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CHAPTER 2

STUDY AREA

2.1.0 INTRODUCTION

In the management of water resources groundwater has its own significance in

development and planning at various levels. It is important to have a detail insight

into approach the geochemical study of the groundwater for planning and

management in irrigation, industries and domestic purposes. Impulse of monsoon and

withdrawl of groundwater in excess to replenishment of aquifer system in many parts,

result in continuous declining of water table causing detoriation in water quality. The

study will be absolute only with a detailed background regarding geology,

geomorphology, drainage and ecological development of major groundwater potential

regions.

2.2.0 LOCATION

The area chosen for study is in and around Nagapattinam coastal region, which

is situated on the eastern margin of Tamilnadu. The study area extents between

Latitude of 10 deg 10 min N to 11 deg 20 min N and Longitude of 79 deg 15 min E to

79 deg 50 min E. The study area falls in the Survey of India toposheets 58 M/11,

M/12, M/15, M/16, N/09, N/10, N/11, N/13, N/14 and N/15 with a total area of about

2877 km2. It includes the taluks of Sirkazhi, Mayiladuthurai, Tharangambadi,

Nagapattinam, Kilvelur, Thirukkuvalai and Vedaranyam. The area has also been

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Fig: 2.1 Study Area

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extended into the Karaikkal Union Territory so as to get a complete overview along

the coast. The study area is bounded by Thiruvarur District on the west, Cuddalore

district on north, Palk strait on south and Bay of Bengal lies on east of the study area.

All the major towns of the study area are well connected to the head quarters,

Nagapattinam and with other main cities of Tamil Nadu by metalled roads and

railways.

2.3.0 POPULATION

As per the Census (2001), the study area has a total population of 15,59,479 which is

2 % of state population. Of the total population, 8,23,429 are male and 8,35,940 are

female.

2.4.0 INDUSTRIES

The Study area is deprived of any major industry, but it is a flourishing centre

of cottage industries and handicrafts alike. This region is equally well known for its

pith articles consisting of beautiful models of Hindu idols, temples, mosques, flower

garlands, bouquets, parrots and peacocks. The flower garlands and bouquets are much

in demand during Christmas days. Pith is grown on the beds of tanks in the Sirkazhi,

and Mayuram taluks. The making of musical instruments of jack wood like the

veena, the tambura, the violin, the mridangam, the tabla and the kanjara exhibit

excellent taste, knowledge and workmanship. The jack wood has special quality for

producing musical sounds. Government has established an industrial training institute

at Nagapattinam. This is to promote industrial development in the area

(www.nagapattinam.tn.nic.in). There were 26 pottery units in Karaikal engaged in the

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manufacture of utensils, flower pots, water jugs etc. Some of the units also produced

tiles in their kilns. In the year, 1823, as many as 100 brick kilns and 71 brick makers

were counted. The same report revealed the existence of 35 oil mills manufacturing

coconut oil, gingili oil, besides producing oil from elipe (bassia longifolia) and laurel

seeds. Of the three soap units, two were located in Karaikal and the other in

Tirumalarajanpatinam. The three coir manufacturers in Karaikal engaged lascars or

coolies according to the type of coir to be manufactured. They used six different

types of looms for the purpose. The work was carried out generally between January

and October every year. (www.karaikal.gov.in)

2.5.0 ACCESSIBILITY

The region is very much developed in terms of Transport and communications.

The nearest airport to Nagapattinam is at Tiruchirappali at distance of about 150 kms.

It is well connected to Chennai airport by regular flights. The rail head at

Nagapattinam is well within city limits. Nagapattinam is well rail connected to all

major cities in India through Chennai and Tiruchirapalli. The Railway stations near

Nagapattinam are Kumbakonam (53 km) and Thanjavur (77 km). Bus facilities are

available from Nagapattinam to all cities round the clock.

2.6.0 TOURISM

Poompuhar (Sirkazhi block), Tharangampadi (Sembanarkoil block),

Velankanni (Velankanni block), Nagore (Nagapattinam block) Thirunallar

(Karaikkal) and Point Calimere (Vedaranniyam block) are the main tourist spots in

the study area. The first 5 tourist spots are visited throughout the year and the

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last tourist spot is visited from August to March. The foreign tourist arrivals have

fluctuations and domestic tourist arrivals have been steadily increasing except in the

years 1992-93 and the tourist arrivals both domestic and foreign are estimated at

2,99,150 during 1996. These six tourist spots are also included in the tourist circuits

identified by the Tourism Department.

