Ground Water Potential and Utilization Pattern
GEOMORPHYLOGY AND SOIL TYPES
The Puducherry region in general is a flat peneplain with an average elevation of 15 m above mean sea level. The terrain becomes a little undulating with prominent high grounds varying from 30 to 100m above mean sea level towards northwest and northeastern parts of the region. Three major physiographic units are generally observed, viz., (i) Coastal plain, (ii) Alluvial plain and (iii) Uplands.
The coastal plain extends as a narrow stretch for about 22 km and of four to six hundred meters width on the eastern part of the region along the Bay of Bengal. The major part of the coastal plain comprises gently sloping land with a chain of sand dunes extending all along the coast. Other physiographic units which are characteristic of the coastal plains such as spit bars, mud flats, lagoons and tidal inlets also occur.
The alluvial plain, formed due to two major rivers namely Gingee and Ponnaiyar, in general is a monotonous plain with slope ranging from 1 to 3 percent. Besides the rivers and major canals, there are depressions acting as storage tanks, which are spread all over the terrain, to serve as surface water reservoirs.
The high grounds are known as Uplands with elevations of about 30 to 100m above mean sea level. These uplands which are popularly known as “Les Montagnes Rouges” or the “Red Hills of Puducherry” are intersected by a number of gullies and deep ravines giving rise to bad land topography
Soils in the area have been classified into i) Red soil ii) Black soil iii) Alluvial soil and iv) Colluvial soil. The major part is covered by Red soil of red sandy/clay loam type. Ferruginous red soils are also seen at places. Alluvial soils occur along the river courses and eastern part of the coastal areas. Sandy coastal alluvium (arenaceous soil) are seen all along the sea coast as a narrow belt.
GROUND WATER SCENARIO
Ground water occurs in all the geological formations ranging in age from the Achaeans to Recent which can be broadly classified into two hydrogeological units viz., (i) Fissured and fractured crystalline formations and (ii) Porous sedimentary formations.
Ground water generally occurs under phreatic conditions in the weathered mantle and under semi-confined conditions in the fissured and fractured zones at deeper levels. The thickness of weathered zone in the district is in the range of 2 to 12 m. The depth of the wells ranged from 4.00 to 15.00 m bgl.
The yield of large diameter wells tapping the weathered mantle of crystalline rocks ranges from 100 to 500 lpm and are able to sustain pumping for 2 to 6 hours per day.
The porous sedimentary formations occur in almost the entire region and are represented by the semi-consolidated formations of Cretaceous and Tertiary and the unconsolidated Quaternary formations of Recent age. Among the porous sedimentary aquifers, the Vanur-Ramanathapuram Sandstone (Cretaceous) and the Cuddalore sandstone (Tertiary) aquifers and the shallow alluvial (Quaternary) aquifers constitute the three major potential aquifer systems, in the region. Ground water occurs in these formations both under water table as well as under confined conditions and is being developed by means of dug wells, dug-cum- borewells and tube wells.
The phreatic aquifer comprises mainly of alluvial aquifer and in patches Tertiary and cretaceous aquifers are also found as part of phreatic aquifer. Tertiary aquifer is not present at all places and hence while drawing the piezometric surface contours, only area having the Tertiary aquifer has been considered and the same has also been marked in the map. In case of Cretaceous aquifer, some of the areas have not been considered for development as the overlying Tertiary aquifer is highly potential. Hence observation wells have also been established only at places where cretaceous aquifer is being developed at present and hence contouring of piezometric surface has been attempted only for such areas and the same has been marked on the map.
Among the various water bearing formations of Cretaceous age, the Ramanathapuram and Vanur formations form potential aquifers. They occur in the north-western part of Puducherry Region and are encountered in the boreholes drilled in the major part of the region. The aquifers of the above formations include sands and calcareous sandstones. They are coarse grained in the western part and grade into finer facies towards east and northeast. The thickness of these aquifers ranges from 38 to 92 m. The yields of the tube wells with depths between 65 and 400 m, tapping these aquifers vary between 800 and 1500 lpm.
