With the help of Major James Rennell's maps (1764 to 1773) and of the Revenue Survey it is possible to reconstruct the history of the Bengal Delta and its river systems. It was Rennell who carried out the first ever accurate cadastral surveys and laid the basis for the geographical study of Bengal. At the end of the 18th century, probably as a result of the great Tista floods in 1787, the Brahmaputra changed its course and joined the Padma at Goulundo. No piece-meal study of an intricate river system is possible, without distortion and inadequacy.