Agniyar Basin Introduction The Agniyar river basin is situated between latitudes 09o55’00’’-10 o45’00’’ N and longitudes 78o15’00’’ - 79o 30’00’’E and is located in the middle part of Tamil Nadu on the coastal side. In this basin, there are 3 prominent rivers namely Agniyar, Ambuliyar and South Vellar with small streams. The north and western part of Agniyar basin is occupied by Cauvery river basin, south by Pambar and Kottakaraiyar river basin and east by Palk Strait and Bay of Bengal. The total geographical area of Agniyar basin is 4663.04 Sq.Km. It falls in the Survey of India degree sheets 58‘J’, 58 ‘N’ and 58’O’’ on 1:250,000 scale covering part of Pudukkottai, Thanjavur, Trichirappalli and a portion in Sivagangai and Dindigul districts. The administrative setup of the Agniyar river basin is given below. Sl.No. District Taluk Block Block/Area falling within the basin area in Sq.Km. 1 Trichirappalli Manaparai Marungapuri 330.41 2 Trichirappalli Manaparai Manaparai 3.52 3 Pudukkottai Aranthangi Aranthangi 370.71 4 Pudukkottai Alangudi Thiruvarankulam 305.53 5 Pudukkottai Alangudi Karambakudi 256.81 6 Pudukkottai Pudukkottai Pudukkottai 338.55 7 Pudukkottai Avudaiyarkovil Manamelkudi 250.89 8 Pudukkottai Avudaiyarkovil Avudaiyarkovil 161.58 9 Pudukkottai Thirumayam Arimalam 133.81 10 Pudukkottai Thirumayam Thirumayam 80.77 11 Pudukkottai Thirumayam Ponnamaravathi 220.03 Sl.No. District Taluk Block Block/Area Falling Within The Basin Area in Sq.Km. 12 Pudukkottai Kulathur Annavasal 365.05 13 Pudukkottai Kulathur Viralimalai 18.01 14 Pudukkottai Kulathur Kunnandarkoil 260.45 15 Pudukkottai Gandarvakottai Gandarvakottai 245.00 16 Thanjavur Orathanadu Orathanadu 116.00 17 Thanjavur Peravurani Peravurani 343.99 18 Thanjavur Peravurani Sethubhavachattiram 275.59 19 Thanjavur Pattukottai Pattukottai 218.65 20 Thanjavur Orathanadu Thiruvonam 173.55 21 Thanjavur Thanjavur Thanjavur 116.27 22 Sivagangai Karaikudi Sakkottai 0.28 23 Sivagangai Thiruppathur Semmampattipudur 65.46 24 Dindigul Natham Natham 12.13 Total 4663.04 Physiography Agniyar basin is one of the seventeen major river basins of Tamilnadu. It is a cone shaped or triangular basin located almost in the middle and eastern side of Tamilnadu. It falls in the Survey of India Toposheets of 58 /J, 58 / N and 58 / 0 in the Latitude from 90 55’00” to 100 45’00” and longitude from 780 15’00” to790 30’ 00”. Agniyar basin is embedded in between Cauvery basin in the north and northeastern side and Pambar Kottakkaraiyar basin in the south. In the southeastern side it is bordered by the Palk Strait and Palk Bay. Hence it has a small coastal stretch in the southeastern side. Administrative boundary wise, it spreads in part of Pudukkottai, Thanjavur and Trichy districts and with a small extent in Sivagangai and Dindigul district. The western half of the basin is hard rock terrain and the eastern half of the basin is sedimentary terrain. The landforms are observed as erosional and depositional regimes along with the fluvio marine regime in the eastern coastal part. Physiographically this basin is divided into three regions viz, hilly region in the western fringes of the basin, pediplain region in the middle part of the basin and the coastal region in the eastern side of the basin. Generally Agniyar basin is gently an undulating terrain sloping towards east – southeast direction. The slopes vary in the pediment and pediplain regions from 20 to 40 and 10 to 20 respectively, and in the flood plain, the slope is less than 1 0 to 20 and in the coastal plain area the slope is less than 10. Geology Most of the area in Agniyar river basin is a gentle undulating terrain with dissected hill ranges occupying the west and central portion. The quartzite and charnockite forms many of the hill ranges while gneissie and sedimentary rocks occupy the plain. The important drainage systems are Agniyar, Ambuliyar and South Vellar rivers. The basin area is traversed by crystalline rocks of Archaean and Proterozoic age and Sedimentary rocks of Miocene and Quaternary sediments. The oldest group of rocks recognized is the khondalite group comprising Garnetiferous Silliminite gneiss with or without graphite, quartzite and calc gneiss. The charnockite group of rocks comprises charnockite and their pegmatoidal variants, Pyroxene granulite and migmatite quartzite. The khondalite and charnockite group of rocks occur closely associated with each other and intricately co- folded. The pink granite is occuring an intrusive body in the country rock migmatite complex of proterozoic age. The eastern part of the study area is covered by hard laterite and lateritic soil within which isolated patches of Cuddalore sand stone is found to occur. The south eastern part of the study area is covered by fluvial, fluvio marine and marine sediments of quaternary age. The