2.7.0 METEOROLOGY

2.7.1 CLIMATE

The study area has tropical climate. The summer season starts in the end of March and

remains till the advent of monsoons in early June. The average maximum temperature

during the summers remains around 35°C. The average minimum temperature is

24.75ºC. The winters are relatively very pleasant when average minimum temperature

remains around 20°C.

2.7.2 HUMIDITY

The relative humidity of the study area ranges from 70% to 77% and it is high during

the period of October and November.

2.7.3 WIND

Dust Storms, whirl winds and dusty winds blow from various quarters towards

the end of May. The Southwest winds sets in during April, it is the strongest in June

and continues till September. Northeast monsoon starts during the month of October

and blow till January. Cyclonic storm with varying wind velocity affects once in 3 or

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4 years during the month of November-December. Both these storms affect the

plantation crop. During Southwest monsoon the air is calm and undisturbed.

2.7.4 RAINFALL

The district receives rainfall under the influence of both southwest and

northeast monsoon. A good part of the rainfall occurs as very intensive storms

resulting mainly from cyclones generated in the Bay of Bengal especially during

northeast monsoon. The Northeast monsoon , which starts in October and ends in

December, contributes about 60% of the total annual rainfall. The Southwest

monsoon rains from June to September and from March to May accounts equally for

the rest of the annual rainfall. The district receives rainfall almost throughout the

year. Rainfall data analyzed (period 1901-70) shows the normal annual rainfall of the

district is 1230 mm. The monthly average rainfall in the district was 108.87 mm in

1991-96. The rainfall pattern in the study area shows interesting features. Annual

rainfall, which is 1500 mm at Vedaranyam, the southeast corner of the district, rapidly

decreases to about 1100 mm towards west of the district. The district enjoys humid

and tropical climate with hot summers, significant to mild winters and moderate to

heavy rainfall.

The rainfall distribution was studied in seven different locations of

1.Nagapattinam, 2.Thirupoondi, 3.Thalagnayiru, 4.Thrangampadi, 5.Sirkazhi,

6.Mayiladuthurai and 7.Vedaranyam during 2000 and 6 locations of 1.Nagapattinam,

2.Thirupoondi, 3.Thalagnayiru, 4.Tharangampadi, 5.Sirkazhi and 6.Mayiladuthurai

during 2009. The total rainfall obtained from these observation stations during 2000

account for about 11345.1mm, and that during 2009 accounts for about 8635.9mm.

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Fig.2.2 Rainfall for 2000

Fig.2.3 Rainfall for 2009

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Hence it is understood that the region had experienced heavier rainfall during

2000 than 2009. The rainfall was dominant in both the monsoons at all the stations

during 2000, but during 2009 only NE monsoon was predominant. Some of the

researchers have identified that the decrease in vegetation cover has resulted in

decrease of rainfall (Sarma, 2001; Dengiz et al., 2009).

2.8.0 GEOMORPHOLOGY

The present geomorphic set up in the study area is the result of action of the major

rivers with their distinct tributaries, oscillations in the sea level, tidal effects of Bay of

Bengal and forces of wind. This forms a part of the fertile Cauveri delta and the

region is completely covered by the distributaries of Cauveri. The landforms are

delineated under erosional and depositional regime. The depositional regime

comprises of a coastal plain under marine influence, a flood plain of fluvial regime

with an intermixing section of both fluvial and marine influence. The study area is

covered completely by a mantle of alluvium of variable thickness, the region is flat

having a gentle slope towards the Bay of Bengal in the east.

The entire area is a peneplained terrain with a gentle slope towards east and

southeast. The maximum elevation is about 21 m above mean sea level in the west.

