In hydrology, time-series analysis has several traditional analysis techniques to help users better understand rivers. One of the most common techniques is flood frequency analysis. In this case, the technique determines the chance of a particular magnitude flood happening during any one year. For instance, a ten-year flood had a probability of 1 over 10, or one-tenth, and is a little over 500 flow units for this particular location.
Although useful for various planning purposes, it is important to know that a flood frequency analysis is not a forecasting tool.