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1引言在英格兰和威尔士,每年用于防洪和海岸防护上的费用约为3亿英镑。若没有防洪设施,大约7%的英格兰和威尔士的土地(10000km~2)将受到非潮汐型洪水灾害;没有防浪堤设施,大约7000km~2土地将受到潮水影响。此外,在英格兰和威尔士,50%以上的农业区和几乎所有“Ⅰ”类土地均依赖于排水系统和防洪设施。河道养护的主要工作是,控制水生植物生长、清障疏浚河道、护岸岁修以及对防洪设施和排水系统的维护。通过河道养护,提高河道泄洪能力,改善农田排水条件,达到减少洪涝灾害的目的。因此,河道养护是一种包括效益和费用的综合经济活动。
1 Introduction In England and Wales, the annual cost of flood control and coastal protection is about 300 million pounds. In the absence of flood protection facilities, about 7% of the land in England and Wales (10,000km ~ 2) will be exposed to non-tidal flood disasters; without breakwater facilities, about 7,000km2 will be affected by tides. In addition, in England and Wales, more than 50% of agricultural areas and almost all “I” land depend on drainage systems and flood control facilities. The main tasks of river maintenance are controlling the growth of aquatic plants, clearing away the dredging river courses, rehabilitating shores, and maintaining flood control facilities and drainage systems. Through river maintenance, improve river discharge capacity, improve farmland drainage conditions, to achieve the purpose of reducing floods. Therefore, river maintenance is a comprehensive economic activity that includes benefits and costs.