Unit 4: Groundwater, GPS, and Water Resources
GPS data can measure ground elevation change in response to the changing amount of groundwater in valleys and snow cover in mountains. In this module, students will learn how to read GPS data to interpret how the amount of groundwater in the Central Valley of California is changing, in particular in reaction to the 2012–2015 drought. They will then apply the skills they develop and knowledge they gain to demonstrate their understanding of how GPS data has implications for the future of groundwater resources in California.
Unit 4 Learning Outcomes
- Students will observe, describe, analyze, interpret, and apply time-series GPS data with reference to ground motion related to the amount of groundwater and snow cover.
- Students will explain how changing amounts of groundwater and snow cover causes annual ground motion as measured by GPS.
- Students will explain how groundwater withdrawal and drought conditions cause longer-term trends in ground motion as measured by GPS.
- Students will draw on GPS data to make a societal recommendation relative to groundwater withdrawal.
Unit 4 Teaching Objectives
- Cognitive: Promote an understanding of the relationship between ground elevation and amount of groundwater or snow cover; provide examples of evidence of society's influence on the natural world through groundwater withdrawal and the natural world's influence on society through drought conditions; provide students with a framework to understand groundwater budget, inputs, and outputs; give students the opportunity to learn and apply the concept of correlation
- Behavioral: Promote skills development in reading and interpreting GPS time-series data and understanding its relationship to changes in groundwater volume or snow cover; provide a framework for students to approach data reading and interpretation to solve problems like a scientist; give students opportunities to convert units, identify trends, and calculate rates
- Affective: Encourage reflection about approaches to and difficulties with working with time-series GPS data
Context for Use
The content for Unit 4 is appropriate for introductory geology, environmental science, and other geoscience courses; sophomore-level courses in which hydrology, geodesy, and/or climate studies are being introduced; or non-geoscience courses where climate studies and/or the nature and methods of science are being investigated. Unit 4 activities can easily be adapted to serve small- or large-enrollment classes. They are designed to be flexible in their context and can be executed in lecture and lab settings as an in-class activity, a homework activity, and/or a collaborative lab exercise. For example,
- Activities 1 and 2 can be completed as homework, and Activity 3 can be completed as an in-class activity or lab exercise;
- Activity 1 can be completed in class, Activity 2 completed as homework, and Activity 3 completed in lab; or
- All activities can be completed in-class and/or in lab.
In the Measuring the Earth with GPS module, this unit can be used in sequence with the other units or alone. However, we recommend that it is used after Unit 3: Glaciers, GPS, and Sea Level, because the glaciers unit develops skills that students will then build on in this unit. This unit can be used as a summative assessment of the Measuring Earth with GPS module. This unit is an adaptation of the upper division module Measuring Water Resources - Unit 3: Monitoring Groundwater Storage with GPS Recording Vertical Position. Another introductory module that address water resources using other data sets besides GPS is Eyes on the Hydrosphere: Tracking Water Resources.
Description and Teaching Materials
Introductory Lecture (10 minutes)
This brief lecture introduction provides context for Unit 4 by introducing students to:
- Groundwater concepts such as how it fits in the water cycle, aquifers, pore spaces, and budget (withdrawals and recharge)
- Think-pair-share asking students to determine how the amount of groundwater changes if the additions and subtractions are out of balance
- Brainstorm how scientists can measure the changing amount of groundwater and introduce the idea that GPS can be used to measure it
- Graphs, photos, and maps that can be shown to students to aid in discussion for each part of Unit 4.
- Calculating the annual range when there is an overall downward trend (this can be used in Activity 3, and should not be presented in the introduction)
Slides: Unit 4 Introductory slides (PowerPoint 2007 (.pptx) 16.8MB Jul11 19)
Activity 1: Observe and Describe (20–40 minutes)
In this activity, students will be guided to learn how to describe scientific data by making careful observations of it. Students will conclude by using that data to test predictions they made using multiple working hypotheses. The questions guide students through the process that scientists use when they work to solve scientific questions. This particular activity uses data from a GPS station in Puerto Vallarta, Mexico, to better understand the impact precipitation has on the vertical motion of the ground.
Students can complete this handout as homework, in-class individually or in small groups, or in a lab in small groups. The graphs in the handout itself should be supplemented with the large version for easier readability (see below)—if students are working in groups, one large set of graphs per group is enough. If this is done in class, suggestions for formative assessment discussions are given in the teaching tips, below.
If students completed the Unit 3: Glaciers, GPS, and Sea Level unit and understand correlation, then Activity 1 could be skipped, although they may need to learn the concept of correlation before completing Activity 3.
