rkillings Jun 17, 2013:

On second thought … … I think I understand the plural here. In practice, i.e., in actual usage in English and, evidently, in French, "100-year flood" has TWO meanings: the flooding event with p=.01 in any one year AND the *category* of historical floods of magnitude greater than or equal to (or maybe just roughly comparable to) the theoretical 100-year flood -- BUT not as great as the 500-year or the 1,000-year flood. Thus, in 2005, the Yangtze was considered to have experienced 100-year floods in 1931, 1935 and 1954 [not 1998?] and a 1,000-year flood in 1870. (See http://www.ehs.unu.edu/file/get/3632). Surely the three biggies in the 20thC were not all identical.
If this interpretation is correct, then 'crues séculaires' is analogous to, say, Category 3 hurricanes. And the source text is saying that the amount of water that flowed during 60 days of the 1998 flood was comparable to total flows during historical 100-year floods. (Maybe the water level never rose as high?)

Tony M Jun 17, 2013:

@ SafeTex Ouch, that's AWFUL! :-)

SafeTex Jun 17, 2013:

Hello again Did I get.... "sold down the river" by Tony M? (wink wink) .

Tony M Jun 17, 2013:

@ RK I see what you mean! I'd taken it as meaning 'as great as the flow for a 100-year (i.e. exceptional) flood'; however, reading it again, I wonder if perhaps poor SafeTex wasn't right after all: 225 billion cubic metres is an awful lot, so it could indeed be the accumulated total of all the floods over the last hundred years.

Asker, you may never get to the bottom of this, but you do at least need to be aware of the potential ambiguity here; and I have to confess, for once I'm stumped as to how on earth one could translate this while keeping the same ambiguity in EN :-(

rkillings Jun 17, 2013:

Wait a minute … No question that 'crue séculaire' is the French term for the concept called the "100-year flood" in English. Usually, this means the estimated magnitude of *a* flooding event with probability = 0.01 of occurring in any one year. See http://www.mah.gov.on.ca/Page3729.aspx

Here, this term is in the *plural*. Are they talking about flooding equivalent in magnitude to multiple 100-year floods occurring in the space of sixty days, without saying how many? Please explain!

SafeTex Jun 16, 2013:

Withdraw answer Tony M (and wiki) have shown me that my answer was wrong so it's humble pie for me tonight !!!