InTeGrate Modules and Courses >Interactions between Water, Earth’s Surface, and Human Activity > Unit 4: Hazards from Flooding
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Unit 4: Hazards from Flooding

Kyle Gray, University of Northern Iowa (

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In this unit, students examine detailed hydrologic data from one river to identify ways in which precipitation and stream discharge influence flooding which often impacts nearby human societies. They also research a local river and determine the hazard associated with flooding, describe historic flooding, and assess ways a local community mitigates the risks associated with flooding.

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Learning Goals

Unit 4 Learning Goal

By the end of this unit, students will be able to:

  • Describe that flooding is periodic and probabilistic, caused by short-term and annual meteorological factors, and can have profound impacts on humans living along a river system.

Unit 4 Learning Objectives

In order to achieve that learning goal, students will meet the following objectives:

  • Objective 4-1. Students will interpret hydrographic and meteorological data to draw conclusions regarding the interaction between precipitation, discharge, and flooding.
  • Objective 4-2. Students will calculate recurrence intervals of major flooding for one river system using stream gauge data.
  • Objective 4-3. Students will define a "100-year flood" and explain why floods of that magnitude can occur in successive years.
  • Objective 4-4. Students will describe hazards associated with a river system and evaluate their impact on ecosystems and human society.

Context for Use

Unit 4 is an activity designed for an introductory geoscience content course that is aimed primarily at pre-service teachers. It may be used as part of the Interactions between Water, Earth's Surface and Human Activity module, or as a stand-alone activity. The curriculum is designed to build a strong foundation of pedagogical content knowledge for teaching Earth science. This type of course is common at state and regional schools with large teacher preparation programs. Activities are designed to foster group collaboration as students work in small groups (ideally in groups of 3–4) with a faculty member acting as the facilitator.

Unit 4 is designed to take two hours in a lab setting. It is not recommended for implementation in a large lecture class.

The content in this unit aligns well with Science and Engineering Practices, Disciplinary Core Ideas and Crosscutting Concepts in the Next Generation Science Standards (NGSS):

Description and Teaching Materials

In this unit, students use data from the United States Geological Survey (USGS) and the Federal Emergency Management Agency (FEMA) to identify both short-term (hours or days) and long-term (months to years) factors that influence flooding along a river. The Cedar River in Iowa is the initial focus of their explorations of annual variations in discharge and the connection between precipitation and discharge. Then students analyze the floods along the Mississippi River in 1993 and 2008 to calculate recurrence intervals. Finally, they apply these skills to analyze a river system near them and develop an informational brochure for the community.

Student Handouts and Materials

Required Materials

Students ideally work in small groups of three or four; each group will need:

  • A workspace for group work.
  • A whiteboard and markers (recommended as a way to facilitate group discussions and presentations to the larger class).
  • Access to a spreadsheet program like Microsoft Excel, if students download discharge data from the USGS website.

Initial ideas

To begin this unit, elicit students' ideas about flooding and its impacts. These questions are included in the student handout for this unit (Microsoft Word 2007 (.docx) 1.2MB Jan9 15):

  • Where does the water come from when a river floods?
  • What is meant by the phrase "a 100-year flood?" How often would one occur?
  • Brainstorm a list of ways that a river can impact a home or a city.

This can be done in class or as homework prior to class. Students should have time to write down their own ideas first, then share them in small groups and with the class.


All of this information is also included in the student handout.

In 1993, much of the Midwest experienced record flooding due to a wet spring combined with a persistent rain. Cities along the Mississippi and Missouri Rivers experienced record flooding. Des Moines, Iowa, is located between those two rivers and was without power for several days. This flood displaced tens of thousands of people, destroyed hundreds of homes, and affected an area 1,200 km long and 700 km wide. This flood was one of the largest and costliest floods in US history. Scientists who study streams called it a "500-year flood." These links describe the floods and show some photos from the event:

In 2008, many parts of the Midwest were again under water. In Cedar Rapids, Iowa, over 5,200 homes were flooded. See these links for a description of the flood as well as some photos of the floodwaters:

Scientists calculated the size of the 2008 flood and determined that it was also a "500-year flood." This meant that Iowa had experienced two "500-year" floods in just 15 years! In this unit, students will explore why rivers flood and how they impact the people who live along their banks. Students will also learn how floods are rated and how scientists calculate a 500-year flood. Finally, students will investigate flooding for a city in your area.

Part 1: Annual Changes in River Level

In this part of the unit, students examine data from the Cedar River in Iowa to learn about the concepts of annual variability and shorter-term changes in discharge. Students work through questions in small groups, then discuss their answers with the whole class.

