45

CHAPTER 3

STUDY AREA AND DATA COLLECTION

3.1 GENERAL

India experiences extremes of climate within its 329 million

hectares of geographical area. The rainfall is monsoon based and unevenly

distributed both spatially and temporally. Mean annual rainfall varies from

100 mm in western Rajasthan to over 11000 mm at Cherrapunji in Meghalaya

(Indian Water Resources Society 1995). The incidence of rainfall is also

seasonal, occurring mainly during the Southwest monsoon (June to

September) in most parts of the Country except Tamil Nadu. The water

resources potential of India is shown in Table 3.1.

The average annual flow in the river systems of India has been

assessed to be 1869 TM m3. The major constraint in utilising all the available

water is the fact that it is necessary to store the river flows that occur mainly

during monsoon months. Nearly sixty percent of India’s river flow is carried

by the Ganga - Brahmaputra - Barak, which command only thirty three

percent of the geographical area of the Country.

Though India’s per capita availability is greater than “Water Stress

Index”, there are regions and States which fall into the category of “Water

Scarce” territory, i.e., less than 1000 m3/person/year. Tamil Nadu is one of the

water scarce States of India.

46

Table 3.1 Water resources potential of India

Sl. No. River Basin

Water Resources Potential ( B m3)

1 Indus 73.30

2 Ganga 525.00

3 Brahamaputra 537.00

4 Barak 48.40

5 Godavari 110.50

6 Krishna 78.10

7 Subernarekha 12.40

8 Cauvery 21.40

9 Brahmani-Baitarani 28.50

10 Mahanathi 66.90

11 Pennar 6.30

12 Mahi 11.00

13 Sabarmathi 3.80

14 Narmada 45.60

15 Tapi 14.90

16 West Flowing From Tapi to Tadri 87.40

17 West Flowing From Tadri to Kanyakumari 113.50

18 East Flowing Between Mahanathi to Pennar 22.50

19 East Flowing Between Pennar to Kanyakumari 16.50

20 West Flowing - Kutch and Sourashtra 15.10

21 Minor Rivers draining into Mynmar and Bangladesh

31.00

TOTAL 1869.10 Source: Central Water Commission, Govt. of India, New Delhi

47

3.2 TAMIL NADU

3.2.1 Physical Features

Tamil Nadu lies at the Southeastern extremity of Indian peninsula

between Latitudes 85’ N and 1320’ N and Longitudes 7615’ E and

8020’E. Bounded by the Bay of Bengal on the East, the Indian Ocean on the

South, Western Ghats on the West, Karnataka and Andhra Pradesh on the

North, the State has a long coastline of about 1000 km. The geographical area

of the State is 1.30 lakh km2, which constitutes four percent of the

geographical area of India.

3.2.2 Climate and Rainfall

Tamil Nadu has a tropical climate. The normal maximum and

minimum temperatures (except in the hill areas) are 45C and 18C

respectively. The State has four distinct seasons:

(i) Southwest Monsoon June to September

(ii) Northeast Monsoon October to December

(iii) Cool Weather Dry (winter) January to February

(iv) Hot Weather Dry (summer) March to May

The Western part of the State, especially the portions closer to

Western Ghats benefit from the Southwest monsoon. But the Eastern coastal

belt gets most of the rain during the Northeast monsoon. The intermediate

plateau has poor rainfall and there are pockets that are chronically drought

prone. The total average rainfall is 925 mm of which 60-65% of rainfall

comes during Northeast monsoon and 25-30% comes during Southwest

monsoon.

48

The distribution and variability of rainfall in Tamil Nadu are quite

significant. Rain is not evenly spread throughout the year, but is concentrated,

on an average of 23 rainy days each during Southwest and Northeast

monsoons. The Northeast monsoon is considerably more erratic than the

Southwest monsoon. All these factors indicate the importance of irrigation to

Tamil Nadu.

3.2.3 River Basins

There are thirty three river basins in Tamilnadu. The Cauvery is the

only major river basin (Area of basin is more than 20000 km2). It originates

from Coorg district of Karnataka. There are ten medium river basins (Area

between 2000 km2 and 20000 km2). There are twenty-one minor basins that

have less than 2000 km2 of basin area. Some of the tributaries of the west

flowing rivers of Kerala such as Chaliyar, Periyar, Chalakkudi and

Bharathapuzha originate from Tamil Nadu.

Tamil Nadu, besides being vulnerable to the fluctuation of rainfall,

is dependent heavily on inter-state co-operation for its water resources.

Sharing of Cauvery water is the bone of contention between Tamil Nadu and

Karnataka and marked by a prolonged dispute, still unresolved.

The total annual water potential available from the river basins is

36,000 M m3. The river basins are shown in Figure 3.1 and their annual water

potential available are given in Table 3.2.

49

Figure 3.1 River basins in Tamil Nadu State, India

27

50

Table 3.2 Basin wise runoff in Tamil Nadu

Sl. No.

