This means that the time available for water to percolate into the ground and replenish supplies may further go down. In addition, sea level rise can affect coastal aquifers because of higher salinity intrusion.
However, the relationship is very complex, and as mentioned earlier, not studied in any detail. Overall, one can only conclude that climate change will surely further strain groundwater resources – in terms of both quality and quantity.
Solutions and Recommendations
What then are the solutions? In many areas that BEDROC studied, the traditional methods maintenance of water channels as well as water harvesting and storage structures had fallen into disuse. These needs to be resuscitated to ensure that rainwater, especially during bouts of heavy rain, does not flood the area or drain off uselessly into the sea, but is effectively harnessed, stored and utilised.
While Rainwater Harvesting is being extensively promoted, the compliance or effectiveness of this practice has not as yet been fully proved. In fact, though rainwater harvesting has been implemented on a large scale in the coastal area of south Chennai, no appreciable improvement in chemical quality of ground water has been observed. This, according to the CGWB’s recent report on cities
, is mainly due to the seawater ingress in the fresh water aquifers that is over-riding the rainwater harvesting at Thiruvanmiyur area. This essentially means that in addition to promoting and practicing artificial recharge mechanisms, it is also extremely necessary to reduce dependency on groundwater.
All sectors that require large quantities of water must recycle and put in artificial recharge structures where possible. Measures have to be short term as well as long term depending on the area, the harvest potential, rainfall and other conditions. The CGWB recommends that artificial recharge to ground water be given priority in blocks where the development of ground water resources is comparatively high.
Site specific design has to be adopted depending on the on the aquifer geometry and availability of surplus non committed runoff. Most important of all is sensitising every stakeholder that groundwater harvest must be done judiciously and recharging of groundwater aquifers has to be done scientifically.
Considering the fact that the policies are decreed by one set of people, the research and studies by another, the field level implementations by yet another, and usually in a state of parallel bliss of ignorance of each other, it is not strange to hear of ad-hoc short term measures without due diligence to long term impacts. What we do forget to respect is that each of the negative reverberations of such short-sighted interventions are impacting the lives and livelihoods of yet another group of communities who, unseen, unrecognised and unheard, continue to eke out a day to day living in stoic silence and grim resignation.