DISTRICT SURVEY REPORT APPENDIX – IV • Thiruvallur district is the northern most coastal district of Tamil Nadu. • The district is bounded by the Bay of Bengal in the East, Vellore district of Tamil Nadu and Chittoor district of Andhra Pradesh on the West, Nellore district of Andhra Pradesh on the North and on the South by Kancheepuram district. • It lies between 12º 55'N to 13º 34'N Latitude, 79º 17'E to 80º 21'E Longitude and has an areal extent of 3550 sq.km. • There are 14 Blocks, 526 Villages and 3842 Habitations in the District. Physiography and Drainage: • Thiruvallur district varies from featureless pediplain to residual and structural hills. • The Thiruthani and R.K.Pet hills form part of the important landmarks. The Coastal tract is marked by beach ridges with a general slope towards the east. • The Araniar, Kortaliyar, Adayar and Coovum are important rivers draining the district. • The Araniar originating in Andra Pradesh flows between Ponneri and Thiruvallur taluks and joins the Bay of Bengal near Pulicat • The Coovum has its origin in the Surplus water from the Coovum tank in Sriperumbudur taluk and feeds the Chembarampakkam tank through a Channel. • The Poondi reservoir and Red hills are important tanks. The Pulicat tank is considered to be an important lagoon. Rainfall: The average annual rainfall and the 5 years rainfall collected from IMD, Chennai is as follows: Acutal Rainfall in mm Normal Rainfall in mm 2013 2014 2015 2016 2017 1067.0 938.10 2015.8 814.2 1198.5 1138.86 Geology: Rock Type Geological Formation Charnockite, Gneiss, Conglomerate, Sedimentary Rock 80% Sandstone, Shale, Laterite, Hard Rock 20% Alluvium and Marine deposits Hydrogeology: Type of Aquifer Water table conditions in Hard Rock Areas. Aquifer parameters Hard rock Alluvial formation Well yield in lpm 45 – 220 150 – 400 Transmissivity (T)m2/day 10 – 80 200 – 300 Permeability (K)(m/day)) 0.5 – 2.5 20 - 30 Depth of Water level 5m to 12.5m Groundwater Potential as on March 2011 (as per CGWB): Net Groundwater Availability (in MCM) 728.40 Existing Gross Groundwater draft for all users (in MCM) 492.89 Stage of Groundwater development (in %) 68% Categorization of District Safe Categorization of Firkas: The status of Categorization of firkas as of March 2011 for the District is shown below. Categorisation based on No. of Firkas Extraction (as on 2011) Firkas Over Exploited (>100%) 4 Ambattur, Cherukkanoor, R.K.Pet, Vengathur Uthukkottai, Balapuram,Erumbi, Kadambathur, Critical (90%-100%) 8 Mappedu, Gummidipoondi, kannigaipair,Thirunindravur. Kanagammachattram, Kattur, Madhavaram, Periyapalayam, Semi Critical (70%-90%) 14 Poonamallee, Poonimangadu, Pothattur Redhills, Thirumazhisai, Tiruttani,Ammanbakkam, Avadi, Pallipattu, Morai, Velakapuram. Elavur, Gnayiru, Kolur, Madhapakkam, Maduravoil, Manavor, Pothatturpettai Pandur, Pennalurpett, Ponneri, Safe (<70%) 19 Poondi, Poovalambedu, Sholavaram, Arani Thirupalaivanam, Thiruvalangadu, Thiruvallur, Tirur, Velliyur. Others (Poor& Saline) 1 Minjur Total 46 Source- TWAD .