Student activity handout:
- Student version:
- Activity 4.1 Student Exercise (Microsoft Word 2007 (.docx) 357kB Jul11 19)
- Activity 4.1 Student Exercise PDF (Acrobat (PDF) 445kB Jul11 19)
- Full size GPS graphs for easier viewing are below, beneath Activity 3
- Instructor version:
Activity 2: Animation (10–15 minutes)
In this activity, students will watch an animation that illustrates how GPS can be used to determine the changing amount of snow cover in mountains and groundwater in valleys. It describes the relationship between changing water resources (snow cover, groundwater) and vertical bedrock motion.
This handout helps students organize information in the animation. However, students can watch the animation before completing Activity 3 without completing this handout. Students can complete this handout as homework, in-class individually or in small groups, or in a lab in small groups.
Student activity handout:
- Student version:
- Activity 4.2 Student Exercise (Microsoft Word 2007 (.docx) 4.3MB Jul12 19)
- Activity 4.2 Student Exercise PDF (Acrobat (PDF) 3.4MB Jul12 19)
- Instructor version:
- YouTube: Measuring Drought: A GPS Network Offers a New Perspective. English and Spanish closed captions are available in YouTube; click "Settings" icon and select the subtitle version of your choice
- File: Measuring Drought: A GPS Network Offers A New Perspective (MP4 Video 16MB Jun3 17)
Activity 3: Analyze, Interpret, and Apply (60–120 minutes)
In this activity, students will learn how to analyze and interpret scientific data after describing it. Students will conclude by using that data to support a recommendation they make about an issue relevant to society. The questions guide students through the process that scientists use when they work to solve scientific questions. This particular activity uses data from GPS stations in the Sierra Nevada Mountains and the Central Valley in California to better interpret long-term water resource trends that can be interpreted by analyzing GPS position of the ground.
Students use four GPS stations throughout the activity. In the first part of the activity, they are directed to observe and describe the set of data for only two of them, and then work with students who described the set of data for the other two stations. This initial work can be done individually as homework, in class individually or in pairs, or in lab individually or in pairs. The instructor will need to ensure that equal numbers of students describe the two sets of GPS data, either by allowing student groups to divide them up between themselves or by assigning GPS sets. When they are directed in the activity, students working on the two sets of GPS data should compare their observations and work together to analyze and interpret all four sets of GPS station data, resulting in them working in pairs or groups of four for the remainder of the activity.
The GPS graphs in the handout itself should be supplemented with the large version for easier readability (see below)—if students are working in groups, one large set of graphs per group is enough. During the activity, students will reach the point where they need the additional location data, precipitation data, and data on groundwater withdrawal impact on society. Those data should be given to each group at that point; they should not be given to the students before, since they give away answers when students are making predictions.
Student activity handout:
- Student version:
- Activity 4.3 Student Exercise (Microsoft Word 2007 (.docx) 1.5MB Jul12 19)
- Activity 4.3 Student Exercise PDF (Acrobat (PDF) 2MB Jul12 19)
- Instructor version:
- Includes examples of high- and low-quality student work.
- Additional data (to support answering Question 22):
- Activity 4.3 Student Exercise: Additional Data (Microsoft Word 2007 (.docx) 203kB Oct14 19)
- Activity 4.3 Student Exercise: Additional Data PDF (Acrobat (PDF) 315kB Oct14 19)
All graphs and original data files
Below are files with handouts, graphs, and data used throughout Unit 4. GPS data come from https://www.unavco.org/instrumentation/networks/status/pbo and http://geodesy.unr.edu/NGLStationPages/gpsnetmap/GPSNetMap.html.
- All graphs of GPS data: Unit 4 GPS graphs (Microsoft Word 2007 (.docx) 1.1MB Aug28 18) Unit 4 GPS graphs PDF (Acrobat (PDF) 1005kB Jan14 19)
- This handout contains larger versions of the GPS graphs. You may find it helpful to have a copy of these printed out for each table group—particularly for the graphs in which the students need to calculate an annual range of motion as well as a rate.
- All Excel files with GPS data: Unit 4 GPS data (Zip Archive 4.4MB Aug28 18)
- Contains information on the data sources as well as the original spreadsheet data and graphs from which the student exercises and handouts were generated. For instructor reference or to make changes to the way data are displayed.
Teaching Notes and Tips
- Students do wrestle with some misconceptions related to what GPS data is measuring. For instance students sometimes think that the "0 mm" position on a GPS graph is the same thing as being at sea level. This is more likely for locations near sea level, such as Houston. Students also confuse positions (mm) with rates (mm/yr).
Activity 1: Observe and Describe
- If you have already implemented Unit 3: Glaciers, GPS, and Sea Level, then having students complete Activity 1 may not be necessary, since students have already learned and practiced some of the necessary skills for observing and describing vertical motion of GPS data. However, they will need to learn the concept of correlation of data, since that is introduced in Activity 1.
- If Activity 1 is done as homework, you may wish to have students compare their answers for the first few minutes of class or lab to ensure they understand it. In particular, it may be useful for them to compare their answers to Questions 9 and 17.
