Unit 4: Irrigation and Groundwater Mining

Unit 4 is designed to help students advance in achievement of the following Module Learning Goals:

• Module Learning Goal 3: Explain what controls geographic variability in irrigation, groundwater mining, and ecosystem impacts of agriculture in the United States.
• Module Learning Goal 4: Apply geoscience information and methods in interdisciplinary assessments of the sustainability of water systems.

Unit 4 has the following specific learning objectives. Upon completion of the unit, students should be able to:

1. Relate groundwater withdrawal rates and water table levels to geographic location, precipitation, and agricultural practices.
2. Assess groundwater-use sustainability using quantitative, long-term well data.

This unit has been designed as part of the Agriculture and Water Sustainability module and uses some of the concepts introduced in previous units, such as the water footprint and irrigation patterns across the United States. In this unit, students will look specifically at groundwater wells in those same states and compare how water table levels may have changed over the past 40+ years.

Class Size: This can be adapted for a variety of class sizes.

Class Format: The activities in this unit are suitable for a lecture or lab setting; portions can also be adapted as a homework assignment or part of an online course. If done in class, students should work in groups.

Time Required: The activity described here should take one 50- to 60-minute class period. Students finish the activity as homework if needed. There is an optional second discussion-based lesson that, if used, will require a second class period.

Special Equipment: Students will need access to the internet before class to watch a video and to read background materials. During class, students will need computers with Google Earth; if this is not possible, then the images can be printed out before class.

Skills or concepts that students should have already mastered before encountering the activity: Students should have covered Unit 3 before starting the lessons in this unit. Familiarity with Google Earth would be helpful. Students should already know the basics of groundwater and be familiar with such terms as water table and aquifer. If not, then the instructor should have students read General Facts and Concepts About Groundwater and review those concepts before beginning this unit.

Unit 4.1 - Irrigation and Groundwater Mining (one 60 minute class period)

In this unit students compare and contrast long-term (decades) groundwater well levels in six states representing the East Coast, West Coast, and Midwest Plains states. Satellite imagery maps of the well locations will give students an idea of the land cover, specifically the presence of irrigated crops. Using groundwater well data from the USGS, students will recognize the depletion of aquifers in the western United States (e.g., the Ogallala/High Plains Aquifer), or groundwater mining, is an unsustainable practice.

Activity 4.1a - Pre-class Homework Assignment

Students should first be given the responsibility to learn about large, deep, ancient aquifers in the United States. Our suggestion is to have students first watch a five-minute NBC video on the Ogallalla/High Plains aquifer. They can then read about the topic from the USGS High Plains Aquifer website—we suggest one section on the Physical and Social aspects aspects and another section explaining the geology of the aquifer. An additional reading and is offered as an option below. It can be used to foster either an online or in-class discussion.

Activity 4.1b - Introductory Lecture/Reflection (10 minutes)

The instructor starts the class by reviewing some of the major concepts of the class exercise using the Unit 4 Slides (PowerPoint 2007 (.pptx) 1.3MB Jul16 24).

• Slide 1 Groundwater and Irrigation- you can make the following points:
• Aquifers can be shallow and deep.
• In order to use groundwater for irrigation, a well must be drilled (expensive) and the water is pumped to the surface using gas/diesel engines or electric motors.
• Center pivot irrigation uses a long arm supported by wheels from which hang sprinklers. The arm moves in a circle as it irrigates the field.
• Slide 2 Crop Circles - Using the satellite image, ask students what could be the source of this pattern. They will use this in the exercise to recognize fields irrigated from center pivots systems, very likely from a groundwater well.
• Slide 3 Ogalalla or High Plains Aquifer – ask students what they learned in the reading and video.
• Slide 4 – This gives the prompt "How do we measure how much water is in aquifer? Is it increasing or decreasing over time?" This offers the class an opportunity to think about geoscientific methods; what data do we need and what tools can be used to gather that data? You should lead the students to determine that water level water table depth) measured over time is appropriate. For this, a well drilled into the aquifer with a float can be used.
• Slide 5 – USGS Groundwater Watch. If you click on the link in the PPT page, you can show the students how the USGS coordinates monitoring of groundwater wells across the United States. You should click on an example and demonstrate to students.

