High water marks along rivers?

Question

Can high water marks along rivers mark only the last time the river flooded, or the highest it has been over a long period of time?

Answer 1

Hi. I believe the high water marks erode fairly quickly, maybe 100 years or less, so they would only mark fairly recent levels.

Answer 2

Cirric is basically correct, but high water marks (depending on what they were made upon) can disappear in matter of weeks, sometimes even days. Some trees, soil etc can retain the marks for centuries.