在美国，一些在建堤坝在施工时下沉，也有一些已建堤坝必须加高，以防遣受可能发生的洪水漫溢或承受加大了的地震标准。小型土现更是这样，因为根据判断，它们的溢洪道的泄流能力不够，不能调蓄或通过安全洪水。按现行规范，它们应该承受那怕是一半的理论最大可能洪水（PMF）。 In the United States, some dykes under construction sink during construction, and some dams that have been built must be raised to prevent possible flooding of floods or increased seismic standards. This is even more so for small plots because, judging from their judgment, their spillways have insufficient discharge capacity and can not be used for storage or passage of safety floods. According to the current rules, they should withstand even half the theoretical maximum possible flood (PMF).