Name of River Basin Runoff (M m3)

1 Cauvery 7,173.32

2 Medium River Basins

1. Palar

2. Pennaiyar

3. Vellar

4. Vaigai

5. Thamiravaruni

6. Kortaliar

7. Gundar

8. Vaippar

9. Manimuthar

10. Kottakkaraiar

2,173.32

1,640.44

1,574.95

1,272.81

1,706.79

562.47

342.48

310.08

355.08

218.34

3 Minor River Basins - 21 3,190.70

4 West Flowing Rivers 3.073.07

Total 23,597.84

5 Runoff from other States 12,126.07

Grand Total 35,723.93 Source: Water Resources Organisation, Public Works Department, Government of

Tamil Nadu.

51

3.3 THAMIRAVARUNI RIVER BASIN

Thamiravaruni river basin was selected as the focus catchment in this study. This basin is one of the oldest systems in Tamil Nadu. The river is short but a perennial source in the Southern part of this State. Irrigation development is a major source of income for the people living adjoining the

Thamiravaruni river. The monsoon behaviour was erratic and the major portion of the area under this basin is prone to droughts with intensity ranging from mild to severe. Also, major portion of this basin is economically weaker in terms of industrial development. Hence, frequent droughts pose serious

consequences for the poor economy and the people livelihood. Hence, Thamiravaruni river basin was selected to study the behaviour of droughts

with a reference to meteorological and agricultural perspective. Archaeological discoveries on the banks of the river indicate a civilized life in the area around 400 BC. According to historians, the

Thamiravaruni holds a high position amongst the Indian rivers. This river is fed by both monsoons. It flows through a narrow but rich alluvial valley

originally formed by itself. Such a river is ideally suited for practising agriculture, especially irrigated rice cultivation. Thamiravaruni was in the state of Pandyas and pearls were found near the place where the river joins the sea. The port of Korkai was situated at this point. This port was cited in

both “The Periplus of the Erythraen Sea” and Ptolemy’s “Geography”. The cradle of Tamil culture lay on the rice growing low lands adjoining the Thamiravaruni river. The British considered the “Tinnevelly District” as it was called then, a key to international trade with its proximity to Colombo.

The earliest Sangam Literature in Tamil refers this river as

“Porunai”. There are many versions for its present name and its origin. The Sanskrit “Tamra” means copper or red and “Parna” means leaf and “Varna” means colour. Hence we have either copper coloured river or river with red

52

leaves. Bishop Dr. Caldwell identified the word Tambapani mentioned in Asoka inscriptions with the word Tamraparani and with Taprabone, the name

by which Sri Lanka was known to the Greeks before the Christian era. The details of Thamiravaruni river basin are presented in the following sections.

3.3.1 Physical System of Thamiravaruni Basin

Thamiravaruni river originates from the peaks of Pothigai hills on the Eastern slopes of the Western Ghats at an altitude of 2000 m and confluences with the Bay of Bengal at Gulf of Mannar. The Thamiravaruni river is 125 km long from its origin to the Gulf of Mannar. It is the lifeline for the people of Thirunelveli and Thoothkudi districts. The total area of the

basin is 5,969 km2, of which hilly portion is 688 km2. The basin is situated between 8o 21’ N and 9o 13’ N Latitudes and 77o 10’ E and 78o8’E Longitudes. The Thamiravaruni basin map is shown in Figure 3.2. It enjoys the benefit of both the Southwest and Northeast monsoons as it receives

supply from the rainfall over Western Ghats. The river traverses about 125 km through Thirunelveli and Thoothukudi districts in Tamil Nadu, India.

District wise area of the basin is furnished in Table 3.3.

Table 3.3 Districtwise area of Thamiravaruni basin

Sl. No.

Name of district Area falling in

Thamiravaruni basin (km2)

1 Thirunelveli 5317 2 Thoothukudi 652

Total 5969

There are 26 administrative blocks either partly or fully covered in

this basin. The administrative block boundary map of Thamiravaruni basin is

shown in Figure 3.3.

53

Figure 3.2 Thamiravaruni river basin map

54

Figure 3.3 Block boundary map of Thamiravaruni river basin

55

3.3.2 Tributaries

The Western Ghats provide a beautiful landscape along the Western

boundary of Thirunelveli District. There are 20 peaks with heights of more

than 1500 m above mean sea level. “Pothigai” is the most striking peak at

1867 m above mean sea level. The peak receives an annual rainfall of more

than 3500 mm. The Thamiravaruni river originates from this peak and has

around 500 km2 of catchment area in the Western Ghats. From Pothigai, the

river flows down in a rapid current through dense forest valley up to

“Vanatheertham” waterfalls.

The “Peyar” and “Ullar” are two tributaries in this region. At

Vanatheertham the river falls as a cascade. The “Pambar” on the right and

the “Korayar” on the left join the river below the waterfalls. From then on,

the river has a mild fall and traverses in a flat terrain. The “Servalar”, which

is the most significant tributary in the Western Ghats, joins the river on the

left at Mundanthurai. Then the river reaches Papanasam and makes a fine

waterfall of 100 m called “Agasthiar falls” and “Kalyani theertham”. From

here onwards, the river traverses in the plains.

Manimuthar

The first tributary to join the river in the plains is the Manimuthar.

