Flood Frequency and Risk Assessment

Contributed by Carol Ormand, Wittenberg University.

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In this lab, students calculate recurrence intervals for various degrees of flooding on a portion of the Des Moines River in Iowa, based on historical data. Then they plot these calculations on a flood frequency curve. Combining flood frequency data with a topographic map of the region, students do a risk assessment for the surrounding community.

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Learning Goals

After this activity, student should:

  • Be able to define river stage
  • Be able to describe recurrence interval in your own words, and relate it to the probability of a particular level of flooding
  • Be able to describe how recurrence interval is determined, including what data are necessary to calculate it
  • Be able to explain why it is difficult to make long-term predictions of large-scale disasters
  • Know how often, on average, a typical river (like the Des Moines) overtops its banks
  • Be able to describe some of the problems associated with flooding of the Des Moines River

Context for Use

This activity was designed to be started in a laboratory period and completed outside of class to be turned in the following week. Students work in groups and turn in one set of products.

Description and Teaching Materials

Activity Sheet (Microsoft Word 48kB Mar16 04)
Excel data file (Excel 19kB Mar16 04)

Teaching Notes and Tips

To do the lab as written, you need data on the Des Moines River. Alternatively, it would be fairly easy to adapt to a different river, as long as the USGS has a gaging station there.

It is necessary to obtain topographic maps and profiles of the Des Moines River around Des Moines, IA. Basic tools are also needed and are listed on the first page of the Activity Sheet.

I provide my students with a blank, formatted graph, with flood stage on the vertical axis (ranging from ~760-800 ft above sea level, for the data set provided) and recurrence interval using a log scale on the horizontal axis (ranging from 1 to 100).


Groups turn in a data table, flood frequency graph, map and topographic profile, and the answers to the bulleted questions in the text of the activity.