The thickness of the aquifers in upper Cretaceous Ottai formations varies between 42 and 56 m and the water bearing property is mainly dependant on the few bands of fine grained sandstones and limestones. The yields of the wells tapping these aquifers vary between 1015 and 2210 lpm for drawdowns ranging from 6.6 to 25 m. The piezometric head varied between 8.60 to 63.24 m bgl (Jume 2006) during premonsoon and 8.14 to 54.32 m bgl during post monsoon.
Cuddalore sandstone, Kadapperikuppam formation and Manaveli formation are the three stratigraphic units of Tertiary aquifers. Out of the three, the Manaveli formation of Paleocene is mainly an aquitard and the localised granular zones do not provide any appreciable yield. Another unit of this group namely the Kadapperikuppam formation contains some productive auifers. The thickness of this aquifer shows wide lateral and vertical variations.
The Cuddalore sandstones of Mio-Pliocene age constitute the most potential aquifers. The Cuddalore sandstones comprising sandstones, sands and gravels occupy an extensive area. The thickness of these aquifers ranges between 20 and 245 m. Ground water occurs in this aquifer mainly under confined conditions and is developed by means of tubewells ranging in depths between 27 and 366 m. The yields of the tube wells range between 200 and 3000 lpm for drawdowns varying from 5 to 10 m.
The Kadapperikuppam aquifers are constituted by the fine grained sandstones and give moderate to good supplies of water as seen around Sedarapalli, Pillaiyarkuppam and further northeast. The thickness of aquifer ranges between 52 and 90 m south of Gingee river, whereas in the area north of Gingee river river, it is between 13 and 37 m.
The piezometric head varied between 6.09 to 33.87 m bgl (June 2006) during premonsoon and 6.07 to 32.35 m bgl during post monsoon.
Sands and gravels constitute the alluvial aquifers. Alluvial deposits occupy nearly threefourth of the region. These aquifers form the most potential shallow aquifer system in the area. The thickness of these aquifers ranges between 5 and 34 m. Thick alluvial aquifers occur in the area bordered by Thirukanji, Odiyampet, Tavalapet, Villiyanur, Mangalam and Satyamangalam. In these, ground water occurs under water table or semi-confined conditions. The depth of tubewells tapping these aquifers range between 25 and 50 mbgl.
Long Term Fluctuation
|Aquifer||Pre monsoon (m)||Post Monsoon (m)|
|Alluvial||0.08 – 7.88||0.09 – 6.94||1.19 – 17.76||0.21 – 12.24|
|Tertiary||0.78 – 1.32||1.33 – 8.64||-||2.27 – 16.01|
|Cretaceous||6.30||0.58 - 25.54||1.16||4.61 – 36.37|
|Aquifer||Transmissivity (m2/day)||Storability||Specific Yield|
|Alluvial||275 – 770||-||6 - 15 %|
|Tertiary||1000 – 2000||9.583 x10-5 and 8.9 x 10-4.||-|
|Cretaceous||100 – 2000||2.93 x 10-5 to 1.36 x 10-4||-|
|Weathered Crystallines||< 1 – 15||-||1.5 – 2%|
Ground Water Resources
The dynamic ground water resources have been computed jointly by Central Ground Water Board and Groundwater Unit of Department of Agriculture, Government of Puducherry as on 31st March 2004. The salient features of the computations are furnished below.
|Status||Requirement per Milli Cubic Meter|
Net Groundwater Availability
Existing Gross Draft for Irrigation
Existing Gross Draft for Domestic and industrial water supply
Existing Gross Draft for all uses
Allocation for Domestic and Industrial Requirement supply upto next 25 years (2029)
Net groundwater Availability for future Irriation Development
Stage of Groundwater Development (%)
Category of Block
Ground Water Potential (per milli cubic meter)
|Total Ground Water Potential||Puducherry Region||Karaikal Region|
i) Consumption for Agricultural Activities
|116 (82.84%)||5.1083 (56.85%)|
ii) Consumption for Drinking Water Purposes
|18.5413 (13.24%)||2.5262 (28.11%)|
iii) Consumption for Industrial Purposes
|5.4750 (3.92%)||1.3505 (15.04%)|
The analytical data of water samples from shallow tubewells tapping the alluvial aquifers are almost neutral to alkaline in nature, with pH values ranging from 7 to 9. The water is generally bicarbonate-chloride type, the bicarbonate predominating over chloride. Carbonate was generally absent or occurs in traces. The chloride content was generally within the permissible limit except few wells along the coastal belt in alluvial formations where it reached a maximum of 8650 mg/l at Murungapakkam. However in recent years due to unscrupulous development of ground water the shallow alluvial aquifers along the coast show signs of quality deterioration probably due to sea water intrusion leading to the occurrence of Sodium-Chloride type of water from Sodium-bicarbonate.