The river Manimuthar originates in a thick forest above “Sengaltheri” in the

erstwhile “Singampatty zamin”. Varattar, Kusunkiliyar and Kilmanimuthar

are tributaries to Manimuthar in the hilly region. There is an Anicut called the

Thalai Anai, from which the Perunkal takes off. Through this Perunkal, the

Manimuthar provides irrigation for the Singampatti area.

56

The river splits into two arms below this anicut which join again

into a single course before entering the Thamiravaruni. There is an anicut

clled Kothikal across the broader arm on the right side. A channel takes off

from this anicut to provide irrigation. The left arm carries flood flows only

and remains dry most of the time. The river Manimuthar joins the

Thamiravaruni at the Kannadian anicut near Ambasamudram.

A jungle stream called “Koraiyar”, which carries flash floods,

joins the Thamiravaruni on the right near Velangudi village.

Gadananadhi

The Varahanadhi, which brings down the combined supply of

Ramanadhi and Jambunadhi, joins Gadananadi. These rivers originate in the

hills of Melakkadayam. There are anicuts across Ramanadhi. The Gadanadhi,

which originates in Sivasilam hills, has two tributories Kallar and

Karumeniar before Varahanadhi joins. The Gadananadhi has 6 anicuts. The

Gadananadhi joins the Thamiravaruni near Thiruppudaimarudur.

Pachaiar

The Pachaiyar originates in the Kalakkadu hills and joins the

Thamiravaruni near Tharuvai. There are 12 anicuts across Pachaiyar.

Chittar

Chittar is the last affluent tributary originating from the Courtallam

hills of the Western Ghats. The river traverses about 80 km and infalls into

Thamiravaruni near Sivalapperi village. The river Chittar has five tributaries

namely Ayndaruviar, Hariharanadhi, Aludhakanniar, Hanumanadhi and

57

Uppodai. The first four tributaries have their origin in the high rainfall region

of the Western Ghats. The Hariharanadhi has Gundar and Mottaiar as

tributaries. Hanumanadhi has Karuppanadhi as a tributary. All these

tributaries have systems of anicuts and channels and provide irrigation. The

main river Chittar has seventeen anicuts diverting flows to its command area.

The river Thamiravaruni, after the confluence of the Chittar, travels

another 53 km and enters the gulf of Mannar near Palayakayal. There are

reservoirs across the tributaries Manimuthar, Gadana, Ramanadhi, Gundar,

Mottaiar and Karuppanadhi of the Thamiravaruni river. Only the Manimuthar

reservoir has a separate canal to feed 308 tanks and their ayacut and other

reservoirs only stabilize the old ayacut areas of the respective rivers. The

system has seven major reservoirs, eight major anicuts and eleven channels

irrigating an area of 1,04,098 ha.

3.3.3 Major Reservoirs

Thamiravaruni river system has seven reservoirs of which

Papanasam, Servalar and Manimuttar are the major ones. The details of

reservoirs are listed in Table 3.4.

Papanasam reservoir was constructed across Thamiravaruni and is

in use since 1944. This has a gravity dam with a storage capacity of 156 Mm3.

The dam is 336 m long and 53 m high. This reservoir is also called as “Hope

Lake”. A diversion weir below this dam at the confluence of Servalar diverts

water to a power house with a head of 91 m. The purpose of the reservoir is to

impound the flood flows which go as waste below the last anicut viz.,

Srivaikuntam Anicut and utilizing the water for both irrigation and power.

58

Table 3.4 Reservoirs in Thamiravaruni basin

Sl. No.

Name of reservoir

Location Catchment

(km2) Capacity (M m3)

Ayacut (ha) Latitude Longitude

1 Papanasam 8o 38’ 43” N 77o 18’ 06” E 150.0 156.0 34848

2 Manimuttar 8o 39’ 00” N 77o26’ 00” E 162.0 156.0 9879

3 Gadana 8o48’ 00” N 77o19’ 00” E 46.5 10.0 3685

4 Ramanadhi 8o50’ 00” N 77o19’ 15” E 16.6 4.3 2000

5 Karuppanadhi 9o08’ 00” N 77o18’ 00” E 29.3 5.2 3851

6 Gundar 80 55’ 05” N 77o13’ 04” E 9.9 0.7 454

7 Servalar 8o41’ 18” N 77o18’ 06” E 106.0 35.0 Nil

Source: Report of District Water Resources Conference held at Thirunelveli in March 1999.

Servalar reservoir has been constructed across the tributary Servalar

in the year 1986 with a storage capacity of 35 M m3. The dam is 450 m long

and 53 m high. The full reservoir level is kept at the same level as that of the

Papanasam. These two reservoirs are interconnected by a 3,323 m long tunnel

with a carrying capacity of 30 m3/s. Now, all the irrigation demand is let

through the Servalar hydropower house, which is having a power generating

capacity of 20 MW.

Manimuthar reservoir was constructed across the tributary

Manimuthar in the year 1958. It has a storage capacity of 156 M m3. As the

river sluice is constructed with its sill at the bed level, there is no dead

storage. The Manimuthar reservoir stabilizes the Thamiravaruni system

through its river sluices.

