Near surface geophysical measurements are performed by moving sensors across the Earth's surface. Active geophysical sensors transmit a signal into the Earth and record a returned signal that contains information on the physical and chemical properties of the Earth (see Unit 2). This unit introduces the student to the basics of geophysical data acquisition using two techniques that record variations in the electrical conductivity (see Unit 2) of the Earth: [1] electrical imaging (EI), and [2] electromagnetic (EM) conductivity mapping.











Basic concept of electrical imaging measurements

Provenance: Lee Slater, Rutgers University-Newark
Reuse: This item is in the public domain and maybe reused freely without restriction.
Electrical imaging is a galvanic geophysical approach whereby electrical contact with the Earth is made directly via electrodes (typically metal stakes) that are inserted into the ground. Electromagnetic conductivity mapping is a non-contact approach whereby the physics of EM induction is used to sense changes in electrical conductivity. The advantages and disadvantages of using galvanic (EI) and non-contact (EM) techniques for measuring electrical conductivity are described. Ohm's Law is introduced and students investigate how electrical resistance measurements are related to the electrical conductivity of soils. Field implementation of both EI and EM techniques is demonstrated using surveys performed in Harrier Meadow as an example. Students investigate how variations in survey configuration parameters (e.g. electrode configuration and electrode spacing in EI, frequency and coil spacing in EM) control investigation depth (how far into the ground the signals sense) and spatial resolution (what size objects can be detected). The concept of pre-modeling a geophysical survey (i.e. running some simulations of likely effectiveness of the methods before going to the field) to evaluate expected investigation depth and sensitivity is introduced. The Excel-based Scenario Evaluator for Electrical Resistivity (SEER) tool provided by the United States Geological Survey (USGS) is used to demonstrate some key concepts.

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This unit shows how GPS records of surface elevation can be used to monitor groundwater changes. Students calculate secular trends in the GPS time series and then use the original and detrended records to identify sites that are dominated by the elastic response to regional groundwater changes versus those dominated by local subsidence. They then compare the magnitude and timescales of fluctuations in Earth's surface elevation that result from sediment compaction, regional groundwater extraction, and natural climatic variability. This unit provides students with hands-on experience of the challenges and advantages of using geodetic data to study the terrestrial water cycle. The case study area is in California and the GPS records include the period of the profound 2012 -- 2016 drought.

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Note: Although the term GPS (Global Positioning System) is more commonly used in everyday language, it officially refers only to the USA's constellation of satellites. GNSS (Global Navigation Satellite System) is a universal term that refers to all satellite navigation systems including those from the USA (GPS), Russia (GLONASS), European Union (Galileo), China (BeiDou), and others. In this module, we use the term GPS even though, technically, some of the data may be coming from satellites in other systems.

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Online-ready: The exercise is electronic and could be done individually or in small online groups. Lecture is best done synchronously due to the technical nature. Discussion would be better that way too.

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In this unit students will explore surface water and its relationship to the water cycle via watersheds and drainage divides. These topics will inform their analysis of the social and environmental impacts of the planned increase of hydroelectric dams in the Amazon. Case studies include the Ene River and the MaraÃÃn River in Peru.

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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.

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Online-ready: All exercises are electronic and could be done individually or in small online groups. Lecture as currently provided is best done in synchronous format to retain interactive components.

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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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Is groundwater mining sustainable? In Unit 4 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, as an unsustainable practice.

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The concepts of forward modeling and inverse modeling

Provenance: Lee Slater, Rutgers University-Newark
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This unit introduces the student to the concept of geophysical inversion, which is the process of estimating the geophysical properties of the subsurface from the geophysical observations. The basic mechanics of the inversion process used to estimate spatial variations in electrical conductivity from electrical imaging (EI) datasets are introduced in a way that avoids the heavy mathematics. The challenges of inverting two dimensional geophysical datasets and the strategies for limiting the inversion to geologically reasonable solutions are described. The unfortunate characteristics of geophysical images (blurriness, imaging artifacts) are explained to highlight the limitations of inversion and to emphasize that the inverted images never match with geological reality. Students use the Excel-based Scenario Evaluator for Electrical Resistivity (SEER) tool introduced in Unit 3, Field Geophysical Measurements, to investigate key inversion concepts associated with measurement errors and the benefits of adding boreholes to surface data using synthetic datasets. Students are then led through an inversion of the two-dimensional EI dataset acquired in Harrier Meadow using ResIPy, a Python-based graphical user interface developed for instructional use. Following the instructional video, students then perform the inversion in ResIPy themselves and explore how variations in inversion settings related to the errors in the measurements result in distinctly different images.

