DESCRIPTION OF THE STUDY AREA

- S;ro Brundtlanii, Our Common Future

CHAPTER V

STUDY AREA

5.1 LOCATION

The Union Territory of Pondicherry is comprised of four interspersed geographical

entities namely Pondicherry, Karaikal, Mahe and Yanarn. Pondicherry region is the

largest of the four. and is situated on the Corarnandal Coast between 1 l o 45' and 1 2 O

0' North Latitude and 79' 37' and 79' 50' East longitudes. The region covers 293 sq.

km. (60.66% of the U.T.), consisting of five "Communes" (Derived from French

word, meaning rural settlements) viz. Ariyankuppam, Bahour, Mannadipet,

Nettapakkam and Villiyanur Commune and two Municipalities (Urban settlements)

viz. Pondicherry and Oulgaret Municipality. It is surrounded by Bay of Bengal on

the East, Cuddalore District on the South and Villupurarn District on the North and

West sides (Fig.5.1).

5.2. CLIMATE

I'he climate of Pondicherry region is humid and tropical. The mean monthly

temperature ranges from 22OC to 33OC and maximum temperature is observed during

the months of May and June and minimum during December and January. The

relative humidity varies between 70% and 85% and it is highest during the months of

December and January and lowest during the month of June.

'The average annual rainfall in Pondicherry is about 1254 mm (1960-2000). The

region receives rainfall from both SW and NE monsoons with annual rainfall

spreading over a period of seven months. The North East monsoon during October to

December constitutes 62% of the annual rainfall and the South West monsoon

prevailil~g from June to September accounts for 28% and (Table 5.1).

A study of the distribution of rainfall (Central Ground Water Board, 1993) reveals

that there is a decrease in the rainfall from East to West, i.e., from about 1300 mm

near the coast on the East to 1100 rnm in the Western and North Western border. The

precipitation increases from West to East during South West monsoon where as the

reverse occurs during the North East monsoon.

Table 5.1. Rain fall data of Pondicherry Region (1999-2003)

Monthly total rainfall (mm)

Number of rainy days (2.5 mm and above)

Source: Indian Meteorology Department, Chennai

Year

1999

2000

2001

2002

12003 L

Apt

53.0

34.1

43.1

1.3

1.2

Feb

0.6

236.7

0.0

80.3

0.0

Jan

6.5

41.4

7.4

38,7

0.0

Mar

0.0

0.0

0.0

0.0

2.9

May

13.7

12.9

52.2

24.6

49.3

Jun

61.3

29.0

27.9

42.7

11.6

Jul

72.6

20.9

124.1

57.8

76.9

Aug

78.4

82.6

136.9

69.5

167.3

Sep

24.9

202.1

107.3

59.8

76.2

Oct

439.5

157.9

227.1

242.4

206.8

Nov

284.5

171.6

121.3

212.6

514.7

Dec

297.4

177.0

101.1

121.9

28.1

The wind frequency classification in terms of different wind speed categories and 16

wind directions are given for summer, pre-monsoon and winter seasons in the

Appendix 5.1, 5.2 and 5 -3 respectively. The predominant wind direction is from S W

during summer and SW monsoon seasons. During NE monsoon season, the wind

direction is variable, while during the winter season, the NNE-ENE direction is

predominant (33.4%). Wind roses are drawn on the basis of three hourly data

collected for a period of one year. The wind roses are drawn for June, August, and

January, which are representative of summer, pre-monsoon and winter seasons

respectively and presented in Fig.5.2.

5.3 POPULATION

The population of U.T. of Pondicherry as per 2001 census is 9,73,829. Out of this the

population of Pondicherry region is 7,35,004 (75% of U.T.) with an urban population

of 5,05.7 1 5 (3 1% of the total population) and rural population of 229289 (68.8%).

The average density of population in Pondicherry region is 2534 persons per sq.km.,

which is about 6.8 times higher than the National average of 324 persons1 sq.km. The

average population growth rate of Pondicheny region is 2.7% Literacy in

I'ondicherry region is 80.90%,

5.4 PHYSIOGRAPHY

Thc Pondicherry region in general is a flat plain with an average elevation of about

15 m above the mean sea level (MSL). The terrain becomes little undulating with

prominent high grounds varying from 30 to 45 m above the MSL towards interior

North and North Western part of the region. There are three major physiographic

units: Coastal Plain, Alluvial plain and Uplands.

I'he coastal plain extends as a narrow stretch of 400 to 600 m width on the Eastern

part of the region along the Bay of Bengal. The major part of the plain comprises of

gently sloping land with a chain of sand dunes extending all along the coast. Other

characteristic physiographic units of the coastal plains such as spit bars, mud flats.

lagoons and tidal inlets also occur in the study area to a limited extent.

he alluvial plain, which occupies major portion of Pondicheny region is, formed

due to two major rivers namely Gingee and Ponnaiyar River that pass through the

area. This is covering Bahoor, Nettapakkam, Ariyankuppam, Southern part of

~annadipet and Villianur and part of Oulgaret municipality on the South. The

alluvial plain is generally a monotonous plain with a slope ranging from 1 to 3%.

