This plain is known as the Coromandel Coastal Plain and it is more than 80 km. in width at some places. Raised beaches along the coast and deposits of sandstones signify that the coastal plain was once under the sea. The strip of land along the coast is generally fringed with dunes or wind-blown sand and lagoons. The dunes develop particularly along the coast of Tirunclveli district where it is called Teris.
There is a low plateau of Archaean gneisses and granites and is studded with small or large hill masses. The eastern margin of this plateau is fringed from north to south with a chain of discontinuous hills such as Javadi, Shevaroy, Pachaimalai and the hills of Madurai district.
The Cardamom hills throw spurs to the east; Palni, Andipatti and Sirumalai hills are important spurs. These hills and spurs rise abruptly from the plateau and are generally flat topped.
Three level areas with height stand out (1) the Coimbatore Plateau drained by the Cauvery (Kaveri) and its tributaries (2) the Upper Vaigai Valley and (3) the low country formed due to the subsidence of land between the Karnataka. Plateau and the hills stretching from the Javadi hills to the Pachaimalai hill. The most useful and important rivers are Cauvery, the Palleru, the Vagai and the Tambraparni:
Both south-west monsoon and north east monsoon influence the climate of this region but it less influenced by south west monsoon due to being on rain shadow zone of it. The coastal plain and the southern parts receive more rainfall during October to January than during the months from June to September. The Palghat Gap, however, allows moist westerly winds to penetrate into the northern part of this region in the summer season.
These winds not only give some rain which varies about 28 cm. in the plains to heavy showers on the western slopes of the Shevaroy and the Kollumalai hills, but also bring down temperature by a few degrees. Average monthly temperature throughout the year remains above 21 °C. May is the hottest month.
This region has thorny stunted tress of acacia species the main flora. Grasses appear during the rainy season only. On the hills, where rainfall is relatively high, deciduous forests appear. The forest covers 16.5 percent of the total area of this region. Forest products found here are however, an important source of sandal wood, teak, rosewood, vengai and sleeper wood such as poon and nangal.
About 61 percent of the total workers of this region derive their livelihood from agriculture.
There are eight months of agricultural season with little summer rain. People, therefore, resort to irrigation. Numerous tanks have been constructed for storing rain-water received during the winter season. This water is utilized for irrigating the crops during the summer season when it is mostly needed.
Tanks irrigate about 20 percent of the total irrigated area. Canal-irrigation is important in the Cauvery delta accounting for almost half of the total area irrigated by canals in this region. Wells are important source of irrigation in north-eastern Tamil Nadu and Kanyakumari district.
Only tropical crops are grown. The distribution of the crops is, however, greatly influenced by rainfall and irrigation. Parts of the coastal plain which receive more than 100 cm. of rainfall annually and have facilities of supplemental irrigation, mainly produce a variety of crops such as rice where irrigation is available, jowar, bajra, small millets, groundnut and cotton.
Chingleput and Kanyakumari are also important rice producer. Rice cultivation is particularly important in Thanjavur and Chingleput districts. Owing to a very high percentage of the irrigated area in Thanjavur district, crop failures are unknown in this district. More than four-fifths of the sown area of this district is under paddy. It is only this district which is surplus in the production of food grains and is rightly called ‘ the granary of Tamil Nadu’
The autumn crop (harvested in August and September) is the dominant crop and accounts for 75 percent of the total rice produced in this region. An soon as the yield of rice falls below economic level, crops such as sugar-cane and banana are introduced in the wet land. Two crops of paddy a year in the same field is, however, the general rule in the coastal plain, particularly in the deltas where irrigation in available.
Jowar and bajra are also raised over a large area in the interior plateau and in the coastal plain. Millets form staple food of nearly one-third of the human population of this region. Jowar, bajra and ragi are important among about 8 millet crops raised in the interior drier Tamil Nadu.
