AMSL 101 Lecture Notes - Hydrograph
Document Summary
When water falls within a stream"s drainage basin it enters the stream by infiltration/base flow and by runoff contributing to the streams discharge. To predict flooding for a particular stream, geologists make use of long term records of previous floods on that stream. The recurrence interval (also called the flood frequency) is the average length of time, in years, between floods of a particular size, or magnitude . 140 years a flood 20 feet above normal was the fourth largest flood (i. e. during those 140 years there were three floods larger than 20 feet). The on average part is important! It does not mean such a flood will occur exactly every 35 years. Again, it is important to remember that this wording reflects the average time interval between floods of a particular size. In other words, there is a 2. 8% chance of a 20 foot flood happening each year on this stream.
