Vaigai Basin Introduction There are 34 river basins in Tamil Nadu. For hydrological studies, they are grouped into 17 river basins. The Vaigai River basin is one of them. Vaigai river basin covers an area of about 7009.13 sq.km and hilly area extends to 2,101.68 sq.km and located in the Theni, Dindugal, Madurai, Sivaganga, and Ramanathapuram Districts of Tamil Nadu. Vaigai, the main river originating from Varushanadu valley with its tributaries forms a well-defined, compact drainage basin. It has a varied climatic condition resulting often in unreliable rainfall, drought prone, sudden floods, etc. This gives rise to unpredictable water resources condition but for the Periyar reservoir water flowing through this basin due to the construction of the Periyar trans-basin scheme which made it possible to divert water from the Periyar basin in the State of Kerala to Tamil Nadu.The index map of Vaigai River Basin is shown in figure 1. Figure 1 Index Map of Vaigai River Basin Location and Extent Vaigai river basin lies between the geographic co-ordinates Lat. 9o 15’ – 10o 20’ N and Long. 77o 10’ - 79o 15’ and falls within the Survey of India toposheets, 58F, 58G, 58J and 58k. The total extent of the area is covered within the administrative boundaries of 20 taluks and 37 blocks. Figure 2 shows the Administrative boundaries. Figure 2 Administrative Map of Vaigai River Basin The Vagai basin is surrounded by Cauvery and Pambar Kottakaraiyar basins, on the north, Gundar basin, on the south, west by Periyar basin and east by Bay of Bengal. The length of the basin is about 289.59 km and the width varies from 15 to 55 km. The important urban settlements like Madurai, Cumbum, Uthamapalayam, Bodinayakkanur, Theni, Periyakulam, Nilakottai, Melur, Manamadurai, Paramakudi and Ramanathapuram are located in the study area. The basin is an arcuate in shape, stretching from the Western Ghats mountain of Kerala in the west to the Bay of Bengal on the east, with a general gradient towards North east, up to Theni and then south eastern direction up to the sea. The river basin is flanked by Western ghats on the south and west, southern slope of Palani hills (Kodaikanal hills), Sirumalai hills, Alagar hills etc. on the north, and Bay of Bengal on the east. The relief Map of the Vaigai Basin is shown in Figure 3. Figure 3 Relief Map of Vaigai River Basin Physiographical study of vaigai basin reveals that the basin area can be broadly classified into three units namely 1. Western mountainous terrain with valley complexes, 2.Central elevated terrain and 3. Eastern coastal plain. Drainage The river Vaigai originates in the eastern slope of the Western ghat mountainous offshoot in the Varushanad area and flows northwards through Gandamanayakkanur. The Suriliyar and Theniar join Vaigai near Kottapatti. There after Vaigai flows east and south east directions till it confluences with Bay of Bengal. Varattar, Nagalar, Varahanadhi, Manjalar, Marudhanadhi, Sirumaliar, Sathaiyar originate in Palani hills and Sirumalai hills which are the main tributaries, joining Vaigai along its course. Uppar river originates in the Alagar hills and joins Vaigai near Manamadurai. Then Vaigai enters into the Ramnad big tank and the surplus only reaches the sea. The length of the Vaigai river upto Ramnad big tank is 266.71 km and Ramnad big tank to sea is 28.40 Km. Vaigai river and its tributaries are semi perennial to ephemeral in nature, and the flow in the Suriliyar and Vaigai is mainly due to the Periyar lake water diverted through Viravanar and then to Suriliyar during the monsoonal periods. Figure 4 Shows the drainage details of Vaigai Basin. Figure 4 Drainage Map of Vaigai River Basin Based on the natural drainage pattern, the vaigai basin is divided into ten sub basins they are Upper Vaigai, Suriliyar, Theniar, Varattar - Nagalar, Varahanadhi, Manjalar - Marudhanadhi, Sirumalaiar, Sathaiyar, Uppar and Lower Vaigai basin. The areal extent of each sub basin, hills, plains etc. are given in the Table 1. Table 1 Area and Percentage of Sub Basins in Vaigai Basin Sl. Total area Hilly area Plain area Name of the sub basin Percentage Percentage No. in Ha. in Ha. in Ha. 1 Upper vaigai 822.02 558.97 67.99 263.05 32.01 2 Suriliyar 640.10 217.95 34.05 422.15 65.95 3 Theniyar 651.65 310.84 47.69 340.81 52.31 4 VarattarNagalar 631.82 231.31 36.62 400.51 63.38 5 Varahanadhi 380.28 200.65 52.75 179.65 47.25 6 Manjalar 612.74 309.68 