It began in 1972 and was most severe during a drought in 1980 when it reached five centimeters a month. Chiatung has sunk 2.24 meters to date and is now half a yard below sea level.
從水利局的測量紀錄來看，下陷約始於民國六十一年，至六十八年起較顯著，而以六十九年前期的乾旱期最厲害，平均每月下陷五公分左右。到現在為止，塭豐村已經「降」了二點二四公尺，比海平面還低半公尺。