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The California Drought of 2012 -- 2016 had significant social and economic consequences. This final unit focuses on this drought as a case study for measuring the hydrologic system so that we can better understand fluxes, variability, uncertainties, and methods to measure them. Students analyze a variety of data that are relevant to basin-scale water budget: precipitation, terrestrial water storage, and snow pack. Traditional monitoring systems used are precipitation and snow pillow sensors. The newer geodetic methods are GRACE (Gravity Recovery and Climate Experiment satellite) and Reflection GPS. The students then use these data to consider water storage changes during the drought and how these changes compare in magnitude to human consumption. The work can start during a lab period and carry over into work outside of the lab time. The student exercise takes the form of responses to questions and tasks that tests a student's abilities to synthesize information and identify challenges in monitoring the terrestrial water cycle. Students then take the step-by-step exercise results and synthesize it into a report for California water policy makers to highlight the findings and pro/cons/uncertainties for the different methods. Unit 4 is the summative assessment for the module.

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Note: Although the term GPS (Global Positioning System) is more commonly used in everyday language, it officially refers only to the USA's constellation of satellites. GNSS (Global Navigation Satellite System) is a universal term that refers to all satellite navigation systems including those from the USA (GPS), Russia (GLONASS), European Union (Galileo), China (BeiDou), and others. In this module, we use the term GPS even though, technically, some of the data may be coming from satellites in other systems.

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Online-ready: The exercise is electronic and could be done individually or in small online groups. Lecture is best done synchronously due to the technical nature.

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Students explore water quality and freshwater access issues around the globe. The activities require students to investigate region-specific water problems in different parts of the world and analyze how those issues are sometimes remedied. The materials in this unit may be used as a stand-alone day of instruction or as part of the complete Environmental Justice and Freshwater Resources InTeGrate Module.

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The assignment is to calculate an annual water balance for a tree using data gathered at the Southern Sierra Critical Zone Observatory. In the framework of experimental design, students will organize around a research question "Is there enough water in the soil to account for transpiration?" After gathering and organizing data, students will calculate the annual water fluxes and reservoirs using a mass balance approach. Later these lessons can be expanded to catchment-scale calculations.

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Units 3 and 4 of this module explored how water resources are used for agriculture in the United States and how this can vary depending on location. In Unit 5, students explore how agricultural practices can affect the water quality in streams, rivers, lakes, and coastal areas. Important concepts in this unit include processes that transport suspended material (e.g., sediment) and dissolved material (e.g., nutrients) away from crop fields and into regional water bodies. The effects of dissolved nutrients on the health of the water ecosystems will be presented with examples of hypoxic zones in coastal areas and lake eutrophication. This last unit is well-suited to foster student advancement in systems thinking.

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Students explore the classic case of Love Canal, New York, in which Lois Gibbs -- originally described as a "hysterical housewife" -- mobilized her community and called attention to the contamination of groundwater by buried hazardous waste and the resulting impact on the health of local residents. The activities require the students to investigate the history of events at Love Canal. The materials in this unit may be used as a stand-alone day of instruction or as part of the complete Environmental Justice and Freshwater Resources InTeGrate Module.

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Screenshot of the slider tool used to relate geophysical images to vegetation pattern

Provenance: Lee Slater, Rutgers University-Newark
Reuse: This item is in the public domain and maybe reused freely without restriction.
In this unit, students explore spatial associations between the three-dimensional electromagnetic (EM) conductivity inversions and the visible patterns of Salicornia (Pickleweed) introduced in Unit 1, Exploring Harrier Meadow. The Arcview Storymap started in Unit 1 allows students to overlay inverted electrical conductivity patterns for different depths on aerial photographs of Harrier Meadow that highlight the patches of Pickleweed. Students analyze how conductivity patterns vary with depth and explore for evidence for a relationship between electrical conductivity and Pickleweed patches based on the hypothesis introduced in Unit 1. Students then perform an integrated interpretation of both the EM and electrical imaging inversions along with the results of direct sampling (coring, pore water sampling, soil characterization) conducted at locations selected using the electrical conductivity patterns observed in the EM dataset. Students perform basic qualitative assessments of the correlation between physical and chemical properties of the sampled soils and soil electrical conductivity from the EM inversions. Students finish the module by evaluating the extent to which the geophysical dataset and supporting direct measurements support the hypothesis pertaining to the cause of the Salicornia clusters introduced in Unit 1.

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In this unit, students address the issue of groundwater demands and environmental justice in the arid Southwest, a region with some of the largest percentages of Hispanics and Latinos in the United States. Students discuss the Rule of Capture, the overuse of water resources, and the dwindling supply of groundwater in many parts of the Ogallala Aquifer. Students connect groundwater's role to the hydrological cycle and consider how issues of inequity can occur when groundwater is not properly regulated.