The geomorphology consists of the younger coastal plain which acts on a margin

between the older coastal plain and the Bay of Bengal. Alluvial plain is noted along

the coast in the central part of the study area which extends inward in both North and

South directions. The plain occupies the major part of the study area. There are also

flood plains noted along the river course. This area also has sand dunes and paleo

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Fig: 2.4 Geomorphology of the study area

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beach ridges. The Cauvery and its offshoots are the principal rivers. Rising in the

Coorg Mountains, this river bifurcates about nine miles at the west of Trichy into two

branches, of which the northern one takes the name of Coleroen and the southern one

retains that of the Cauvery. All along the course of Cauvery and its dis-tributaries, on

both the banks numerous narrow strips of river porombokes lands called Paduagais

that are cut up by countless patta lands. These strips ranging in width from about 3

metres to 100 meters are made up of bits of lands. Even though the Padugais and

Poromboke lands are very dry they are very fertile. Flood banks of Cauvery and its

dis-tributaries are away from the watercourses in the upper reaches where the river is

wide and closer in the lower reaches and the river become narrow gradually. The

marine land or coastal land has plain lands except for few sand dunes. However there

is a general tilt from coastal line to inland area. The Vederanyam salt swamp, which

is the largest swamp in Tamilnadu, runs along the coast from Point Calimere

westwards to Muthupet. It runs along the coast from Point Calimere for about 48

kms. and is about 7 to 8 km. wide. This is the longest swamp of its kind in the state.

It is filled by two periodical high tides during the full moon of months, May and June

and retains sea water to a depth of two feet over a considerable area enclosed by low

earthen banks, which when closed prevent the water from flowing back into the sea

after the tide recedes. It is in this manner the well-known Vedaranniyam spontaneous

salt is produced. Consequently extensive lagoons have been formed in these areas.

The terrain is an open plain, sloping towards the east and devoid of any hills.

In south and Southwest of Thanjavur the country rises and forms a small

plateau known as Vallam table land, broken by small ridges of grits and sandstone’s.

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Most of the rivers flow to the east into the Bay of Bengal. The most important feature

of the district is the Cauvery River spread over with its numerous branches.The

district is the most part of a flat plain, slopping very gently to the sea on the east.

2.9.0 GEOLOGY

ERA Period Formation Lithology

Quaternary Recent to

Pliestocene

Alluvium Soils,Coastal and River Sands

Tertiary Pilocene Podakkadi Sands and Clays

2.9.1 Pliocene Formation:

The Pliocene deposits are exposed in the south-western part of the study area

comprising north-eastern, central, southern and western part of Mannargudi taluk and

south-western part of Nidamangalam taluk. The main litho logical units are sands,

sandy-clay, grey and variegated clay with gravel beds. They form a flat terrain

marked by a net work of wide, shallow and long depressions, remnants of the old

drainage. Most of the area is blanketed by reworked laterite gavel which in turn is

overlain by the wind blown grey sands. Pliocene formations underlie the quaternary

deposits in the Cauvery and Vennar sub basins. In the sub stratum, Pliocene

formations are composed of sandy deposits with major clay intercalations and silt in

varying unknown proportions. It was deposited under fluvial and semi-marine

environments. In the study area, the semi marine deposits occur in vennar sub-basin

and partly in non-deltaic dunes covering tirutturaippundi, Nagapattinam,

Vedaranyam, part of Muttupet and Mannargudi taluks. The thickness of the Pliocene

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Fig: 2.5 Geology of the study area

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deposits increases from 50m in New Delta area in Thanjavur District area to above 75

m along the coast, in a depth ranging from 40 to 515 mbgl. The transition from

Pliocene to Quaternary is marked by red mottled clay down to depth of about 35m

below ground surface.

2.9.2. Quarternary Formations

The formations of this group occupy almost entire study area. They are fluvial and

semi-marine in origin. The fluvial deposits consisting of sands intercalated with

brown and black clays are seen on the either side of the present Cauvery river course.

The thickness of these deposits increases in the easterly direction and is about 40m

near the coast.

The sandy silts of 3 to 6 m thickness on the top; partly confine the coarser deposits

beneath. The semi-marine sandy clay deposits of the Vennar sub-basin are about 50 m

in thickness near the coast. Quaternary formations in the Vennar sub-basin are about

50m in thickness near the coast. Quaternary formation in the Vennar sub-basin is

characterised by a thin lower layer of sandy horizon separated by clay bed from a top

layer of sandy zone between 8 to 12 m thickness. The lower thin layer of sand occurs

mainly in the eastern part of Vennar sub-basin. The upper sandy zone is semi-

confined by the deposits of grey silt of 8 m thickness.