59

3.3.4 Small Reservoirs

Even after the construction of the major reservoirs, it was found

that a substantial quantity of water is being surplused at the last anicut at

Srivaikuntam. But some regions in the command area suffered for want of

water. This is due to flash and erratic flows occurring in the river system

particularly in more affluent small tributaries of the Thamiravaruni river.

Therefore, small reservoirs were constructed as below.

(a) Gadana with a storage capacity of 10 M m3 across Gadana

river.

(b) Ramanadhi of storage capacity 4.33 M m3across Ramanadhi

river.

(c) Karuppanadhi of storage capacity of 5.2 M m3 across

Karuppanadhi river.

(d) Gundar of storage capacity of 0.7 M m3 across Gundar.

3.3.5 Anicuts

Local weir is called as “Anicut”. Thamiravaruni river has eight

anicuts which act as important irrigation diversion structures. The first seven

anicuts were built by the Pandia Regime, centuries ago. The details of anicuts

are listed in Table 3.5. These anicuts are either ‘L’ shaped or 'Horseshoe'

shaped depending upon whether one channel takes off or two channels take

off respectively. The last anicut viz. Srivaikuntam anicut was constructed

during the years 1869 - 1873. This is the only anicut under the system, which

has been constructed straight across the river. The surplus water over this

anicut joins the Gulf of Mannar.

60

Table 3.5 Hydraulic particulars of Anicuts on Thamiravaruni basin

Sl. No.

Name of Anicut Name of channel

Channel length (km)

Command area (ha)

Number of tanks

1 Kodaimelalagian South Kodaimelalagian

8.64 357 - 357 -

North Kodaimelalagian

18.51 532 393 925 20

2 Nadhiyunni Nadhiyunni 11.55 1053 - 1053 -

3 Kannadian Kannadian 33.95 4182 876 5058 16

4 Ariyanayakipuram Kodagan 29.04 1295 1133 2428 17

5 Palavour Palayam 42.26 1862 1983 3845 59

6 Suttamalli Tirunelveli 29.14 1022 1572 2594 23

7 Marudur Melakkal 19.84 1843 3330 5173 16

Keelakkal 17.91 1202 1952 3154 15

8 Srivaikuntam South main canal

33.87 1090 4076 5166 15

North main canal

36.32 1331 3850 5181 6

Total 15796 19165 34934 187

3.3.6 Land Use Pattern

Classification of land use pattern in Thamiravaruni basin (in

Tamil Nadu State, as per State Frame Work Water Resources Plan, Institute

for Water Studies, Government of Tamil Nadu, Report No.4/97) is given in

Table 3.6 and pictorially represented in Figure 3.4. It contains 67.27% of

agricultural land and 10.49% of wasteland. In the wasteland, 8.05% of area is

unrecoverable for cultivation purpose as they are rock outcrops and coastal

swamps. This shows that the entire cultivable area was exploited to the

maximum for production purposes.

61

Table 3.6 Land use pattern of Thamiravaruni basin

Sl. No.

Description Area

(km2) Percentage

1. Agriculture Land

i) Intensively irrigated crop land

ii) Sparsely irrigated crop land

iii) Dry crop land

iv) Cashew farms

1010.14

318.68

2672.03

15.00

16.94

5.35

44.83

0.28

Sub-total 4015.85 67.40

2. Waste Land

i) Barren / Rocky outcrop

ii) Sand dunes / Teri

iii) Grass land

iv) Uncultivable waste coastal shrub / Marshes / Swamps / Saltpan.

380.47

83.79

62.50

100.00

6.37

1.40

1.05

1.68

Sub-total 626.76 10.50

3. Forest Land

i) High dense forest

ii) Medium dense forest

iii) Low dense forest

iv) Scrub Forest

102.03

604.17

378.93

101.56

1.71

10.13

6.36

1.70

Sub-total 1186.69 19.90

4. Water Bodies

i) Reservoirs, Tanks, Ponds and Streams

139.95

2.20

Overall total 5969.25 100.00

62

Figure 3.4 Land use map of Thamiravaruni river basin

63

3.3.7 Soils

The soils in the head reach are deep, stratified, dark grey, medium

to heavy textured, non-calcareous, alluvial soils and are lighter in colour.

They are mostly formed by the deposition of the nearby hill wash materials in

the depressions.

In the middle reach, the soils are very deep, dark grayish brown,

medium to heavy textured and calcareous with moderate permeability. In the

tail end, the soils are deep, light to medium textured and calcareous. Moderate

saline to sodic soils are also present in this area. The soils are clay loam to silt

clay loam in texture. All these soil types are suitable for rice, banana and

sugar cane cultivation.

3.3.8 Agriculture

The main crop in Thamiravaruni basin is paddy. As the flow is

perennial, as much as 95% of paddy crop area has two crop seasons. The first

crop season is synchronised with the Southwest monsoon between June and

September called Kar and the second is with Northeast monsoon called as

Pishanam between October and February. There is summer paddy crop in

some areas called as Advance Kar utilizing summer rain during April- July.

