CHENNAI: Chief Secretary K Gnanadesikan noted that Chembarambakkam accounts for only 44 per cent of the catchment of the Adyar, which received more water from the breached tanks from Kancheepuram district.
Pointing out that Adyar receives water from other sources like Adanur and Manimangalam tanks, he said even before the release of water from the Chembarambakkam Tank, due to heavy rain of 47 cm that occurred at Mudichur, Tambaram and Thiruneermalai areas of Kancheepuram and the surplus from Vandalur, Urapakkam, Irumbuliyoor,
Guduvancheri, Nandivaram, Somangalam, Mambakkam, Thirumudivakkam, Kundrathur eri, Mannivakkam and Manapakkam canals and about 166 tanks in that area, the Adyar River carried a huge flow downstream of the confluence point of Chembarambakkam Tank surplus.
Further, due to heavy rains, four tanks - Nandhivaram, Urappakkam, Mannivakkam and Adanur tanks - breached on reaching their maximum water level. This, in turn, resulted in heavy inflow into the Adyar River. Chennai city also received a rainfall of more than 30 cm on December 1. The flow in Adyar River reached its full capacity due to the surplus from Chembarambakkam Tank, the inflow from the catchment areas of Adyar within Chennai city and the surplus received from the other tanks. In view of the heavy flow in the Adyar River, the high intensity runoff of local rain in Chennai and adjoining urban areas could not fully drain into the Adyar and hence contributed to the inundation of the city.
Quoting the IMD prediction for December 1, he said the it had said” “Scattered heavy to isolated very heavy rain would occur over coastal Tamil Nadu and Puducherrry. Isolated extremely heavy rain would occur over Tiruvallur, Chennai, Kancheepuram districts of Tamil Nadu. Isolated heavy rain may occur over interior Tamil Nadu.”
Therefore, it is clear that the IMD has only given an advisory of isolated extremely heavy rain but has not mentioned anything about 50 cm of rainfall as is being alleged in certain sections of the media. The allegation that NASA has predicted 50 cm of rainfall is totally false. NASA itself has clarified that they do not predict rainfall, the Chief Secretary said.
The flooding on December 1 was caused primarily due to the very high rainfall in November last, the second highest recorded in more than 100 years followed by high intensity of rainfall.