Research in Aquifer Mechanics and Land Subsidence

Dr. Tom Burbey

Using horizontal and vertical deformation signals to characterize aquifers
Using InSAR as a tool to characterize storage properties in systems with complex basin-fill deposits
Earth fissures resulting from aquifer pumping in Las Vegas Valley

Using horizontal and vertical deformation signals to characterize aquifers

Land-subsidence research has been ongoing since the 1940's under the leadership of Joe Poland of the US Geological Survey. Our understanding of the mechanisms of subsidence has grown to maturity regarding the elastic vertical compression of fine-grained deposits (Galloway and others, 1998). In quantifying the mechanics of land subsidence, horizontal strain has been largely ignored. Recent evidence from field data and from the physics of first principles suggest that horizontal strain is important and may actually lead to a greater quantity of water released from storage than vertical compaction (Burbey, 2001). Furthermore, ignoring horizontal deformation in estimates of aquifer storage, will lead to overestimates of vertical compaction and storage.

The use of horizontal deformation can help characterize aquifer systems where little hydraulic head data is available. At a study in Mesquite, NV, we used a network of GPS stations placed at different radial distances from a large municipal pumping well to monitor vertical and horizontal deformations during pumping. Even without the benefit of hydraulic head data from observation wells, we were able to characterize the aquifer system from the vertical and horizontal deformation patterns. What we discovered was an obliquely aligned fault that resulted in horizontal deformation of even the pumping well that was influenced by the fault boundary. The figure below shows the observed deformation patterns at the GPS stations. Well WL31 is the pumping well.

We have shown in numerous studies that (1) horizontal deformation patterns reflect important aspects of aquifer systems that can not be obtained from only vertical deformation or water levels alone, (2) ignoring horizontal deformation can lead to misrepresentation of storage or compressibility characteristics and/or miscalculation of future hydraulic head distributions. We are one of the only groups in the world who consistently use 3D deformation patterns to characterize aquifer properties and understand the source of water of pumped aquifers.

Related Papers

Galloway, D.L., and Burbey, T.J., 2011 (in press) Review: Regional land subsidence accompanying groundwater extraction: Hydrogeology Journal
Burbey, T.J., 2008, The influence of geologic structures on deformation due to ground-water withdrawal: Ground Water, v. 46, no. 2, p. 202-211.
Burbey, T.J., 2006, Three-dimensional deformation and strain induced by municipal pumping, Part 2: Numerical analysis: Journal of Hydrology, v 330, p. 422-434.
Burbey, T.J., Warner, S.M., Blewitt, G., Bell, J.W., and Hill, E., 2006, Three-dimensional deformation and strain induced by municipal pumping, Part 1: Analysis of field data: Journal of Hydrology v. 319 p. 123-142.
Pope J.P. and Burbey T.J., 2004, Multiple-aquifer characterization from single borehole extensometer records: Ground Water, v 42, no. 1, p. 45-58.
Burbey, T.J., 2003, Use of time-subsidence data during pumping to characterize specific storage and hydraulic conductivity of semi-confining units: Jour. of Hydrology, v. 281, no 1-2, pp. 3-22.
Burbey, T.J., 2002, The influence of faults in basin-fill deposits on land subsidence, Las Vegas, Nevada, USA: Hydrogeology Journal, v. 10, no. 5, pp. 525-538.
Burbey, T.J., 2001, Stress-strain analyses for aquifer-system characterization: Ground Water, v. 39, no. 1, pp. 128-136.
Burbey, T.J., 2002, Three dimensional aquifer deformation and flow modeling: Proceedings of the 14th Inter. Conf., Comp. Methods in Water Resour., June 23-28, 2002, Delft, The Netherlands, p. 129-136.
Burbey, T.J., 2001, Storage coefficient revisited: Is purely vertical strain a good assumption?: Ground Water, v. 39, no. 3, p. 458-464.
Burbey, T.J., 2000, Evaluation of Subsidence and skeletal specific storage from stress-strain hysteresis loops using one- and three-dimensional deformation models: Proceedings of the Sixth Inter. Symp. On Land Subsidence, Ravenna Italy, Sept. 24-29, 2000, Land Subsidence, Vol. II, p. 255-266.
Burbey, T J., 1999, Effects of horizontal strain in estimating specific storage and compaction in confined and leaky aquifer systems: Hydrogeology Journal, v. 7, no. 6., pp. 521-532.
Burbey, T.J., and Helm D.C., 1999, Modeling three-dimensional deformation in response to pumping of unconsolidated aquifers: Environmental and Engineering Geoscience: v. 5, no 2, pp. 199-212.

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Using InSAR as a tool to characterize storage properties in systems with complex basin-fill deposits

The advent of InSAR (interferometric synthetic aperture radar) and PS-InSAR (permanent or persistent scatterer InSAR) has become an important and powerful tool in understanding and characterizing aquifer properties. Surface deformation measurements at regular pixel (30m intervals) intervals at the basin scale, can provide important clues to the nature of both elastic and inelastic storage properties of aquifer systems when pumping patterns are known and InSAR measurements are made at selected time intervals. The figure below is an interferogram of Mesqute, NV showing the deformation pattern around pumping well WL31. The pattern of deformation reveals an unseen fault that runs northeast-southwest just west of the well. In the north part of the figure you can see how faults (black lines) can constrain vertical deformation.