After the harvest of Advance Kar in the above areas, pulses and gingelli are

grown from July to October. Details of cropping pattern and crop calendar

being adopted in the Thamiravaruni basin are presented in Figure 3.5.

64

Sl. Cropping No pattern Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May

1 Paddy (Kar Crop)

2 Paddy (II crop Pishanam)

3 Paddy (Advance Kar)

4 Sugarcane and Banana

(Annual Crop)

5 Ragi, Cumbu etc. (Dry Crop)

Figure 3.5 Generalized crop calendar for Thamiravaruni basin

65

3.4 DROUGHT PRONE AREAS PROGRAMME (DPAP)

Drought Prone Areas Programme (DPAP) is one of the area

development programmes launched by the Government of India in 1973-74 to

tackle the special problems faced by those fragile areas which are

constantly affected by severe drought conditions. These areas are

characterized by large human and cattle populations which are

continuously putting heavy pressure on the already fragile natural resource

base for food, fodder and fuel. This continuous biotic pressure is leading

to fast and continuous depletion of vegetative cover, less and less rainfall,

increasing soil erosion and fast receding ground water levels due to

continuous exploitation without any effort to recharge the underground

aquifers.

The districts covered under Thamiravaruni basin are Thirunelveli

and Thoothukudi. The areas covered under these districts are 5317 km2 and

652 km2 respectively. Though it is advisable to carry out any water resources

analysis on watershed/sub-watershed basis, the implementation of any

Government programme is on block / taluk – revenue subdivisions basis. The

details of blocks and those coming under DPAP in Thamiravaruni basin are

presented in Table 3.7.

66

Table 3.7 DPAP coverage in Thamiravaruni basin

Sl. No.

Name of district

Name of Taluk Name of Block Status under DPAP

1 Thoothukudi Kovilpatti Kayattar Included Ottappidaram Ottappidaram Included

Srivaikuntam Srivaikuntam

Karunkulam Not included Not included

Tiruchendur Tiruchendur

Azhwartirunagari Udangudi

Included Not included Included

Sattankulam Sattankulam Included Thoothukudi Thoothukudi Included

2 Thirunelveli Senkottai Senkottai Not included

Sankarankovil Sankarankovil

Melanilidanallur Kuruvikulam

Included Not included Not included

Sivagiri Vasudevanallur Not included

Tenkasi Tenkasi Kilpavur Alangulam Kadaiyanallur

Not included Not included Not included Not included

Amabasamudram Amabasamudram Kadaiyam Pappakudi Cheranmadevi

Not included Not included Not included Not included

Thirunelveli Manur Not included

Palayankottai Palayankottai Not included

Nanguneri Kalakkadu

Nanguneri Not included Not included

67

3.5 DATA COLLECTED

The data needed for assessing the drought can be grouped into three

categories viz. meteorological, hydrological and agricultural. The above data

collected from various departments are detailed below.

3.5.1 Meteorological Data

Monthly rainfall data for 26 raingauge stations were collected from

the State Surface and Ground Water Data Centre, Water Resources

Organisation (WRO), Public Works Department (PWD), for the period 1971-

2000. Climatological data such as temperature, humidity, sunshine, wind

velocity, pan evaporation, etc., were collected for Malaipatty meteorological

station from the Institute for Water Studies (IWS), WRO, PWD. Similar

meteorological data were collected for the weather station at Palayankottai

from the India Meteorological Department.

3.5.2 Hydraulic and Hydrological Data

Hydraulic particulars of the reservoirs Papanasam, Manimuthar,

Gadana, Ramanathi, Karuppanadhi, Gundar and Servalar were collected from

IWS. Stream flow data were collected for the gauging stations at

Kodaimelalagian, Nadhiyunni, Kannadian, Palavour, Suttamalli, Marudur and

Srivaikuntam Anicuts from the State Surface and Ground Water Data Centre,

WRO, PWD, Chennai and other WRO offices in Madurai, Thirunelveli and

Tenkasi for the period 1991-2000.

The hydraulic particulars such as water spread area, capacity,

ayacut, etc. for 1300 tanks located in Thamiravaruni basin were collected

from WRO, Thamiravaruni Basin division at Thirunelveli.

68

3.5.3 Agricultural Data

The agricultural data such as land utilization, crop calendar, crop

pattern and crop area particulars were collected for Thirunelveli and

Thoothukudi districts from the Statistical and Agricultural Departments at

Thirunelveli and Thoothukudi. The block wise agricultural data were also

collected from the concerned district offices of the statistical department.

3.5.4 Maps

The following maps pertaining to Thamiravaruni basin were

collected. All maps are of scale 1: 2,50,000.

(i) Basin map;

(ii) Administrative boundary map;

(iii) Land use map;

(iv) Hydrogeology map; and

(v) Geomorphology map.

3.6 PRELIMINARY ANALYSIS

The meteorological, hydrological and agricultural data collected for

Thamiravaruni river basin has been analysed to study the distribution of

rainfall, surface water availability and agricultural practices being adopted.

The following section describes the preliminary analysis carried out for the

study area for identifying the drought proneness of the river basin.