- If Activity 1 is done in class, you may wish to have the students pause after certain questions for discussion. Students can compare their answers to the answers of other groups, or you may wish to lead a full-class discussion. In particular, it may be useful for them to discuss Questions 9 and 17. For Question 6, if desired, you can assign different years to groups, and they can compare answers across years.
- Here are slides showing the GPS data and stations to aid in class discussions, if desired: Unit 4 GPS photos, locations, and graphs (PowerPoint 2007 (.pptx) 11.6MB Jul11 19)
Activity 2: Animation
- The animation should be watched when directed, after students have begun Activity 3. The student handout activity is provided for students to fill out while watching the animation to help focus and organize what they are learning. You may wish to have students compare their answers to Question 4 plus Question 2 if there is enough time.
- If Activity 2 is done as homework, you may wish to have students compare their answers for the first few minutes of class or lab to ensure they understand it. Or, you may wish to show the animation again and have a full-class discussion. In particular, it may be useful for them to compare their answers to Question 4 plus Question 2, if there is enough time.
- If Activity 2 is done in class, you may wish to have the students discuss the animation after they watch it. In particular, students can compare their answers to the answers of other groups, or you may wish to lead a full-class discussion. In particular, it may be useful for them to compare their answers to Question 4 plus Question 2, if there is enough time.
- If you do not wish to assign the handout for students to complete while watching the animation, you can instead ask Question 4 and parts of Question 2 as discussion questions after watching the animation.
Activity 3: Analyze, Interpret, and Apply
- We recommend that students work on Activity 3 in small groups, so they can work collaboratively to solve the problems. In fact, without modifying the activity and giving the students more space to analyze all four stations, the students must work collaboratively so they can share the descriptions they made about the four GPS stations. If only two stations are used, then we recommend station P567 for the mountain data and P056 for the valley data.
- Activity 3 builds on skills learned during Activity 1 and concepts learned during Activity 2, so those parts should precede this activity. However, if your students are proficient at observing and describing data in graphs and understand correlation, it may be possible to skip Activity 1.
- Question 14 asks students to calculate the annual range of vertical motion for the valley data. You can let the students figure out how to calculate it on their own (high point minus low point). However, because there is an overall slope to the line, you can also provide them with guidance to calculate the range by removing that slope. There are directions in the PowerPoint slides provided in the introduction of Unit 4.
- Here are slides showing the GPS data and stations to aid in class discussion, if desired: Unit 4 GPS photos, locations, and graphs (PowerPoint 2007 (.pptx) 11.6MB Jul11 19)
- The Activity 3 Answer Key also includes a rubric for the more complex question related to groundwater policy and examples of student answers. If your students struggle with how to write high-quality answers, you could consider sharing the rubric and example student answers and asking students to evaluate what makes a high-quality answer. This may help them improve for next time.
Activities 1 and 2 can be assessed formatively by using some of the questions as prompts for discussions, as described above in Teaching Notes and Tips. In addition, if the students are working in class or lab on the questions, the instructor can circulate and listen to student conversations and answer questions to ensure that the desired learning is occurring.
Activity 3 (as well as Activities 1 and 2, if desired) can be used as the summative assessment for this unit (Unit 4: Groundwater, GPS, and Water Resources). In addition to the student activity handout, the following assessments can be used as homework, quiz, or exam questions. There are open-ended and multiple-choice questions included. Also note that the Assessment page includes more general summative assessments that can be used for this unit as well.
References and Resources
This unit is an adaption of the upper-division module Measuring Water Resources, Unit 3: Monitoring Groundwater Storage with GPS Recording Vertical Position.
Resources quoted in the additional data for Student Activity 4.3:
- Report: Land Subsidence from Groundwater Use in California, a 2014 report by Borchers and Carpenter of the California Water Foundation
- All This Recent Rain Won't Stop California from Sinking, a 2017 news article by Halverson
- Water Stress and a Changing San Joaquin Valley, a 2017 report by Hanak and others of the Public Policy Institute of California
- Land Subsidence: Cause & Effect, a webpage by the United States Geological Survey (USGS), California Water Science Center (CWSC)
Additional Resources for Instructors:
- If your students have difficulties converting units, a helpful webpage is The Math You Need When You Need It: How Do I Change Units
- There is a UNAVCO GPS Spotlight on GPS and Water Use briefly introducing GPS and aquifer depletion in California and water loading in Japan.
- There is a UNAVCO GPS Spotlight on Station P056, a GPS station in the San Joaquin Valley in California and used in this unit.
- There is a UNAVCO GPS Spotlight on Station P349 describing crustal loading from Lake Shasta in California and relating it to seasonal changes and drought conditions.
- There is a UNAVCO GPS Spotlight on GPS and Snow Depth introducing how snow depth is measured. There are links to GPS Snow Depth case studies at the bottom on the page.