Drainage: Kolkata district was traditionally drained by two channels and various minor water ways. Human efforts tried to supplement the natural system. William Tolly tried to develop an eastward drainage-cum-communication channel by excavating the almost dead bed of the Adi Ganga. The 27 km long Tolly's Nullah was completed in 1777. The Lake Channel was cut through the Salt Lake later on. Some of the other channels were; Beliaghata Canal (1800), Circular Canal from Entally to Hooghly river (1820), Bhangor Khal (1897–98) and the 16 km long Krishnapur Khal, a navigational channel connecting Kolkata with Nona-Gang-Kulti Gang in South 24 Parganas (1910). Since 1742 the Bidyadhari served as an outlet for the drainage of the city, but with deterioration of the Jamuna, Bidyadhari lost much of its fresh water flow. Dr. Birendranath Dey renovated and revived the Bidyadhari in 1943.