This site describes how and when 100-year floods occur. It states that flood designations are based on statistical averages, not on the number of years between big floods. It also suggests that it would make more sense to refer to 100-year floods as 1-in-100 chance floods. This resource is a United States Geological Survey (USGS) Fact Sheet. It can be used in teaching quantitative skills.
Subject: Geoscience:Hydrology:Surface Water:Water Management and Policy, Geoscience:Hydrology:Surface Water Resource Type: Scientific Resources:Overview/Reference Work Topics: Hydrosphere/Cryosphere:Surface Water:Water Management and Policy, Hydrosphere/Cryosphere:Surface Water Theme: Teach the Earth:Teaching Topics:Water, Teach the Earth:Course Topics:Hydrology/Hydrogeology