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前言(略) 一、长江流域的洪水和防洪形势 (一)长江流域的洪水长江的流域面积180万平方公里,雨量丰沛,常发生峰高量大、持续时间长的暴雨洪水。由于流域位于东亚副热带季风区,以及各地区气候和地形等自然条件的差异,在正常年份,洪水出现的时间不同,赣江、湘江洪水一般出现在4～6月,沅水、资水和乌江的洪水一般发生在5～7月,金沙江下游和四川盆地各水系的洪水一般出现在7～9月,汉江洪水一般出现在7～10月,干流最大洪峰一般出现在6～9月。一般年份下游洪水早于上游,南岸支流早于北岸支流,洪峰可以互相错开,不致酿成大灾。如果各地雨季出现的时间提前或推后,上下游南北岸各支流的洪水重叠,或某一地区
Preface (omitted) First, the flood and flood control situation in the Yangtze River valley (a) flood in the Yangtze River Basin Yangtze River basin area of 1.8 million square kilometers, abundant rainfall, often occur high peak volume, long duration of storm floods. Due to the differences of natural conditions such as climate and topography in subtropical monsoon region of East Asia and climate and topography in different regions, floods occur in different times in normal years. Floods in Ganjiang River and Xiangjiang River generally occur from April to June, while in Yuanshui, Zishui and Wujiang The flooding generally occurs from May to July. The floods in the lower reaches of the Jinsha River and the Sichuan Basin are generally from July to September. The flood in the Hanjiang River generally occurs from July to October. The maximum peak of the main stream usually occurs from June to September. In general, floods in the lower reaches are earlier than those in the upper reaches, and tributaries of the south bank are earlier than tributaries of the north bank. Flood peaks can stagger each other without causing catastrophes. If the rainy seasons occur earlier or later, the floods of the tributaries in the upper and lower reaches of the north and south shores overlap, or a certain area