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Presentation: Unit 3 background information
- 1. This work is supported by the National Science Foundation’s Directorate for Education and Human Resources TUES-1245025, IUSE- 1612248, IUSE-1725347, and IUSE-1914915. Questions, contact education-AT-unavco.org MEASURING WATER RESOURCES Unit 3: Monitoring groundwater storage with GPS vertical position
- 2. OUTLINE 1. Groundwater Mining: a Global Problem 2. GPS vertical position and hydrologic loading 3. Subsidence: compaction and poroelastic effects 4. Introduction to California physiography
- 3. 1. GROUNDWATER MINING: A GLOBAL PROBLEM These figures are from Konikow, 2011 See also Figure 2 from Famiglietti, 2014 Konikow, Geophysical Res. Letters, 2011 NASA EarthObservatory
- 4. 2. GPS VERTICAL POSITION Solid earth responds elastically to changes in load, such as water loss from regional drought instantaneous, reversible, linear Extract groundwater Total Water Storage decreases The land surface moves up Plate Boundary Observatory station P037
- 5. GPS NETWORKS Thousands of stations across continental United States Data latency of ~1 day http://geodesy.unr.edu/NGLStationPages/gpsnetmap/GPSNetMap.html
- 6. GPS DATA Cycles in vertical position are related to the seasonal water changes.
- 7. HOW MUCH VERTICAL MOTION FROM TWS VARIATIONS? Response to loading depends on elastic parameter, Young’s modulus (E) E = tensile stress / extensional strain Units, are force/area (N/m2) or pressure (Pa).
- 8. HOW MUCH VERTICAL MOTION FROM TWS VARIATIONS? • 50 cm change in TWS ~20 mm up/down • Noise in daily GPS position estimate ~2-3 mm
- 9. SPATIAL SCALE OF SENSING • Depends on horizontal scale of hydrologic load • For large aquifers, unloading effects of pumping may be sensed 10’s of km away 0 250 500500 250 Distance (km) Displacement(mm) 40 km wide 2 m water equivalent 200 km wide 0.5 m water equivalent
- 10. 3. SUBSIDENCE: GROUNDWATER PUMPING MAY LEAD TO SUBSIDENCE • Two effects – Compaction of aquitard sediments; generally irreversible – Poroelastic effects; reversible
- 13. 3. SUBSIDENCE: DECREASE IN SURFACE ELEVATION MAY EXCEED SEVERAL METERS!
- 14. 3. SUBSIDENCE: GROUNDWATER PUMPING MAY LEAD TO SUBSIDENCE • Effects are local – not extending beyond the pumped area.
- 16. CENTRAL VALLEY GROUNDWATER: PRE AND POST DEVELOPMENT CROSS-SECTION FOR CENTRAL PART OF SAN JOAQUIN VALLEY
- 18. OPTIONAL SLIDES FOR DURING OR AFTER THE STUDENT EXERCISE
- 19. CALIFORNIA DROUGHT SEVERITY AND AREA
- 20. ANIMATION Measuring Drought: A GPS Network Offers A New Perspective https://www.youtube.com/watch?v=5Bzt374u5aU&index=2&list =PLzmugeDoplFOot41MIBBZiLYBCB0M-p1P&t=6s
Editor's Notes
- Plate Boundary Observatory station P422 in Moscow Idaho Image from UNAVCO http://www.unavco.org/instrumentation/networks/status/pbo/overview/p422
- A variety of water measurement methods show that groundwater aquifers from around the world are being depleted. The left image from Konikow, 2011, (http://onlinelibrary.wiley.com/doi/10.1029/2011GL048604/abstract) was derived from a wide range of methods including water level, modeling, and pumpage. The right image from NASA (also detailed in Famiglietti, 2014) was based on GRACE data (Gravity Recovery and Climate Experiment). Left image: Konikow, 2011 – AGU journals allows use of published image for educational purposes Right image: https://earthobservatory.nasa.gov/blogs/earthmatters/2014/11/05/earths-disapearing-groundwater/ (J.T. Reager, NASA Jet Propulsion Laboratory)
- This is not the same as the isostatic adjustment to surface loads (long time scale, spatial pattern affected by flexural characteristics of lithosphere, total magnitude depending on crust/mantle density contrast). The reverse also happens: add groundwater, TWS increases, the land surface moves down During the exercise in this unit, students will be analyzing data from nine GPS stations like this one, which are part of the Plate Boundary Observatory (PBO) run by the UNAVCO for the National Science Foundation. Image from UNAVCO (http://www.unavco.org/instrumentation/networks/status/pbo/overview/P037)
- GPS stations are widely distributed around the USA and most data are available with a day or so. Some are available with seconds. Image from Nevada Geodetic Laboratory (http://geodesy.unr.edu/sitemap.php) and used with permission. Base map by Google Maps.
- GPS stations such as those in the *Network of the Americas (NOTA; https://www.unavco.org/instrumentation/networks/status/all) were originally installed to measure things such as plate tectonic motion (horizontal motions shown in the left image). However, as the data came in, it became clear that elements of the vertical motion is related to changes in the terrestrial water storage (TWS) and there were much wider uses for GPS data than originally imagined. * Many of these GPS stations were originally installed as part of the Plate Boundary Observatory (PBO), which was absorbed into NOTA in 2018. Rear image: UNAVCO Velocity Viewer http://www.unavco.org/software/visualization/GPS-Velocity-Viewer/GPS-Velocity-Viewer.html (base image from Google Maps) GPS and GPS data from https://www.unavco.org/instrumentation/networks/status/nota/overview/CABL
- Drawings by Kate Shervais, UNAVCO
- NLDAS is the National Land Data Assimilation System which provides estimates of hydrologic storage using meteorological forcing. NLDAS TWS is the sum of the Noah model soil moisture (0-200 cm soil depth) and snow for the grid cell that contains PBO station P025. More information about NLDAS can be found here: http://ldas.gsfc.nasa.gov/nldas/ GPS vertical data records very similar pattern via a completely independent means from the methods used by NLDAS. Image: modified from Larson, K.M., GPS Interferometric Reflectometry: Applications to Surface Soil Moisture, Snow Depth, and Vegetation Water Content in the Western United States, WIREs Water, Vol. 3, 775-787, 10.1002/wat2.1167, 2016.
- Elastic response to surface loads extends beyond the area with the load. Two examples of he simulated 1-D response to surface loading are shown. The blue line shows the vertical displacement (downward for a positive load) resulting from a 40 km wide load that is equivalent to 2 m deep water. Red line is the same for a 200 km load with 0.5 m thickness. Image by Eric Small
- Unlike the elastic response to loading subsidence is localized to the pumping area.
- The groundwater movement patterns have modified significantly in the course of agricultural development. Image modified by K. Shevais (UNAVCO) from Faunt, 2009, USGS Professional Paper 1766 (https://pubs.usgs.gov/pp/1766/PP_1766.pdf)
- In the Unit 3 exercise, students will be asked to consider the type of soil/rock that lies beneath each of the stations they look at. They will be given this map as resource to answer those questions. You may want to help them see the areas of bedrock vs. sedimentary fill. Images: http://www.conservation.ca.gov/cgs/information/publications/ms/Documents/MS057.pdf (Courtesy of the California Geological Survey). Map Derived from the Simplified Geologic Map of California, Map Sheet 57.
- It may help to show the students this graph showing the California drought duration and severity. Image from US Drought Monitor (http://droughtmonitor.unl.edu/) via Wikipedia (https://en.wikipedia.org/wiki/Droughts_in_California)