Cotton is cultivated in the black cotton soils of Tirunelveli, Madurai, and Ramanathapuram and Coimbatore districts. Cotton is sown mainly just after the south-west monsoon rains are over, that is, in September and October. The crop depends for moisture on winter rains and it is ready for picking during the months from January to April. The irrigated cotton is sown mainly during February and March and is ready for picking during July. In the irrigated fields long staple cotton is raised.
Groundnut is the third most important crop after rice and millets. It is a rain-fed crop and is grown mainly in the northern districts with more concentration in North Arcot and Salem districts. The region produces about one-fifth of the total groundnut produced in India on the red sandy loams which are well- drained and friable.
Sugarcane is raised in the northern districts. It is an irrigated and heavily manured crop. Frost and hot winds are absent in this region which favour this crop. As a result, yield of cane per unit area is high. Yield of cane per hectare was 101,228 kg. As compared with India’s average yield of 65,375 kg. Per hectare.
Minerals and Power Resources:
The igneous and sedimentary rocks have been the source of good minerals for this region. Salem district has rich deposits of bauxite, magnesite, iron ore, limestone, chromite, corundum and beryl. Large deposits of good quality iron ore which occur in Salem district have been exploited for the establishment of a large-scale iron and steel industry.
There is a large deposit of bauxite in the Shevaroy hills and of gypsum in Tiruchchirappalli district. Bauxite and gypsum are mined in a limited quantity to meet local needs. Limestone and dolomite deposits are fairly extensive and are mined for cement and chemical industries of this region.
This region has important lignite deposit around Neyveli. Lignite deposit covers an area of nearly 260 square km. The mining of lignite was started in 1961. It is used for (1) the generation of electricity, (2) manufacture of urea, a chemical fertilizer and (3) the production of briquettes utilized as domestic and industrial fuel. Thermal power-house, fertilizer plant and briquetting and carbonisation plant are situated at Neyveli. The seam is covered with a layer of white china clay 1 to 3 metres thick.
The oil has also been found in sedimentary rocks of States. Oil was first stuck in 1964 near Karaikal. Gas was discovered in 1981 in the Palk Bay. But it was in 1985 that oil of good quality was discovered. The important sites where oil and qas have been discovered are Narimanam, Kovilkallappal and Nannilam in the Thanjavur district, Bhuvanagiri to the north-east of Nagappattinam. The region derive significant amount of power from hydro-electricity.
The important projects connected with the development of hydro-electric power are: (i) Kundah, (ii) Mettur, (iii) Parambikulam Aliyar, (iv) Periyar, (v) Kodayar, (vi) Sholayar, (vii) Pykara and (viii) Aliyar. The hydro-electric schemes accounted for 55.2 percent of the installed capacity of electricity in Tamil Nadu. The nuclear power unit Kalpakkam and thermal power plants also add to power supply of the region.
The region has diversified industries. Cotton textile is significant so far as the value of total output is concerned.
Cotton textile is important industry of the region. The industry employs nearly 40 percent of the total workers. Majority of the mills produce only cotton yarn. This region ranks second in India in the production of cotton yarn and is next only to Maharashtra. An appreciable quantity of yarn is used by handlooms and a power looms which are scattered in this region.
A large quantity of yarn is dispatched to Maharashtra State and the states in East India for power loom and handloom industry. Coimbatore, Madurai and Chingleput are important centre. Sugar is produced in this region on large scale. It has 30 sugar factories located in the sugar cane growing areas. Salem Steel Plant is located at Salem.
It was completed in two stages. The first stage which has a capacity to produce 32,000 tonnes of cold rolled stainless strips and sheets in thin gauges per year, started commercial production in March 1982. The second stage of the plant was completed in March 1991 with the completion of the second stage, capacity of the plant has increased from 32 000 tonnes of cold rolled stainless strips and sheets to 70,000 tonnes.
Coimbatore and Chennai are the principal industrial centres of this region. Tamil Nadu is the third most important industrial State in the country. Tanning of hides and skin is a well established industry in north Arcot, Chennai and Chingleput district.