上海市区防汛标准和工程建设的变化大抵可分为三个时期。一.无防汛设施时期(上海建埠至1955年)1921年以前市区地势较高,地面高程大都在4.0米以上,(吴淞标高,下同)。1921年市区发现地面下沉,到1945年后市区地面下沉已对防汛安全产生明显影响,反映在潮水倒灌上岸次数增加,但除1949年外,灾情并不严重。在这一时期,市区黄浦江,苏州河沿岸陆续由沿河单位、市政部门修建了一些护岸工程,岸顶标高大抵在4.7米 Shanghai flood control standards and construction changes can be roughly divided into three periods. I. Floodless Facilities Period (Shanghai Jianbu to 1955) Before 1921, the urban area had a high terrain and the ground elevation was mostly above 4.0m (Wusong elevation, the same below). The surface subsidence was found in urban areas in 1921. Subsequent ground subsidence in urban areas after 1945 had a significant impact on flood control and safety. It was reflected in the increase in the number of inundated tidal flats, but the situation was not serious except in 1949. During this period, a number of bank protection works were successively built along the Huangpu River and the Suzhou River in the urban areas along the river and municipal departments.