The Electrical Conductivity values, in major part of the region were less than 1500 µS/cm at 25°C, which increases to around 2000 µS/cm at 25°C near the coast in the east, central and small patch on southwestern part. A localised patches with increase in salinity of EC more than 30,000 µS/cm at 25°C was noticed along the coastal belt which may be due to sea water contamination.
The quality of ground water tapped from Tertiary aquifers is alkaline with pH ranging from 7.4 to 9.8. Carbonate is almost nil in most of the samples. The water from these aquifers is, in general, Calcium-Magnesium-Bicarbonate type. However, formation water in most of the deeper wells constructed along the coast showed a change in quality leading to Sodium-Chloride type of water. Among the different hydro- stratigraphic units, the water from Cuddalore sandstone group of Mio-Pliocene was comparatively better in quality than Kadaperikuppam and Manaveli aquifers. The chloride content was generally within permissible limit except few wells along the coastal belt where it reached a maximum of 2975 mg/l at Murungapakkam. The fluoride value in general ranged fro 0.2 to 0.4 mg/, except at Kanniakoil, Kizparikalpet, Murungapakkam and Utchimedu falling in the extreme southeastern parts of the region where recorded from 1.1 to 1.6 mg/l. However, higher concentrations of iron were recorded in some pockets ranging from 0.29 to 20 mg/l and the maximum value was at Odiampet.
The Electrical Conductivity values were less than 1500 µS/cm at 25°C in major part of the region, except some patches along the coast where maximum EC value of 8280 µS/cm at 25°C were recorded at Murungapakkam, which may be due to sea water intrusion.
The quality of ground water in the Cretaceous aquifer system is slightly alkaline with pH ranging from 7.7 to 9.4. The concentration of chloride is generally within 150 ppm, except for the isolated areas at Madagadipet and Thondamanatham. The content of fluoride ranged from 0.2 to 0.6 mg/l in the region. The concentration of iron was varied from 0.3 to 5.5 mh/l abd the maximum at Katterikuppam. The maximum value of sulphate 288 mg/l was noticed at Sedarapet.
The Electrical Conductivity values are less than 1500 µS/cm at 25°C except a pocket in the western part where higher EC values of 7280 µS/cm at 25°C were observed at Madagadipet. Ground water from all the aquifer systems is, in general, suitable both for domestic and irrigational needs except for isolated patches where high iron and chloride concentrations are reported. The water from Phreatic/Alluvial, Tertiary and Cretaceous aquifers from major parts of the region is of medium to high salinity and low sodium hazard as per U.S. Salinity lab classification. However water with high salinity and medium sodium hazard are reported from both Alluvial and Tertiary aquifers in the coastal areas of Puducherry region. Very high salinity and high sodium are reported from select wells along the coast due to sea water intrusion. The suitability of ground water for industries depends on the type of industry and the process involved. The waters have to be treated for softening for industrial uses at times.
Status of Ground Water Development
The estimation of groundwater resources for the region has shown that the Puducherry Region is over exploited. Tube wells are the only ground water abstraction structures used for both domestic and irrigation in the region. The yield of tube wells in shallow Alluvial aquifers is of the order of 1 to 2 lakh litres / day. The extraction of ground water by shallow tube wells in the Alluvium is of the order of 2.5 ha.m. / year. The average command area for tube well is about 3 ha.
