Unit 5: Mapping the Impact of 100 and 500-year Floods
Most often, we characterize floods based on their return periods. Considering new land developments and the changing climate, what was once a 100-year flood may change over time. Thus, if we are going to experience the previously defined 100-year flood more frequently, the new 100-year flood may be what was a 500-year flood before. One may then wonder what will be the impact of this 500-year flood compared to a 100-year flood? Is it five times bigger and more damaging than a 100-year flood? The goal of this Unit 5 is to let students quantify floods for 100 and 500 year return periods, and map the corresponding flood inundation extents. The students will then use these results to see how the flood magnitude and the inundation area changes for these floods. The final inundation maps can also be used to estimate key infrastructure that may be vulnerable.
This unit serves as the Summative Assessment for the module. Data sets are provided for students to apply concepts learned in prior units to a new scenario. As with Unit 4, this unit uses HEC-RAS. It can be done by students largely outside of class time.
Unit 5 Learning Outcomes
This unit is intended to provide the summative assessment for the entire module. As such, students should demonstrate a mastery of the learning goals for the entire module. These include the following:
- Describe flooding and its role as natural process versus hazard
- Apply probability concepts to determine relationships between flow rates and return periods
- Create flood inundation maps for a given flow rate using a hydraulic model
- Translate flood occurrence to societal risk
Unit 5 Teaching Objectives
- Affective: Provides students with the opportunity to understand and convert streamflow data into meaningful maps of flood inundation
- Behavioral: Promotes students skills to use streamflow data, conduct flood frequency analysis and perform hydraulic simulations using HEC-RAS for mapping flood inundation extent
- Cognitive: Facilitates students ability to interpret streamflow data for identifying historical floods
Context for Use
The content of Unit 5 is appropriate for advanced geoscience, earth science, civil engineering courses at the junior and/or senior level in which the basics of hydrology and hydraulics are taught. Some of the concepts in the unit are little advanced for a junior level class, so it is recommended to do it later in the course, when students have learned about open channel hydraulics and Manning's equation. Unit 5 is intended for use as a summative assessment for the entire Flood Hazard module and gives students the opportunity to apply the knowledge and skills learned in Units 1-4 for creating a flood inundation map for a new river reach that has not been used in the earlier units. Most likely it would not be possible to use this unit without first also doing at least Unit 4: Hydraulic Modeling and Flood Inundation Mapping using HEC-RAS.
Description and Teaching Materials
As Unit 5 serves as the summative assessment for the entire Flood Hazard module, the teaching material mainly includes the data and the model that students will need to complete for this unit. There is no new instructional material for this unit, so students should be referred to material from Units 2-4 for completing this unit. Unit 5 can be assigned as an assignment outside of class. Little class time is needed other than to introduce the assignment (which can be done early in the module) and answer student questions as they arise.
HEC-RAS models for multiple reaches are provided here, and the instructor can pick one reach for Unit 5 or distribute different data sets to different students. A presentation is provided to give a brief overview of the reaches and the corresponding models. The student exercise does not specifically ask for exploring societal impacts by looking at any infrastructure data, but a KMZ file is provided for these sites if the instructor wishes to include this part in the exercise. Students can overlay the infrastructure KMZ file with the inundation map in Google Earth to explore the impact of 100- and 500-year inundation on existing infrastructure. If the instructor chooses to select another reach relevant to his/her geographic interest, it is important to make sure that there is a stream gauge at that reach for conducting the flood frequency analysis and that the HEC-RAS model for the reach is available/created for students to perform the hydraulic simulations.
The student exercise consists of the following four parts:
- Obtaining streamflow data for a selected reach
- Conducting flood frequency analysis to compute 100- and 500-year return period floods
- Performing hydraulic simulations using HEC-RAS to create flood inundation maps for the three return period floods
- Writing a brief report on their flood modeling analysis by comparing the flood inundation extents corresponding to the three return periods
- Data for Weiser River in Idaho (Zip Archive 51.4MB Sep17 20) - This zip folder contains the HEC-RAS project for Weiser River in Idaho.
- Data for Brazos River in Texas (Zip Archive 168.1MB Nov10 18) - This zip folder contains the HEC-RAS project for Brazos River in Texas.
- Data for St Joseph River in Indiana (Zip Archive 18.5MB Nov10 18) - This zip folder contains the HEC-RAS project for St. Joseph River in Indiana.
- Data for Tippecanoe River in Indiana (Zip Archive 42.5MB Nov10 18) - This zip folder contains the HEC-RAS project for Tippecanoe River in Indiana.
- Data for White River in Indiana (Zip Archive 120.1MB Nov10 18) - This zip folder contains the HEC-RAS project for White River in Indiana.
- Infrastructure Data (Zip Archive 12kB Sep17 20) - This zip folder contains a Google Earth file with infrastructure information (hospitals, schools, etc) for the case study sites. It is very helpful for students making the final determination of vulnerabilities at the different sites.
- Unit 5 Study Area Descriptions (PowerPoint 2007 (.pptx) 2.9MB Dec6 19)
- This file contains information related to each study reach for hydraulic modeling and flood inundation mapping.
- Unit 5 Student Assignment (Microsoft Word 2007 (.docx) 207kB Dec6 19)
- This file contains the student exercise for this unit, including the template for the report.
- Unit 5 Student Assignment Rubric (Microsoft Word 2007 (.docx) 17kB Jan8 19)
- Students should also be given a copy of the rubric so they understand the grading criteria.
Teaching Notes and Tips
- It is unlikely you would be using this unit without previously having completed at least Unit 4; so presumably HEC-RAS is already installed and functional. See Unit 4 for HEC-RAS guidance.
- It can work well to let students know about the Unit 5 exercise at the beginning of the module. It can help students to focus on the value of the skills they are learning. You might even consider giving them the Unit 5 assignment early on. Some more advanced
Unit 5 serves as the summative assessment for the flood hazard module.
Unit 5 Student Assignment Rubric (Microsoft Word 2007 (.docx) 17kB Jan8 19)