In the last December's floods, slums in Chennai suffered the most devastation. On the edge of rivers, rail ways tracks and in low-lying areas the scale of vulnerability of residents of these slums in heavy rain has increased manifold as their numbers have proliferated over the past few decades. A survey by Tamil Nadu Slum Clearance Board (TNSCB) has found that there was a 51.85% increase in slums in the city from 2001 to 2014.These shanty towns increased from 306 in 1956 to 2,173 in 2014.As part of its slum-free city plan, TNSCB recently completed a socio-economic survey in 1,131 slums spread across 17.28sqkm in the city . It found that north Chennai that consists of Tiruvottiyur, Manali, Madhavaram, Tondirapet and Royapuram has the maximum slums in the city , with 470. It is followed by central Chennai (Thiru-Vi-Ka Nagar, Ambattur, Anna Nagar, Teynampet and Kodambakkam) with 389. There are 272 slums in south Chennai -in Valasaravakkam, Alandur, Adyar, Perungudi and Sholinganallur.Activists say the condition of most slums in the city is poor. Thousands of families are exposed to various health hazards. Rain or sun, they remain the most vulnerable group in urban Chennai -floods can wash away their belongings or accidental fires in summer can raze their houses to the ground.Activists say north Chennai has a higher slum population since migrants usually flock to the region due to employment opportunities, especially in manufacturing units, availability of affordable land and proximity of houses to workplaces. Many slums have come up along the coastline in addition to the slums populated mostly by fishermen.According to the survey , about 79% (896 slums) are tenable (those located on lands earmarked for residential land use and environmentally safe area) and about 21% (235 slums) are untenable (located in unhealthy and environmentally unsafe areas).It also revealed that at least Rs 32,369.98 crore will be required to develop 1,131 slums that were surveyed. Around 1.15 lakh house holds in 896 existing slums should be up graded and 61,830 in 235 slums relocated the survey recommended.“The cost for housing is worked out to convert kutcha and semi-pucca houses in each slum into pucca houses. Infrastructure requirement of each slum is arrived at from which the infrastructure costing is worked out,“ the report said.Not surprisingly , the study found that 51% of the population in slums belong to SCST communities and most of them are casual labourers (73%). It also revealed that 4% of the households don't have access to any toilets and defecate in open.A TNSIC official said the survey started under Rajiv Awas Yojana in 2009. It has now been replaced by NDA's Pradhan Mantri Awas Yojana, which aims to provide `every family a pucca house and amenities.