Initial Publication Date: June 22, 2017

Instructor Materials: Overview of Measuring Water Resources with GPS, Gravity, and Traditional Methods module

Module Goals

  1. Analyze and integrate observations that describe the state of the hydrosphere at regional scales.
  2. Quantitatively compare and contrast different data types, and their uncertainty, for use in the context of the water balance equation.
  3. Critique/evaluate the utility of traditional versus geodetic data for quantifying fluxes and storage.
  4. Compare the magnitude of human use in the basin to deficits associated with drought.

Summative Assessment

Unit 4: A Water Balance Approach for Assessment of the California Drought is the summative assessment for the module. In this exercise, students combine the different types of data sets used in the previous units, plus reflection GPS to determine snow depth, and write a report as if they were a California science advisor to policy makers in the state of California. Learn more about assessing student learning in this module.


The module covers material sequentially, but the units can also often be taught as stand-alone lessons. For instructors who do not wish to use the module in its entirety, suggested pairings are included in the "Context for Use" section on each unit's page.

Students find it particularly interesting to learn that the geodetic methods featured in this module were not necessarily intended for hydrologic purposes. In particular, high precision GPS stations were initially installed to measure tectonic plate motions and give insights into geohazards such as earthquakes and volcanoes. Only later did researchers realize that the vertical GPS positions and even GPS signal reflected off the ground before hitting the receiver could give information on different components of the hydrologic cycle.

Unit 1Introduction to the hydrologic cycle and stakeholder analysis

This unit introduces the hydrological cycle to provide context for the module as a whole. It particularly focuses on those portions of the hydrological cycle that take place on land and that form the basis for water that is used by society. Students conduct a stakeholder analysis to better understand societal issues around water. Then the scientific exercise of the unit emphasizes quantitative approaches to describing the critical portions that humans have access to: surface water and shallow ground water. Students calculate residence times and fluxes between reservoirs and track water particles on an annual basis. They also explore available data sets for specific reservoirs such as snowpack and rivers.

Unit 2Characterizing groundwater storage with well and GRACE data

This unit provides students with experience analyzing traditional (depth to water table measured in a well) and geodetic (GRACE) data for monitoring changes in groundwater storage in the High Plains Aquifer. Variations across timescales are compared, from seasonal to interannual to decadal. This comparison highlights some of the challenges associated with quantifying changes in groundwater storage at the regional scale. Aquifer properties are used to consider changes in terms of both 'depth to water table' and water storage. Students are asked to formulate explanations for the observed variations in the context of the water balance equation. Students compare their results to a multi-decadal trend reported in the literature.

Unit 3Monitoring groundwater storage with GPS vertical position

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.

Unit 4Water budget assessment of a California drought

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.

Making the Module Work

To adapt all or part of the module for your classroom you will also want to read through