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CHAPTER 3

DESCRIPTION OF THE STUDY AREA

3.1 INTRODUCTION

The Gadilam river sub basin is located in the northern part of

Tamilnadu. It is one of the sub basin of Ponnaiyar river basins. The sub basin

lies between the Ponnaiyar basin in the north and the Vellar basin in the

south. It is an important sub basin from times of immemorial and had been the

centre of activity as many historical events have occurred from the early

Pallava Kings (10th century AD) to till the later British Period. Panruti,

Nellikuppam and Cuddalore are the major towns developed in a contiguous

manner in the study area. The Male Population of study area is calculated as

98,621 whereas the Female Population is 97,214. The Rural Population of

study area is calculated as 1,31,194 and Urban Population is 64,641. The total

population of the area is 1,95,835 according to 2001 census. The study area is

generally rural in nature except for a few towns mentioned above. This area is

located in a semi arid zone and faces acute water shortages.

The Gadilam rising in the Kallakurchi taluk flows eastwards across

the district. After passing South of Caddalore New Town, it runs into the Bay

of Bengal by two mouths rounding up the ruined Fort St.Davis. It is reported

that the river gets a supply of occasional floodwater from the Ponnaiyar

through the Malattar. There are three anicuts at Thiruvadigai (11045’N,

79035’E) at Vanamadevi (11045’N, 79040’E) and at Thiruvandhipuram

(11045’N, 79040’30”E), which are situated at heights of 55.70 ft., 39.70 ft. and

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16.97 ft. above sea level respectively. Between Thiruvadigai and Vanamadevi

the riverbed grades at 2 feet a mile, while over the rest of the river coarse its

fall is about 6 feet per mile.

South of Panruti (11045’N: 79034’E), the Cuddalore formation is

covered with a thick layer of clay of brick-red colour. Running water cuts

deep gullies, often with practically vertical sides, into the clays. About half a

mile south of the Gadilam, off Panruti, white clay-beds were noticed in gully-

sections.

3.2 LOCATION AND EXTENT

The Gadilam river sub basin is located between 110 39’12’’ to 110

47’34’’ N latitude and 790 28’00’’ to 790 47’24’’ E longitudes. The area

falling mostly with in the Survey of India topographic sheets of 58 M/5, 58

M/6, 58 M/9 and 58 M/10 on 1:50000 scale covering Panruti and Cuddalore

taluks of Cuddalore district in Tamilnadu, India.

In Tamilnadu, the river basins are divided into 17 basins and the

Ponnaiyar is one of them. The Ponnaiyar river basin includes 9 sub basins and

the Gadilam river sub basin is one among them.

The Gadilam river lower sub basin is bounded by Ponnaiyar basin

in the north, Vellar basin in the south, Bay of Bengal in the east and the

Gadilam river upper sub basin in the west. The index map is presented in the

Figure 3.1.

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Figure 3.1 Index Map

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The sub basin falls in Panruti, Annagramam and Cuddalore blocks

of Panruti and Cuddalore taluks in Cuddalore district. The aerial extent of the

study area is 315.17 sq. km. and the length of the Gadilam River is only

51 km in this sub basin. Villupuram bound the study area, east by Cuddalore

town, west by Thirukoilur, south by Vadalur and north. The map indicating

the administrative boundary is presented in the Figure 3.2.

3.3 ROAD NETWORK

The study area is well connected to the neighboring towns like

Cuddalore, Panruti and Nellikuppam, which help the farmers to market their

agricultural products. The State highway running between Chennai and

Tanjavur passes through this Gadilam river sub basin in Panruti taluk of

Cuddalore district. Panruti is one of the major towns situated at the northwest

of the study area, which is the junction place of Kumbakonam from the South

and Chennai from the north.

Cuddalore is another major town situated at the northeast of the

study area and the State highway passes through the town. A few other State

highways connecting Panruti and Cuddalore with other adjacent towns like

Villupuram, Neyveli, Puducherry and Chidambaram passing through the sub

basin. The good condition of these roads is due to the fairly dry climate that

prevails within the region Panruti and Cuddalore is linked by railway lines

connecting Chennai and Tanjavur. This railway line run across Gadilam River

near Vilangalpattu and the only railway station is situated at Cuddalore.

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Figure 3.2 Administrative Map

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3.4 PHYSIOGRAPHY

The catchment area of the Gadilam river sub basin consists of

extensional hills of the gently dipping Eastern Ghats hill ranges, having an

elevation of 167 m above MSL in the west. The study area has a gentle slope

towards east and the physiography of the study area is very much subdued

due to prolonged sub tropical weathering. The mean elevation here is around

50 m above mean sea level. The maximum elevation in the plain is 80 m and

the minimum elevation is 20 m. The relief of the sub basin is shown in the

Figure 3.3.

The Ponnaiyar River originates on the southeastern slopes of

Channakesava hills, northwest of Nandhidurg in Karnataka State at an altitude

of 1000 m above MSL. The river is called Dhakshina in Karnataka State.

