East Flowing Rivers from Pennar to Kanyakumari

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East Flowing River basin  Between Pennar and Kanyakumari can can be divided in two parts :



East Flowing Rivers between Pennar and Cauvery

The region covers the east flowing rivers between the Pennar and the Cauvery extending over a large area of 64,751 km2. The basin lies between east longitudes 7735' to 8021' and north latitudes 1115' to 1430'. Lying in peninsular India, the area covers large areas in the State of Andhra Pradesh, Karnataka, Pondicherry and Tamil Nadu.  The State-wise distribution of the area is shown in the following Table.



Drainage Area (km2 )

Andhra Pradesh




Tamil Nadu







On the eastern side of the area lies the Bay of Bengal. On the remaining other sides, it is bounded by the various ranges of the Eastern Ghats. These are the Velikonda Range, the Nagari Hills, the Javadi Hills, the Shevaroy Hills, the Chitteri Hills, the Kalrayan Hills, the Kollaimalai Hills, the Pachai Malai Hills etc. The area has an irregular shape; it has a maximum length of about 290 km and a maximum width of about 360 km.  There are three major topographical divisions in the basin, namely: the hill ranges of the Eastern Ghats; the table land or the plateau region; and the coastal plains. The basin can be divided into 12 sub-basins, of which the Palar, the Ponnaiyar and the Vellar are the more important.  The shape of the Palar basin is like a rhombus.  The Ponnaiyar basin is elongated in shape, whereas the Vellar basin is fan shaped.


The major rivers that flow in the area (listed from the north to the south) include: the Kunleru; the Swarnamukhi; Small streams draining into the Pulicat Lake; the Araniar; the Kortalaiyar; the Cooum; the Adyar; the Palar; Minor streams between the Palar and the Gingee; the Gingee; the Ponnaiyar and the Vellar.


East Flowing Rivers South of Cauvery

The area where east-flowing rivers between Cauvery and Kanyakumari are located lies between longitudes 7709' E to 79 17' E and latitudes 8 5' N to 10 30' N. The total catchment area of these rivers is 35,026 km2, which lies completely in the state of Tamil Nadu. The area is bounded by the Varushanad hills, the Andippatti hills, the Cardamom hills and Palani hills on the west, by the Indian Ocean on the south, by the Palk-Strait, Palk Bay and the Gulf of Mannar on the east and the ridge, which separates it from the Cauvery basin on the north. Shape of the area is irregular; it has a maximum length of 236 km in the northwest-southeast direction and a maximum width of 275 km in the northeast-southwest direction. There are two major topographical divisions in the basin: the hilly area; and the plains. The area can be divided into 11 sub-basins, of which the Vaigai and the Tambraparni are the most important.  The Vaigai basin is elongated in shape, whereas the Tambraparni basin is fan-shaped.


The various river systems in the area north to south are: the Vellar; a small stream between the Vellar and the Varshalei; Varshalei; a small stream between the Varshalei and the Vaigai; the Vaigai; the Gundar; a small stream between the Gundar and the Vaippar; the Vaippar; small streams between the Vaippar and the Tambraparni; the Tambraparni; and small Streams south of the Tambraparni up to Kanyakurnari.


Water Resources Projects in the Basin

Periyar-Vaigai System

The Periyar-Vaigai system is one of the oldest irrigation systems in India. It is a trans-basin scheme, which came into existence towards the end of the nineteenth century. The system consists of two reservoirs namely, the Periyar reservoir on the Periyar river in the Kerala state, the Vaigai reservoir on the Vaigai river in the state of Tamil Nadu, and the irrigation command areas in the Vaigai basin. The Periyar River, which originates on the western slope of the Western Ghats, flows westwards and discharges into the Arabian Sea. The Vaigai River, which originates on the eastern slope of the Western Ghats, flows east and discharges into the Bay of Bengal.


The system is benefited from both the South-West monsoon and the North-East monsoon. The Periyar catchment receives rainfall during the South-West monsoon. The Vaigai catchment and the command area receive rainfall during the North-East monsoon. The natural flows in the Vaigai basin (east of the Western Ghats) were fully utilized by the end of the nineteenth century and water shortage was experienced in the basin. This led to the construction of Periyar reservoir and the Periyar-Vaigai trans-basin scheme which made it possible to divert the waters from the Periyar basin in the state of Kerala to the Vaigai basin in the state of Tamil Nadu for supplementing the irrigation in the command area of the system.


The irrigated command area of the Periyar-Vaigai system covers parts of the Madurai and Ramanathapuram districts of Tamil Nadu and is located on the plains between the Western Ghats and the Bay of Bengal. It covers a gross area of 1,300 Mm2 of which 734 Mm2 is cultivable. Madurai, the second largest city in Tamil Nadu is located on the fringe of the project area.


The area has a tropical monsoon climate; the normal annual rainfall of the Periyar being about 2,000 mm. Major portion of the rainfall in this area falls during the South-West monsoon from June to September. In clear contrast to this, the normal annual rainfall for the Vaigai reservoir catchment is about 750 mm. This area receives a major portion of the annual rainfall during the North-East monsoon from October to December.