50.54 303.06 49.46 7 Surumalaiyar 541.59 131.66 24.30 409.91 75.70 8 Sathiyar 782.76 119.29 15.24 663.45 84.76 9 Uppar 882.29 21.35 2.42 860.94 97.58 10 Lower Vaigai 1063.88 - - 1063.88 100.00 TOTAL 7009.13 2101.68 - 4907.43 - Geology Vaigai river basin is covered by hard crystalline rock masses of Archaean age on the western portion; nearly 74% are sedimentary rocks of Upper Gondwana, Tertiary and quaternary age are on the eastern portion (26%). Aerial photographs and satellite data were also utilized in the demarcation of the boundary conditions of various lithological units and to delineate structural features. Figure 5 shows the geologic formations in the Vaigai Basin. Figure 5 Geology Map of Vaigai River Basin From Manamadurai to the Bay of Bengal, rocks of upper Gondwana, teritiary alluvium and coastal alluvium are spread over the Archaean formations unconformably. Aeolian sands are also found to occur in isolated pockets in the Cumbum valley and coastal areas. Land Use Vaigai basin reappraisal study uses LISS IV Mx of IRS P6 satellite imagery of March 2009 for analysis of land use changes over a decade in Vaigai river basin. In the present study high resolution satellite imagery was used to classify the land use at micro level. Finally the interpreted land use themes were digitized using Geo media professional GIS software V5.2 and all the spatial data have been converted into vector format for GIS analysis. Figure 6 Shows the Land use Classification of the Vaigai Basin. Figure 6 Land use Map of Vaigai River Basin The Land use category of Vaigai basin is shown in Table 2 Table 2 Vaigai Basin-Land Use Category Sl. Land use category Percentage Area in Sq.Km No I Level II Level % 1 Built up land Settlement 124.00 1.77 Wet crop land- Paddy, Sugar cane 1574.20 22.45 2 Crop land and banana. Dry crop land- Groundnut, ragi, 670.10 9.56 cholam, cumbu, maize, cereals, cotton, chilies, black gram, vegetables, floriculture etc. Grooves 115.00 1.63 3 Forest land Medium Dense forest 217.00 3.09 Dense forest and plantation 1324.50 18.89 Hills covered by shrubs/ scrubs 532.80 7.60 Reserved Forest 11.00 0.16 4 Waste land Barren land, Rocky out crop, stony 1636.00 23.33 waste Area affected by alkalinity/salinity 242.30 3.50 Land covered by shrub/ scrub 356.10 5.07 5 Water bodies Back swamp 25.10 0.36 Tanks 148.40 2.12 Reservoir 32.43 0.47 Total area 7009.13 100 Land use change detection The land use change detection study is analysed for the period of 2001 to 2009. The land use study reflects that the following category have increased in its extent i.e built-up land 82.76 Sq.km i.e. 1.18%, dry crop land 202.50 Sq.km i.e. 2.86%, waste land 188.36 Sq.Km i.e. 2.60% and decreasing trend have also been observed especially in the category of crop land area 270 Sq.Km i.e. 3.86% which is mainly due to the depletion of water level found to occur in many parts of the basin area. A comparative statement is shown in the table 3. Table 3 Comparison of Change in Land Use Area in Land use category Area in Percenta Sl. Sq.Km Percenta Sq.Km ge No. As on ge % I Level II Level As on 2001 % 2009 1 Built up Settlement 41.24 0.59 124.00 1.77 land 2 Crop land Wet crop land- Paddy, Sugar cane and banana. Dry crop land- Groundnut, ragi, cholam, cumbu, maize, cereals, cotton, 2629.5 38.03 2359.30 33.64 chilies, black gram, red gram, vegetables, floriculture etc. Grooves 3 Forest Medium Dense forest land Dense forest and plantation Hills covered by shrubs/ scrubs Reserved Forest 2075.55 29.68 2085.30 29.74 4 Waste Barren land, Rocky out crop, land stony waste Area affected by 2049.04 29.30 2234.40 30.9 alkalinity/salinity Land covered by shrub/ scrub 5 Water Back swamp bodies Tanks 198.47 2.83 205.90 2.95 Reservoir Total area 7009.13 100 Geomorphology The different land forms of Vaigai Basin are shown in the figure 7. Figure 7 Geomorphology Map of Vaigai River Basin Soils The Soils of Vaigai Basin is classified as Deep Red Soil, Red Soil, Red Sandy Soil, Black Clayey Soil, Laterite Soil and Alluvial Soil. Deep red soil is prevalent in cumbum valley near Chinnamanur, Uttamapalayam and Cumbum areas. Between Vaigai dam and Peranai red soil is prevalent. The soil is red to yellowish red and sometimes brownish in colour and has a thickness varying from 0.25m to 3m in this area. The Red Sandy soil is the soil mixed with sand or quartz fragments. These are found in the area in vicinity of quartzite outcrops.