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Students will utilize the desert Southwest region of the United States and the Ogallala Aquifer in a case study to evaluate issues regarding groundwater and its scarcity. Groundwater is often seen as a limitless resource in the Southwest since there is little regulation controlling the amount that is withdrawn (Rule of Capture). This mentality has led to overuse and to the dwindling supply of groundwater in many parts of the Ogallala Aquifer. This module will help students connect groundwater's role in the hydrological cycle to issues of inequity that can occur when groundwater is not properly regulated.

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Unit 7 continues the use of the CME Building Case Study to explore water sustainability in the context of a building. The activity is extended to the catchment level, and a new tool for catchment level storm water management is introduced. Students are exposed in the pre-class assignments to low impact development (LID) and green infrastructure and the EPA National Stormwater Calculator. In class, the central activity is applying the EPA National Stormwater Calculator to evaluate an LID control plan for the CME building case study. The unit brings together concepts from previous units through the use of the calculator. The impact of landscapes, buildings, and other features on storm water runoff is illustrated. And the potential benefit of LID controls is analyzed. The homework assignment engages students in the search for a local green infrastructure site to take a picture and summarize the site in the context of a sustainable site.

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In preparation for the activity a lecture is given on the properties and history of polychlorinated biphenyls and other contaminants. Each student is assigned to one of six groups with an interest in the outcome of the debate. The teams must meet and prepare a position paper on the proposed environmental dredging in the Upper Hudson River. Each team must represent the interests of its assigned constituency. Data and background information is found on the world wide web and from the instructor's collection of related articles. On the day of the debate the student's orally present their position paper (some make posters or powerpoint presentations). After each group has made their opening statement the invited guest senators on the panel (other faculty, myself, interested students, those who were absent for the preparation) ask each group a series of questions related to their stance. After this a general debate begins with detailed and sometimes heated discussions between the groups and the panel. A few moments are saved at the end of class and everyone is allowed to drop their assumed affiliation and speak their mind on what should be done. Before leaving the class is give a series of big picture topics to think about over the weekend and these are discussed during the next class.

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Engineers design and implement many creative techniques for managing stormwater at its sources in order to improve and restore the hydrology and water quality of developed sites to pre-development conditions. Through the two lessons in this unit, students are introduced to green infrastructure (GI) and low-impact development (LID) technologies, including green roofs and vegetative walls, bioretention or rain gardens, bioswales, planter boxes, permeable pavement, urban tree canopies, rainwater harvesting, downspout disconnection, green streets and alleys, and green parking. Student teams take on the role of stormwater engineers through five associated activities. They first model the water cycle, and then measure transpiration rates and compare native plant species. They investigate the differences in infiltration rates and storage capacities between several types of planting media before designing their own media mixes to meet design criteria. Then they design and test their own pervious pavement mix combinations. In the culminating activity, teams bring together all the concepts as well as many of the materials from the previous activities in order to create and install personal rain gardens. The unit prepares the students and teachers to take on the design and installation of bigger rain garden projects to manage stormwater at their school campuses, homes and communities.

In an out-of-class assignment, students receive background information for the site and the pump test performed, including the aquifer properties determined. Through a series of questions, students are asked to evaluate the pump test method, results, interpretations made by the consultant that performed the test, and the significance of a rain event that occurred during the test.

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In 1978, the Egyptians constructed a canal known as the Toshka Spillway from Lake Nasser into a low area to the west to allow spillover of Lake Nasser water. Despite the fact that the spillway was created in 1978, it wasn't until the late 1990s that Lake Nasser actually filled up to the level of the spillway canal and the overflow lakes began to form. In November of 1998, US astronauts orbiting in the Space Shuttle noticed the lakes filling for the first time, and they have had water in them ever since.

Egypt has embarked on a long-term and far-reaching irrigation plan to create habitable land away from the Nile River Valley. The Toshka Lakes are not, however, a formal part of the project. One of the main points of the exercise is to have students use both their knowledge of Saharan hydrogeology and GIS analyses to evaluate whether the Egyptians are wise not to use the lakes as part of the proposed system of water distribution.

In this exercise, students download and prepare their own SRTM DEMs and learn how to determine areas and volumes using ArcGIS. They can then ask questions and use ArcGIS to determine the answers. How much water is in the Toshka Lakes? What happens if Lake Nasser rises and more water flows down the canal? Will more lakes form, or will the lakes that are there just get bigger? How much water might be evaporating from the lake surfaces? How much water has to flow down the canal to keep the lakes at a particular level? What might happen as the annual Nile flood fluctuates from year to year?

The document posted for downloading contains two homework assignments, two in-class activities, and a wrap-up assignment.
You can also download a GIS Primer (Acrobat (PDF) PRIVATE FILE 1.2MB Mar30 10) that we have written, which is a simple GIS "how-to" manual for tasks including those used in this exercise.

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