Note that such probabilities are the same for every year. So, for example, the probability that discharge of the Red River at Fargo, North Dakota will exceed 25,000 ft3/sec (the discharge of the 100-year flood) this year or any other year would 1%. You can think of this in the same way you would think about rolling dice. The probability on any roll that you will end up with a six, rolling only on die, is 1 in 6 or 16.67%. Each time you roll that one die the probability is the same, although you know that it is possible to roll two or three sixes in a row.