The deep tube wells of 200 mm dia and 100 – 400 m depth in Tertiary and Cretaceous aquifers can yield as high as 1000 lpm discharge, which can be pumped with 10 to 15 HP submersible pumps. The average annual draft of deep tube wells varies from 70 – 200 m3/hr. Assuming 200 days pumping in a year, with average daily pumping of 10 hours, the annual draft varies from 0.14 to 0.40 MCM.
GROUNDWATER MANAGEMENT STRATEGY
In absence of forests and barren lands cover, about 49 percent of the total geographical area of the Puducherry region of U.T. of Puducherry has been categorised as land not available for cultivation, including current and other fallow lands. Hence, about 51 percent of the total geographical area is available for planning of ground water management in the regions.
As per the groundwater resource estimation based on GEC 1997 norms, the level of groundwater development as in March 2004 is 179 percent in Puducherry region. As the ground water development in the Puducherry region is rather very high, no further groundwater development is to be encouraged. On the other hand, there is an urgent need for regulation of over-exploitation, protection and augmentation of ground water resources to recharge the depleted aquifer systems. In order to achieve this goal, the following activities may have to be taken up in the area.
- realistic assessment of groundwater draft by various sectors
- strict regulatory measures to ensure no further development of groundwater in over-exploited areas, except for drinking water supplies
- measures for augmenting groundwater resources through rain water harvesting and artificial recharge
- creation of mass awareness for change of cropping pattern to suit groundwater availability and
- revitalisation of existing water harvesting structures and their supply channels.
The deeper semi-confined and confined aquifers in the area are also being extensively developed by various sectors. Study of the behaviour of groundwater levels in the area indicate the development of land ward hydraulic gradient in parts of both Tertiary and Cretaceous aquifers. In view of these and considering the fact that the overlying phreatic aquifers are already desaturated, no further development is considered feasible for the deeper aquifers as well.
A programme of intensive water level and water quality monitoring may be implemented in the area to monitor the efficacy of regulatory measures and recharge augmentation schemes being taken up in the area. Further development of groundwater resources could be considered only when significant improvements in the groundwater resources in these aquifers have been established.
Water Conservation and Artificial Recharge
The topography of Puducherry region, in general, is suited for construction of various artificial recharge structures such as percolation ponds and check dams. However, detailed studies are necessary to formulate a comprehensive scheme for artificial recharge of phreatic ground water in the district in view of the variations in the geomorphic set-up and the complex hydrological and hydrogeological conditions.
The number and type of artificial recharge structures recommended for Puducherry region are furnished in Table 1. The exact locations of these structures, however, are to be decided on the basis of detailed field investigations and implementation of the schemes may be taken up in phases.
Table: Details of number and types of Artificial Recharge Structures recommended in Karaikal Region of UT of Puducherry
Area Suitable for Ground water Develop- ment (sq.km)
Categorization as on March 2004
Surplus available for AR (MCM) *
Number of Structures - PP (1 in 15 sq.km). Capacity - 0.1 M.Cu.m
Cost of Structures (Lakhs) - PP (Unit Cost - ₹ 20.00 Lakhs)
* Data Source : Groundwater Unit of Department of Agriculture, Government of Puducherry
It is also recommended that recharge wells may also be drilled to recharge the deeper aquifers wherever necessary as the deeper aquifers are also equally being developed in the region.
Free technical guidance for implementation of roof-top rain water harvesting schemes is also being provided by Central Ground Water Board.
GROUNDWATER RELATED ISSUES & PROBLEMS
Based on the high level of ground water development, it is inferred that a major part of the region could be considered vulnerable to water level depletion. Poor recharge conditions and over draft of available groundwater resources are mainly responsible for the high-level ground water development in the region. As the ground water in all the porous sedimentary formations in the eastern part of the region is in hydraulic connection with the sea, the region is also vulnerable to saline water ingress.
The deeper semi-confined and confined aquifers in the area are also being extensively developed by various sectors. Study of the behaviour of groundwater levels in the area indicate the development of land ward hydraulic gradient in parts of both Tertiary and Cretaceous aquifers.