After flowing through Karnataka the river enters Tamilnadu near Bagalur

village of Hosur taluk and takes the name of Ponnaiyar. Gadilam is one of the

sub basin of Ponnaiyar river basins. Gadilam river coarse at

Thiruvanthipuram is shown in Plate 3.1.

Figure 3.3 Relief Map

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Plate 3.1 Gadilam river coarse at Thiruvanthipuram

The aerial extent of the study area is 315.17 sq.km. The length of

the Gadilam River lower sub basin is 51 km and there is no flow in the river

normally except monsoon season. Gadilam River near confluence with sea

Cuddalore is shown in Plate 3.2.

Plate 3.2 Gadilam river near confluence with sea - Cuddalore

There are several tanks are located and are very smaller in extent,

hence they are not marked in the map. The major drainage is represented by

river Gadilam and it flows from west to east. The entire stretch of riverbed is

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covered with recent river alluvium. Though the study area has numerous

small to medium sized tanks connected with canals, these are noticed to be

mostly dry. Hence, the farmers mainly depend on the groundwater for the

cultivation.

3.5 DRAINAGE

The Gadilam River originates at an altitude of 167 m above MSL from Mayanur hills in the west and after a long run of 112 km., it empties in the Bay of Bengal, 2 km east of Cuddalore. The Gadilam is a small ephemeral river when compared to the rivers like Cauvery, Ponnaiyar of Tamil Nadu State. This study area is almost a plain with poking relief hills and is dominated by numerous tanks to a small extent. The Gadilam River receives the drainage of its own catchment and forms a definite coarse and flows towards east. The major drainage patterns found in the study area are trellis and dendritic types. The Gadilam River has many supply canals and these canals are mainly used for irrigation purposes. Malattar is a misfit river in the northeastern part, which occupies as inter basinal area between Gadilam and Ponnaiyar basin. In this study area three anaicuts are constructed across the Gadilam River. They are namely Thiruvadhigai, Vanamadevi and Thiruvanthipuram. The drainage map is shown in Figure 3.4.

Figure 3.4 Drainage map

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3.6 CLIMATE

In general the climate of the area is mostly hot and dry except

winter season. As per the Indian Meteorological Department (IMD) records,

the temperature ranges from 200 C to 420 C. Though the basin is not subjected to extreme climate in the summer months, it is quite hot. The climatological

data for the sub basin is obtained from Lekkur Weathering Station and is

furnished in Table A.1.4.

During January and February, the study area has a very pleasant

climate with warm days and cool nights, but by the close of February the climate becomes very sultry. The temperature shoots upto 420 C till May and

nearly June with the setting of the southwest monsoon in the later part of

June, the heat abates and strong wind blow from the southwest bringing sporadic rainfall. The climate during September and October is cool, through

sultry after the set of northeast monsoon. In the middle of October, cold

weather begins with wind velocities of 5 to 15 km /hour from northeast. The actual average annual pan evapotranspiration is found to be 192.25 mm.

Humidity of the study area varies relatively from 55 to 63 %.

3.6.1 Rainfall

For any water resources evaluation, planning, development and management studies, the knowledge of the rainfall over the sub basin area as

well as other hydro meteorological features is a pre requisite. The basic

factors, which influence agriculture, are climatological data such as rainfall, temperature, humidity, wind speed, sunshine and evaporation. Rainfall is the

major input for the water resources in a sub basin.

Generally, the distribution of rainfall in Tamilnadu is scanty with

respect to other States. As far as the study area is concerned almost 60 percent

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of the year remains dry though it receives rain during both the southwest and northeast monsoons. The basin receives appreciable rainfall during the

northeast monsoon season especially Cuddalore and the western part of the

study area, which area brought by the troughs of low pressure established in the southern part of Bay of Bengal during October and December. However

southwest monsoon alone has a precipitation of about one third of the average

rainfall, which helps the farmers to take the rainfall water for cultivation.

There are three raingauge stations. They are Cuddalore,

Vanamadevi and Panruti available in and around the study area. The rainfall breakup Figures for Cuddalore, Vanamadevi and Panruti with respect to the

various seasons are given below. Rainfall data for the past 35 years were

collected and analysed to study the influence of the rainfall in various seasons in the sub basin. The average rainfall recorded in the sub basin is 1250.30 mm

The average rain fall data for 35 years are furnished in Table A.1.5.

To study the rainfall distribution in the sub basin, contour maps

prepared for annual, southwest, northeast, winter and summer seasons for the

average rainfall of 35 years were shown in the Figures 3.5 to 3.9.

Figure 3.5 Annual Rainfall Contour Map of 35 years

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The 35 years annual rainfall contour map shows the highest rainfall ranging between 1270 and 1300mm received in the coastal area of the sub basin. The minimum rainfall ranging between 1180 and 1210 mm was recorded in the most of the study area.