Karaikal is an important stratigraphic horizon which indicated the prospects of ‘oil

shows'. This in turn attracted the attention of the Geological Survey of India

between 1959-61 and later on the O.N.G.C., who carried out detailed studies for

determining the possibility of the occurrence of oil. The Karaikal area is completely

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covered by a thick mantle of alluvium and no exposures are met with anywhere. The

following was the interpreted geological succession of the regions: Recent and Sub-

recent Blown sands, alluvium Pliocene Karaikkal beds, Mio-Pliocene Cuddalore

formations.

2.10.0 DRAINAGE

The study area is drained by Kollidam and Cauvery in the north, Virasolanar,

Uppanar in the central part and Arasalar, TirumalairajanAr, Vettar, Kedurai AR,

Pandavai Ar, Vedaranyam canal and Harichandra Nadi in the southern part of the

study area.

2.11.0 AGRICULTURE

This coastal district abounds in green paddy fields, tall coconut groves, vast gardens

of mango and plantain tree and other verdant vegetations. Paddy is the main crop of

this district and it is grown three times in a year. The first crop is known as `Kuruvai'

(the short-term crop) with duration of three and a half to four months from June-July

to October-November. The second crop called the `Thaladi' has duration of five to six

months from October - November to February-March. Third is the 'Samba' (the long-

term) crop and has duration of almost six months from August to January. Other

cereal crops of the district are cumbu, ragi, maize, korra and varagu. The pulses

grown in the district are redgram, greengram and blackgram. Other food crops are

condiments and species, sugar crops, fruits and vegetables. Among the non-food

crops, cotton/fibre, edible oils crops (groundnuts, coconut and gingelly) non-edible

oils crops (castor, miger seeds, though in very small area) are the important ones.

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2.11.1 IRRIGATION

Nearly canals serve 80 percent of the total net area irrigated and only the river

Cauvery feeds these canals. The Cauvery Delta system is the most ancient of all

irrigation schemes in the undivided Thanjavur. This comprises mainly of three

important projects. They are the famous Grand Anicut, the Upper Anicut and the

Cauvery Vennar Regulator Project. Tanks and wells are rarely used for irrigation in

the area. The gross area irrigated by canals and other sources are 1,13,374 hectares

and 21,405 hectares respectively. The gross area irrigated by the tanks and the wells

are 40 hectares and 50 hectares respectively. Therefore canal irrigation constituting

84.07 of the total irrigated area remains the predominant source of irrigation. On an

average about 58.20% of the total cropped area are irrigated. Mayiladuthurai block

achieves about 74% irrigation at the maximum and Vedaranniyam achieves 17.85% at

the minimum. Some blocks achieve irrigation at about 60%. (CGWB,Chennai)

2.12.0 SOILS

The major part of the study area is covered by black clay and isolated patches of

brown clay loam in the area bordering the NE boundary of Karaikal is seen. Some

patches of Arenacious soils are also found along the coastal line. Sandy Coastal

Alluvium and Black Soil types cover 88.71% and 6.58% respectively in this study

area. The other Soils in the district comprise 4.71%. The soil of the district is mostly

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Fig: 2.6 Soil map of the study area

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alluvial but varies greatly in quality. The rich soil is found in the north and the south

of the railway line between Mayuram and Thiruthuraippundi. The worst land in the

delta is found in the Tirutturaippundi and Nagapattinam taluks where the soil is saline

and arenaceous and drainage is very defective. The chief sources of irrigation in the

district are the rivers, a few rainfed tanks and wells. These tanks and wells occur

mostly in the upland regions. About 7.09% of the lands are affected by water logging

and marshy land and 56.21% are prone to floods. About 3.49% of the lands available

for cultivation suffer from salinity/alkalinity and 17.69% of the lands are coastal

sand. Thus the lands affected by soil problems constitute about 84.48% of the total

geographical area excluding forest area and area not available for cultivation. The

data given are the composite old Nagai- Quaide- Milleth district comprising

bifurcated Nagapattinam district.

2.13.0 HYDROGEOLOGY

The entire study area covered by semi-consolidated formations consisting of

sand, silt and clays. Ground water occurs under water table, semi-confined and

confined conditions. The important aquifer systems in the study area are i) Lower

Miocene deeper aquifers and ii) Pliocene – Quaternary shallow aquifers.

