五十年一遇

建立了海城河城区段五十年一遇洪水演进模型，得出了行洪水面线，对现状堤防的防洪能力进行了分析。（2）多光谱样本库的建立。

A fifty year return period numerical model for flooding was established , and from which flood surface level was obtained and the flood control capacity was analyzed . ( 2 ) Construction of Multispectral Image Database .

我们多久以后又会看到一次所谓的“五十年一遇”的旱灾？

How long until we again see a so-called'once in50 years'drought ?

北京周二遭受了半个世纪以来的最寒冷天，而此前的降雪量甚至超过了五十年一遇。

Beijing faced the coldest weather in half a century on Tuesday as its residents dug out from the worst snowfall in even a longer period of time .

这场危机与众不同，它是一次五十年或者百年一遇的事件，深深根植于人们对主要金融机构资不抵债的恐惧。

This crisis is different – a once or twice a century event deeply rooted in fears of insolvency of major financial institutions .