In Las Vegas, for example, we have collected seasonal InSAR data that show the complex patterns of rise and fall of the land surface resulting from both pumping and injection based on seasonal water needs. These patterns reflect the storage and conductivity patterns of the aquifer at a very detailed scale. We are using these patterns to characterize the storage values at scales never before calculated.
Furthermore, we are developing algorithms calculate zones of parameter estimates automatically. Using MODFLOW_2005, UCODE_2005, and our own developed algorithms, we can show that InSAR data with hydraulic head information can be used to very accurately calculate storage estimates of both the aquifer and confining units of the aquifer system. We are looking for students who want to develop advanced models that use InSAR data in groundwater flow and deformation models to advance our capabilities of characterizing aquifers at the basin scale.

Related Papers

Zhang, M., Nunes, V.T., Burbey, T.J., and Borggaard, J., 2011, A new zonation algorithm with parameter estimation using hydraulic head and subsidence measurements, EOS Trans, American Geophysical Union, Annual Meeting, San Francisco, Dec 5-9, 2011.
Yan, T., and Burbey, T.J., 2008, The value of subsidence data in ground-water model calibration: Ground Water, v. 46, no. 4, p. 438-450.
Burbey, T.J., 2006, Three-dimensional deformation and strain induced by municipal pumping, Part 2: Numerical analysis: Journal of Hydrology, v 330, p. 422-434.
Burbey, T.J., 2006, GPS and InSAR reveal heterogeneous and anisotropic aquifer conditions during an aquifer test, Geol Soc. of Am., Abstracts with Programs, v. 38, no. 7, p. 291.
Bell, J.W., Amelung, Falk, Burbey, T.J., and Blewitt, Geoff, 2004, InSAR and GPS applications in aquifer deformation and subsidence studies: GSA Abstracts with Programs, V. 36, no. 5, p. 299

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Earth fissures resulting from aquifer pumping in Las Vegas Valley

Earth fissures are a consequence of many heavily pumped basin-fill basins. These features are thought to result from extensional strain associated with (1) differential subsidence and surface draping, and (2) heterogeneities associated with changes in aquifer properties or faults. What is unclear is where and how these features occur. We have been investigating the genesis of earth fissures using sophisticated numerical models such as ABAQUS to understand the conditions by which earth fissures from pumping form and how they propagate. In addition we are working to understand the stress and strain conditions leading to failure in heavily pumped basins like Las Vegas Valley. We have found that a sub-vertical fault can lead to rotation of the fault plane and cause extension on the side of the fault farthest from the pumping well. We observe fissures forming in the unsaturated zone and migrating either upwards or downwards toward the water table depending on the conditions of the horizontal deformation in the aquifer (see photos below). Ongoing investigations are aimed at developing hazard maps based on susceptibility of failure at the land surface due to groundwater pumping.

Figure shows the likely location of earth fissuring as a result of rotation of the fault plane due to an induced pumping stress. The fissure is shown to form on the headwall of the fault.

Figure shows that differential horizontal motion induced by the sloping fault may lead to fissure formation on the footwall at land surface.

Figure shows that when stress migrates through the fault into the headwall, the differential horizontal deformation that results may lead to fissures that migrate upwards from the water table to land surface on the headwall of the fault.


Related References

Hernandez-Marin, M., and Burbey, T.J., 2011 (in review) Fault-controlled deformation and stress from pumping-induced groundwater flow in a hydrogeologic setting, Journal of Hydrology
Hernandez-Marin, M., and Burbey, T.J. 2010, Controls on initiation and propagation of pumping-induced earth fissures: Insights from numerical simulation: Hydrogeology Journal, DOI 10.1007/s10040-010-0642-9, v. 18, no. 8, pg. 1773-1785.
Burbey, T.J., 2010, Mechanisms for earth fissure formation in heavily pumped basins: in Land Subsidence, Associated Hazards and the Role of Natural Resources Development; Carreón-Freyre, D, Cerca, M., and Galloway D.L., eds.; IAHS Publication 339, p. 3-8.
Hernandez-Marin, M., Burbey, T.J., 2010 , On the mechanisms for earth fissuring in Las Vegas Valley, a numerical analysis of pumping-induced deformation and stress: in Land Subsidence, Associated Hazards and the Role of Natural Resources Development; Carreón-Freyre, D, Cerca, M., and Galloway D.L., eds.; IAHS Publication 339, p. 27-32.
Hernandez-Marin, M., Burbey, T.J., 2010 , On the mechanisms for earth fissuring in Las Vegas Valley, a numerical analysis of pumping-induced deformation and stress: Eighth International Symposium on Land Subsidence, Queretaro Mexico, Oct. 17-22, 2010.
Burbey, T.J., 2010, Mechanisms for earth fissure formation in heavily pumped basins: [KEYNOTE ADDRESS] Eighth Int. Symp. On Land Subsidence, Queretaro Mexico, October 17-22.
Hernandez-Marin, M., and Burbey, T.J., 2009, The role of faulting on surface deformation patterns from pumping induced ground-water flow: Hydrogeology Journal, 10.1007/s10040-009-0501-8, v. 17., no. 8, p. 1859-1875.
Burbey, T.J., 2008, The influence of geologic structures on deformation due to ground-water withdrawal: Ground Water, v. 46, no. 2, p. 202-211.

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