The land in this plain is intensively cultivated throughout the year by tank and lift

irrigation. Besides the river and major canals, there are depressions acting as storage

tanks, which are spread all over the terrain to serve as surface water reservoirs.

Towards the North West and North East of Pondicheny region (covering Northern

part of Mannadipet and Villianur Communes and Oulgaret Municipality) undulating

high ground occurs with elevations of about 30 to 45 m above MSL. These are

known as uplands and are intersected by a number of gullies and deep ravines giving

rise to bad land topography. A patch of gently sloping fossili ferous limestone terrain

also exists in the Northwestern portion of this region.

In spite of limited land area in the Pondicherry region, it exhibits a wide variety of

soils ranging from sandy soil to heavy clay soil, red soil to black soil. calcareous soil,

non-calcareous soil etc. However, alluvial soil is dominant in the region-covering

85% of'the geographical area (Central Ground Water Board. 1976).

5,s RIVERS

There are two major rivers flowing in the Pondicherq region namely the

Sankaraparani River in the North and Ponnaiyar River in the South. The

Sankarabarani River traverses about 34 km in the region before joining the Bay of

hengal. The river branches off into Ariyankupparn River in the North and

('hunnambar in the South in the Eastern part of the region. The river Ponnaiyar

forms the Southern border of the study area. The Malattar is the distributaries of the

Ponnaiyar river.

5.6 HYDROGEOLOGY

l'he sedimentary formations occurring in the entire region are represented by

Cretaceous, Paleocene, Mio-pliocene and Quaternary formations (multilayered

aquifer system). Ground water occurs in these formations both under water table as

well as confined conditions and is being developed by dug wells, dug-cum-bore

wells and tube wells.

Among the various water bearing formations of cretaceous age the Rarnanathapuram

and Vanur formations form potential aquifers. They occur in the North Western part

of Pondicherry region. The thickness of the aquifer ranges between 38 m and 98 m.

Ground water occurs under confined conditions and the piezometric head is about 20

m to 33 m below ground level. The yields of the tube wells tapping these aquifers

range between 500 to 1500 liters per minute. The transmissivity values of these

aquifers range between 92 to 1925 m2 per day and the storage coefficient value

varies from 2.93 x 1 o - ~ to 1 . 3 6 ~ 1 o - ~ .

The Cuddalore sandstone aquifer (the upper tertiary) occupies an extensive area

(65%) in this region. The aquifer attains great thickness in Bahoor, Ariyankuppam

and PondicherryMunicipalities. Also in some parts of Nettapakkam. Oulgaret,

Villianur communes and south of Sankarabarni river the aquifer has greater

thickness. 'The thickness of the aquifer ranges from 20 m at Oulgaret municipality

and 245 in at Manapet in Bahoor commune. Ground water occurs in the aquifer

mainly under confined conditions and yield is ranging from 200 to 3000 litres per

minute. The average transmissivity is estimated as 2000 sqm per day and the storage

coefficient values range between 9.583 x 10" and 8.9 x lo4. The piezometric level in

the aquifer ranges between 6 m and 25 m below ground level.

Alluvial (recent formations) deposits occupy nearly three fourth of Pondicherry

region. '1 his is the most potential shallow aquifer system in the region. The thickness

of this aquifer ranges between 5 m and 34 m. Ground water occurs under water table

Qr under semi-confined conditions. The transmissivity values of the aquifer in the

West (Madukarai) are 275.4 m2 per day and 770 m2 per day in the ~ a s t

(~himkanjee). The water level in the aquifer ranges fiom 12 m to 15 m below

p u n d level.

5 7 GEOLOGY

The entire area of Pondicherry region is covered by sedimentary formations, ranging

in aye from cretaceous to recent, except a small extent of area in the Northeastern

pad of Pondicherry.

The oldest sedimentary formations are the cretaceous sediments of Mesozoic era and

are exposed in the North Western part of the region and Nonh of Sankarabarani

river. The trend of these formations is North East-South West. Four stratigraphic

units namely Ramanathapuram, Vanur sandstone, Ottai claystone and Thuruvai

limestone formations have been identified.

The Paleocene formations of the Lower Tertiary are represented by the

Kadaperikkuppam and Manaveli formations in the region. The trend of these

formations is similar to the cretaceous formations. The Kadeperikupparn formations

are cxposed near Pillaiyarkuppam, Sedarapattu, Kadaperikuppam and Alankuppam. ? .

1 he thickness of this formation varies widely which may be due to the unevenness of

the cretaceous basement. The thickness of the formation varies from 30 m to 130 m

at outcrob area and maximum thickness of 450 m is observed at Manapet along the

coast in the South Eastern side.

'The recent (Quartemary) formation in the region is represented by laterites and

alluvium laterites occur as thin cap over the Cuddalore formation. Thick alluvial

deposits are built up along the course of Ponnaiyar and Sankarabarani rivers

covering three fourths of Pondicheny region. The thickness of alluvium varies from

10 m to 55 meters at different places.