 In sandy areas such as Tiruvanmiyur, Adyar, Kottivakkam, Santhome, George Town, Tondiarpet and the rest of coastal Chennai, rainwater run-off percolates very quickly.In clayey and hard rock areas, rainwater percolates slowly, but it is held by the soil for a longer time.The city's clayey areas include T. Nagar, West Mambalam, Anna Nagar, Perambur and Virugambakkam.