fluviual deposits of sand, silt, and clay in an admixture of varying degree occur along Agniyar, Ambuliyar and South Vellar. They comprise levee, channel bar, point bar, back swamp and palaeo channels etc. The marine deposits are made up of fine to medium sands and black clays. The tertiary formation are represented by Cuddalore sand stone. The Eastern part of the study area is occupied by Cuddalore sand stone of Mio-Pliocene age and shows pebbly sand stone and clay stone, generally with thick lateritic cover. The sand stone formations are of good aquifers. The Geological formation of Agniyar basin is shown in figure 1. Figure 1 Geological formation of Agniyar basin Landuse IRS P6 LISS III imagery of March 2004 was used and interpreted visually for classification of different landuse categories under level I classification in the basin area. These landuse categories were further divided into different landuse features under level II classification. The land use map of Agniyar basin is shown in Figure 2. The spatial distribution of landuse has been analysed through GIS techniques and furnished in the Table 2.7.3 Table. 2.7.3 Spatial distribution of landuse Landuse Categories Sl. Area in Sq.Km.. Percentage Level I Level II No. 1 Built up land Towns, Villages, industries, roads 44.99 0.96 2 Agricultural Crop land 842.76 18.07 land Dry crop land 312.23 6.70 Plantations Cashew nut and Eucalyptus 75.90 1.63 Casuarinas 12.39 0.27 Grooves 143.96 3.09 3 Forest land Forest covered by scrub 181.05 3.88 Land affected by alkalinity 253.77 5.45 Land with scrub 113.41 2.43 Land with shrub 57.71 1.24 Barren land 1653.56 35.40 4 Wasteland Barren out crop 870.30 18.66 Land covered by Juliflora 5.71 0.12 Barren sand 4.35 0.09 Salt pan 5.19 0.11 5 Water bodies River, canal and tanks 85.76 1.84 Total area 4663.04 100.00 Fig. 2 Land use map of Agniyar Basin Geomorphology Geologically this basin is occupied by both sedimentary and hard rock. The eastern part of the basin is covered by sedimentary formations with marine landforms where as the western part is covered by hard rock terrain, which exhibits denudation landforms. A detailed geomorphological study was carried out in the Agniyar basin and the landforms have been analysed based on the interpretation of image characteristics like tone, texture, shape, and pattern and associated features etc. IRS 1D False Color Composite imagery acquired in the month of January 2004 was used to classify the geomorphic units. Qualitative assessment was made for targeting groundwater potential available with each geomorphic unit. The geomorphology map of Agniyar Basin is shown in figure 3. Figure 3 Geomorphology map of Agniyar Basin Soil The soils of Agniyar river basins have been shown in Figure 4. The major soil in this basin belongs to Alfisols, Vertisols and Entisols. Figure 4 Soil map of Agniyar Basin Demographic And Social Characteristics Population trend and population dynamics are important indicators of future water requirement. So also, the social characteristics of the population such as literacy level, level of housing, electrification, in house facilities, urbanisation trend are having indirect bearing on water planning. Land utilisation pattern, size of land holdings, nature of agricultural employment and industrial employment also would reflect on the water requirement of the population. An analysis of all these parameters, with reference to Agniyar river basin is described hereunder. Population Size: Urban and Rural The Agniyar basin covers five districts namely Pudukkottai, Thanjavur, Trichy, Sivagangai and Dindugul districts. The sub basin wise population is given in Table 4 below. The Urban and Rural Population as per Census 2001 (in Million) Urban Rural Total Sl. Population Population Population No. Name of the Sub basin in Million (2007) 1 South Vellar 0.210 0.595 0.805 2 Ambuliyar 0.068 0.239 0.307 3 Agniyar 0.138 0.685 0.823 Total 0.416 1.519 1.935 Population Density The population density is the highest in Ambuliyar sub basin (428 Persons per Sq.Km.) and the lowest is at South Vellar sub basin (396 Persons per Sq.Km.). Sl. Name of the sub Area Total Population Density basin No (Sq.Km.) in Million Persons / Sq.Km. 1 South Vellar 2033.68 0.805 396 2 Ambuliyar 717.81 0.307 428 3 Agniyar 2057.86 0.823 400 Total 4809.35 1.935 402 Hydrometeorology Rainfall Raingauge Stations Agniyar basin has an area of 4663.04 Sq.Km. spread over in four Districts namely Pudukkottai, Thanjavur, Trichy and Dindigul. Considering the distribution of rain gauge stations and the availability of data, 12 rain gauge stations having long-term records in and around the basin are considered for the detailed analysis. The various agencies maintaining these rain gauge stations, and the number of rain gauge stations maintained by each agency are listed below: S.