Activity 4.1c - Analyzing Well Records and Google Earth Satellite Imagery (50 minutes)

In this exercise, students will look at groundwater well level records for six states to observe changes in water table levels over time. The exercise is based on USGS Groundwater Watch records and Google Earth Satellite imagery. The optimal scenario is for students to have printed records of the groundwater records and Google Earth on a web-enabled computer. If computers are not available, the other option is to use the printed imagery. The advantage of using Google Earth is that students can zoom in/out and get a more complete view of each region.

The full exercise uses two wells in each of the two states. If the instructor is constrained for time or feels that students may be overwhelmed with this much information, there is an option to use one well per state.

If Using Google Earth:

• Students can work independently or in pairs using laptops or desktop computers that have Google Earth installed on them. First, hand out the printed copies of the Unit 4 Student Worksheet (Microsoft Word 2007 (.docx) 30kB Jan23 17) to each student. Each student, for pair of students, should have a copy of the USGS well records (PowerPoint 2007 (.pptx) 119kB Jan23 17) either printed out or as a file that they can download and view on the computer (students seem to do better with a printed handout).
• If the instructor is using the shortened version of the exercise, then use the well records with one well per state (PowerPoint 2007 (.pptx) 119kB Jan23 17).
• Have students download the .kmz file Groundwater Well Sites (KMZ File 946bytes Jul12 16) and have them open this in Google Earth.
• If the instructor is using the shortened version of the exercise, then use the .kmz file with one well per state (KMZ File 801bytes Jul13 16).
• The students can now follow the directions on the worksheet. The main part of this is recording observations from both the water table vs time plots and the terrain characteristics from the satellite imagery. In particular, students should be looking for evidence of agriculture and irrigation (such as crop circles).

If NOT Using Google Earth:

• Students should work in groups of two to four. Each student should receive a printed copy of the Unit 4 Student Worksheet (Microsoft Word 2007 (.docx) 30kB Jan23 17) and each group should have a printout of the USGS well records and terrain images (PowerPoint 2007 (.pptx) 13.6MB Jan23 17).
• If the instructor is using the shortened version of the exercise, then use the well records and maps (PowerPoint 2007 (.pptx) 16.9MB Jan23 17) with one well per state.
• The students can now follow the directions on the worksheet. The main part of this is recording observations from both the water table vs. time plots and the terrain characteristics from the satellite imagery. In particular, students should be looking for evidence of agriculture and irrigation (such as crop circles).

Optional Class Reading Assignment

If you want your students to further explore the concept of groundwater mining and the High Plains/Ogalalla region, you can have the students read Steward et al. (2013) and have them conduct an online discussion or have a discussion during class time.

At the beginning of the first class for Unit 4, the instructor should use the Groundwater Slides. Embedded in the file is a link to the USGS Groundwater Watch website. The intent is for the instructor to demonstrate a monitor well in the region and show how the site works. The data in the class exercise come from this site, so before class time the instructor should review this website and choose a well to show as an example. Most well sites show an image of the level of the water table plotted against time.

After students have completed the worksheet, they should be given access to the

Unit 4 exercise answer key -- private instructor-only file

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Formative Assessment

A formative assessment of the unit goals can be done using the following

exam/quiz questions -- private instructor-only file

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You can use the

answer key -- private instructor-only file

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Alley, W.M., Reilly, T.E. and Franke, O.L. (2013). General Facts and Concepts About Groundwater, in Sustainability of Ground-Water Resources. US Geological Survey Circular 1186.

Steward, D.R., Bruss, P. J., Yang, X., Staggenborg, S. A., Welch, S. M. and Apley, M. D. (2013). Tapping unsustainable groundwater stores for agricultural production in the High Plains Aquifer of Kansas, projections to 2110, Proceedings of the National Academy of Sciences, doi:10.1073/pnas.1220351110

Sanford, Ward E. and Selnick, David L. 2012. Estimation of Evapotranspiration Across the Conterminous United States Using a Regression with Climate and Land-Cover Data. Journal of the American Water Resources Association (JAWRA) 49(1): 217-230. DOI: 10.1111 ⁄ jawr.12010