The minimum rainfall varies between 100 and 180 mm received in

the coastal area whereas the western part of the study area received maximum rainfall 335 to 410 mm during the southwest monsoon period.

Figure 3.6 Southwest Monsoon Rainfall Contour Map

Figure 3.7 North East Monsoon Rainfall Contour Map

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The northeast monsoon contour revealed that the western part

received the maximum rainfall i.e. 600 to 670 mm and eastern part received

370to 445 mm of rainfall.

Figure 3.8 Winter Season Rainfall Contour Map

The rainfall in summer season was high in the western part and low

in the eastern part whereas in winter the maximum rainfall 45 to 50 mm was

recorded in the coastal area and the minimum rainfall 30 to 40 mm was

recorded in the western part of the study area.

Figure 3.9 Summer Season Rainfall Contour Map

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Generally, the sub basin received sufficient rainfall during the monsoon periods and occasional rainfall in the summer and winter season for raising the water levels in the water bodies so as to irrigate in the entire area periodically.

The recent 35 years rainfall data (1971 – 2005) pertaining to Panruti, Vanamadevi and Cuddalore rain gauge stations are also furnished in the Appendix 1 enclosed. 3.6.2 Relative Humidity

The meteorological features of the sub basin have been studied from the data available with Lekkur Weathering Station, which is the nearest weather station, located in south west of the study area (nearly 50 km). The minimum temperature recorded was 22.520 C in 1992 and maximum temperature was 37.190 C in April 1998. The monthly average percentage of relative humidity varies from 54.04 % to 75.56% as per Lekkur weathering Station

3.6.3 Wind Speed Wind velocity is an important meteorological parameter, which has considerable influence on evaporation and Evapotranspiration phenomenon. Wind has direct impact on climate and vegetation and is linked with circulation pattern of the monsoon. The average wind velocity in km/hour varies from 3.73 to 8.51 for Lekkur. 3.6.4 Sunshine & Temperature Temperature is one of the main parameters which is used to

calculate the crop water requirement (i.e. Evapotranspiration). The average

sunshine hours/day varies between 5.55 and 9.67 per day. Generally the

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climatic condition is almost amenable and does not exert any harm to human

and livestock existence.

3.7 SOIL DISTRIBUTION

Soil plays an important role in (a) encouraging or discouraging the

recharge of groundwater and (b) determining the quality parameters of ground

water. The soil map of the Gadilam river lower sub basin is shown in

Figure 3.10.

The major soil types found in this sub basin are Inceptisols, Alfisol,

Entisol and Vertisol. Due to different stage of weathering of parent material,

the above soil types are met with in combination. The list of mapping units

falling in the Gadilam lower sub basin is furnished in the Table A.1.6.

Figure 3.10 Soil Map

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3.7.1 Entisols

These soils show little or no evidence of development of pedogenic (diagnostic) horizons. They are found distributed on steep, actively eroding slopes and on flood plains, which receive new deposits of alluvium. Erosion is active in these soils. 3.7.2 Inceptisols

Inceptisols comprises of immature soils having profile features more weakly expressed. They are poorly drained to well drained with moderate to rapid permeability. Most of them are cultivated under irrigated or rainfed conditions. 3.7.3 Vertisols

This order includes dark brownish grey, very deep, calcareous,

heavy clayey and self-churning soils that have deep wide cracks. They are

moderately well drained with slow permeability except in the cracks.

3.7.4 Alfisols

This consists of deep to very deep, matured soils with alluvial

concentration of clay in the sub horizon. They have moderate to high base

saturation.

National Bureau of Soil Survey and Landuse Planning, Bangalore

(NBSS) have carried out soil Classification in 1996 in co-operation with the

Department of Agriculture, Tamil Nadu. The soil characteristics of Gadilam

lower sub basin are furnished in the Table A.1.7.

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3.8 AGRICULTURE

The first crop is raised with the help of surface water, usually

during September to December in every year, and paddy is invariably

cultivated. In the second crop, generally dry crops like groundnut, ragi,

cumbu etc, are being raised. In most of the places sugarcane, casuarina,

mango trees, jack trees etc are also raised by using surface water and

groundwater. In the third crop by using the sub-surface water, limited wet

crops are raised during the months of June to August which is very rare.

Paddy field at Vilangalpattu is shown in Plate 3.3.

Generally surface water flow is carried out from lakes, ponds, tanks

etc through several streams and canals whereas subsurface water flow is

mainly carried out by means of deep bore wells and bore wells. It is

significant to note that the role of wells (deep bore wells, and bore wells) is

important in the agricultural growth and production activities.

Plate 3.3 Paddy field at Vilangalpattu

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3.8.1 Method of Irrigation

The area is generally irrigated by tanks and wells. The irrigation

wells play a vital role in the dry land (irrigation by rain water) areas. In the

case of canal irrigation areas, they supply water when the surface water flow

becomes scarce. Generally the surface water flow is available in the canal

irrigation area for about 3 to 4 months in a year.