Part 2: Connections with the Hydrologic Cycle

In this part, students connect river discharge to the hydrologic cycle by relating annual and daily variations in discharge to precipitation data. The data they interpret come from the USGS stream gauge and weather station at Waterloo, Iowa, and can be downloaded from the National Water Information System (NWIS) web interface for the Cedar River at Waterloo, IA stream gauge site. The graphs are provided here, but you might also want students to download the data and graph it themselves.

Part 3: Yearly variation and what it means

Students examine graphs of stream discharge from four different years (1977, 1983, 1997, and 2010). In comparing these graphs, they infer the relative amount of rainfall in each year and look for patterns and cycles that are consistent year to year.

Possible extension: Students can look up newspaper stories from this region for that year or investigate the discharge from another stream in the area such as a smaller tributary river or creek.

Part 4: Predicting future floods

In this part, students calculate the recurrence interval (RI) for floods of a given discharge for the Cedar River. Using their calculations, they estimate the RI for the Great Flood of 2008. Then they explore the meaning of the terms "100-year flood" and "500-year flood," and how the recurrence interval is really an indication of the probability of a flood that size occurring in a given year, rather than a prediction.

Part 5: Consequences of living on a floodplain

The Federal Emergency Management Agency (FEMA) publishes maps that define the 100-year and 500-year floodplains for participating communities. People who live within a floodplain are required to obtain supplemental flood insurance to cover the costs incurred in a flood. Cities such as Cedar Falls often use these flood maps to regulate construction within the floodplain. In this part of the unit, students examine FEMA's floodplain map of Cedar Falls, Iowa, and discuss what it means for people living in the area.

Homework and summative assessment

The final component of this unit is a homework project in which students work in pairs (or individually) to develop an informational brochure for a community about the flooding hazards of a given river. The prompt is: Imagine that you and your research partner are writing an informational brochure that a riverfront city like Cedar Falls, Iowa, could use to educate its citizens on the impact of living near a river. All information should be written so a member of the general population could understand it. This means defining ALL technical language. You will use online and any other additional resources that you may find to gather your information.

Teaching Notes and Tips

All of the data and graphs used in this module were obtained from (or generated from) the US Geological Survey's WaterWatch website. Instructors can easily download data for a nearby stream to make this unit more relevant for their students.

Students must be encouraged often to read what is in the activity sheets and not look to the teacher to tell them what to do. Students must also be encouraged to write down their answers whenever a prompt is encountered. Skipping answers may lead to misconceptions or misunderstandings. Skipping answers also denies students the opportunity to later reflect on their thought processes as they learn the material.

Download these

on implementing Unit 4 plus expected outcomes and answers to questions in the unit.


Objective 4-1: Student worksheets: For each graph, infer the relative amount of rainfall for each year in Cedar Falls and describe your observations that support your conclusion.

Objective 4-2: Use the graph on the previous page to estimate the recurrence interval for that flood and determine the probability that a flood of that size could happen again. Explain below how you arrived at those answers.

Objective 4-3: Two students are discussing what that term means and whether it is safe to live near the river . . . Who is right? Explain why. (Question 4-8)

Objective 4-4: Research flood hazards for a city on a nearby river or on a river of choice. Students will create a brochure outlining the following points: Location and size of the river, largest recorded flood, cost of that flood, any measures that the city has done to protect itself from flooding (levees, flood walls, etc.).

References and Resources

General Resources

  • Flood Recurrence Interval activity modeled after Checkpoint 11.19 from McConnell, D., Steer, D. (2015). The Good Earth, 3rd Edition. McGraw-Hill, New York.
  • Allen, Jesse, 1993, NASA, Satellite Images of the Great Flood of 1993 - Earth Observatory using data provided courtesy of the Landsat Project Science Office.
  • Photograph of a house threatened by floodwaters near St. Louis, Missouri. Flooded House Near St. Louis, Missouri — Photograph by Sam Leone and used by permission from the St. Louis Dispatch.
  • U.S. Geological Survey Podcast - Podcast describing the definition of a 100-year flood
  • Graphing and Best-Fit Lines from The Math You Need When You Need It project

Information and Data on Flooding (USGS)

Water Data (including stream discharge)

Annual Peak Stream Discharge Data

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These materials are part of a collection of classroom-tested modules and courses developed by InTeGrate. The materials engage students in understanding the earth system as it intertwines with key societal issues. The collection is freely available and ready to be adapted by undergraduate educators across a range of courses including: general education or majors courses in Earth-focused disciplines such as geoscience or environmental science, social science, engineering, and other sciences, as well as courses for interdisciplinary programs.
Explore the Collection »