3.6.1 Seasonal and Annual Rainfall Analysis

The mean monthly rainfall values were arrived for all the stations

and are presented in Table 3.8 and also graphically represented in Figure 3.6.

It was noted that all stations receive high rainfall during the Northeast

monsoon period from October to December. However, the stations such as

69

Table 3.8 Mean monthly rainfall of Thamiravaruni basin

Sl. No.

Name of station Mean monthly rainfall (mm)

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

1 Sivagiri 22.8 45.3 43.7 79.3 52.4 15.6 18.7 15.5 39.9 182.9 235.8 81.6

2 Gadana dam 43.0 51.6 50.5 72.5 38.7 61.7 59.2 38.5 29.7 208.7 315.5 180.0

3 Kannadian anicut 47.6 37.2 49.2 47.8 33.0 28.9 18.4 10.1 32.1 161.6 265.8 160.2

4 Papanasam 40.5 51.5 29.6 39.6 32.2 46.2 24.6 17.0 40.9 145.3 234.8 188.1

5 Dam camp 51.1 39.9 38.1 32.0 38.2 140.7 68.2 56.1 44.1 147.8 245.2 205.9

6 Ambasamudram 44.4 60.2 51.7 80.8 46.0 36.3 23.8 21.2 34.4 180.4 285.6 186.2

7 Manimuttar 46.3 43.3 35.8 47.4 44.3 47.7 34.4 14.7 40.9 151.9 301.7 214.5

8 Cheranmadevi 26.2 34.1 28.3 46.6 23.3 12.4 7.1 7.4 25.9 120.2 212.5 110.3

9 Nanguneri 16.0 26.1 29.4 45.4 30.9 16.3 16.9 13.1 42.0 154.1 191.5 114.3

10 Radhapuram 15.5 13.4 19.7 42.5 24.5 28.4 23.1 7.4 17.7 134.7 182.4 83.9

11 Nilaparai 9.3 12.4 33.2 53.2 21.4 109.8 55.1 21.9 34.0 59.5 133.6 92.1

12 Thirunelveli 23.4 24.3 32.4 34.4 69.8 11.0 9.1 15.4 43.6 130.2 171.9 90.3

13 Palayankottai 21.9 32.1 33.1 39.0 48.5 12.9 14.4 17.5 51.6 158.8 181.6 98.6

Contd...

70

Table 3.8 (Continued)

Sl. No.

Name of station Mean monthly rainfall (mm)

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

14 Senkottai 22.5 61.6 74.9 114.6 89.2 137.8 108.5 73.0 59.1 249.4 268.6 98.4

15 Tenkasi 25.3 38.1 63.1 75.1 71.2 75.4 70.4 45.4 55.1 177.4 227.8 100.4

16 Karuppanadhi anicut 21.3 32.4 24.7 34.3 39.4 45.7 44.5 26.5 23.7 121.8 188.5 62.3

17 Ayikudi 22.4 25.2 44.2 50.7 47.2 30.1 25.6 16.0 28.3 152.3 196.6 91.4

18 Kadaiyanallur 21.2 25.8 43.7 54.2 47.4 25.0 33.1 12.5 46.5 165.9 196.8 67.1

19 Sankarankovil 14.7 22.4 26.8 52.9 32.9 8.8 8.6 4.8 37.1 152.2 160.6 70.3

20 Kovilpatti-Agri 18.8 16.0 17.5 54.5 69.1 17.7 21.2 30.3 87.5 192.4 151.1 64.5

21 Kayattar 22.3 17.3 21.7 34.4 33.8 6.0 10.9 16.1 62.9 159.3 133.6 47.0

22 Ottappidaram 21.1 20.1 30.5 29.5 31.0 4.5 12.1 9.2 50.1 164.5 135.9 63.9

23 Thoothukudi 22.8 18.9 22.8 40.3 18.5 1.5 4.5 5.1 16.8 138.3 174.3 91.6

24 Srivaikuntam 24.8 16.5 27.8 36.1 32.7 7.1 9.6 8.5 36.5 140.7 157.1 95.6

25 Sattankulam 24.7 19.7 30.5 53.7 18.2 10.8 9.3 10.5 33.6 142.9 196.1 106.9

26 Tiruchendur 31.0 25.4 31.0 35.1 20.5 4.6 5.8 4.1 9.7 155.9 252.5 145.4

71

Figure 3.6 Graphical representation of mean monthly rainfall of all raingauge stations in Thamiravaruni basin

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72

Tenkasi, Senkottai, Gadana dam, Damp Camp and Nilaparai, which are

situated at the foot of Western Ghats, receive substantial rainfall during the

Southwest monsoon period also. The average monsoon seasonal and annual

values of rainfall for all stations were analysed and presented in Table 3.9.

Figure 3.7 depicts the average rainfall during the monsoon seasons. The

spatial variation of monsoon rainfall are presented in Figures 3.8 and 3.9 As

seen from these table and figures, the entire basin is receiving high rainfall

during Northeast monsoon compared to other seasons, following the general

trend of Tamil Nadu State.