The water from Phreatic/Alluvial, Tertiary and Cretaceous aquifers from major parts of the region is of medium to high salinity and low sodium hazard as per U.S. Salinity lab classification. However water with high salinity and medium sodium hazard are reported from both Alluvial and Tertiary aquifers in the coastal areas of Puducherry region. Very high salinity and high sodium are reported from select wells along the coast due to sea water intrusion.
Many water based industries have been established in the Puducherry Region during early eighties because of availability of ground water and electricity. Some of the chemical industries started dumping the chemicals, both used and unused, in open yards and releasing untreated effluents on open ground/unlined channels. As a result, in Puducherry region, ground water is found polluted in the industrial estates, particularly in Mettupalayam area, leading to environmental degradation.
The State Ground Water Department has constructed a battery of tubewells tapping both shallow and deep aquifers along the coast to monitor the sea water intrusion and the salt-fresh water interface movement due to large scale development of ground water in recent years. Water levels and water samples are collected once in every one or two months. Effects of sea water intrusion and interface movement are noticed in some of the observation wells.
AWARENESS & TRAINING ACTIVITY
Mass Awareness Campaign (MAP) & Water Management Training Programme (WMTP)
One WMTP was organized on “Rain Water Harvesting Training” at the meeting hall of PASIC complex, Thattanchavadi, Puducherry during the year 2003-2004. The training was attended by 36 officers from various State Government agencies, Representatives of Commune Panchayat Administration, Farmers Association, Social Welfare Organisation, Voluntary Organisation, Builders Association etc.
One Mass Awareness Campaign on “Ground Water Management, Regulation & Conservation” was organized at PASIC complex, Thattanchavadi, Puducherry during the year 2003-2004.
The findings of exploration carried out by CGWB, the results of Geophysical investigations for source finding and their limitations, Ground water resource potential of Puducherry Region of U.T. of Puducherry, Techniques on Ground water resource management and need for regulation and water conservation were explained to the gathering of 250 people.
AREA NOTIFIED BY CGWA / SGWA
Central Ground Water Authority has not notified any area in the region. Government of Puducherry has enacted “The Puducherry Control and Regulation Act 2002” and subsequently “The Puducherry Groundwater Control and regulation rules 2003” has been enacted for the purpose of regulation and control of development of groundwater. In accordance to the rules, Puducherry Ground Water Authority has also been constituted and it is taking care of groundwater control and regulation.
In addition, Government of Puducherry vide Act No 27 of 1999, made following provisions in the said act in connection with the groundwater development.
- No person shall extract or use groundwater in the scheduled area for any purpose other than domestic purposes.
- no person shall transport groundwater by means of lorry, trailer or any other goods vehicle
As per the groundwater resource estimation based on GEC 1997 norms, the level of groundwater development as in March 2004 is 179 percent in Puducherry region. As the ground water development in the Puducherry region is rather very high, no further groundwater development is to be encouraged. On the other hand, there is an urgent need for regulation of over-exploitation, protection and augmentation of ground water resources to recharge the depleted aquifer systems. Intensive monitoring of ground water levels and water quality has to be taken up in the coastal areas of the district to monitor the movement of fresh water – saline water interface.
Artificial recharge of ground water through cost-effective rain water harvesting systems may be popularised in the district by providing incentives to individuals/communities embarking upon such initiatives. A concerted effort involving various Government agencies and NGOs can create the necessary awareness among the rural masses.
Remedial measures and isolation of pollution by industrial units may be taken up to reduce the damage to the ground water resources in the region. A long term strategy to control and reverse the sea water ingress by limiting the ground water extraction by involving local state holders is necessary. Also, the flood water diversion and recharge to coastal aquifer in the western side of established interface line is necessary and action plan in this direction with participation of state and central agencies and industrial establishments is recommended. Effective aquifer remediation technology can be identified and practiced to minimize the aquifer contamination in vulnerable pockets.
Since there are a large number of irrigation tanks in the region suitable measures for increasing the quantum of storage by desilting, raising of bunds etc have to be taken up immediately which will facilitate recharge of the shallow water table aquifer to a considerable extent. For recharging deeper aquifers and to prevent sea water intrusion, recharge tube wells in all favourable tanks and coastal areas is recommended.