Liu Tsung-yung takes a case in point to illustrate how necessary it is to make long-term observations, even for ten or twenty years. Someone observed ocean flow for only a year, and based on their partial conclusions undertook expulsion of waste water into a certain area. In the end the water simply did a complete circuit of the island and the pollution ended up right where it started.
劉宗勇舉例說，海岸邊飄沙的方向必須進行一、二十年的長期觀察，曾經有人只觀察一年海流，就斷定局部的潮流方向，結果做海洋放流管將汙水排出去，廢水繞了幾圈，又繞回原地。