2.13.1. Lower Miocene Deeper Aquifers:

These are the deeper aquifer system which can be divided into two hydraulically

interconnected aquifers namely a) Lower Orathanadu aquifer zone b) the upper or

Main flowing aquifer zone.

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a) Orathanadu Aquifer: These aquifers occur throughout the entire Cauvery delta

area. The aquifers of “Primordial delta” grade laterally into fine facies Vennar sub

basin of the district. The facies changes are effected due to presence of sub stratum

ridges in the basement. The thickness of the aquifer ranges between 30 and 70 m.

Ground water occurs under confined conditions in these aquifers.

b) Main flowing zone: The main flowing zone consisting of the coarse grained sands

lies over the “Primordial delta” of the Cauvery basin. The aquifers occurring east of

the line Okkanadu-Kilaiyur and Ottangadu in the new delta area and in the Vennar

sub basin comprising fine-grained sand with clay. The thickness of the aquifer is

around 35 m. Ground water occurs under confined conditions in these aquifers. Tube

wells tapping these aquifers range in depth between 100 m bgl in the west and about

250m bgl in the east. It was established that the ground water from the Lower

Miocene Orathanadu aquifer flows upward to this overlying main flowing zone,

which in turn recharges the shallow aquifer system by upward leakage through the

semi-confined upper and middle Miocene formations.

2.13.2. Pliocene – Quaternary Aquifer: Shallow aquifer system can be classified as

Pliocene and Quaternary. These aquifers occur over the entire area of the district.

a.) Pliocene Shallow Aquifers: The Pliocene shallow aquifers are represented

by sands, gravels, sandy clays and variegated clays. Heterogeneity in lithology is

noticed. The aquifer is more clayey in east and south-eastern parts of the district. The

formation materials are deposited under fluvial and marine environment. The marine

aquifers are in the east towards coast of Cauvery sub basin and entire Vennar sub

basin of the district except the northeast corner of the district. The thickness of the

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aquifer ranges from 10 to 35 m. Ground water occurs under water table as well as

confined conditions and is developed by means of shallow tube wells and dug cum

bore wells. The depth of tube wells ranges from 30 to 100 m bgl.

b) Quaternary Shallow Aquifers: The delta shows wide variations in the positions

of sands clays and silts both laterally and depth-wise resulting in wide variation of

permeability values and consequently in the yields of wells from depth to depth in the

same location. The aquifer of this group occurs at about 2 to 3 m bgl in major part of

Cauvery sub basin, which are partly confined by sandy silty formations overlying

these aquifers. Ground water occurs in these aquifers under water table, semi-

confined and confined conditions. The thickness of the aquifer ranges between 5 to 25

m within the depth of 45 m bgl. The aquifer at shallow depth ranges are tapped by

filter point wells, whose depth ranges between 8 to 12 m bgl and also by dug wells.

These aquifers are also developed by means of shallow tube wells whose depth ranges

mostly between 20 and 50 m bgl (below ground level).

2.13.3 Long term Fluctuation (2000-2009)

The long-term water level fluctuation for the period 1998-2007 indicates rise in

water level in the area to the maximum of 0.31m/year. The fall in the water level

ranges from 0.022 to 0.29 m/year. The spatial distribution of groundwater level for

2000 shows that the groundwater is deeper in the central part of the study area and is

shallow in the northern and southern part of the study area, similar trend was noted in

the groundwater contours of 2009 but the water table was comparatively shallower

than that of 2000. This may be due to the decrease of surface infiltration and increase

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Fig.2.7 Spatial distribution for Goundwater level 2000

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Fig.2.8 Spatial distribution for Goundwater level 2009

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of sea water intrusion onset. Removal of land cover exposes soil to erosion (wind and

water), which when combined with soil disturbances by livestock, speed the erosive

processes leading to reduction in infiltration and increased runoff (Lal, 2001).

2.13.4 Aquifer Parameters

In the porous formation the depth of the tube wells ranges from 76 to 711 m bgl. The

Specific Capacity value ranges from 13.43 to 870 lpm /m of drawdown and the

transmissivity value ranges from 11 to 1202 m2/day. The storability is in the order of

4.81 x 10-1 to 4.40 x10-10.