The basin also receives considerable amount of rainfall during the

Southwest monsoon and summer seasons. The rainfall during the Northeast

monsoon varies spatially from 285.2 mm at Nilaparai to 704.2 mm at Gadana

dam. During the Southwest monsoon, it varies spatially from 24.2 mm at

Tiruchendur to 378.4 mm at Senkottai. The annual rainfall ranges from

555.4 mm at Thoothukudi to 1149.6 mm at Gadana dam.

In the Northeast monsoon period, nearly 60-65% of the basin area

gets rainfall from 450 to 500 mm. The basin receives maximum rainfall

particularly on the Western and Southern sectors. Tenkasi, Ambasamudram,

parts of Cheranmadevi, Kalakkadu and Senkottai receive heavy rainfall due to

the presence of Western Ghats. Kadaiyanallur, Vasudevanallur,

Melanilidanallur, Kayattar, Manur, Ottappidaram, Srivaikuntam,

Azhwartirunagari and Karunkulam receive comparatively low amount of

rainfall. Thamiravaruni basin receives 16% of total rainfall during the

Southwest monsoon season. Due to the presence of Western Ghats,

Senkottai, Tenkasi and Ambasamudram receive considerable amount of

rainfall during the Southwest monsoons also. Alangulam, Manur,

Melanilidanallur, Kuruvikulam, Sankarankoil, Vasudevanallur, Ottappidaram,

Karunkulam, Nanguneri, Srivaikuntam, Azhwartirunagari and Tiruchendur

receive very low amount of rainfall during this season.

73

Table 3.9 Average seasonal and annual rainfall in Thamiravaruni basin

Sl. No. Name of station Seasonal rainfall (mm) Annual rainfall (mm) Northeast Southwest

1 Sivagiri 500.3 89.7 833.5 2 Gadana dam 704.2 189.1 1149.6 3 Kannadian anicut 587.6 89.5 891.9 4 Papanasam 568.2 128.7 890.3 5 Dam camp 598.9 309.1 1107.3 6 Ambasamudram 652.2 115.7 1051 7 Manimuttar 668.1 137.7 1022.9 8 Cheranmadevi 443 52.8 654.3 9 Nanguneri 459.9 88.3 696 10 Radhapuram 401 76.6 593.2 11 Nilaparai 285.2 220.8 635.5 12 Thirunelveli 392.4 79.1 655.8 13 Palayankottai 439 96.4 710 14 Senkottai 616.4 378.4 1357.6 15 Tenkasi 505.6 246.3 1024.7 16 Karuppanadhi anicut 372.6 140.4 665.1 17 Ayikudi 440.3 100 730 18 Kadaiyanallur 429.8 117.1 739.2 19 Sankarankovil 383.1 59.3 592.1 20 Kovilpatti 408 156.7 740.6 21 Kayattar 339.9 95.9 565.3 22 Ottappidaram 364.3 75.9 572.4 23 Thoothukudi 404.2 27.9 555.4 24 Srivaikuntam 393.4 61.7 593 25 Sattankulam 445.9 64.2 656.9 26 Tiruchendur 553.8 24.2 721

Statistical properties for the annual rainfall of raingauge stations

were computed and are shown in Table 3.10. Standard deviation estimated

for the raingauge station shows the distribution of rainfall over the years. It is

also observed that large variation of annual rainfall from a maximum of

1357.6 mm to a minimum of 555.4 mm over the basin. Hence, the data is

normalized to get the Standardized Precipitation Index for drought

forecasting.

74

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Figure 3.7 Variation of monsoon seasonal rainfall in Thamiravaruni basin

Stations

Rai

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75

Figure 3.8 Spatial distribution of Northeast monsoon rainfall in Thamiravaruni basin

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Figure 3.9 Spatial distribution of Southwest monsoon rainfall in Thamiravaruni basin

77

Table 3.10 Statistical Analysis of Rainfall in Thamiravaruni basin

S. No. Station Mean (mm)

Standard Deviation

(mm)

Coefficient of Variation Skewness Kurtosis

1 Sivagiri 833.5 392.838 0.471 0.165 -0.49 2 Gadana dam 1149.6 404.845 0.352 0.869 2.729 3 Kannadian anicut 891.9 323.379 0.368 0.777 0.523 4 Papanasam 890.3 652.631 0.735 0.303 -0.632 5 Dam camp 1107.3 761.126 0.726 0.271 -0.259 6 Ambasamudram 1051 373.761 0.35 -0.142 -0.648 7 Manimuttar 1022.9 386.471 0.392 0.046 0.23 8 Cheranmadevi 654.3 348.421 0.529 -0.178 -1.13 9 Nanguneri 696 194.885 0.283 0.447 -0.345