January and February are the months of cold and dry weather while April and May months have hot and dry weather when the maximum daily temperature sometimes exceeds 40C. Although the project area experiences two monsoons in a year, the distribution pattern of rainfall is not suitable to grow crops without irrigation. The actual pan evaporation is high, nearly 2,400 mm per year. Evaporation rates in the Vaigai catchment in the months from March through August are of the order of 7 to 8 mm per day.


Paddy is the principal crop raised in the project area. The farmers use short duration varieties of paddy for the first crop, which has a crop period of 105 days commencing from 1st June. For the second crop, medium duration varieties of paddy are used which have a crop period of 135 days commencing from the middle of September to the end of January. In single cropped area, paddy is raised from mid August with a crop period of 120 days. Other crops raised under irrigated area are groundnut (2 to 3 percent), sugarcane and cotton.


In a year of normal rainfall with respect to time and space, water is released for the cultivation of two crops (rice crops) in double crop area and single crop in the rest of the pre-project. Depending on the availability, water is released to raise single rice crop in extension area. If water available in the system is inadequate to raise two crops in double crop area, water is released for cultivation of single rice crop in the entire pre-project area. The farmers grow rice crop of 105 days duration in the double crop area and of 120 days duration in the main crop area and the extension area.


There are three main hydraulic structures in the Periyar-Vaigai system. The most important among them is the Periyar reservoir, which is located in the state of Kerala and satisfies most of the demands of the system. The credit for the Periyar Dam goes to the noted British engineer, Colonel John Pennyquick.  Releases from the Periyar reservoir are picked up at the Vaigai reservoir, which is a balancing reservoir. Upstream of Vaigai reservoir, the releases from the Periyar reservoir are required to satisfy the irrigation demands of the Cumbum valley. Peranai regulator is located downstream of the Vaigai dam. Vaigai reservoir was constructed across Vaigai River during 1954-59. Its catchment area is 2,253 sq. km and capacity at FRL is 194.78 MCM.


Periyar Irrigation System

After coming out of the Periyar power house, the releases of the Periyar reservoir and the natural flows of the Vaigai basin flow through the Cumbum valley. The Cumbum valley agriculture areas are irrigated through the channels taking off from 15 anicuts constructed across the rivers Vairavanar and Suruliyar. This command area enjoys the perennial supply of water from the Periyar reservoir in addition to the natural inflows. It consists of two distinctive areas: a) The old command of 6,017 ha, served by 17 channels and b) New command of 2,082 ha, served by recently constructed P. T. Rajan channel.


The old command is designed for two paddy crops (June-February): the first coinciding with the South-West monsoon; and the second with North-East monsoon. The new command is designed for single crop during September - March.


Vaigai Irrigation System

The command area of the Vaigai irrigation system lies downstream of the Vaigai reservoir and is in the rain shadow region of the Western Ghats. The total command area of this system is 76,736 ha. Paddy is the principal crop grown in this area. The command area consists of pre-project area of 58,827 ha and extension area of 17,909 ha. The pre-project area and the extension areas are distributed in PMC and TMC. Of the pre-project area, 53,312 ha lies in PMC and 5,515 ha in TMC. In the pre-project command area of PMC, double crops are cultivated in 18,227 ha as per the present practice. In other area, single crop is cultivated. Of the total extension area, 15,567 ha lies under PMC command and 2,342 ha lies under TMC. In the extension area, single rice crop is cultivated. Pre-project area and extension area are together known as the post-project area. The double crop areas lie between the Peranai regulator and the Kallandiri regulator. The single (main) crop areas get distributed in the entire system. As far as normal irrigation supply is concerned, the pre-project areas have priority for irrigation water over the extension areas.


In addition, the command area has a number of system tanks which store the runoff from their own catchment areas and the irrigation return flows. There are 251 tanks up to the Kallandiri regulator which is located downstream of the Peranai regulator. The water available in the tanks is used for irrigation. This irrigation system is mainly operated for cultivation of rice crop in the command area. The command area consists of double crop area and the single crop area on the downstream of the Vaigai reservoir.


Various demands of the system

The various demands of the system include Periyar Irrigation System Demands (Cumbum valley), Vaigai Irrigation system demands (PMC and TMC) and the Madurai water supply demands. While releasing water from the Periyar reservoir, normally highest priority has been given to the Cumbum valley irrigation demands and the Madurai city water supply demands. Next priority has been given for meeting single crop area demands under the Vaigai irrigation. If water is still available, then the double crop requirements and the extension area demands are satisfied.


Lower Periyar

Lower Periyar is a concrete gravity dam on Periyar River, located at a distance of 32 km from Kothamangalam in Idukki District, Kerala. The catchment area at the dam is 181.3 km2. The height and length of the dam is 32 m and 284 m respectively. The reservoir has a live storage capacity of 4.55 MCM at FRL 253.00 m and the MDDL is at 237.74. Lower Periyar power house has 3 units of 60 MW each. It has a firm power of 57 MW. The project was commissioned by the KSEB in 1997.


Hydropower Potential in the Basin

The hydroelectric potential of the East flowing Rivers basin has been assessed 14511 MW. Out of the identified schemes in the basin, schemes with a total installed capacity of 7843 MW are in operation as on 31.7.2014 and schemes with an installed capacity of about 410 MW are in various stages of construction. (Source: www.cea.nic.in )