The sinking was first noticed in 1921, but Shanghai went on using ground water for decades, according to Liu, the senior geologist for the Shanghai Institute of Geological Survey. The problem got so bad by the 1950s and 1960s that the ground was sinking by four inches a year. in 1963, banning most wells and limiting use of the rest. Still the decline continued, and Liu said that since the mid-1960s the city has settled 16 more inches.