10 Radhapuram 593.2 317.653 0.506 1.253 2.291 11 Nilaparai 635.5 201.137 0.316 -0.126 -0.243 12 Thirunelveli 655.8 303.864 0.433 2.302 8.241 13 Palayankottai 710 208.486 0.294 0.352 0.286 14 Senkottai 1357.6 298.549 0.234 0.765 0.573 15 Tenkasi 1024.7 398.635 0.395 1.282 1.497 16 Karuppanadhi anicut 665.1 252.462 0.377 1.032 1.664 17 Ayikudi 730 244.513 0.335 0.374 -0.392 18 Kadaiyanallur 739.2 213.667 0.288 0.999 1.125 19 Sankarankovil 592.1 239.425 0.384 0.808 -0.12 20 Kovilpatti 740.6 182.893 0.246 0.163 -0.236 21 Kayattar 565.3 175.570 0.311 0.758 1.449 22 Ottappidaram 572.4 290.794 0.549 0.194 -0.369 23 Thoothukudi 555.4 228.070 0.424 0.096 0.635 24 Srivaikuntam 593 227.433 0.364 0.761 2.432 25 Sattankulam 656.9 269.619 0.445 -0.469 -0.195 26 Tiruchendur 721 266.519 0.373 0.576 0.486

3.6.2 Rainfall Analysis For Crop Seasons

Mean Seasonal rainfall for different crop seasons in Thamiravaruni

basin is presented in Table 3.11 and is represented in

Figure 3.10. Figure 3.11 shows the irrigated and non irrigated blocks of

Thamiravaruni basin.

78

Table 3.11 Average crop seasonal rainfall in Thamiravaruni basin

Sl.No Name of station Crop seasonal rainfall (mm)

Kar Pishanam Dry crop 1 Sivagiri 89.7 568.4 265.1 2 Gadana dam 189.1 798.8 350.8 3 Kannadian anicut 89.61 672.35 219.58 4 Papanasam 128.7 660.2 230.1 5 Dam camp 309.05 689.94 417.36 6 Ambasamudram 115.65 756.89 294.22 7 Manimuttar 137.70 757.65 265.11 8 Cheranmadevi 52.74 503.23 150.94 9 Nanguneri 88.25 502.08 193.98

10 Radhapuram 76.58 430.00 163.30 11 Nilaparai 220.75 306.89 328.47 12 Thirunelveli 79.10 439.99 215.71 13 Palayankottai 96.39 492.95 216.94 14 Senkottai 378.50 700.48 657.21 15 Tenkasi 246.22 568.91 455.57 16 Karuppanadhi anicut 140.49 426.19 238.89 17 Ayikudi 100.13 487.82 242.22 18 Kadaiyanallur 117.02 476.81 262.28 19 Sankarankovil 59.3 420.2 171.9 20 Kovilpatti 156.7 442.8 297.8 21 Kayattar 95.84 379.51 185.75 22 Ottappidaram 75.9 405.5 166.9 23 Thoothukudi 27.9 445.9 109.50 24 Srivaikuntam 61.77 434.7 158.3 25 Sattankulam 64.2 490.30 166.6 26 Tiruchendur 24.20 610.20 110.8

79

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Figure 3.10 Spatial variation of crop seasonal rainfall in Thamiravaruni basin

80

Figure 3.11 Irrigated blocks with channels in Thamiravaruni basin

Non-Irrigated Blocks

81

The analysis indicates that the mean crop seasonal rainfall values

for the basin during the Pishanam season are more compared to the Kar

season rainfall values.

The Kar crop is influenced by the Southwest monsoon. Heavy

rainfall during this crop period is isolated and confined to the Western Ghats

and the head reaches of Thamiravaruni river. Blocks like Tenkasi and

Senkottai receive substantial rainfall during Southwest monsoon months. The

North and Northeastern parts of the basin like Kayathar, Kadayanallur,

Vasudevanallur, Ottapidaram are receiving less rainfall than others. The

average rainfall is 514.8 mm, 124.9 mm and 248.9 mm during the Pishanam,

Kar and Dry crop seasons respectively.

In the Northeast monsoon months ie., during Pishanam crop

season, nearly 60-65% of the basin area gets rainfall slightly less than 500

mm. The basin receives maximum rainfall particularly on the Western and

Southern sectors. The Southern parts of the basin include the blocks

Ambasamudram, Cheranmadevi and Palayankottai, which are mostly

benefited by the Northeast monsoon. The rainfall amount during the

Pishanam crop season is high. In the analysis of crop seasonal rainfall values,

it may be seen that most of the area is influenced by the Northeast monsoon.

The Western Ghat pockets get high rainfall, which diminishes rapidly towards

the East on the plains.

The spatial variation of rainfall was also analysed. The variation

was analysed for Kar and Pishanam crop seasons as shown in Figures 3.12

and 3.13. It is indicated from the analysis that the upper part of the basin

which includes the blocks like Manur, Vasudevanallur and Kuruvikulam, and

the Eastern blocks like Srivaikuntam, Azhwartirunagari, Tiruchendur and

82

Thoothukudi receive low rainfall. Tenkasi, Senkottai and Ambasamudram

receive substantial rainfall.

During the Northeast monsoon period, the basin receives high rainfall.

The blocks like Kayattar, Manur, Ottapidaram and Kadayanallur receive

considerably low rainfall.

83

Figure 3.12 Spatial variation of Pishanam seasonal rainfall in Thamiravaruni basin

84

Figure 3.13 Spatial variation of Kar seasonal rainfall in Thamiravaruni basin